We Hereby Approve the Dissertation of Phil Blake Mcbride

MIAMI UNIVERSITY The Graduate School

Certificate for Approving the Dissertation

We hereby approve the Dissertation

Phil Blake McBride

Candidate for the Degree:

Doctor of Philosophy

Committee Chair Richard T. Taylor

Research Director Arlyne M. Sarquis

Committee Member Jerry L. Sarquis

Committee Member James W. Hershberger

Graduate School Representative Allen Berger ABSTRACT

REVITALIZING CHEMISTRY LABORATORY INSTRUCTION

by Phil Blake McBride

This dissertation involves research in three major domains of chemical education as partial fulfillment of the requirements for the Ph.D. program in chemistry at Miami University with a major emphasis on chemical education, and concurrent study in organic chemistry. Unit I, Development and Assessment of a Column Chromatography Laboratory Activity, addresses the domain of Instructional Materials Development and Testing. This unit outlines the process of developing a publishable laboratory activity, testing and revising that activity, and subsequently sharing that activity with the chemical education community. A laboratory activity focusing on the separation of methylene blue and sodium fluorescein was developed to demonstrate the effects of both the stationary and mobile phase in conducting a separation. Unit II, Bringing Industry to the Laboratory, addresses the domain of Curriculum Development and Testing. This unit outlines the development of the Chemistry of Copper Mining module, which is intended for use in high school or undergraduate college chemistry. The module uses the learning cycle approach to present the chemistry of the industrial processes of mining copper to the students. The module includes thirteen investigations (three of which are web-based and ten which are laboratory experiments) and an accompanying interactive CD- ROM, which provides an explanation of the chemistry used in copper mining with a virtual tour of an operational copper mine. Unit III, An Alternative Method of Teaching Chemistry: Integrating Lecture and the Laboratory, is a project that addresses the domain of Research in Student Learning. Fundamental Chemistry was taught at Eastern Arizona College as an integrated lecture/laboratory course that met in two-hour blocks on Monday, Wednesday, and Friday. The students taking this integrated course were compared with students taking the traditional 1-hour lectures held on Monday, Wednesday, and Friday, with accompanying 3-hour lab on Tuesday or Thursday. There were 119 students in the test group, 522 students in the Shelton control group and 556 students in the McBride control group. Both qualitative data and quantitative data were collected. A t-test was used to test significance.

REVITALIZING CHEMISTRY LABORATORY INSTRUCTION

A DISSERTATION

Submitted to the

Faculty of Miami University

in partial fulfillment of the requirements

for the degree of

Doctor of Philosophy

Department of Chemistry and Biochemistry

Phil Blake McBride

Miami University

Oxford, Ohio

2003

Dissertation Director: Arlyne M. Sarquis

Phil Blake McBride

2003

TABLE OF CONTENTS

List of Tables...... v List of Figures ...... vi Dedication...... vii Acknowledgments ...... viii Introduction to the Dissertation ...... 1

Unit I – Development and Assessment of a Column Chromatography Laboratory Activity Chapter 1: Introduction and Conceptual Framework...... 5 1.1 Statement of Problem...... 5 1.2 Background ...... 5 1.3 Purpose...... 6 1.4 Description of Terms ...... 7 Chapter 2: Methodology...... 8 2.1 Framing ...... 8 Setting Project Goals/Audience Analysis ...... 8 Idea Development...... 8 Review of the Literature...... 10 2.2 Alpha Stage ...... 10 Initial Drafting/Revision...... 10 Preliminary Design ...... 11 Microtesting ...... 13 Creation of Alpha Draft...... 14 Internal Review of Alpha Draft...... 14 2.3 Beta Stage ...... 15 External Review by Content Experts ...... 15 Classroom Test with Target Group ...... 17 Document Design ...... 17 2.4 Pilot Stage ...... 17 Test and Revise...... 17 Pilot Tested by Intended End Users ...... 17 Revision/Final Production...... 17 2.5 Field Stage...... 18 Field Testing ...... 18 Final Testing After Revision is Complete...... 18 2.6 Dissemination ...... 18 Chapter 3: Description of Project Content ...... 19 3.1 Overview of the Laboratory Investigation ...... 19 3.2 Experimental Procedure...... 20 3.3 Preparation of a Chromatography Column ...... 20 3.4 Safety, Handling, and Disposal ...... 21 3.5 Sample Student Data...... 23 3.6 Discussion ...... 26 3.7 Conclusion...... 28 Unit I References ...... 30

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Unit II – Integrating the Chemistry of Copper Mining into the Chemistry Curriculum Chapter 1: Introduction and Conceptual Framework...... 33 1.1 Statement of Problem...... 33 1.2 Overview of the Copper Mining Project...... 33 1.3 Goal and Objectives...... 34 Chapter 2: Description of the Copper Mining Project...... 35 2.1 Curriculum and Materials Development...... 35 2.2 Potential Impact and Significance...... 37 2.3 Project Team, Plan and Evaluation ...... 38 Chapter 3: Review of the Literature...... 39 Chapter 4: Chemistry of Copper Mining...... 40 4.1 Phase I: Leaching...... 40 4.2 Phase II: Solution Extraction...... 41 4.3 Electrowinning...... 45 Unit II References...... 47

Unit III – Integrating Lecture with Lab in the Introductory Chemistry Course Chapter 1: Introduction and Conceptual Framework...... 50 1.1 Background and Significance...... 50 1.2 Review of the Literature ...... 51 1.3 Statement of the Problem...... 52 1.4 Statement of the Null Hypothesis...... 52 Chapter 2: Methodology...... 53 2.1 Subjects ...... 53 2.2 Instrument ...... 53 2.3 Design of the Study...... 55 2.4 Procedures...... 55 Chapter 3: Results...... 56 3.1 Quantitative Analysis...... 56 3.2 Qualitative Analysis...... 57 Chapter 4: Summary ...... 59 Unit III References...... 61

Appendix A: Descriptive Statistics and t-Tests for Learning Project ...... 62 Appendix B: Fundamental Chemistry Survey Results ...... 66 Appendix C: Chemistry of Copper Mining Student Manual...... 74 Appendix D: Chemistry of Copper Mining Instructor’s Manual...... 152 Bibliography: ...... 222

LIST OF TABLES

Number Page 1. Physical Properties 23 2. Sample Student Results: Alumina, Basic 24 3. Sample Student Results: Alumina, Neutral 24 4. Sample Student Results: Alumina, Acidic 25 5. Sample Student Results: Silica Gel 25 6. Copper Mining Laboratory Activities 36

LIST OF FIGURES

Number Page 1. Chromatographic Column and Setup 21 2. Typical Student Column Chromatography Setup 26 3. Structures of Sodium Fluorescein, Fluorescein, and Methylene Blue 27 4. Leach Field at Phelps Dodge Morenci Copper Mine 40 5. Leach Field of Crushed Ore 41 6. Organic Reagent 42 7. Extraction of Cu2+ 43 8. Settling Tank and Solution Extraction Plant 44 9. Separation of Organic and Rich Electrolyte 44 10. Insertion of Steel Blanks 45 11. Removal of Copper Cathodes 45 12. Separation of Copper Sheets 46

DEDICATION

To my beautiful wife Paula, my beautiful daughter Nicole, and my three handsome sons, Braden, Dakota, and Ethan for unselfishly sacrificing time with their husband and father as he pursued one of his dreams.

Families are of an eternal design. As each member grows and progresses you’ll find, That working together is essential, For each member to reach his potential.

Thanks for helping me stretch to reach mine!

Love, Dad

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ACKNOWLEDGMENTS

I wish to acknowledge a loving Heavenly Father who guided me to Miami University, and for His continued guidance, direction, and inspiration in my coursework and research. I could not have accomplished this goal without His help. I express sincere appreciation to my wife, Paula and our four children, Nicole, Braden, Dakota, and Ethan. They have been very supportive in their willingness to move for a season to the Midwest, attend new schools, and leave friends behind. They have been a great support as they watched their father work and grow through this experience. I express my deepest gratitude for my wife. Without your support Paula, I would never have accomplished this goal, this dream. Thanks for your love and support. A special thanks to my parents, Clarence and Joan McBride, and parents-in-law Max and Wanda Thatcher, for their willingness to travel to Ohio to visit their children and grandchildren, and for their continued support over the years. Dad, your example as a chemistry instructor and father has helped me throughout my life. You have always been, and will always be my hero. I express gratitude to Eastern Arizona College for granting a sabbatical for the 1997-1998 academic year, so that I could complete my coursework for this degree. Gratitude is also expressed to the Faculty, Staff, and Administration at Eastern Arizona College for their concern and support as I sought to accomplish my dream. A special thanks to Dean Jeanne Bryce and Dean Ron Keith for their support and words of encouragement. Sincere thanks to Glen Snyder and Adina Morris from Institutional Research, for the personal time and support they provided in computing the statistics for Unit III. Thanks to the Allied Health Workshop participants for their input, constructive criticism, and support of the chromatography unit. These included Robert Banks, Wheeler Conover, Mary Graff, Minnie Herrick, Susan Holladay, Barbara Mowery, Noreen Gibson, Rosemary Leary, Margaret Skouby, Dorothy Kurland, Jeff Hutton, Cyndi Lewis, Ray Crawford, and G. Lynn Carlson. A special thanks to Susan Hershberger for her review of the chromatography laboratory activity, her insights, and expertise.

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Thanks to all the chemistry students at Eastern Arizona College, who have over the past several years participated in microtesting, classroom testing, and were a major part of the entire research projects. The copper mining project could not have occurred without the support of Phelps Dodge Copper Mine, located in Morenci, Arizona. A special thanks to Pat Brown, Pete Escobedo, Oscar Baca, Jim Bailey, John Uhrie, and Ric Bryce. Ric, you were always positive as you coordinated the field trips, organizing chemists, engineers, and hydrometallurgists to give personal tours of the copper mine. Owen Tinkler of Avecia Inc supplied the organic extractant, Acorga M5850 for the workshops and classroom testing and was always there to answer technical questions. I wish to acknowledge William (Bill) Nietfeld and his students at Thatcher High School for field-testing the copper mining laboratory experiments. Thanks to chemistry students of Thatcher High School, Safford High School, Ft. Thomas High School, Wilcox High School, and Morenci High School for testing the chromatography experiment as part of the Student Chemistry Adventure. In addition, I would like to acknowledge and give special thanks to my dissertation committee, Professors James W. Hershberger, chair, Arlyne M. Sarquis, Jerry L. Sarquis, Richard T. Taylor, James E. Poth, and Allen Berger. I express my deepest gratitude for your guidance, teaching, and encouragement. Dr. Taylor was my first contact with Miami University as he taught a summer workshop titled Chemistry and Crime, Elements of Forensic Science. It was in part due to this first positive experience, that I selected Miami University to further my education. A special thanks to Arlyne M. Sarquis, my Research Advisor. You have always been there to encourage me to stretch. Thanks for all of the marked up drafts that always led me to reach higher. You have been a mentor and a critic. Above all, you have been a friend, cheerfully encouraging me onward. I feel it a great privilege to have been taught and mentored by the person I consider to be the best chemical educator out there. Part of this research was funded through Using Chemistry to Enhance the Technical Workforce in the Innovation Age; NSF Grant No. 0101400 and Partnership for the Advancement of Chemical Technology; NSF Grant No. ATE DUE-9454518.

INTRODUCTION

Anyone who teaches chemistry in the K-12 system or who is employed as a faculty member in a chemistry department is considered a chemical educator. Each is interested in helping others understand chemistry and its applications in our lives. Chemical educators can participate in instruction, practice, and/or research. Most chemical educators participate in instruction as they focus on teaching chemical concepts, laboratory techniques, and critical thinking skills. Many chemical educators are also practitioners. These individuals coordinate and direct programs that are used to teach chemistry. This list would include textbook authors, individuals involved in curriculum development, teacher preparation, and outreach programs, and reviewers. A few chemical educators conduct research in chemical education. These individuals focus on the how and why of student learning (1). Interest in chemistry education is increasing. The American Chemical Society’s Division of Chemical Education Chemical is alive and thriving. There has been an increase in tenure-track positions in Chemical Education at four-year colleges and universities (2). Chemical education research at these institutions and elsewhere is a vital part of chemistry education. Chemical education research focuses on variables that affect learning chemistry and the value of strategies to increase that learning (3). This research involves: Instructional materials development and testing Curriculum development and testing Instructional technology Student learning. Chemical education research includes both quantitative and qualitative research. Quantitative research in chemical education involves the same components of chemistry research: formulating an hypotheses, research design, collecting and analyzing data according to accepted protocols, and producing results that can benefit teaching and learning (4). Key elements of qualitative research include the setting, the participants, and the researcher. The results of qualitative research are most valuable to others working in a similar setting. If the settings are vastly different, the results may have little value (5).

Questionnaires and surveys are common methodologies employed in qualitative research. They allow researchers to see trends. They allow the voice of the student to be heard. This is especially true in large lecture classes, where the instructor never gets to know the students (6). “Miami University’s Ph.D. in Chemistry with emphasis in Chemical Education is intended for those interested in becoming teachers of chemistry where comprehensive knowledge of advanced chemical concepts is required and where scholarly activity can include the pursuit of chemical education knowledge (3).” The dissertation for this degree consists of three projects, one of which must be from the area of student learning. The other two projects are typically curriculum development projects selected from materials development, course development, or instructional technology development. One of these projects must be in the area of the student’s concurrent study. The projects must undergo testing and revision, and must be used in the course for which they were designed for at least one semester. One project must have a laboratory or computational component. Unit I of this dissertation describes a materials development laboratory project that was developed to be used in any chemistry course with a chromatography component. Chromatography was chosen as the chemistry concept to be taught. The project involved the development of a laboratory experiment that could be used to teach the importance of the stationary phase and mobile phase in conducting chromatographic separations. The project went through numerous testing and revision stages before being submitted to the Journal of Chemical Education for publication. Unit II describes a course development project that integrates the chemistry of copper mining into the chemistry curriculum. Thirteen laboratory experiments were developed around the chemistry of copper mining. These laboratory experiments were designed to help students witness industrial applications of chemistry. The laboratory experiments underwent established protocol for development and testing of materials as outlined by Storer (7). These laboratory experiments underwent external review and testing by Thatcher High School’s chemistry class taught by William (Bill) Nietfeld. These laboratory experiments are currently part of the Fundamental Chemistry laboratory curriculum at Eastern Arizona College. This project is part of an NSF grant to use chemistry to enhance the technical workforce (8). The student-learning project is described in Unit III of this dissertation. Concern about academic achievement in the fundamental chemistry course led to this project. The project

determined the effect of teaching chemistry as an integrated lecture/laboratory course as measured by performance on a post-test. This project is being submitted to the Journal of College Science Teaching.

References

1. Bunce, D. M.; Robinson, W.R. J. Chem Educ. 1997, 77, 1076. 2. Metz, P. A. J. Chem Educ. 1994, 71, 180. 3. Miami University’s Ph.D. in Chemistry with Emphasis in Chemical Education. http://www.terrificscience.org/miami/muphdchemed.pdf (accessed Oct 2003). 4. Nurrenbern, S. C.; Robinson, W. R. J. Chem Educ. 1994, 71, 181. 5. Phelps, A. J. J. Chem Educ. 1994, 71, 191. 6. Pribyl, J. R. J. Chem Educ. 1994, 71, 195. 7. Storer, D. A. Doctoral Dissertation, Miami University, Oxford, OH, 2000. 8. Sarquis, A. M., Using Chemistry to Enhance the Technical Workforce in the Innovation Age; NSF Grant No. 0101400, Miami University, Oxford, OH, 2001.

Unit I: Development and Assessment of a Column Chromatography Laboratory Activity

Chapter 1 – Introduction and Conceptual Framework

1.1 Statement of the Problem The National Science Education Standards are based on four principles (1). Science is for all students. Students learn best by active participation in the learning process. Education should reflect the way that science is done. Improving science education requires a coordinated effort of many stakeholders. Scientific problem solving follows five basic steps: identification of a problem, collect known facts related to the problem, propose a specific plan to solve the problem, carry out the proposed plan, and evaluate the results. If we want students to be problem solvers, we need to provide them the opportunity to solve problems. Students often conduct experiments in the laboratory to verify what has already been taught in class. The students are passive learners, not really having to think to complete each laboratory exercise.

If students learn by active participation, the laboratory activity must allow them the freedom to try different options to solve a problem. The laboratory activity must reflect the scientific method where students make observations, hypothesize a plan to solve a problem, conduct experiments to test their hypothesis, and evaluate their results. The chromatographic separation of methylene blue and sodium fluorescein was designed to provide students such an opportunity.

1.2 Background As an instructor of Organic Chemistry, I had my students conducting a laboratory activity to help them learn the techniques and theory of thin-layer chromatography. The laboratory activity involved the separation of a mixture of methylene blue from sodium fluorescein (2). Students were able to visually identify components of this mixture as the sodium fluorescein moved up the silica-gel plate with the solvent, and as methylene blue remained stationary at the bottom of the plate. The students determined the Rf values and appeared to master the technique of thin-layer chromatography (TLC). The next week students conducted a column chromatography lab, using the same mixture of methylene blue and sodium fluorescein. Instead of silica gel as the stationary phase, the students used alumina. The students witnessed a complete reversal of the elution order with methylene blue eluting first out of the column and sodium fluorescein remaining at the top of the column. The students didn’t seem to make any

connections between the previous week’s lab and this lab. They didn’t show any excitement nor express any concern that the elution order had reversed. Even though students were conducting a hands-on laboratory activity, they weren’t truly, actively engaged. They were following the instructions outlined in the laboratory manual, working to ensure that their results matched those predicted, and answering the questions “correctly.” This is not how science is done. The students didn’t appear to care about why things happened as they did. This was disturbing, and so I set out to develop a laboratory activity that would teach students the techniques of chromatography, while encouraging them to be actively engaged in the learning process. The goal was to help students think, analyze, and investigate as they conducted laboratory activities, and to help them experience the excitement of discovering something not predicted. Thus began the development of an inquiry-based laboratory activity that would bring excitement and learning to students. This laboratory activity would have students actively involved in solving a problem. They would investigate different situations and make their own recommendations. They would conduct this laboratory activity the same as if they were functioning as a chemist in industry. While I did not initially have the expertise to design this laboratory activity, my interaction with the Center for Chemistry Education (CCE) at Miami University, the National Science Foundation funded project, The Partnership for the Advancement of Chemical Technology, (PACT) (3), and my graduate studies at Miami University provided the basis for this work. The PACT consortium includes two-year and four-year institutions, school districts, industry, government, professional societies, and the private sector; all of whom share the goal of bringing chemistry and chemical technology education into closer alignment with the skills, methods, problem solving, and content used in today's industrial and governmental laboratories. PACT was awarded the first Model Project award through the National Science Foundation’s Advanced Technology Education (ATE) initiative. This grant brought industrial applications of chemistry into the high schools and two-year colleges (4).

1.3 Purpose The laboratory activity was designed to help students understand the techniques and theory of chromatography, provide them an opportunity to use the scientific method to propose a solution to a problem, and provide active learning.

The steps involved in bringing this activity from an idea to a usable instructional document involved much testing and revisions utilizing established protocol within chemical education. In Unit II of his dissertation, Donald Storer outlines the method used for this development protocol (5), which is a standard used for all instructional materials developed by the Center for Chemistry Education (6). This protocol involved the following steps: Framing o Setting Project Goals/Audience Analysis o Idea Development o Review of the Literature Alpha Stage o Initial Drafting/Revision o Preliminary Design o Micro Testing o Creation of an Alpha Draft o Internal Review of Alpha Draft Beta Stage o Beta Draft o External Review by Content Experts o Classroom Test with the Target Group o Document Design Pilot Stage o Test and Revise o Pilot Tested by intended end-users o Revision/Final Production Field Stage o Field Testing o Final Draft after Revision is complete 1.4 Description of Terms While most of the items on the above list are self explanatory, the concept of “microtesting” might be new to the reader. This important step involves the testing of an activity by a member of the target audience as the developer silently watches and takes notes.

Chapter 2 – Methodology

2.1 Framing

Setting Project Goals/Audience Analysis The activity would engage freshman and sophomore college level chemistry students enrolled in Fundamental Chemistry, General Chemistry, and Organic Chemistry courses, in an activity that would teach them the basic techniques of column chromatography, while leading these students to an understanding of the role of the stationary and mobile phases in chromatographic separations. Column chromatography is a very useful method for separating and purifying solids and liquids. This technique is often employed during the first semester of organic chemistry courses, but seldom in introductory or general chemistry courses. This laboratory investigation is designed for introductory chemistry courses as well as general and organic chemistry courses. It fits well into the discussion on solution chemistry in the introductory and general chemistry curricula, as well as in separation techniques in organic chemistry.

The laboratory investigation involves the complete reversal of elution of methylene blue and sodium fluorescein in which solubility and acid/base interactions play a part in controlling the separation. Students learn the significance of mobile and stationary phases involved in chromatography as they work in teams to discover the best method to separate a mixture of sodium fluorescein (D&C Yellow No. 8) and methylene blue.

Idea Development The Center for Chemistry Education (CCE) Model involves the use of a development workshop, which was successfully employed in the development of the Sample Preparation for Chemical Analysis Monograph (5). The development workshop involves a small group of participants from academia and industry who meet together for up to two days brainstorming ideas, developing rough drafts of activities to use in the project, and sharing those ideas with others in the group. The idea development for this project was part of an Allied Health Development Workshop, which was held July 12-16, 1999 at Eastern Arizona College. The focus of the workshop was to brainstorm chemistry concepts and laboratory techniques that are important to allied health students, and subsequently develop scenario and discovery-based laboratory activities based on those techniques and concepts.

Mayuree Sozanski, director of Nursing at Eastern Arizona College joined a group of two high school chemistry teachers, four community college chemistry teachers, two technology school chemistry teachers, and one university professor to form the development group. Sozanski addressed the group about what she perceives as important chemistry concepts for Nursing students. She stressed the need for laboratory activities that would include problem solving.

Participants toured the Clinical Lab at Mount Graham Hospital. The Medical Technicians (Med Techs) discussed the laboratory techniques and chemistry concepts that were important for them in their line of work.

A brainstorming session provided chemistry specific and global skills that would be useful for an allied health student.

Chemistry Specific Global Skills Electrophoresis Pipetting Chromatography Use of computers Colorimetry – Protein Calibrations Specific Gravity Dealing with hazardous materials Ion-selective electrodes Measurement Acids & Bases Concentration (meq/mmol) Buffers Unit Conversion Dip Sticks (Hach Kits – Test Strips) Separation Techniques Osmosis Error Analysis Diffusion Data Interpretation Gas Laws Graphical Analysis Sugars Quality control-standards Dialysis Record keeping Functional Groups

Chromatography was listed as a specific topic and separation techniques was listed as a global topic that would be useful for allied health students. Based on this workshop, the audience was revised from strictly organic chemistry students to also include allied health courses in chemistry.

Review of the Literature A review of the literature is conducted to ensure that the project being developed has not already been done, that there is a need in the scientific community for such a project, and to find supporting ideas to help further the development of the project. Wendy Pierce states that according to the National Science Education Standards, all children should be able to do scientific inquiry by the fourth grade (8). Based on the National Science Education Standards, 12th grade students should be able to recognize and classify mixtures, and separate mixtures into purer substances by chromatography, distillation, and crystallization (9). Pierce describes a paper chromatography activity that uses question wheels as a format for inquiry learning in first- through fifth-grade classrooms (8).

A few examples of chromatography laboratory activities taught at the college level include separating a mixture of Oil Red O, Victoria Blue R, and fluorescein dyes using alumina as the stationary phase with 95% ethanol as the mobile phase (10), separating fluorescein, rhodamine B, and methylene blue using a 3:2:1 v/v mixture of acetone, n-propanol, and water (11), and separating a mixture of fluorescein, bromocresol green, methyl red, basic fuchsin, rhodamine B, and new methylene blue (12). Each of these laboratory activities involves the students conducting the separation, but none really have the students actively engaged in exploring the role of the stationary and mobile phases. Even though chromatography is taught at the college level, Schmaefsky expresses frustration that few students gain enough information about the theory of chromatography to be able to design a simple chromatography application. Because of this he has developed a simple paper chromatography activity to explore the roles of different mobile phases in liquid chromatography (13). Though chromatography is used from the first grade on, there are few activities that allow the students to be actively engaged in exploring the roles of both the mobile and stationary phases. This laboratory activity was designed to do just that.

2.2 Alpha Stage

Initial Drafting/Revision The proposed procedures for this laboratory activity were tested in the laboratory at key points in the development to make sure that the procedures could yield the desired experiences and results. Procedural steps were drafted as the procedure was tested. Diagrams, graphics, and

other visual components of the document were also created at the time to facilitate subsequent student testing.

Preliminary Design A preliminary document design was created to make the project information available to the target audience. The chromatography project involved a laboratory activity that would be used by college chemistry students in a laboratory setting. The design for this project was based on the needs of the target audience (student and instructor) and had a student handout and instructor notes as the main design. The template designed by the Center for Chemistry Education to be used for all materials developed through the Partnership for the Advancement of Chemical Technology (PACT) workshops was used in this project’s design. The template provides information for both the student and the instructor: Introduction o Description o Student Audience o Goals for the Experiment o Recommended Placement in the Curriculum Student Handout o Purpose o Scenario o Safety, Handling, and Disposal o Materials o Background o Procedure o Questions Instructor Notes o Time Required o Group Size o Materials o Safety, Handling, and Disposal o Points to Cover in the Pre-Lab Discussion o Procedural Tips and Suggestions o Sample Results o Plausible Answers to Student Questions o Extensions and Variations The introduction was designed for both student and instructor. A brief description of the activity was presented. The student audience was identified, the goals for the experiment were outlined, and the appropriate placement for this experiment in the chemistry curriculum was identified.

The student handout began with a purpose statement to give the students direction. The scenario provided a link to the industrial world as students were put into a situation that mimics a problem or task that an industrial chemist or technician might encounter. The scenario provided relevance to the experiment.

As this laboratory activity was inquiry-based, it was important for the students to understand the nature of the chemicals they would be using. Safety, handling, and disposal guidelines listed the chemicals being used, hazards associated with each chemical, and the proper method of disposal.

The materials list was a quick reference guide to help students visualize required laboratory equipment and chemicals.

The background was a section of the student handout that provided information that would be useful to the student. The background for the chromatography project defined key terms such as mobile phase, stationary phase, column chromatography, and the theory of chromatography in general.

The procedure was a description of the process that the students follow as they conduct the laboratory investigation. In inquiry laboratory activities, the procedure is often a paragraph describing the general direction that must be taken, followed by step-by-step directions to teach the laboratory technique. The technique of preparing a column was outlined in step-by-step form and included a diagram visualizing the various parts of the column. The method of loading the column was described, along with a caution statement informing the student not to ever let the column go dry. Questions were designed to help the students evaluate and make sense of their data. Some questions were very specific while others were more open ended to help the students think critically about their work. Students write a conclusion at the end of the laboratory activity summarizing their results. The Instructor Notes are critical for scenario and inquiry-based labs because the instructor is probably not familiar with the lab. Time requirements help the instructor plan the activity into the curriculum. A detailed materials list with solution preparation instructions was developed. These instructions save the instructor a tremendous amount of preparation time. The safety, handling, and disposal guidelines provide the instructor with needed guidelines to ensure that the activity is conducted in a safe manner.

Points to cover in the pre-lab along with procedural tips and suggestions provide the instructor with details on how to prepare the students for the lab and ensure that the lab runs smoothly. Sample results give the instructor an idea of what to expect without having to conduct the investigation personally. This also saves instructors a large amount of time if they want to use the activity with their students. A grading rubric with plausible answers to student questions makes grading easier and timelier for the instructor. The instructor notes are designed to allow an instructor to run the activity with minimal preparation time. An instructor will be more likely to try a new experiment when detailed instructions and guidelines are provided.

Micro Testing The procedure was micro-tested by a student in the target audience. The developer provided the person from the target audience (microtester) a copy of the student handout. The microtester began the activity. The developer observed. No verbal or written comments came from the microtester unless there was a chance the microtester would be harmed. The microtester verbally expressed her feelings as she tested the activity. This helped the developer understand the tester’s thought processes. The developer took notes while observing the microtester conduct the lab, watching for misconceptions, misinterpretations of the written document, and places where the microtester had trouble or became confused. At the conclusion of the activity, the developer interviewed the microtester. Don Storer points out several advantages of the microtesting methodology (5): 1. The tester cannot rely on others to perform the task. 2. The developer can observe misinterpretations of the written document, which might not be evident with classroom testing. 3. The developer may observe that the lab procedure is cumbersome to the microtester even though it seemed very clear to the developer. 4. Through the interview process, the microtester will usually provide some valuable insights in how to improve upon the activity. Even though microtesting occurs between the developer and the microtester, it is ideal that a third person be present while the microtesting occurs. This is to ensure the safety and well being of both the developer and the microtester.

Creation of an Alpha Draft The developer revised the document based on the results of the microtesting. The objective of the alpha draft was to provide a document that was ready to be peer reviewed and classroom tested. If a lot of revision had occurred after microtesting, a second phase of microtesting would have been undertaken. The microtesting of the chromatography lab helped the developer revise the procedural notes. It was found that specific step-by-step procedural steps for the construction of a chromatographic column were needed to help the student focus on the chemistry of the lab without becoming bogged down with designing a chromatographic column.

Internal Review of Alpha Draft The alpha draft was given to a respected colleague to be reviewed for content, correct chemistry, readability and grammar. The project editor and/or participants of the development workshop often internally review the document. Susan Hershberger, Visiting Assistant Professor at Miami University, reviewed the chromatography laboratory activity for chemistry content. She provided valuable insights into the chemistry involved with components of the mixture interacting with the mobile and stationary phases. The activity was classroom tested by the developer in the General Chemistry lab, CHM 144, at Miami University Middletown during the 1997 fall semester. The initial procedure had the students conducting a separation of methylene blue and sodium fluorescein by thin-layer chromatography. Silica gel plates were used as the stationary phase, with ethanol, acetone, n- propanol, glacial acetic acid, and water as the mobile phase. Students were given the opportunity to explore any combination of the mobile phases provided. Rf values were calculated and comparisons were made to determine the best solvent system to effect the separation. The students proceeded with a column chromatography experiment using alumina as the stationary phase. The students had the freedom to choose any of the previous mobile phases. Groups compared data and discussed their results.

The developer observed as the students struggled for 3 hours through the chromatography activity. It was apparent that the laboratory activity was too long and complicated for the students to attain the goal, that of understanding the role of the mobile and stationary phases.

2.3 Beta Stage

Creation of a Beta Draft Creation of the beta draft came as a result of the internal peer reviews, microtesting, and internal classroom testing by the developer. External Review The document was sent to an outside reviewer, Joel Shelton, for review. Shelton is an instructor of fundamental organic chemistry and is knowledgeable in the content and pedagogy. The beta draft was tested and reviewed by participants in the Allied Health Development Workshop. The participants in this workshop were experienced high school, community college, and university chemistry instructors. The participants were given the student handout and went though the activity as students. A review of the comments are listed: The activity itself can work. It is highly visual, and individual results depend on student technique, but even careless students can attain success. Fluorescein and methylene blue can readily be separated on silica gel using water as eluent, and there are significant differences in their behavior on alumina and silica gel that make this suitable for a discovery activity. However, the directions need to allow the students more freedom. Currently, the procedure is highly directive, and cannot be considered truly “discovery-based.” The handout seems to be written at too high a reading level. Many of the sentences are long and cumbersome, and the vocabulary level is rather high for allied health students, who generally are weak in science preparation. The background information seems insufficient to really give the students an understanding of the process of chromatography. The concepts of solid and liquid phase, adsorbance, and polarity are very difficult for inexperienced students to grasp, and they are all treated in only two paragraphs in the student handout. The analogy of aluminum cans and wood being caught by grass in a creek is weak; it seems likely that their different buoyancies might cause differences in floating rate, even without the grass. On the other hand, a suitable introductory activity might be made out of posing the question, “Compare the travel rates of a piece of wood and an aluminum can in a flowing stream.” The theoretical background for this activity needs to be expanded significantly, too. 15

The physical manipulations that the students do (actual procedure) will work if you already know what you are doing. If the students prepare a column, they will need an instructor demonstration of how to prepare a good column. The figure does not address how to hold it in the vertical position. The lack of controls is an issue in the solvent selection. The students try up to 8 solvent systems, some of which are quite complicated, but there is no obvious control of variables. Instead of so many wildly different solvents, a pure good one, perhaps water, and a pure bad one, perhaps acetone, can be studied, with the students responsible for trying mixtures in between. This would allow the students some opportunity to grasp the notion of systematic alteration of variables, an important concept in science. The students should probably not go directly from TLC on silica gel to an alumina column. For them the experience is probably clearer if TLC plates are done with silica gel and alumina, and then they can try a column of the total system that worked best on TLC. This should shorten their work time, which would be helpful. It is not clear that any inexperienced group could complete the lab in its current form in a reasonable time. In summary, we recommend that the activity be rewritten to include TLC on both alumina and silica gel, using fewer solvents, more attention to controls, and at most one column for isolation of a significant amount of material. An expanded scenario and less prescriptive instructions will be important. Based on the review from these experienced teachers, the beta draft was revised. The developer chose to focus strictly on column chromatography. Only two solvents were included in the subsequent draft: ethanol and water. The students now have the opportunity to make various mixtures of the two solvents as they investigate the role of the mobile phase. The background section was expanded to define key terms, and provide a more detailed description of the theory of chromatography. The activity was also revised to provide more detailed instructions on how to prepare the column. The reviewers also mentioned that the procedure was highly directive. Revision resulted in a few introductory paragraphs describing the goal. The only detailed instructions that remained involved the technique of preparing and loading the column.

Classroom Test with Target Group Because of the large number of revisions that were made, the revised draft was microtested by a chemistry student at Eastern Arizona College and classroom tested in the General Chemistry and Fundamental Chemistry courses at Eastern Arizona College. The activity flowed more smoothly, and the developer felt good about the changes that had been made.

Document Design Graphics needs and organization of visuals are evaluated. The readability and usabilty of the document are taken into consideration. The document design and illustrations are completed by editorial staff, which includes production manager, technical writers and editors, page designers, and illustrators. The readability based on the Flesch-Kincaid Grade Level Score was 10.0 for the chromatography laboratory activity, which means that a sophomore in high school could read and understand the document. The Flesch Reading Ease Score was 47.7. A score of 60-70 is recommended. Based on these scores, the developer shortened some of the sentences making them more concise. This helped to lower the readability of the document, and increase the reading ease.

2.4 Pilot Stage

Test and Revise

Further classroom testing was conducted in McBride’s General Chemistry and General Organic Chemistry labs at Eastern Arizona College. A few more revisions were made based on the results of these classroom tests.

Pilot Testing

Pilot testing occurred during a National Science Teacher’s Association National (NSTA) Conference held in San Diego, California. The developer conducted a workshop at the conference in which several high school educators from across the country went through the chromatography experiment. Several of these educators asked that the experiment be sent to them via email so that they could use it in their classes.

Revision/Final Production Final revisions were made as needed and the final document was prepared for publication.

2.5 Field Stage

Field Testing

Field-testing occurred by Joel Shelton in his chemistry courses taught at Eastern Arizona College. High school chemistry students from several Arizona high schools conducted further field-testing as part of the laboratory section of the annual Student Chemistry Adventure, a chemistry competition for rural Arizona high schools.

Final Draft

The final draft was completed and is now part of the chemistry laboratory curriculum at Eastern Arizona College.

2.6 Dissemination Dissemination is the sharing of the project with others in the chemical education community. The chromatography activity was disseminated through presentations at the following conferences: 1998 (Spring) ACS Conference Dallas, TX (Presentation) 1998 (Summer) BCCE Waterloo, Canada (Presentation) 2000 (Summer) BCCE Ann Arbor, MI (Presentation) 2002 (Spring) NSTA San Diego, CA (Hands-on Workshop) During the 2002 NSTA conference in San Diego, the developer hosted a hands-on- workshop in which participants actively participated in the chromatography activity. Additionally the document was submitted to the Journal of Chemical Education and was included on the CCE web site http://www.terrificscience.org/lessonexchange/chromatography.shtml - Methylene as a part of the Terrific Science Lesson and Lab Exchange (4).

Chapter 3 – Description of Project Content

3.1 Overview of the Laboratory Investigation Column chromatography is a very useful method for separating and purifying solids and liquids. This technique is often employed during the first semester of organic chemistry courses, but seldom in introductory or general chemistry courses. This laboratory investigation is designed for introductory chemistry courses as well as general and organic chemistry courses. It fits well into the discussion on solution chemistry in the introductory and general chemistry curricula, as well as in separation techniques in organic chemistry.

Separation of components of a mixture depends on their respective adsorptivity with respect to a stationary phase and a mobile phase. Different adsorbents attract molecules differently. A highly polar adsorbent such as alumina adsorbs polar molecules to a much greater extent than it adsorbs nonpolar molecules. The adsorption process is the result of intermolecular attractions (dipole-dipole and hydrogen-bonding). Alumina and silica gel are the two most common stationary phases used in column chromatography. Alumina is more active and slightly basic, and will adsorb polar substances more strongly. It is the stationary phase of choice when nonpolar substances are being separated. Silica gel is less active and slightly acidic, and is normally used to separate polar substances. The decision of selecting a mobile phase is also very important in separating a mixture. Polar solvents will carry polar molecules resulting in faster elution of the polar molecules. The same is true for nonpolar solvents carrying nonpolar molecules (14,15,16).

When acidic or neutral alumina is employed as the stationary phase, ethanol provides the best separation of methylene blue and sodium fluorescein, with methylene blue eluting first from the column and sodium fluorescein remaining adsorbed at the top of the column. When basic alumina is employed as the stationary phase, sodium fluorescein elutes first when water is used as the mobile phase, but methylene blue elutes first when ethanol is used as the mobile phase.

When silica gel is employed as the stationary phase, water provides the best separation, with sodium fluorescein being eluted first and methylene blue remaining adsorbed at the top of the column. It is interesting to note that the choice of stationary and mobile phase results in different elution orders for the two substances being separated.

3.2 Experimental Procedure The class is divided into at least four teams of three to four students each. Each team selects an individual as their team leader. The instructor assigns each team one of the following stationary phases.

• aluminum oxide, activated, acidic, Brockmann I

• aluminum oxide, activated, basic, Brockmann I

• aluminum oxide, activated, neutral, Brockmann I

• silica gel

The team leader organizes the team and assigns each member a specific mobile phase to experiment with. All members of the team use the assigned stationary phase. The team leader assigns each person one or more of the following five solvent systems: (pure water, 25:75 (v:v) water/ethanol mixture, 50:50 (v:v) water/ethanol mixture, 75:25 (v:v) water/ethanol mixture, and pure ethanol). The team leader must ensure that all solvent systems are tested. Some members of the team will have to conduct more than one chromatography experiment so that all five solvent systems are tested.

The team leader consolidates the team data and makes a verbal report of the experimental results to the rest of the class. After all the team leaders have presented their results, the instructor, or one of the team leaders, leads the class in a discussion to develop the best plan to separate the methylene blue/sodium fluorescein mixture.

3.3 Preparation of a Chromatography Column The preparation and setup of a chromatography column is represented in Figure 1. This microscale chromatographic column is inexpensive, easy to use, and versatile. A small plug of glass wool or cotton is inserted into the neck of a 5.75-inch Pasteur pipette. The glass wool or cotton is lightly packed into the neck using the end of a 9.00-inch Pasteur pipette or an “opened” paperclip. If the cotton or glass wool is packed too tightly, the solvent flow will be restricted. The glass wool or cotton is covered with a thin layer of sand to create a level surface upon which 20

to place the stationary phase (17). A beral pipet, with part of the top section cut off, makes a nice funnel to add the sand and stationary phase.

The stationary phase (alumina or silica Solvent Level gel) is added to the column until it reaches half way up the column. This stationary phase is packed by gently tapping the outside wall of

Sand the column with a pencil. A second layer of sand is added on top of the stationary phase. A Stationary Phase (alumina or silica gel) thermometer clamp, attached to a ring stand, Sand Glass Wool is helpful in securing the chromatography column and keeping it in an upright position.

A small beaker (50-mL works well) is placed

under the column to collect the eluate. Figure 1: Chromatography Column and Setup The column is filled with solvent, which is allowed to flow through to “wet” the column. The column is considered “wet” once solvent begins to elute. The solvent is allowed to continue to flow through the column until the solvent level drops just below the top sand layer. Two drops of the methylene blue/sodium fluorescein mixture are then carefully added to the top of the column. This dye mixture is allowed to flow just below the top sand layer. The column is then filled with eluting solvent (16,17).

The solvent is allowed to elute through the column. When the solvent level gets close to the top sand layer, more solvent is added. The column must never be allowed to become dry. It is important, however, to add the additional solvent carefully so that no mixing occurs with the dye. Once the first component has been eluted, the beaker is removed and properly labeled.

Members of the team record the identity of the stationary and mobile phase, the component of the mixture that eluted first (methylene blue or sodium fluorescein), and the level of separation (great, fair, or poor).

Each team leader collects data from the individual team members and shares those data with the class. Discussion follows as to the best mobile phase and the best stationary phase to use to effect the separation. There are several systems that give great separations. Students discuss

which mobile phase/stationary phase system would be best if the goal is for methylene blue to be eluted first, and which system would be best if the goal is for sodium fluorescein to elute first. The instructor can lead the discussion to help the students see how changing the mobile phase or stationary phase can make a big difference in a separation. Depending on the class and the time, students can conduct further experiments. Students can test the yellow colored solution that elutes to determine if it is in the salt (sodium fluorescein) or acid (fluorescein) form. Adding acid to sodium fluorescein causes the fluorescence to disappear resulting in a duller orange/yellow color. Adding base to fluorescein will result in the solution turning to a brighter yellow/green fluorescent color. Students can also test the solubility of fluorescein, sodium fluorescein, and methylene blue in water and ethanol. Students can investigate other solvents such as acetic acid, or mixtures of acetic acid, ethanol, and other alcohols.

3.4 Safety, Handling, and Disposal Students and instructors are expected to conduct the laboratory activity in a safe, non- threatening manner. Safety, handling, and disposal instructions are provided in the instructor notes. Most of the safety, handling, and disposal instructions for this lab come from the Flinn Chemical and Biological Catalog Reference Manual (18).

Students are required to wear chemical splash goggles! Alumina Hazard Alert: Body Tissue irritant; avoid inhalation of dust Storage: Inorganic #4 Disposal: Bury it in a landfill approved for the disposal of chemical and hazardous waste.

Ethyl Alcohol Hazard Alert: Dangerous fire risk; flammable; addition of denaturant makes the product poisonous. Toxic by ingestion. Storage: Organic #2 in a dedicated flammables cabinet. Disposal: May be disposed of, not to exceed 100 grams per day, by rinsing down the sink followed by large amounts of water.

Silica Gel Hazard Alert: NONE Storage: Organic #4 Disposal: Bury it in a landfill approved for the disposal of chemical and hazardous waste.

Sodium Fluorescein (D&C Yellow No. 8) Hazard Alert: NONE

Storage: Organic #9 Disposal: Bury it in a landfill approved for the disposal of chemical and hazardous waste.

Methylene Blue Hazard Alert: Moderately toxic. LD50 1180 mg/kg. Storage: Organic #9 Disposal: Bury it in a landfill approved for the disposal of chemical and hazardous waste.

3.5 Sample Student Data Students look up physical data of fluorescein, sodium fluorescein, and methylene blue in reference manual such as the Merck Index (19) in preparation for the laboratory investigation. A sample data table showing these physical properties is shown in Table 1.

Table 1: Physical Properties Substance M.W. Color Solubility (g/mol) Fluorescein, 376.28 Yellowish-red and water, slightly soluble in alcohol disodium salt intense yellowish- (D&C Yellow No. 8) green fluorescence C20H10Na2O5 Fluorescein 332.31 Yellowish-red to red Hot alcohol, glacial acetic acid, C20H12O5 powder alkali hydroxides or carbonates Methylene blue 319.86 dark green, odorless water, alcohol, chloroform crystals with bronze luster

The class is divided into at least four teams. Each team is assigned a specific stationary phase to investigate. The teams collect data and share the data with the class. At the end of all presentations, each student has data for all four stationary phases. The students analyze and interpret the data to determine the best choice of stationary phase and mobile phase to effect the separation of methylene blue and sodium fluorescein. Samples of student results are shown in Table 2, Table 3, Table 4, and Table 5.

Sample Student Results Table 2: Sample Student Results: Alumina, Basic Stationary Phase Mobile Phase Component Separation Observations eluting first Aluminum oxide, Water Sodium Fluorescein Great Fluorescent activated, basic, yellow solution Brockmann I elutes first Aluminum oxide, 75:25 Sodium Fluorescein Fair Fluorescent activated, basic, Water:Ethanol yellow / Green Brockmann I elutes first Aluminum oxide, 50:50 Mixture Poor Green solution activated, basic, Water:Ethanol (Mixture) (no separation) Brockmann I Aluminum oxide, 25:75 Water Methylene Blue Fair Blue solution activated, basic, Ethanol elutes first Brockmann I Aluminum oxide, Ethanol Methylene Blue Great Blue solution activated, basic, elutes first Brockmann I

Table 3: Sample Student Results: Alumina, Neutral Stationary Phase Mobile Phase Component Separation Observations eluting first Aluminum oxide, Water Methylene Blue Great Blue solution activated, neutral, elutes first Brockmann I Aluminum oxide, 75:25 Methylene Blue Great Blue solution activated, neutral, Water:Ethanol elutes first Brockmann I Aluminum oxide, 50:50 Methylene Blue Great Blue solution activated, neutral, Water:Ethanol elutes first Brockmann I Aluminum oxide, 25:75 Water Methylene Blue Great Blue solution activated, neutral, Ethanol elutes first Brockmann I Aluminum oxide, Ethanol Methylene Blue Great Blue solution activated, neutral, elutes first Brockmann I

Table 4: Sample Student Results: Alumina, Acidic Stationary Phase Mobile Phase Component Separation Observations eluting first Aluminum oxide, Water Methylene Blue Great Blue solution activated, acidic, elutes first Brockmann I Aluminum oxide, 75:25 Methylene Blue Great Blue solution activated, acidic, Water:Ethanol elutes first Brockmann I Aluminum oxide, 50:50 Methylene Blue Great Blue solution activated, acidic, Water:Ethanol elutes first Brockmann I Aluminum oxide, 25:75 Water Methylene Blue Great Blue solution activated, acidic, Ethanol elutes first Brockmann I Aluminum oxide, Ethanol Methylene Blue Great Blue solution activated, acidic, elutes first Brockmann I

Table 5: Sample Student Results: Silica Gel Stationary Mobile Phase Component Separation Observations Phase eluting first Silica Gel Water Sodium Great Fluorescent Yellow Color Fluorescein elutes first Add H+, fluorescence disappears Silica Gel 75:25 Sodium Great Fluorescent Yellow Color Water:Ethanol Fluorescein elutes first Add H+, fluorescence disappears Silica Gel 50:50 Sodium Great Fluorescent Yellow Color Water:Ethanol Fluorescein elutes first Add H+, fluorescence disappears Silica Gel 25:75 Sodium Great Dull Yellow Color elutes Water:Ethanol Fluorescein first Add OH-, fluorescence appears Silica Gel Ethanol Sodium Fair Dull Yellow Color elutes Fluorescein (Methylene first Blue is starting Add OH-, fluorescence to come down appears the column)

Students use Pasteur pipettes as columns, with thermometer clamps to hold the columns in a vertical position. Beakers are used to collect the eluent. An example of a typical student setup with the experiment in progress is shown in Figure 2.

Acidic Alumina – Basic Alumina Solvent: Water Figure 2: Typical Student Column Chromatography Setup

3.6 Discussion Sodium fluorescein and methylene blue are both soluble in water. Methylene blue is soluble in alcohol. Sodium fluorescein is slightly soluble in alcohol. Fluorescein (the acidic form of sodium fluorescein) is insoluble in water, but soluble in hot alcohol and glacial acetic acid (19).

The adsorption of methylene blue and sodium fluorescein onto the stationary phase of silica gel or alumina is due to dipole-dipole attractions and hydrogen bonding. Alumina has a greater adsorptive power for polar molecules than does silica gel (20). Silica gel shows stronger retention for methylene blue. Alumina shows stronger retention for sodium fluorescein. This reversal in retention order for the mixture of methylene blue and sodium fluorescein is likely due to the acidic functional group (carboxyl) found on sodium fluorescein. Sodium fluorescein is a more polar molecule than methylene blue. Thus sodium fluorescein is expected to be adsorbed more strongly onto the alumina than it would be adsorbed onto the silica gel. Methylene blue does not have an acidic functional group and is weakly retained on the alumina.

Danielson noted similar reversals in retention between fluorescein and methylene blue using silica and zirconia as the stationary phase and hexane/methanol (33:67) as the mobile phase. Silica showed stronger retention for methylene blue and methylene green and zirconia

showed greater retention for fluorescein, rhodamine B, methyl red, and methyl orange which all contain an acidic functional group (21).

The structural formulas for sodium fluorescein, fluorescein, and methylene blue are shown in Figure 3.

O O

O O + H+ Na+ O- HO - H+

O O

O- Na+ O H fluorescein sodium fluorescein

N N

Cl- N

Methylene Blue

Figure 3: Structures of Sodium Fluorescein, Fluorescein, and Methylene Blue

Silica Gel as the stationary phase

With silica gel as the stationary phase, methylene blue, which is basic and less polar than sodium fluorescein, is adsorbed onto the slightly acidic silica gel. Sodium Fluorescein is more polar, very soluble in water, and is easily carried through the column. Sodium fluorescein is very soluble in water, but only slightly soluble in ethanol. With ethanol as the solvent, the sodium fluorescein abstracts hydrogen, forming fluorescein. This is evidenced by the dull orange/yellow color that elutes from the column. Fluorescein is slightly acidic, and is not readily adsorbed by the acidic silica gel but is readily carried through the column by the ethanol. 27

Acidic Alumina as the stationary phase

With acidic alumina as the stationary phase, and water as the solvent, sodium fluorescein abstracts a hydrogen forming fluorescein, which is not soluble in water. The fluorescein is adsorbed onto the acidic alumina column, which has a stronger absorptive power for polar molecules. The methylene blue, which is less polar, is not as strongly adsorbed by the acidic alumina, is soluble in water, which carries it through the column. The same pattern follows when ethanol is used as the solvent. The sodium fluorescein abstracts a hydrogen forming fluorescein, which is only slightly soluble in ethanol, and is adsorbed onto the column. The methylene blue, which is soluble in ethanol, is carried through the column.

Neutral Alumina as the stationary phase

With neutral alumina as the stationary phase, sodium fluorescein is adsorbed onto the column and methylene blue is readily carried through the column by the polar solvent, water. When ethanol or water is used as the solvent of choice, the polar sodium fluorescein is strongly adsorbed onto the neutral alumina. Methylene blue, which is less polar, is readily carried through the column by the solvent.

Basic Alumina as the stationary phase

With basic alumina as the stationary phase, and water as the solvent, sodium fluorescein, being in a basic alumina medium remains in the salt form, which is very soluble in water. The sodium fluorescein is therefore carried through the column by the water, while the methylene blue is adsorbed onto the alumina column. When ethanol is used as the solvent, methylene blue elutes first out of the column. The sodium fluorescein is less soluble in ethanol than methylene blue. With sodium fluorescein being more polar than methylene blue, the sodium fluorescein is more strongly adsorbed onto the alumina column, which has a greater adsorption power for polar compounds, resulting in methylene blue eluting first out of the column.

3.7 Conclusion Students discover the complete reversal of elution orders as they investigate various mobile and stationary phases. Through experimentation and sharing of class data, students are able to witness for themselves how the mobile phase and stationary phase play a vital role in the separation of components of a mixture.

Chapter 4: Summary and Conclusions

The development of a laboratory activity that challenged the students to work together to solve a problem provides a learning experience that causes the students to be actively engaged, teaches laboratory techniques, and creates an atmosphere of learning science based on the scientific method. The development of this activity took several years to bring it to its present level. The developer classroom tested the activity after each revision. The document went through several peer reviews. The expertise of many students, scientists and educators, including Mickey Sarquis, external reviewer Susan Hershberger, the Journal of Chemical Education referees, members of the Allied Health Workshop, and student microtester Noelle Nielson, played a role in the development of this activity. The development of materials to provide opportunities for students to be actively engaged in their own learning is not a quick, easy process, but involves much testing and revision. However the final product can provide students with wonderful learning experiences.

Unit I References

1. Siebert, E. D.; McIntosh, W. J., Eds. College Pathways to the Science Education Standards; NSTA Press: Arlington, VA, 2001; p XV. 2. Svoronos, P.; Sarlo, E.; Kulawiec. Organic Chemistry Laboratory Manual; Wm. C. Brown Publishers: Dubuque, IA, 1997; pp 42-50. 3. Partnership for the Advancement of Chemical Technology; NSF Grant No. ATE DUE- 9454518, Arlyne M. Sarquis, PI. 1994. 4. Teacher Resources at the Center for Chemistry Education. http://www.terrificscience.org/PACT/index.shtml (accessed August 2003). 5. Storer, D. A. Doctoral Dissertation, Miami University, Oxford, OH, 2000. 6. Using Chemistry to Enhance the Technical Workforce in the Innovation Age; NSF Grant No. 0101400, Arlyne M. Sarquis, PI, 2001. 7. Storer, D. A. Sample Preparation for Chemical Analysis; Terrific Science Press: Middletown, OH, 1998. 8. Pierce, W. Science and Children 2001, May, 39-41. 9. Scope, Sequence, and Coordination: A Framework for High School Science Education. http://dev.nsta.org/ssc/moreinfo.asp?id=930 (accessed August 2003). 10. Bonicamp, J. M.; Moll, E. B. Microchemical Journal 1997, 55, 145. 11. Scism, A. J. J. Chem. Ed. 1985, 62, 361. 12. Calvey, R. J.; Goldberg, A. L. J. Assoc. Off. Anal. Chem. 1985, 68, 471. 13. Shmaefsky. B. R., Shmaefsky, T. D., Shmaefsky, K. M. J. of Coll. Sci. Teach. 2001, 30, 344. 14. Mayo, D. W.; Pike, R. M.; Trumper, P. K. Microscale Organic Laboratory; Wiley & Sons: New York, 1994; pp 97-104. 15. Williamson, K. L. Microscale Organic Experiments; DC Heath and Company: Lexington, MA, 1987; pp 108-111. 16. Svoronos, P.; Sarlo, E. J. Chem. Educ. 1993, 70, A158. 17. Reynolds, R. C.; O’Dell, C. A. J. Chem. Ed. 1992, 69, 991. 18. Flinn Chemical & Biological Catalog Reference Manual 2002; Flinn Scientific Inc.: Batavia, IL, 2002. 19. Budavari, S., Ed. The Merck Index, 12th ed.; Merck & Co.: Whitehouse Station, NJ, 1996; pp 705, 1035.

20. Fessenden, R. J.; Fessenden, J. S. Techniques and Experiments for Organic Chemistry, PWS: Boston, MA, 1983; pp 106-107. 21. Danielson, N. D.; Katon, J. E.; Bouffard, S. P.; Zhu, K. Anal. Chem. 1992, 64, 2185.

Unit II: Integrating the Chemistry of Copper Mining into the

Chemistry Curriculum

Chapter 1 – Introduction and Conceptual Framework

1.1 Statement of the Problem As we enter the 21st century in the Innovation Age with tremendous technological advances, employers are seeking highly qualified workers who are honest, can work cooperatively in a team setting, are able to follow directions, exhibit leadership skills, have a positive mental attitude and are dependable (1). With a shortage of highly trained, qualified workers, employers are often turning to the community colleges to create training programs for their employees (2).

Often workers in the technical areas are hired without any chemistry background; yet they are required to make decisions that are based on chemical principles. Supervisors at Phelps Dodge Morenci have expressed an interest in developing programs that will help future employees exhibit knowledge of the chemical processes of copper mining before they are hired (3).

The effort described in this unit is designed to meet the challenge of preparing students for advanced technology careers through the development of industry-based curriculum (4,5).

1.2 Overview of the Copper Mining Project This project considers the research on laboratory methods and the national call to develop industry-based chemistry curriculum (6-13). I worked with the Center for Chemistry Education, CCE, at Miami University, high school teachers and students across the nation, and the Phelps Dodge copper mining industry, as part of a National Science Foundation Grant “Using Chemistry to Enhance the Technical Workforce in the Innovation Age” (14) to develop laboratory experiments that are industry-based, and help students to develop higher-level thinking and problem-solving skills. These laboratory activities incorporate cooperative learning, discovery learning, and problem-based learning as a means of bringing the chemistry student to a higher level of critical thinking and problem solving. An academy was held to provide a professional development course for college and high school educators. This course reinforced the teachers’ chemical knowledge and provided an opportunity for them to experience discovery- based and problem-based laboratory experiments developed around an industrial situation. Through hands-on experience, the teachers are better able to return to their classrooms and integrate these laboratory experiments into their own curricula (15).

1.3 Goal and Objectives The overriding goal of this project was to provide an opportunity for high school and college students to learn chemistry content through experiences that mirror the workplace. The goal of this project was addressed through four objectives: 1) “Create standards-based college and high school resource materials” that integrate chemistry content with workplace readiness and safety skills (14). 2) Create a set of themed laboratory experiments that are inquiry-based and culminate in a research experience doable at the high school and 2-year college levels. 3) Provide an opportunity for high school students, college students, and teachers to experience industrial chemistry through Phelps Dodge Copper Mine Tours (in person, via through an interactive CD-ROM, or through accessing an interactive website). 4) Provide high school and college teachers an opportunity for professional development.

Chapter 2: Description of the Copper Mining Project The Copper Mining Project incorporates curriculum and materials development, professional development, local partnership development, and dissemination.

2.1 Curriculum and Materials Development The Chemistry of Copper Mining module is intended for use in high school or undergraduate college chemistry. The module uses the learning cycle approach to present the chemistry of the industrial processes of mining copper to the students. The module includes thirteen investigations (three of which are web-based and ten which are laboratory experiments) and an accompanying interactive CD-ROM, which provides an explanation of the chemistry used in copper mining with a virtual tour of an operational copper mine. The thirteen investigations are based on chemical concepts and principles as listed in Table 6. Student handouts for these laboratory investigations are located in the Student Manual (Appendix C). The instructor notes for the investigations are located in the Instructor’s Manual (Appendix D). The laboratory investigations were developed using the CCE Continuous Quality-Control Materials Development Protocol developed through research conducted by Mickey Sarquis (14). This process was described in Unit I-Chapter 2 of this dissertation. The laboratory investigations were developed using the Learning Cycle. These investigations focus on the three phases of copper mining, which are leaching, hydrometallurgical solution extraction, and the electrowinning processes. The laboratory investigations were developed to emphasize the practical aspects of chemistry in the mining industry. The laboratory investigations were designed to allow students to learn about the nature of science and technology, learn problem-solving skills, learn manipulative skills, learn major chemical concepts and principles, and develop positive interests, attitudes, and values (16). The laboratory investigations employ cooperative learning and teamwork, are discovery-based and problem-based, and encourage the students to apply the Scientific Method to an industrial situation (17). Students are expected to collect and interpret data, formulate hypotheses, test those hypotheses, and communicate their results through verbal and written means.

Table 6: Copper Mining Laboratory Investigations (Refer to Appendix C for Student Manual and Appendix D for Instructor’s Manual) Learning Cycle Activity Skills or Concepts Reinforced Teaching Method

Leaching Exploration Copper Bearing Minerals chemical formulas, percent by mass, physical properties Exploration Properties of Copper Ores physical properties, solubility, weighing, volume measurements Application Leaching Copper weighing, sample preparation, pH, acids/bases, graphing Concept Chemistry of Leaching physical properties, solubility, chemical Introduction (Website or CD Activity) formulas, concentration Concept Colorful Transition Metals Electromagnetic radiation, light, color, Introduction spectrophotometry, graphing Application Spectrophotometric Solution preparation-dilutions, Beer’s Determination Law, graphing, spectrophotometry, buret reading Solution Extraction

Exploration Purification Techniques Solubility, single-replacement reactions, activity series of metals Concept Chemistry of Extraction Solubility, intermolecular forces, Introduction (Website Activity) extraction, organic functional groups Application Solution Extraction Solubility, intermolecular forces, extraction techniques, mixing, Le Chatelier’s Principle Electrowinning

Awareness Copper Replacement Activity series of metals Concept Electrochemistry Oxidation/Reduction, electrochemistry, Introduction acid/base chemistry Concept Chemistry of Electrowinning Oxidation/Reduction, electrochemistry, Introduction (Website Activity) acid/base chemistry Application Electrowinning Electrometallurgy of copper, oxidation/reduction potentials, reading meters

A two-day academy conducted at Miami University, held during the summer of 2003, provided an opportunity for high school and community college chemistry instructors to reinforce their chemical knowledge, strengthen their understanding of scientific problem solving, and establish contacts with industrial chemists. An interactive CD-ROM and website (weblet) that includes the thirteen investigations and a description of the process of mining copper, from core sampling to final copper product, was developed in an effort to bring industrial chemistry into classrooms across the nation.

2.2 Potential Impact and Significance The potential impacts from this project include the following: • Teachers and students will learn the importance of teamwork, accurate data collection and reporting, the high priority placed on safety in industry, and the importance of continued research to develop better and more efficient methods of mining. • Through summer academies and subsequent follow-up, teachers will witness the continuing research in copper mining, and the importance of discovery in the industrial world. • Chemistry students at Eastern Arizona College will visit with researchers at the Phelps Dodge Process Technology Center and watch as scientists, technicians, and college students, work together to conduct research into better, and more efficient methods of mining copper. Through an interactive CD-ROM or website, students and teachers will enjoy a better awareness of chemistry as it is employed in the industry. • The chemistry-rich process of copper mining will be shared with chemistry students everywhere. • Students will gain insights into the vast number of job opportunities that exist in the mining industry, i.e. chemists, technicians, metallurgists, machinists, and engineers. • Students and teachers will gain a greater appreciation of chemistry. It is expected that the awareness and experiences gained by students visiting industrial sites, either personally, or indirectly via an interactive CD-ROM, will be beneficial as those students seek employment in today’s technological world. Critical thinking skills, problem solving skills, and teamwork, developed through cooperative learning, discovery-based laboratory activities, and problem-based laboratory activities will help students be competitive as they vie for jobs in the technological workplace.

Laboratory investigations and the interactive CD-ROM developed from this project will be incorporated into high school and college chemistry courses at institutions across the nation as these materials are disseminated.

2.3 Project Team, Plan and Evaluation A Developmental Team was organized to brainstorm and develop ideas for possible laboratory activities, and conduct the video shooting for the CD-ROM. This team consisted of Phil McBride, Chemistry Instructor at Eastern Arizona College and students in the General Organic Chemistry course. Ric Bryce, supervisor at Phelps, arranged the tour with Phelps Dodge. Oscar Baca, chemist at Phelps Dodge Morenci took the development team on a tour of the Phelps Dodge Chemistry Lab to help the team witness the chemical analyses and testing done at the mine. James E. Bailey, Technical Services Superintendent of the Hydrometallurgical Division took the development team on a tour of the open pit mine, the leach fields, the solution extraction site, and the electowinning tank house to provide an overview of the macro chemistry involved in the entire process of mining copper. Helen Brooks of Synaps ChemTools was involved in the first filming and storyboarding of the copper mine CD-ROM. Filming for the CD-ROM continued with the developer shooting the footage and incorporating photos from several years of taking students on field trips to Phelps Dodge copper mine.

Chapter 3: Review of the Literature Methods of teaching in the laboratory have come to the forefront in chemical education. “Tightly structured and directed laboratory investigations are dull and demoralizing for the students and generate little in the way of concept development or physical understanding (6).” Laboratory situations that are completely unstructured are also ineffective (6). Discovery-based labs find a comfortable medium providing students with enough guidance to lead them into the thinking and forming of insights, but not so much as to give them all the answers. According to the Constructivist theory, knowledge must be actively constructed by the learner, and cannot be transferred from one person to another (8). Each individual takes communicated expressions and, each in his/her own way, constructs their own knowledge (7). Discovery-based and problem-based laboratory experiments provide a means for the individual to construct their own knowledge. Cooperative learning, inquiry learning, and active learning are considered viable alternative methods of teaching chemistry (9). Johnson and Johnson found that having students work together is more powerful than having students work alone or competitively (10). Meta- analysis of research studies show that cooperative learning strategies enhance learning and problem-solving skills (18). Problem-based learning (PBL) has proven effective in the sophomore chemistry laboratory at Emory University (11). Guided inquiry is being used in the classroom and laboratory at Franklin and Marshall College demonstrating a substantial increase in retention rates for the General Chemistry course (12). Case studies have been used in chemistry courses resulting in students exhibiting an increased interest in chemical topics(13). Inquiry Instruction, Discovery Instruction, and Problem-Based Instruction all have merits (8). The risks and choices associated with opening a copper mine have been explored in relation to the proposed Crandon Mine Project (19). ChemConnections developed a module with a major goal of having students gather information and evaluate the value of copper mining in terms of a natural resource and global market (20). The Copper Mining Project focuses on an active copper mine, explores the chemistry behind each process, and enables students to witness the application of chemistry in industry as they conduct their own scientific investigations.

Chapter 4: Chemistry of Copper Mining

4.1 Phase I: Leaching

Leaching is the dissolution of a valuable metal from minerals into an aqueous solution. In the leach cycle, copper-bearing ore bodies, typically in the form of low-grade ore or tailings containing copper carbonates (azurite and malachite) and hydroxy- silicates (Chrysocolla), is sprinkled with raffinate (a Figure 4: Leach Field at Phelps Dodge 15-20 g/L sulfuric acid solution). As the sulfuric acid Copper Mine, Morenci, AZ permeates through the ore bodies, the minerals dissolve releasing Cu2+ ions, evidenced by the blue color of the solution. The solution that comes off the leach fields contains copper (II) sulfate and is termed pregnant leach solution or PLS because it is full of copper (II) ions. The leaching occurs as shown in the following chemical reactions: • Malachite 2+ 2- Cu2CO3(OH)2 + 2 H2SO4 → 2 Cu + 2 SO4 + 3 H2O + CO2 • Chrysocolla 2+ 2- CuSiO3 · 2 H2O + H2SO4 → Cu + SO4 + 3 H2O + SiO2 • Azurite 2+ 2- Cu3(OH)2(CO3)2 + 3 H2SO4 → 3 Cu + 3 SO4 + 2 CO2 + 4 H2O

The leaching occurs in 6 cycle increments. A 20 ft high layer of ore is laid down. Raffinate is sprinkled on the top layer. This acidic solution percolates through the stockpile, dissolving copper minerals. The first cycle of leaching will remove 28-60% of the copper depending on the type of ore. After 90 days of leaching, a second layer of ore is laid on top of the first layer. The raffinate is sprinkled on the top layer, which percolates down through the stockpile leaching copper from both layers. This process continues through six leaching cycles. The PLS is collected in shallow ponds at the bottom of the ore pile in preparation to be piped to the solution extraction plant.

A new process involves the crushing of the ore to reduce particle size, thus increasing the surface area. The crushed ore is carefully spread over a large leach field using conveyer belts as shown in Figure 5.

Figure 5: Leach Field of crushed ore located at Phelps Dodge Copper Mine, Morenci, Arizona.

Workers on 4-wheelers spread the drip lines across the leach field to deliver sulfuric acid. Care must be taken to prevent compaction of the soil. If the soil is compacted too much, the sulfuric acid will not be able to permeate through the ore body.

4.2 Phase II: Solution Extraction The acid leaches the copper out of the ore where it moves into an aqueous solution. Unfortunately other metals, such as iron, are also leached out of the ore. This copper solution, termed “pregnant leach solution” with a concentration between 2.5 and 4.0 grams per liter of copper is contaminated with other metals. The solution extraction process purifies and concentrates the copper solution in preparation for electrowinning. Copper recovery by solution extraction has progressed from a limited application for copper recovery to a process of broad application in the recovery of copper from a variety of leach solutions (21). Kordosky (21) states the objectives of solution extraction: • “Purification of the copper from unwanted contaminants.” • “Concentration of copper values to the point where the final copper recovery process is applicable.”

• “Conversion of the copper to an aqueous matrix compatible with the final copper recovery process.” Pregnant leach solution (PLS), which is low in copper concentration, is transformed into a solution high in copper concentration, termed rich electrolyte, by a countercurrent process focusing on two solutions, aqueous and organic. Aqueous Solution The PLS is mixed with an organic solution that is composed of 13 volume % active chelating extraction reagent and 87 volume % aliphatic kerosene diluent. This organic solution has been specifically designed to extract copper from the PLS. The organic oxime molecule has been specially designed to capture the Cu2+ at the interface between the organic and aqueous phases. The organic reagent is composed of two hydroxy oximes. One is an aldoxime. The other is a ketoxime. Together they work to extract 2+ Cu from the aqueous phase. The aldoxime has a higher strength, which allows it to extract the 2+ 2+ Cu better, but it is also more difficult to strip the Cu from the organic back into the aqueous phase. The ketoxime has a lower strength, but strips more easily. Together they achieve a nice balance.

OH OH N

R = C9H19 or C12H25

Salicylaldoximes A = H A

Ketoximes A = C6H5 or CH3

Figure 6: Organic Reagent

This organic molecule is selective for copper at pH values of 1.5 – 1.8. At higher pH values, other metal ions will also be “captured” by the organic molecule. Acid content is extremely important. If the pH is too high, Fe3+ and any other metal ions present in the solution 2+ will also be extracted into the organic phase. If the pH is too low, Cu will not be extracted.

The organic reagent is dissolved in kerosene, a nonpolar solvent. This solution is termed “barren organic.” The barren organic is mixed with the PLS in a large tank for several minutes. Mixing allows the organic reagent to make contact with the Cu2+ ions. As the aqueous phase and organic phase contact each other, the Cu2+ exchanges with H+ forming a copper complex. The organic reagent grabs onto the Cu2+ ions forming a stable organic soluble chelate. The organic reagent has a preference for Cu2+, which forms strong complexes with “hard donor” atoms of oxygen and nitrogen. Divalent copper has a preference for forming square planar complexes with chelating ligands. This is easily achieved with the sterically unhindered oximes. Additional stability is added by hydrogen bonding interactions which result in a structure composed of two five-member rings, and two six-member rings. 3+ Most of the impurities such as Fe remain in the aqueous phase, giving it a light reddish- brown color. Figure 7 shows the process by which the organic molecule (a mixture of ketoxime and aldoxime) extracts the Cu2+ from the aqueous phase.

2+ + 2 L-H(org) + Cu (aq) ' L2Cu (org) + 2H (aq)

Figure 7: Extraction of Cu2+, Phelps Dodge Copper Mine, Morenci, AZ

The organic solution is now termed “Loaded Organic.” Since the organic and aqueous solutions are immiscible, gravity is used to separate them. The mixture flows through a settling tank (Figure 8) with the organic phase rising to the top. The aqueous solution is denser and settles to the bottom. After phase separation, the Figure 8: Settling Tank at Solution Extraction Plant, aqueous solution, which is now weak in Phelps Dodge Copper Mine, Morenci, AZ. copper ions, is termed the “Aqueous Advance.” The aqueous advance is sent through a second extraction where the organic reagent will have one more opportunity to remove Cu2+ from the aqueous solution. After the second extraction, the aqueous solution termed “Raffinate” is pumped back to the stockpiles to begin another leaching cycle. Organic Solution The organic solution becomes more and more concentrated in copper ions as it moves through the two extraction processes. The Cu2+ must be returned to the aqueous phase for the final stage, electrowinning. According to Le Chatelier’s Principle (22), if acid is added to the solution (lower the pH), the equilibrium will shift to the left as shown: 2+ + 2 L-H(org) + Cu (aq) ' L2Cu (org) + 2H (aq) 2+ The Cu would be returned to the aqueous phase. This is accomplished by adding lean electrolyte, which

consists of 200 g/L H2SO4 (sulfuric acid solution), to the loaded organic. This solution is mixed and sent to a settling tank to separate (Figure 9). Lean electrolyte is very Figure 9: Separation of Organic and Rich Electrolyte acidic and wants to exchange its Phelps Dodge Copper Mine, Morenci, AZ hydrogen ion for the copper ion in

the organic reagent. In this fashion, the lean electrolyte is said to “strip” the copper from the organic, transforming into “Rich Electrolyte.” The rich electrolyte is sent to the electrowinning tankhouse. The organic, now stripped of Cu2+, is sent back to the extraction site as barren organic.

4.3 Phase III: Electrowinning

Figure 10: Insertion of Steel Blanks Figure 11: Removal of Copper Cathodes Phelps Dodge Copper Mine Phelps Dodge Copper Mine

The rich electrolyte is pumped through a series of cells in the tankhouse (Figures 10). A set of stainless steel blanks are rinsed and then inserted into cell (Figure 11). Alternating plates of lead and stainless steel hang in cells. Each lead plate serves as the anode pole of an electric circuit. The stainless steel “blank” is the cathode. Direct current passes from the anode through the electrolyte, causing the copper ions in the electrolyte solution to plate onto the cathode. The electrolyte is now partially depleted of its copper and is termed “lean electrolyte.” The lean electrolyte is returned to the stripping process. The net effects of electrowinning are copper metal plated at the cathode, oxygen gas generated at the anode, and regenerated sulfuric acid in the 2+ 0 solution. Oxidation of H2O to O2 occurs at the lead anode and reduction of Cu to Cu occurs at the stainless steel cathode resulting in elemental copper. 2+ - 0 Cu + 2e → Cu Eo =+0.34V + - o ½O2 + 2 H + 2e → H2O E =+1.23 V 2+ 0 + o Cu + H2O → Cu + ½O2 + 2 H E = 0.34 + (– 1.23) = -0.89 V

These copper sheets are removed (Figure 11) and then mechanically separated from the stainless steel plates, corrugated and prepared for sale (Figure 12).

Figure 12: Copper cathodes are separated from stainless steel blanks, corrugated and prepared for shipping at Phelps Dodge Copper Mine, Morenci, AZ.

During this whole process, chemists, metallurgists, and technicians are constantly monitoring the concentration of the various solutions, testing for impurities, and running assays on samples to determine the amount of copper recovered. In addition, research is on going to identify factors that will make the process more efficient. An entire small-scale test facility in Morenci, Arizona is dedicated to research. This site is a miniature of the large process so that new hypotheses can be tested, and small-scale explorations and experiments can be conducted. Discovery and problem-based labs are going on at this site all the time, on an industrial scale.

Unit II References 1 Murphy, C. What Sets Apart Top Performing Technicians. Presented at the Partners for the Advancement of Chemical Technology (PACT) Forum on Developing Work Ethic and Self- Motivation in Students through Science Courses; Middletown, OH, 1999. 2 Shavers, C. L. J. Chem. Educ. 1999, 76, 458. 3 Bryce, R., Phelps Dodge, Morenci, AZ. Personal Communication, 2001. 4 Sarquis, A. M. Chemical Technicians in Industry [CD-ROM]; Center for Chemistry Education: Middletown, OH, 1998. 5 Kenkel, J. J. Chem. Educ. 1999, 76, 889-891. 6 Arons, A. B., The Physics Teacher 1993, 31, 278-282. 7 Herron, J. D. The Chemistry Classroom, Formulas for Successful Teaching; American Chemical Society, Washington, DC, 1996; pp 43. 8 Domin, D. S. J. Chem. Educ. 1999, 76, 543-547. 9 Paulson, D. R. J. Chem. Educ. 1999, 76, 1136-1140. 10 Johnson, R. T.; Johnson, D. W. ERIC Document Reproduction Service No. ED 266 960, 1986. 11 Ram, P. J. Chem. Educ. 1999, 76, 1122-1126. 12 Farrell, J. J.; Moog, R. S.; Spencer, J. N. J. Chem. Educ. 1999, 76, 570-574. 13 Bieron, J. F.; Dinan, F. J. Presented at the13th Biennial Conference on Chemical Education, Lewisburg, PA, 1994. 14 Sarquis, A. M., Using Chemistry to Enhance the Technical Workforce in the Innovation Age; NSF Grant No. 0101400, Miami University, Oxford, OH, 2001. 15 Cogan, M. L. Current Issues in Education of Teachers. In Handbook of Research on Science Teaching and Learning; Gabel, D. L. Ed.; Macmillan Publishing: New York, 1975; p 22. 16 Simpson, R. D.; Anderson, N. D. Science, Students, and School; Wiley & Sons: New York, 1981; p 111. 17 Abraham, M. R.; Pavelich, M. J. Inquiries Into Chemistry, 3rd Ed.; Waveland Press, Inc.: Prospect Heights, IL, 1999; p 3. 18 Herron, J. D.; Nurrenbern, S. C. J. Chem. Educ. 1999, 76, 1354-1361. 19 Miami University. Crandon Mine Project. http://www.terrificscience.org/risks/dailyplanet/crandon/index.shtml (accessed Oct 2003).

20 Walczak, M.; Zarzana, L.; Williams, D.; Charlesworth, P. Should We Recommend Building a Copper Mine?; Wiley & Sons: New York, 2001. 21 Kordoscy, G. A. J. of Mining 1992, 44, 40-45. 22 Burns, R. A. Fundamentals of Chemistry, 4th Ed.; Prentice Hall: Upper Saddle River, NJ, 2003; p 454.

Unit III: Integrating Lecture with Lab in the Introductory

Chemistry Course

Chapter 1 – Introduction and Conceptual Framework

1.1 Background and Significance

Community colleges throughout the nation face the task of educating a diverse group of students. Large numbers of part-time students versus full-time students, decreased academic preparation of entering students, and high rates of attrition lead faculty to develop innovative instructional approaches to address retention rates and academic achievement (1). The Task Force on the General Chemistry Curriculum stresses a need to serve a wider audience. The report notes that students are not provided with the type of experiences that teach them scientific reasoning skills. Yet for these students to be successful in their chosen fields, they must attain competency in science, math, engineering, and technology (SMET) (2). Don Storer recommends looking at ACT and SAT scores as predictors of student success in General Chemistry. He also suggests looking at GPA and rank in class (3). These indicators can be used to help identify those students who are at risk of failing. Once those students have been identified as at-risk, it is important to provide them with the help and resources to succeed. At Eastern Arizona College, 57% of the students enrolled in the fall semester of 2003 were pre-nursing students. Several others were considering the medical field. Most of the remaining students were taking introductory chemistry as the laboratory science requirement for graduation. Many of these students were working full-time and attending college part-time. Some of these students were returning to college after raising a family, others were forced to return to college due to divorce, and still others were returning to school to attain job skills which would help them provide a second income to support a family. With such a diverse population, each with specific needs, it became apparent that the introductory chemistry course should be revisited and possibly modified to meet the needs of these students. I taught Introductory Chemistry at Eastern Arizona College from August 1991 through May 2000 using the traditional method of teaching three 1-hour lectures on Monday, Wednesday, and Friday with an additional 3-hour lab being held on a Tuesday or Thursday. Students were completing the laboratory activities after 2 hours of laboratory time, and then wishing to leave to fulfill “other responsibilities,” promising to complete the post-lab questions at home. Other students asked for permission to miss the first part of lab, or the last part of lab, because it conflicted with another course that was only offered during the conflicting time. The students were visioning the laboratory as a separate class from lecture and didn’t see how the

laboratory and lecture were closely linked to provide the full chemistry experience. I desired to revise the laboratory part of the course to make it more relevant and appealing to the students. Unit III of this dissertation presents a research project that studied the effects of teaching introductory chemistry as a non-traditional, integrated lecture/laboratory course, meeting three times a week in two-hour blocks. The goal of the study was to develop a successful introductory chemistry course with an integrated lecture and laboratory, which could be taught three times per week, thus allowing part-time students with work and family more flexibility in their scheduling.

1.2 Review of the Literature Teaching chemistry to pre-nursing and non-science majors is a difficult assignment. Most of these students are taking the course as a pre-requisite to the Nursing Program or to fulfill their laboratory science requirement for graduation. The majority of these students are not interested in chemistry and many have postponed taking the course because they are scared of it. The pre- nursing students don’t see the relevance of chemistry to their field and want to know when they will ever use it again. Many nurses declare that they learned very little from their chemistry course or forgot what they did learn before they actually applied it in a clinical setting (1,4,5). Taft, Kaesz, Gillespie, and Lloyd mention that the introductory chemistry course should be aimed at all students who show an interest in majoring in any field of natural science, engineering, or medicine (6). Yet this course should also provide an opportunity for students from all fields to experience the relevance of chemistry in their lives and the world around them. One of the goals at North Carolina State University is to provide all entering freshman the opportunity to participate in at least one course with a maximum of 20 students, with an emphasis on increasing student-driven learning through fostering critical thinking, promoting student inquiry, and encouraging growth toward intellectual maturity (7). New Directions for General Chemistry, a resource for curricular change from the Task Force on the General Chemistry Curriculum (6), expresses the need for the laboratory to be an integral part of the General Chemistry course. This resource references an NSF Workshop on undergraduate chemistry (8) listing laboratory experience as “an essential part of learning chemical concepts and how new knowledge in chemistry is generated.” One of the greatest challenges of chemistry instructors is to help students develop connections between laboratory work and chemistry concepts. Many times, students focus on completing the laboratory as soon as possible so that they can leave class, and don’t focus on obtaining quality data (9). The students then return home to complete their discussion or post-lab 51

questions. Then when students are given laboratory data on an exam and asked to apply the chemical concepts to answer a question, they are unable to do so.

Courses have been designed at Inter American University, Hato Rey, Puerto Rico and at the College of Holy Cross that follow the laboratory-centered approach to teaching chemistry (6). The University of Michigan (10), Rensselaer Polytechnic Institute (11), and California Polytechnic State University (12) have merged classroom discussion and laboratory work in what is known as “Studio Chemistry.” Studio Chemistry at Rensselaer involves two 150-minute studio sessions and a one-hour weekly test. Each session has a one-hour discussion followed by a 50-minute laboratory. The laboratory is situated adjacent to the classroom (11). Christina Bailey is the project director of Studio Chemistry at California Polytechnic State University. Bailey states that the students do everything in the same classroom, which is set up with computers as well as equipment for wet chemistry (12).

In the laboratory-centered approach to teaching chemistry at Eastern Arizona College, chemical concepts are introduced first in the laboratory. Experimental results are discussed further in class and used to develop chemistry concepts. Students then return to the laboratory to apply the chemistry concepts they have learned. With the integrated lecture/laboratory approach, students relate the lecture with the laboratory.

1.3 Statement of the Problem The primary focus of the present study was to teach an introductory chemistry course three days a week in 2-hour blocks, with the laboratory portion of the course integrated with the lecture, to determine whether teaching the course in this manner increases student performance in introductory chemistry as measured by a quantitative final exam. A secondary focus of this study was to discover any changes in completion rate (retention) for students enrolled in the integrated lecture/laboratory course.

1.4 Statement of the Null Hypothesis There will be no significant difference in student academic achievement between introductory chemistry students taught in the traditional method and introductory students taught in the integrated lecture/lab method, as measured by a an introductory chemistry post-test.

Chapter 2 – Methodology

2.1 Subjects The participants for this study were selected from the population of students attending Eastern Arizona College. The student population is composed of 57% part-time students and 43% full-time students. This population is composed of 40% male and 60% female. There is 2% black, 5% Native Americans, 17% Hispanic, 73% Caucasian, with the remainder coming from Asian or Pacific Islander and those that didn’t declare their race. The students in the study self- selected themselves for the study by enrolling in an introductory chemistry course for non- science majors at Eastern Arizona College during the time period ranging from 1994-2003. All students enrolled in this course were participants in the study. Eastern Arizona College has provided educational opportunities to residents of Southeastern Arizona for over 110 years. While the college has experienced tremendous growth, its commitment to providing educational opportunity for all continues to shape its programs and services. The mission of Eastern Arizona College is to provide open access to quality higher education primarily to residents of its service area. The instructors for this study were Phil McBride and Joel Shelton. McBride taught introductory chemistry at Eastern Arizona College from 1994-2000 in the traditional method, which is defined as: three, 1-hour lectures held on Monday, Wednesday, and Friday, with an accompanying 3-hour laboratory section held on Tuesday or Thursday. Shelton taught using this same design from 1999-2003. Students enrolled in McBride’s Fundamental Chemistry course from 1994-2000 were classified as the McBride control. Students enrolled in Shelton’s Fundamental Chemistry course from 1999-2003 were classified as the Shelton control. Treatment began with the Fall 2001 semester. McBride taught the introductory chemistry course from Fall 2001 through Spring 2003 in 2-hour blocks, with students meeting on Monday, Wednesday, and Friday. The lecture and laboratory were integrated with no specific day or time set aside for laboratory investigations. All students enrolled in McBride’s Introductory Chemistry course were classified as the McBride treated.

2.2 Instrument The post-test for Fundamental Chemistry taught at Eastern Arizona College, developed in 1994, served as the evaluation instrument. I evaluated this test for reliability and validity with the stipulation that the reliability coefficient and the correlation coefficient both be greater than 0.70

for this instrument to be considered reliable and valid (13). Means and standard deviations from the post-test, along with a paired t-test, were used to compare the control subjects with the treated subjects. The Department of Institutional Research at Eastern Arizona College used the statistical package SPSS to analyze the data. SPSS is the industry leader of statistics and data mining software (14). I made every effort possible to ensure that the test instrument was valid and reliable. Criterion-related validity was demonstrated as post-test scores correlate with final course grades, i.e. Pearson correlation coefficients were greater than 0.7 (Appendix B). To ensure content validity, the majority of test items were taken from test banks and selected based on course objectives. To ensure construct validity, the test was designed to take approximately one hour for the average student. The students were given 1 hour and 50 minutes to complete the test. All students were able to complete the test within the allotted time. The Kuder Richardson (KR-21) calculation is a measure of internal (inter-item) consistency of a test instrument. The formula for KR-21 is: N 1− []M(N − M) KR − 21 = * N −1 N * V N - Number of items in the test M - Arithmetic mean of the test scores V - Variance of the raw scores or the standard deviation squared The KR-21 reliability coefficient for the post-test was calculated for each group. The values of KR-21 range from 0-1. Higher KR-21 values indicate a strong relationship between items on the test. A lower value indicates a weaker relationship between test items. A coefficient of 0.700 or higher is considered an adequate benchmark for internal consistency. The McBride control group had a KR-21 of 0.801, the Shelton control group had a KR-21 of 0.796, and the McBride treated group had a KR 21 of 0.837. All are greater than 0.700 demonstrating internal consistency of the test instrument. Three paired t-tests on Pre-test scores were conducted to determine if the classes were significantly different. • McBride Control / Shelton Control P value = 0.0714 Not significant • McBride Treated / McBride Control P value = 0.2208 Not significant • McBride Treated / Shelton Control P value = 0.5477 Not significant

There is no significant difference between control and treated test groups. The test instrument was found to be valid and reliable. The control groups are not significantly different in ability from the treated groups. Based on these results a t-test was chosen to compare control and treated groups.

2.3 Design of the Study This study involved a control group/experimental group design. The effectiveness of the integrated lecture/laboratory course was explored with students enrolled in a one-semester introductory chemistry course. Students taught by McBride from 1994-2000 were instructed using the traditional method. Students taught by Shelton from 1999-2003 were also taught in the traditional method. Students from both of these groups served as the control group. Students taught by McBride from Fall 2001 – Spring 2003 were taught using the integrated lecture/laboratory method and served as the treated group. The same textbook, Chemistry, A First Course, was used for all courses taught from 1994-2003 (15). The same laboratory manual (16,17) was used from 1994-2003. Instructor bias has been controlled for by using McBride’s classes taught in the traditional method from 1994- 2000 as one of the control groups.

2.4 Procedures Students in the control groups met on Monday, Wednesday, and Friday for 50-minute lectures each day. The lectures were accompanied by a mandatory laboratory session on a Tuesday or Thursday from 7:00 – 9:50 AM or from 1:00-3:50 PM. The treated group met on Monday, Wednesday, and Friday for a 2-hour block that was held either from 10:00 – 11:50 AM or from 1:00 – 2:50 PM. Both groups followed the same course outline, performed the same laboratory activities, were given similar chapter tests, used the same textbook, and were administered the same post-test. The laboratory activities in the laboratory manual used by both the control and treated subjects took approximately 2 hours to complete each week. The pre-test was administered during the first week of class to all enrolled students. The post-test was administered during the week of final exams. Achievement data were collected using the post-test developed in 1994. Final grades for each student were collected at the end of each semester.

Chapter 3 – Results

3.1 Quantitative Analysis For the quantitative analyses, the level of significance was set at α = 0.05. The available dependent variables, for each participant, were post-test score and final grade. To test for post- treatment differences in achievement, data were generated for each of the participants in the study. The data included pre-test scores, post-test scores, and the final grade, based on a 4.0 scale.

Table 3.1 Paired Samples Statistics Average Average Pre-Test Post-Test GPA Retention McBride Control 26.25 63.34 2.735 80.18

Shelton Control 24.83 63.65 2.713 69.10

McBride Treated 25.42 69.57 2.990 80.67

Table 3.2 Paired Samples Test

Test Group t Significance (2-tailed)

McBride Treated Shelton Control 3.410 0.001 Statistically Significant

McBride Control Shelton Control -0.532 0.595 Not Statistically Significant

McBride Treated McBride Control 3.789 0.000 Statistically Significant

The results of the t-test shown in Table 3.2 show that there is a significant difference between each control group and the tested group. Considering this information, the null hypothesis that there is no significant difference between the mean of each control group and that of the treated group was rejected. Paired samples statistics indicate a higher retention rate for the McBride courses and compared with the Shelton courses, but indicate no significant difference between the McBride control and the McBride treated.

3.2 Qualitative Analysis A survey was designed as a qualitative measurement tool. This survey was administered to all students enrolled in Fundamental Chemistry at Eastern Arizona College during the Spring 2002 and Fall 2002 semesters and designed to assess student attitudes towards lab and lab instruction. The first section of the survey was designed to look at gender, age, and college background. The second section focused on the math and science backgrounds of each class. The third section of the survey uses a Likert scale to measure student attitudes towards laboratory activities and techniques. Students responded to eleven statements with scaling ranged from 1 to 5. Example: 11. The labs are an important part of the chemistry experience. 1 2 3 4 5 Strongly Agree Agree Neutral Disagree Strongly Disagree 1.39T 1.80C

The average for each question is indicated below the scale. The numbers in green, which also have a “C” after the number, are the average of the control subjects. The numbers in blue, which also have a “T” after the number, are the average of the treated subjects. According to question 11 in the above example, on a range of 1-5, the average for the treated group was 1.39, which lies closer to the strongly agree choice. The average for the control group was 1.80, which lies closer to the agree choice. Though both groups feel that labs are an important part of the chemistry experience, the treated group feels more strongly about it. The entire survey with percentiles and averages is included in Appendix B. Survey results indicate that there are more female students taking chemistry than male students. This correlates with the demographics of Eastern Arizona College, which has a student population of 60% female. The make-up of both the control and treated groups shows slightly more freshmen than sophomores. The average age for both groups is in the 21-25 year range. The highest percentile of students was in the 18-20-age range. The background data from the survey (Questions 4-8 in Appendix B) indicate that students from the control group had a better math and science background coming into the course. The control group felt more strongly that the math in the course was not too difficult, which correlates with their stronger math background. Almost every student in both groups had

taken a previous biology course in high school or college. The control group reported a higher percentage of students having completed chemistry, biology, and physics courses. The laboratory activities section of the survey was designed to determine the feelings of the students towards their laboratory experience. Both groups felt that they spent between 2 and 2.5 hours in the laboratory each week. These data indicate that the students in the 3-hour lab (control group) are leaving lab early. Both groups felt that they spent about 1 hour outside of class completing the write-up. Those students in the integrated lecture/lab course indicated that they spent approximately the same amount of time in the lab as the control group, but spent more outside time finishing up the laboratory write-up. Both groups indicated that the time spent conducting laboratory experiments was just right. The students in the integrated lecture/lab course felt more strongly that labs play an important part in the chemistry experience, and that the laboratory activities were a valuable learning experience. The majority of students in both groups agreed that the labs help them to understand the concepts discussed in class. The Lab Technique section of the survey was designed to determine the students’ perceptions on their ability to perform basic laboratory techniques. Students in the integrated lecture/lab course felt slightly more comfortable in their ability to carry out a laboratory experiment and report the results in a logical manner. The students in both groups felt capable of using basic laboratory apparatus such as a graduated cylinder, balance, and buret. The course organization section of the survey allowed students the opportunity to express their feelings about the format of the course. Students were asked to express their preference for taking the traditional course or the integrated lecture/lab course, if they had the chance to choose either format, and there were no work or course conflicts. The students enrolled in the traditional course chose to remain with the traditional format, with a few expressing an interest in the lecture/lab format. Students in the integrated lecture/lab course chose to remain with the integrated lecture/lab format with a few expressing interest in the traditional format. It appears that students in both groups were happy with the format of the course they took. Students from both groups agreed that they would recommend this course to other students, with the integrated lecture/lab group agreeing a little more strongly.

Chapter 4 – Summary A comparison of the traditional chemistry course (laboratory section separate from the lecture) with an integrated lecture/lab chemistry course highlights the benefits of each. The traditional format lends itself to larger class sizes for lecture accompanied by several smaller laboratory sections from which students can choose. The integrated lecture/lab format requires more flexibility and smaller class sizes. At large universities, a faculty member often teaches the lecture, with the lab being taught by a graduate assistant. At community colleges, a faculty member teaches both the lecture and the lab. The integrated lecture/lab course would appear to flow more smoothly if taught by one individual. Could this work in a large university, where teaching assistants play a major role in the teaching of lower level labs? Instead of teaching assistants (TAs) teaching only the labs, they could be given the responsibility to teach both lecture and lab in an integrated format. A faculty member would supervise the teaching of these courses and would serve as mentor and trainer. In this manner, one faculty member could supervise several TAs, each teaching an integrated lecture/lab course. In the traditional format, with laboratory sections spread throughout the week, it is often difficult to coordinate the lecture with the lab. Some lab sections complete a lab for the concept is discussed in lecture, while others in the same lecture may complete the lab after the concept is discussed. In contrast, with the integrated lecture/lab course, the concept is discovered in the laboratory and then developed in the subsequent lecture. However, lab rooms must be carefully coordinated to ensure that one is available when needed. In the integrated lecture/lab course, students have an easier time relating the laboratory experiments with the concepts they are learning because discussion of the concept follows the lab. Students develop a greater appreciation for how the labs help them learn and understand chemistry concepts, and they exhibit a greater feeling for the value of labs in the whole chemistry experience. Students feel better about their chemistry experience and they achieve at a higher level as demonstrated by this research study. Many students attending higher education have outside responsibilities, whether it is work, family, or both. Many are part-time students trying to coordinate classes with work. The integrated lecture/lab course, which meets during the same 2-hour block, three times a week, provides more flexibility and options for students trying to juggle school, work, and family.

With more college students in the United States completing their undergraduate science courses at a community college, these colleges are in a unique situation to strengthen science education. Community colleges are usually more flexible, have smaller class sizes, and are able to reach out to a more diverse population (18). The integrated lecture/lab course is a nice fit in a community college setting. With some flexibility and support, universities can also offer such a course (6). The integrated lecture/lab course is a viable alternative to the traditional lecture/lab course. Results suggest improved academic achievement with no loss in retention rate, and a greater appreciation for the benefits of lab as part of the chemistry experience.

Unit III References 1. Van Lanen, R. J.; Lockie, N. M. J. of Coll. Sci. Teach. 1997, 7, 419. 2. Shaping the Future: New Expectations for Undergraduate Education in Science, Mathematics, Engineering, and Technology; Advisory Committee to the National Science Foundation; Directorate for Education and Human Resources; National Science Foundation: Washington, DC, 1996. 3. Storer, D. A. Doctoral Dissertation, Miami University, Oxford, OH, 2000. 4. Wilkinson, S. L. C&EN 2003, 81, 59. 5. Jones, T. H. D. J Chem. Ed. 1976, 53, 581. 6. Lloyd, B. D. New Directions for General Chemistry; Division of Chemical Education; American Chemical Society: Washington, DC, 1994. 7. Oliver-Hoya, M. T. J Chem. Ed. 2003, 80, 899. 8. J. of Coll. Sci. Teach. 1989/90, 21, 134-147. 9. Rudd, J. A., Greenbowe, T. J. Hand, B., J. of Coll. Sci. Teach. 2001/02, 31, 230-234. 10. University of Michigan Chemistry. Studio 130 Syllabus. http://www.umich.edu/~chemstu/syllabus/list.htm (accessed November 2003). 11. Apple, T.; Cutler, A. J Chem. Ed. 1999, 76, 462. 12. California Polytechnic State University. CalPoly Magazine Annual Report 2002 Advancing the Mission: The Year in Review. http://www.calpolynews.calpoly.edu/magazine/02annual_report/chemstudio.html (accessed November 2003). 13. Jacobs, L. C; Chase, C. I. Developing and Using Tests Effectively; Jossey-Bass: San Francisco, 1992; pp 35. 14. SPSS Inc. http://www.spss.com/applications/higher_education/ (accessed October 2003). 15. Kroschwitz, J. I.; Winokur, M.; Lees, A. B. Chemistry, A First Course, 3rd Ed.; Wm. C. Brown: Boston, MA, 1995. 16. Corwin, C. H. Laboratory Experiments: Basic Chemistry, 6th ed.; Prentice Hall: New Jersey, 1992. 17. Corwin, C. H. Laboratory Experiments: Basic Chemistry, 7th ed.; Prentice Hall: New Jersey, 1996. 18. Crow, L. J. of Coll. Sci. Teach. 2003, 33, 54.

APPENIDIX A

Descriptive Statistics and t-Test for the Learning Project

APPENIDIX A: Descriptive Statistics and t-Test for the Learning Project

Correlations GPA and Post-test (McBride Control)

Descriptive Statistics Mean Std. Deviation N Post-Test Score 63.33856502 14.69586 446 GPA 2.734913793 1.024953 464

Correlations Post-Test Score GPA Post-Test Score Pearson Correlation 1 0.755781439 Sig. (2-tailed) . 2.67246E-83 N 446 444 GPA Pearson Correlation 0.755781 1 Sig. (2-tailed) 2.67E-83 . N 444 464 ** Correlation is significant at the 0.01 level (2-tailed).

Correlations GPA and Post-test (Shelton Control)

Descriptive Statistics Mean Std. Deviation N Post-Test Score 63.65193 14.51469 362 GPA 2.712766 1.015846 376

Correlations Post-Test Score GPA Post-Test Score Pearson Correlation 1 0.713539 Sig. (2-tailed) . 1.39E-57 N 362 362 GPA Pearson Correlation 0.713539 1 Sig. (2-tailed) 1.39E-57 . N 362 376 ** Correlation is significant at the 0.01 level (2-tailed).

Correlations GPA and Post-test (McBride Treated)

Descriptive Statistics Mean Std. Deviation N Post-Test Score 69.57292 15.33468 96 GPA 2.989691 0.895531 97

Correlations Post-Test Score GPA Post-Test Score Pearson Correlation 1 0.707597 Sig. (2-tailed) . 7.64E-16 N 96 96 GPA Pearson Correlation 0.707597 1 Sig. (2-tailed) 7.64E-16 . N 96 97 ** Correlation is significant at the 0.01 level (2-tailed).

Paired Samples Test for Pre-Test

Pre-Test t df Sig. (2-tailed)

McBride Control & Shelton Control 1.8069 464 0.0714

Paired Samples Test for Pre-Test

Pre-Test t df Sig. (2-tailed)

McBride Treated & Shelton Control 0.6032 103 0.5477

Paired Samples Test for Pre-Test

Pre-Test t df Sig. (2-tailed)

McBride Treated & McBride Control 1.2319 103 0.2208

POST TEST COMPARISONS

Paired Samples Statistics

Std. Error Post-Test Mean N Std. Deviation Mean Pair 1 McBride Post-test Treated 70.01 75 14.551 1.680 Shelton Post-test Control 61.77 75 14.157 1.635 Pair 2 McBride Post-test Control 63.05 295 14.863 0.865 Shelton Post-test Control 63.72 295 14.160 0.824 Pair 3 McBride Post-test Treated 71.37 81 14.350 1.594 McBride Post-test Control 62.15 81 15.957 1.773

Paired Samples Correlations

Post-Test N Correlation Sig. Pair 1 McBride Treated & Shelton Control 75 -0.062 0.596

Pair 2 McBride Control & Shelton Control 295 -0.114 0.051

Pair 3 McBride Treated & McBride Control 81 -0.042 0.707

Paired Samples Test

Paired Differences 95% Confidence Interval of the Std. Std. Error Difference Post-Test Mean Deviation Mean Lower Upper T df Sig. (2-tailed) McBride Treated & Pair 1 Shelton Control 8.24 20.924 2.416 3.43 13.05 3.410 74 0.001

McBride Control & Pair 2 Shelton Control -0.67 21.664 1.26 -3.15 1.81 -0.532 294 0.595

McBride Treated & Pair 3 McBride Control 9.22 21.908 2.43 4.38 14.07 3.789 80 0.000

Appendix B

Fundamental Chemistry Survey and Results

Appendix B: Fundamental Chemistry Survey and Results

Personal Data 1. Gender 1 2 Male Female 1.55T 1.61C

Male Female Mean n Shelton (Control) 39.0% 61.0% 1.61 41 McBride (Treated) 45.5% 54.5% 1.55 44

2. What is your college classification? 1 2 3 Freshman Sophomore Other 1.54C 1.64T

Freshman Sophomore Other Mean n Shelton (Control) 58.59% 29.3% 12.2% 1.54 41 McBride (Treated) 47.7% 40.9% 11.4% 1.64 44

3. What is your age category? 1 2 3 4 5 16-17 18-20 21-25 26-30 30+ 2.76C 2.80T

16-17 18-20 21-25 26-30 30+ Mean n Shelton (Control) 58.5% 19.5% 9.8% 12.2% 2.76 41 McBride (Treated) 2.3% 45.5% 34.1% 6.8% 11.4% 2.80 44

Background 4. Which is the highest math course you completed at the college or high school level prior to taking this course? 1 2 3 4 5 Elementary Intermediate College Trigonometry Calculus Algebra Algebra Algebra (HS Algebra 1) (HS Algebra 2) 2.65T 2.88C

Elem. Inter. College Trig. Calculus Mean n Algebra Algebra Algebra Shelton (Control) 7.3% 43.9% 22.0% 7.3% 19.5% 2.88 41 McBride (Treated) 13.9% 27.9% 44.2% 7.0% 7.0% 2.65 44

5. The algebra used in this course was too difficult for me. 1 2 3 4 5 Strongly Agree Agree Neutral Disagree Strongly Disagree 3.84T 4.24C

Strongly Agree Neutral Disagree Strongly Mean n Agree Disagree Shelton (Control) 7.3% 2.4% 48.8% 41.5% 4.24 41 McBride (Treated) 13.6% 25.0% 25.0% 36.4% 3.84 44

6. Have you completed a previous chemistry course in high school or college?

1 2 YES NO 1.39C 1.45T

YES NO Mean n Shelton (Control) 61.9% 39.1% 1.39 41 McBride (Treated) 54.5% 45.5% 1.46 44

7. Have you completed a biology course in high school or college?

1 2

YES NO 1.05C 1.09T

YES NO Mean n Shelton (Control) 95.1% 4.9% 1.05 41 McBride (Treated) 90.9% 9.1% 1.09 44

8. Have you completed a physics course in high school or college?

1 2

YES NO 1.68C 1.82T

YES NO Mean n Shelton (Control) 34.2% 65.8% 1.68 41 McBride (Treated) 18.2% 81.8% 1.82 44

Laboratory Activities 9. The average amount of time that I feel that I spent in the laboratory each week was

1 2 3 4 5 More than 3 3 hours 2.5 hours 2 hours Less than 2 hours hours 3.54C 3.57T

> 3 hrs 3 hrs 2.5 hrs 2 hrs < 2 hrs Mean n Shelton (Control) 0% 4.9% 48.8% 34.1% 12.2% 3.54 41 McBride (Treated) 4.5% 4.5% 27.3% 56.8% 6.8% 3.57 44

10. The average amount of time I spent outside the chemistry laboratory working on the write-up of the week’s experiment was 1 2 3 4 5 More than 3 3 hours 2 hours 1 hour Less than 1 hour hours 3.86T 4.10C

> 3 hrs 3 hrs 2 hrs 1 hrs < 1 hrs Mean n Shelton (Control) 0% 7.3% 17.1% 34.1% 41.5% 4.10 41 McBride (Treated) 4.5% 6.8% 20.5% 34.1% 34.1% 3.86 44

11. The labs are an important part of the chemistry experience.

1 2 3 4 5 Strongly Agree Agree Neutral Disagree Strongly Disagree 1.39T 1.80C

Strongly Agree Neutral Disagree Strongly Mean n Agree Disagree Shelton (Control) 41.5% 39.0% 17.1% 2.4% 1.80 41 McBride (Treated) 63.6% 34.1% 2.3% 1.39 44

12. The laboratory activities were

1 2 3 4 5 Extremely Too Too Long Just Right Too Short Extremely Too Long Short 2.83C 2.93T

Extremely Too Just Too Extremely Mean n Too Long Long Right Short Too Short Shelton (Control) 19.5% 78.1% 2.4% 2.83 41 McBride (Treated) 2.3% 9.1% 81.8% 6.8% 2.93 44

13. The labs helped me to understand the concepts discussed in class. 1 2 3 4 5 Strongly Agree Agree Neutral Disagree Strongly Disagree 2.10C 2.14T

Strongly Agree Neutral Disagree Strongly Mean n Agree Disagree Shelton (Control) 22.0% 48.8% 26.8% 2.4% 2.10 41 McBride (Treated) 27.3% 38.6% 27.3% 6.8% 2.14 44

14. I would have preferred to work by myself in the labs.

1 2 3 4 5 Strongly Agree Agree Neutral Disagree Strongly Disagree 4.07C 4.41T

Strongly Agree Neutral Disagree Strongly Mean n Agree Disagree Shelton (Control) 4.9% 14.6% 48.8% 31.7% 4.07 41 McBride (Treated) 2.3% 6.8% 36.4% 54.5% 4.41 44

15. I feel that the laboratory activities were a valuable learning experience.

1 2 3 4 5 Strongly Agree Agree Neutral Disagree Strongly Disagree 1.75T 1.93C

Strongly Agree Neutral Disagree Strongly Mean n Agree Disagree Shelton (Control) 31.7% 43.9% 24.4% 1.93 41 McBride (Treated) 45.5% 40.9% 9.1% 2.3% 2.3% 1.75 44

Lab Technique 16. I feel that I could take the directions from a laboratory activity that was given to me, perform the laboratory activity, and present my results in a logical manner. 1 2 3 4 5 Strongly Agree Agree Neutral Disagree Strongly Disagree 2.05T 2.18C

Strongly Agree Neutral Disagree Strongly Mean n Agree Disagree Shelton (Control) 15.4% 56.4% 23.1% 5.1% 2.18 39 McBride (Treated) 22.7% 56.8% 13.6% 6.8% 2.05 44

17. I feel confident in using a graduated cylinder. 1 2 3 4 5 Strongly Agree Agree Neutral Disagree Strongly Disagree 1.68T 1.74C

Strongly Agree Neutral Disagree Strongly Mean n Agree Disagree Shelton (Control) 30.8% 64.1% 5.1% 1.74 39 McBride (Treated) 40.9% 52.3% 4.5% 2.3% 1.68 44

18. I feel confident in using a balance.

1 2 3 4 5 Strongly Agree Agree Neutral Disagree Strongly Disagree 1.66T 1.82C

Strongly Agree Neutral Disagree Strongly Mean n Agree Disagree Shelton (Control) 30.8% 59.0% 7.7% 2.6% 1.82 39 McBride (Treated) 43.2% 47.7% 9.1% 1.66 44

19. I feel confident in using a buret. 1 2 3 4 5 Strongly Agree Agree Neutral Disagree Strongly Disagree 1.74T 1.79C

Strongly Agree Neutral Disagree Strongly Mean n Agree Disagree Shelton (Control) 31.6% 57.9% 10.5% 1.79 38 McBride (Treated) 39.5% 48.8% 9.3% 2.3% 1.74 43

Course Organization 20. If you had your choice of the three formats again, and there were no conflicts with work or other courses, which format would you prefer? 1) Three (1-hour) lectures on Monday, Wednesday, and Friday with a 3-hour weekly lab on Tuesday or Thursday. 2) Three(2-hour lecture/lab) sessions on Monday, Wednesday and Friday. 3) Four (75-minute lecture/lab) sessions on Monday, Tuesday, Wednesday, and Thursday 1.25C 1.91T

Choice Choice Choice Mean n 1 2 3 Shelton (Control) 78.6% 20.0% 2.5% 1.25 40 McBride (Treated) 13.6% 83.7% 4.7% 1.91 44

21. At Eastern Arizona College, the Chemistry Laboratory is designed to occupy half of the time spent in class (3 hours per week). Would you prefer more laboratory activities during the week that take between 1 and 2 hours to complete and are integrated with the lecture or longer laboratory activities that allow you 3 hours to complete and are held on a day other than lecture. 1) Shorter, 1-2 hour labs integrated within the lecture. 2) Separate 3-hour labs held on a day separate from lecture. 3) Other, Please specify. 1.30T 1.70C

Choice Choice Choice Mean n 1 2 3 Shelton (Control) 42.5% 50.0% 7.5% 1.70 40 McBride (Treated) 77.3% 18.2% 4.6% 1.30 44

Overall

1 2 3 4 5 Strongly Agree Agree Neutral Disagree Strongly Disagree 1.86T 2.12C 22. I would recommend this class to other students.

Strongly Agree Neutral Disagree Strongly Mean n Agree Disagree Shelton (Control) 19.5% 53.7% 22.0% 4.9% 2.12 41 McBride (Treated) 31.8% 52.3% 13.6% 2.3% 1.86 44

APPENIDIX C

Student Manual

CHEMISTRY of COPPER MINING

By Phil Blake McBride

in partial fulfillment of his requirements

for the degree of Doctor of Philosophy

Department of Chemistry and Biochemistry

Miami University

Oxford, Ohio

2003

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Learning Cycle Teaching Method Activity Page Leaching Exploration Copper Bearing Minerals 76 Exploration Properties of Copper Ores 82 Exploration Leaching Copper 89 Concept Development Chemistry of Leaching (Website Activity) 96 Concept Development Colorful Transition Metals 98 Application Spectrophotometric Determination 107

Solution Extraction Exploration Purification Techniques 117 Concept Development Chemistry of Extraction (Website Activity) 126 Application Solution Extraction 128

Electrowinning Concept Development Electrochemistry 138 Concept Development Chemistry of Electrowinning (Website Activity) 143 Application Electrowinning 145

Student Handout Copper-Bearing Minerals

The Problem Branicoda Mining Operations is considering opening up a new mining site. The geologists feel that there are copper-rich ore bodies present at this new site. Branicoda Mining Operations is looking at sites that might contain azurite, chalcopyrite, chrysocolla, and malachite. They need more information about these minerals. Some of these minerals are blue, while others are green or tan. Branicoda Mining Operations is concerned that only the blue minerals contain copper.

Copper is found in the earth as native copper and in the form of minerals. There are two main types of copper-bearing minerals. Those minerals that contain sulfur are considered sulfide ores, and those that do not contain sulfur, but do contain oxygen are oxide ores. One of the differences between copper in minerals and native copper is the oxidation state of the copper. The oxidation state of the copper, combined with the type of mineral, helps determine the best method for processing in order to make elemental copper that can be sold for a profit.

Your Task Conduct research on the WWW or in your local library to find information on azurite, chalcopyrite, chrysocolla, and malachite to determine the structure and properties of each. Determine the oxidation state of copper in each of the minerals that might be present at the mine. Based on the chemical formula, calculate the percent by mass of copper in each mineral.

Materials

Per class, group, or student azurite chalcopyrite chrysocolla malachite

Safety and Disposal

As instructed by your teacher, follow appropriate safety procedures, including the use of personal protective equipment such as goggles and an apron. No special disposal procedures are required.

76 Student Handout Copper-Bearing Minerals

Procedure

1. Obtain a sample of each mineral from your instructor. Write a detailed description of the mineral. Include the name, formula, color, hardness, specific gravity, and physical description. Amethyst Galleries' Mineral Gallery at http://mineral.galleries.com/minerals/by-name.htm is a good reference to obtain data for the minerals being studied.

2. Conduct a search on the Internet to substantiate your data. List any discrepancies. Provide the site’s address and rank it on a scale of 1-5, with a 5 being excellent, and 1 being poor.

3. Assign oxidation states for all elements present in azurite, chalcopyrite, chrysocolla, and malachite. Oxidation states of some elements are listed in Table !.

Table 1: Oxidation States of Some Elements

Element Oxidation Numbers

Copper +1, +2

Hydrogen +1

Iron +2, +3

Oxygen -2

Silicon +2, +4

Sulfur -2, +4, +6

Example: Brochantite: CuSO4 · 3 Cu(OH)2

First let us consider the part of the molecule that only contains copper, oxygen, and

hydrogen, Cu(OH)2. We know that hydrogen is always 1+ and oxygen is 2-. The only unknown is copper.

Oxygen in Cu(OH)2 : (2-)(2) = -4

Hydrogen in Cu(OH)2 : (1+)(2) = +2

Copper in Cu(OH)2 : x

We can set up a simple algebraic equation to solve for the oxidation state of copper.

Step 1: Write the expression (-4) + (+2) + x = 0

Step 2: Combine like terms on the left side -2 + x = 0

Step 3: Add 2 to both sides +2 +2

x = +2

Since the net charge must be zero for Cu(OH)2, copper must exhibit a 2+ charge.

77 Student Handout Copper-Bearing Minerals

Now let us consider CuSO4.

Oxygen in CuSO4: (2-)(4) = -8

Copper in CuSO4: (2+)(1)= +2

Sulfur in CuSO4: x

(Sulfur must exhibit a 6+ charge to make the overall charge zero. (-8+2+x=0)

The final oxidation states of all elements in Brochantite is as follows:

2+ 6+ 2- 2+ 2- 1+ CuSO4 · 3Cu(OH)2 Assign oxidation states to each element in the following minerals. You will need to write the formula for each mineral before assigning oxidation states.

a. Azurite b. Chalcopyrite c. Chrysocolla d. Malachite

4. The percent by mass of copper can be calculated by dividing the molar mass of copper by the molar mass of the compound.

Example: Brochantite CuSO4 · 3 Cu(OH)2

Element Quantity x Mass (g/mol) = Total (g/mol)

Copper (Cu) 4 63.546 254.184

Sulfur (S) 1 32.066 32.066

Oxygen (O) 10 15.999 159.990

Hydrogen (H) 6 1.0079 6.0474

Total 452.287

molar mass of copper 254.184 Percent by mass of copper = ×100 = ×100 = 56.1997% total molar mass 452.287

Calculate the percent by mass of copper in

a. Azurite b. Chalcopyrite c. Chrysocolla d. Malachite

78 Student Handout Copper-Bearing Minerals

Discussion and Conclusions

Q1: Categorize the minerals as oxide or sulfide ores.

Q2: Rank the minerals based on the percent by mass of copper present.

79 Student Handout Copper-Bearing Minerals

Data Sheet Name ______

1. Description of Mineral

Mineral Formula Color Hardness Specific Description Gravity

Azurite

Chalcopyrite

Chrysocolla

Malachite

2. List at least 2 different websites that you visited to obtain your information. Rank the sites on a scale of 1-5, with 5 being excellent, and 1 being poor.

Site Ranking

3. Write the name and formula for each mineral Assign Oxidation States by writing the oxidation state of each element directly above that element in its formula.

Mineral Formula

Azurite

Chalcopyrite

Chrysocolla

Malachite

80 Student Handout Copper-Bearing Minerals

4. Percent of Copper by mass present in each formula.

Mineral Percent of Copper by Mass

Azurite

Chalcopyrite

Chrysocolla

Malachite

Q1: Which minerals are oxides?

Which minerals are sulfides?

Q2: Rank the minerals according to the percent by mass of copper present.

Student Handout Properties of Copper Ores

The Problem Any element that can be obtained profitably from a mineral is considered an ore. Copper is one such element. There are several copper ores, but they all fall into two main categories: oxide ores and sulfide ores. Azurite, malachite, and chrysocolla are a few examples of oxides ores. Chalcocite, bornite, idaite, covellite, and chalcopyrite are all examples of sulfide ores.

Physical properties of a substance are properties that are specific to that substance but do not result in a change in composition. Physical properties include color, odor, density, solubility, melting point, boiling point, electrical conductivity, hardness, malleability, and viscosity.

Physical properties must be considered when determining a method for mining an element. Some considerations that must be discussed are

• What type of ore is present?

• What is the best method for getting the copper out of the ore?

Branicoda Mining Operations is considering opening up a new mining site. The geologists feel that there are copper-rich ore bodies present at this new site. There is an abundance of water and sulfuric acid that could be used to dissolve (leach) the copper compounds found in the ore if this is possible. Leaching can be defined as the ability of a solvent (such as water or sulfuric acid) to dissolve precious metals from an ore body.

Your Task As chemical technicians of Etapula Laboratories, it is your responsibility to determine the following:

List several physical characteristics of each ore that will allow you to distinguish them from each other.

Given a rock sample, identify the mineral present based on its physical characteristics.

Determine if the copper-bearing mineral could be leached with water or 7.0 g/L H2SO4 (sulfuric acid).

82 Student Handout Properties of Copper Ores

Materials

Per lab team

50-mL of 7 g/L sulfuric acid (H2SO4) 10-20 g of each ore (azurite, chalcopyrite, chrysocolla, and malachite) magnifier (not required but useful) balance two 150-mL beakers 50-mL or 100-mL graduated cylinder

Safety and Disposal

As instructed by your teacher, follow appropriate safety procedures, including the use of personal protective equipment such as goggles and an apron.

Use caution when working with 7-g/L sulfuric acid. This is a dilute solution, but should still be handled with caution. If spills occur, neutralize by sprinkling with baking soda and diluting with water. The 7-g/L sulfuric acid can be disposed of by neutralizing with 1 M

sodium carbonate (Na2CO3) solution and flushed down the drain with 20-fold excess of water.

Follow any additional disposal procedures as outlined by your instructor.

Procedure

1. Your instructor will divide the class into teams of 3-4. Each team will identify someone as Laboratory Director, Scribe, Chemical Manager, and Spokesperson. The Laboratory Director is the leader in charge of the group. The Scribe records everything that occurs during the laboratory session. This record is the official record for the group and will be turned in for evaluation. The Chemical Manager retrieves any chemical substances needed from the instructor. The Spokesperson communicates the team results to other teams. All members of the team work together to accomplish the tasks.

2. The Chemical Manager of each team will obtain one of the following mineral samples: azurite, chrysocolla, malachite, or chalcopyrite from the instructor.

3. Note the physical appearance of each sample, paying close attention to color, clarity, and any other distinguishing characteristics. Record your observations.

4. Test the solubility of each ore sample in water and in sulfuric acid as outlined in steps 5-8.

5. Weigh out two 5-10 g samples of the assigned ore. Record the mass of each sample.

83 Student Handout Properties of Copper Ores

6. Place the ore samples into two separate 150-mL beakers.

7. Add 50 mL of water to the first beaker and label the beaker.

8. Add 50 mL of 7 g/L H2SO4 (sulfuric acid) to the second beaker and label the beaker.

9. Your team will be making and recording observations at six different times for the next 48 hours. Possible times are before school, during class, during lunch, and after school. Check with your instructor about the best times.

10. The Laboratory Director will assign each team member to record observations at the specified times. It is not necessary for all team members to be present for each observation, but each team member is required to attend one of the observation times and record those observations.

11. After the 48-hour observation period has ended, prepare a summary statement to read to the rest of the class. Include answers to the following questions:

Q1: Identify your ore sample.

Q2: Other teams must be able to identify your mineral based strictly on your written observations. What are some physical characteristics of your mineral that will allow it to be identified from a collection of several minerals?

Q3: Can your ore (mineral) be leached with water?

Q4: Can your ore (mineral) be leached with H2SO4?

Discussion and Conclusions

The Spokesperson from each team will present their laboratory results to the rest of the class. Other team members must listen attentively to be able to respond to the following questions:

D1: List the physical characteristics of azurite, chalcopyrite, chrysocolla, and malachite.

D2: Which of the ores (azurite, chalcopyrite, chrysocolla, and malachite) can be leached with water?

D3: Which of the ores (azurite, chalcopyrite, chrysocolla, and malachite) can be leached

with 7 g/L H2SO4?

D4: Which of the ores (azurite, chalcopyrite, chrysocolla, and malachite) appears to react the fastest with sulfuric acid?

84 Student Handout Properties of Copper Ores

Assessment

Branicoda Mining Operations has sent ore samples from several different possible mining sites. These sites include the Nietfeld Site, the Franklin Site, the Bonita Site, and the Graham Site. Your instructor has ore samples from each of these sites. Based on physical characteristics, identity the mineral(s) present in the ore sample from each site.

Write a letter to the Director of Mines describing the results of your laboratory tests. Report any identifiable minerals present at each site. Report the results of your solubility tests. Based on this information, give your recommendation as to which sites should be mined, and whether the ore at those sites should be leached with water or with 7 g/L

H2SO4

85 Student Handout Properties of Copper Ores

Name ______Data and Results

Group Members

Laboratory Director

Scribe

Chemical Manager

Spokesperson

Name of Mineral Sample

Physical Characteristics

86 Student Handout Properties of Copper Ores

Mass of Sample Mass of Sample

Leached with Observations Leached with Observations

water H2SO4

Date: Date: Time: Time:

Q3: Can your ore (mineral) be leached with water? Explain.

Q4: Can your ore (mineral) be leached with H2SO4? Explain.

87 Student Handout Properties of Copper Ores

D1: List the physical characteristics of azurite, chalcopyrite, chrysocolla, and malachite.

Mineral Physical Characteristics

azurite

chalcopyrite

chrysocolla

malachite

D2: Which of the ores (azurite, chalcopyrite, chrysocolla, and malachite) can be leached with water?

D3: Which of the ores (azurite, chalcopyrite, chrysocolla, and malachite) can be leached

with 7 g/L H2SO4?

D4: Which of the ores (azurite, chalcopyrite, chrysocolla, and malachite) appears to react the fastest with sulfuric acid?

Assessment:

H2SO4. Attach the letter to this page.

Student Handout Leaching Copper

The Problem Branicoda Copper Mine is considering opening up some new mining sites based on the recommendations from the chemical technicians at Etapula Laboratories. The geologists with help from Etapula Laboratories confirm that there are copper-rich ore bodies of chrysocolla and malachite present at the Franklin and Bonita sites. Both of these ores have been found to leach well with sulfuric acid.

In the traditional leach cycle, copper-bearing ore bodies, typically in the form of low-grade ore or tailings, are sprinkled with a 7-20 g/L sulfuric acid solution. As the sulfuric acid permeates through the ore bodies, the minerals dissolve forming Cu2+ ions in solution. This acid solution, which now contains Cu2+ ions, is called Pregnant Leach Solution or PLS. The PLS is collected in shallow ponds in preparation to be transferred to the solvent extraction circuit.

A new process involves the crushing of ore to increase the surface area. The crushed ore is carefully spread over a large leach field using conveyer belts. Workers on 4-wheelers spread drip lines across the leach field to bring in the sulfuric acid. Care must be taken to prevent compaction of the soil. If the soil is compacted too much, the sulfuric acid will not be able to permeate through the ore body.

Branicoda Mines is interested in determining the feasibility of this new process, including the benefits of crushing the ore, determining if sulfuric acid is consumed in the leaching process, and determining the amount of copper present in the ore bodies.

Your Task As chemical technicians, it is your responsibility in this lab to determine

If sulfuric acid is consumed (used up) in the leaching process of chrysocolla and/or malachite?

If it would be beneficial to crush the ore before leaching?

In a future lab, you will use the results from this lab to

Determine the amount of copper present per gram of ore?

Determine the benefits of crushing or not crushing the ore before leaching.

89 Student Handout Leaching Copper

Materials

Per lab team

200-mL of 7 g/L H2SO4 (sulfuric acid). This is 0.068 M. 20 g of the ore to be analyzed (chrysocolla or malachite) balance two 250-mL beakers watch glass or parafilm to cover beakers 100-mL graduated cylinder pH meter (preferred) or pH paper

Safety and Disposal

As instructed by your teacher, follow appropriate safety procedures, including the use of personal protective equipment such as goggles and an apron.

sodium carbonate (Na2CO3) solution and flushed down the drain with 20-fold excess of water.

Follow any additional disposal procedures as outlined by your instructor.

Procedure

12. Your instructor will divide the class into teams of 3-4. Each team will identify a Laboratory Director, Scribe, Chemical Manager, and Spokesperson. Remember that all members of the team work together to accomplish the tasks.

13. The Chemical Manager of each team will obtain a crushed and uncrushed sample of either chrysocolla or malachite from the instructor.

14. Describe the physical characteristics of the ore samples. The Scribe should record these observations.

15. Using a graduated cylinder, transfer 100-mL of 7 g/L H2SO4 (sulfuric acid) to a 250- mL beaker.

16. Record the pH of the H2SO4 (sulfuric acid) using a pH meter or pH paper.

17. Obtain a single rock (uncrushed ore) that weighs between 10 and 20 grams. Record the mass of the single ore sample.

18. Transfer the ore to the 250-mL beaker containing the H2SO4 (sulfuric acid). (

90 Student Handout Leaching Copper

19. Observe and record the color and clarity of the solution.

20. Record the pH of the solution using a pH meter or pH paper.

Q1 You will need to conduct a similar experiment with crushed ore to determine the feasibility of crushing the ore. Do you want the mass of the crushed ore to be the same as that for the uncrushed ore? Explain?

21. Based on your answer to Q1, weigh out a sample of crushed ore. Record the mass of this ore.

22. Transfer the crushed ore to a 250-mL beaker.

23. Using a graduated cylinder, transfer 100-mL of 7 g/L H2SO4 to the beaker full of ore.

24. Observe and record the color and clarity of the solution.

25. Record the pH of the solution using a pH meter or pH paper.

26. Put a watch glass or parafilm over the top of each beaker.

Q2 Why must the beakers be covered?

27. Place the beakers in a safe place, out of the way, where they won’t be disturbed.

28. Your team will be taking pH readings and making and recording observations at six different times for the next 48 hours. Possible times are before school, during class, during lunch, and after school. Check with your instructor about the best times for your class.

29. The Laboratory Director will assign each team member to record observations and the pH of each solution at the specified times. It is not necessary for all team members to be present for each observation, but each team member is required to attend at least one of the observation times and record those observations.

30. After the last observation, transfer 5 mL of each solution to a test tube and cover with a stopper or parafilm. Cover the beakers of solution as well, and save all solutions for later work. Note: If you discard the solutions, you will have to repeat this lab.

31. Prepare a written report to give to the other teams. Your report should include the identity of your ore sample, the physical characteristics of the ore, and a data table of your pH measurements and observations.

32. The Spokesperson will give the written report to the instructor, who will make copies for the other teams.

33. Obtain a copy of the other teams’ results.

34. Prepare a graph to compare acid consumption in the leaching of chrysocolla and malachite. Graph pH vs. time for chrysocolla using a colored pen or marker. Graph pH vs. time for malachite on the same graph using a different colored pen or marker.

91 Student Handout Leaching Copper

Discussion and Conclusions

Q3: Analyze your data and graph. What trends do you notice?

Q4: Was acid consumed in the leaching of chrysocolla and/or malachite? Explain your evidence.

Q5: What physical evidence do you have that copper was leached out of the ore body?

Q6: Would it be beneficial to crush the ore before leaching? Explain.

Assessment

Write a summary letter to the director of Mines stating your findings from this lab.

92 Student Handout Leaching Copper

Name ______Data and Results

Group Members

Laboratory Director

Scribe

Chemical Manager

Spokesperson

Ore type being tested

pH of the H2SO4 (sulfuric acid)

Crushed Mass Date: Date: Date: Date: Date: Date: Time: Time: Time: Time: Time: Time:

pH: pH: pH: pH: pH: pH:

Observations

Non-crushed Mass Date: Date: Date: Date: Date: Date: Time: Time: Time: Time: Time: Time:

pH: pH: pH: pH: pH: pH:

Observations

93 Student Handout Leaching Copper

10 20 30 40 Time (hours)

94 Student Handout Leaching Copper

Questions

Q1 Do you want the mass of the crushed ore to be the same as that for the uncrushed ore? Explain?

Q2 Why must the beakers be covered?

Q3: Analyze your data and graph. What trends do you notice?

Q4: Was acid consumed in the leaching of chrysocolla and/or malachite? Explain your evidence.

Q5: What physical evidence do you have that copper was leached out of the ore body?

Q6: Would it be beneficial to crush the ore before leaching? Explain.

Assessment

Write a summary letter to the director of Mines stating your findings.

Name ______Date ______Chemistry of Leaching Copper Access the following web site or use the CD-ROM to answer the following questions. http://teach2.eac.edu/pmcbride

Define the following terms: 1. Leaching

2. Raffinate

3. Run of Mine Ore

4. Pregnant Leach Solution

5. Hydrological Sink

Answer the following questions:

The process of copper mining starts after Geology has made block models identifying the location of ore deposits in different areas of the mine through core sampling. Drilling and blasting begins to expose the oxide and sulfide material for loading and haulage.

Once the area has been blasted, shovels are moved into place and the loading of haul trucks begins for the haulage of ore to the leach stockpiles or the crusher.

1. Once the ore has been hauled to the stockpiles, the leaching begins. What chemical is fed through the driplines to begin the leaching? What is the concentration of this chemical.

2. There are two different kinds of leach fields. One leach field uses haul trucks to bring in the ore. The other uses a conveyor belt. What is the main different between these two leach fields.

96 Student Handout Chemistry of Leaching Copper

3. Provide the name and formula for malachite, chrysocolla, azurite, and chalcopyrite. Identify each as an oxide or sulfide ore.

4. Approximately how many lifts are added each year?

5. How long does it take for a drop of acid to run through the leach field and be collected?

6. How is the solution collected once it runs through the leach fields.

7. Could leaching be done on copper ore if there was not a hydrologic sink? Explain.

8. What is the Cu2+ concentration as it comes off the leach fields?

9. Is the PLS a solution that only contains Cu2+? Explain.

Student Handout Colorful Transition Metals

The Problem Elements with outer electrons located in d orbitals are termed transition metals. These elements are located in the center of the periodic table in what is known as the “d-block” of elements. Several of these transition metals form very colorful compounds. When the d electrons become excited they absorb light. The electrons are not stable in outer energy levels and thus return to their ground states emitting light as they fall back. The colors of the transition metals are related to the frequencies of light absorbed and emitted (1).

Many of the transition elements absorb light in the visible region of the spectrum. Knowing the area of the spectrum in which these compounds have greatest absorbance allows us to take accurate measurements to determine the concentration of solutions that contain these transition metals.

Your Task Your lab has been sent a waste sample from Transition Metallica that is thought to contain cobalt, nickel, or copper. Transition Metallica must know which metals are present in the waste sample in order to properly dispose of the waste. Your lab director has been provided with known concentrations of a cobalt solution, a nickel solution, and a copper solution to use as references.

You have two tasks:

• determine the optimum wavelength of each transition metal solution.

• determine which transition metals are present in the mixture.

Materials

Per Team of 3-4 students 10-mL of 0.15 M Co(NO3)2 (cobalt (II) nitrate) 10-mL of 0.15 M Ni(NO3)2 (nickel (II) nitrate) 10-mL of 0.15 M CuSO4 (copper (II) sulfate) 10-mL of unknown waste sample 1 spectrophotometer (Spec-20 or Genesys-20, both work fine) 5-cuvettes

Safety and Disposal

As instructed by your teacher, follow appropriate safety procedures, including the use of personal protective equipment such as goggles and an apron.

98 Student Handout Colorful Transition Metals

Cobalt nitrate can be harmful if taken internally. Use caution when handling it. Solutions containing cobalt (II) ion should be collected and disposed of as heavy metals according to local regulations.

Nickel(II) nitrate is slightly toxic. Avoid dispersing this substance; dispense with care;

strong oxidant. Nickel compounds are known carcinogens by inhalation of dust. LD50 1620 mg/kg.

Copper(II) sulfate pentahydrate is a strong irritant to the skin and mucous membranes. To avoid inhaling its dust, use copper(II) sulfate only where there is adequate ventilation. It can be harmful or fatal if taken internally. If contact with the skin occurs, flush with running water. Wash your hands after use. Follow local ordinances for disposal of copper(II) salts. It is recommended that unused copper (II) sulfate solution be left to evaporate to dryness.

Follow any additional disposal procedures as outlined by your instructor.

Using a Spectrophotometer

A spectrophotometer is used to make absorbance measurements. Light passes into a monochromator (where only the desired wavelength, or a very narrow range of wavelengths, can pass through). The light then passes through the sample, and on to a phototube, where the light energy is converted to an electrical current that is registered on a meter.

The instruments we will use are capable of quite precise measurements so it will be essential that solutions be made carefully and the directions for making the measurements followed precisely. You need to be sure that you use the same instrument for all of your work. Directions for using the spectrophotometer can be obtained from your instructor.

Absorbance as a function of wavelength

Note: There are two types of cuvettes, cylindrical and rectangular. Cylindrical, glass cuvettes look like regular test tubes, but they are not. They usually have a vertical mark on the front to ensure that the cuvette is inserted into the spectrophotometer exactly the same way each time. Rectangular cuvettes might be made of glass or plastic. Some are transparent to light on all four sides. Others have two sides that are transparent to light and two sides that have grooves to help hold the cuvette. It is important to insert these rectangular cuvettes into the spectrophotometer so that the light beam passes through the transparent sides. In most cases, this involves inserting the rectangular cuvette with the transparent sides facing front to back.

99 Student Handout Colorful Transition Metals

The cuvettes have been carefully and precisely made to have a composition that is transparent to light of the visible range. Cuvettes must be handled with care, being sure to touch them only near the top, and to wipe off the outside with a piece of lintless paper (Kim Wipe) every time before putting it into the instrument. Cuvettes should be stored in wooden/ plastic test tube racks when not in use to prevent scratching. Students should not put these cuvettes in their lab drawers. Students who break cuvettes will be responsible for the cost of replacing them, so be careful!

Procedure

Prepare a spectrum for the given solution.

1. You will be working in teams of 4. One person will record the data for Co(NO3)2,

a second person will record the data for Ni(NO3)2, the third person will record the

data for CuSO4, and the fourth person will record the data for the unknown. Make those assignments right now and record all assignments.

2. Obtain a set of directions for the use of the spectrophotometer from your instructor. Follow these directions carefully and precisely. The directions in the procedure below are for the Spec-20. They may vary slightly if you are using a different instrument.

3. Obtain 10 mL of solution from your instructor. You will be assigned Co(NO3)2,

Ni(NO3)2, CuSO4, or the unknown.

4. Record the formula, name, color, and concentration of the solution you have been assigned.

5. Use the wavelength knob to set the wavelength to 350 nm.

6. With the compartment closed and no cuvette in the compartment, turn the power switch (zero control) to adjust the meter to read 0% T (transmittance). This is the front left-hand knob on the Spec-20.

7. Fill a cuvette approximately ¾ full of water. Wipe off the cuvette with a Kimwipe. Place the cuvette containing water into the sample compartment and align the lines. This is the reference solution (often called the “blank”). Close the cover and set the transmittance to 100% or the absorbance to 0 depending on the instructions for your spectrophotometer.

100 Student Handout Colorful Transition Metals

8. Remove the cuvette of water.

9. Fill a cuvette approximately ¾ full of Co(NO3)2. Wipe off the cuvette with a Kimwipe. Place the cuvette containing

Co(NO3)2 in the sample compartment and align the lines. Close the cover and record the absorbance. Remove the cuvette.

10. Fill a cuvette approximately ¾ full of Ni(NO3)2. Wipe off the cuvette with a

Kimwipe. Place the cuvette containing Ni(NO3)2 in the sample compartment and align the lines. Close the cover and record the absorbance. Remove the cuvette.

11. Fill a cuvette approximately ¾ full of CuSO4. Wipe off the cuvette with a Kimwipe.

Place the cuvette containing CuSO4 in the sample compartment and align the lines. Close the cover and record the absorbance. Remove the cuvette.

12. Fill a cuvette approximately ¾ full of the unknown waste sample. Wipe off the cuvette with a Kimwipe. Place the cuvette containing the Transition Metallica waste sample in the sample compartment and align the lines. Close the cover and record the absorbance. Remove the cuvette.

13. You will now increase the wavelength by 50 nm and repeat steps 7-12.

14. Obtain absorbance readings every 50 nm for the wavelength range 350 – 950 nm by adjusting the wavelength and then repeating steps 7-12. When you get to 600 nm switch the filter as shown in the picture below. Continue obtaining absorbance readings from 600 – 950 nm. Some spectrophotometers such as the Spectronic Genesys change the filter automatically.

15. Review your results. Find the wavelength that gave the greatest absorbance for

Co(NO3)2. Obtain absorbance readings at 5 nm increments on both sides of your maximum wavelength until you determine the absolute maximum absorbance (highest reading) for your solution. (Example: If your highest absorbance reading was 0.875 at 500 nm, then take absorbance readings at 495 nm and at 505 nm. If the absorbance at 495 nm is 0.870 and at 505 nm is 0.895, then take another absorbance reading at 510 nm. You wouldn’t have to continue with 490 nm because the absorbance went down to 0.870 at 495 nm.)

16. Repeat step 15 for Ni(NO3)2 and CuSO4,

17. On a single sheet of graph paper, plot an Absorbance vs. Wavelength graph for

Co(NO3)2, Ni(NO3)2, CuSO4, and the unknown.. It is helpful to use a different color for each compound.

101 Student Handout Colorful Transition Metals

Q1: Where on the graph does the absorbance remain relatively constant when the wavelength changes slightly? At this point the slope is zero. Point these areas out to your instructor. (Hint: There are at least two areas and sometimes three.)

Q2: Inform your instructor what you consider to be the optimum wavelength for your compound? Explain how you made this determination.

Q3: What is the color of, and optimum wavelength for cobalt?

Q4: What is the color of, and optimum wavelength for nickel?

Q5: What is the color of, and optimum wavelength for copper?

Discussion and Conclusions

Prepare a table to compare the colors and optimum wavelengths of the solutions used by you and your teammates for the various transition metal compounds.

Q6: What is the purpose of measuring the absorbance of a solution at different wavelengths?

Q7: Look at the Absorbance vs. Wavelength graph of CuSO4. Use your graph to estimate the absorbance at 790 nm, 800 nm, 810 nm, 820, and 830 nm. Do the absorbencies vary greatly in this 40 nm range?

Q8: Use your graph to estimate the absorbance at 660 nm, 670 nm, 680 nm, 690 nm, and 700 nm. Do the absorbencies vary greatly in this 40 nm range?

Q9: In the next lab we will use absorbance to determine the concentration of a copper solution. The concentration is directly related to the absorbance and so it is very important that the absorbance be recorded accurately. Would it be better to take

absorbance measurements around 610 nm or around 810 nm for CuSO4? Explain.

Q10: Did any of the known compounds have more than one peak? If so, which peak did you use for the optimum wavelength. Why?

Q11: Suppose you had a solution containing a mixture of two solutions used today, would the maximum wavelength be an average of the two maximum wavelengths for each component of the mixture or would there be two maximum wavelengths? Explain.

Assessment

Write a letter to Transition Metallica explaining the experimental method that you used to determine which transition metal compounds were present, and specifically identify those transition metals you found to be present in the waste sample.

102 Student Handout Colorful Transition Metals

Name ______Data Table & Results

Table of Wavelength and Absorbance for Co(NO3)2, Ni(NO3)2, CuSO4, and Waste.

Wavelength (λ) Absorbance (A) Absorbance Absorbance Absorbance (nm) Co(NO3)2 Ni(NO3)2 CuSO4 Waste

350

400

450

500

550

600

650

700

750

800

850

900

950

Additional λ A λ A λ A λ A Wavelengths

103 Student Handout Colorful Transition Metals

Q2: Inform your instructor what you consider to be the optimum wavelength for each of your compounds? Explain how you made this determination.

Q3-5: Summarize your results by comparing the colors and optimum wavelengths of the solutions used by you and your teammates for the various transition metal compounds. Prepare a table for this comparison.

Compound Color of solution Optimum Wavelength

Co(NO3)2

Ni(NO3)2

CuSO4

Q6: What is the purpose of measuring the absorbance of a solution at different wavelengths?

Q7: Look at the Absorbance vs. Wavelength graph of CuSO4. Use your graph to estimate the absorbance at 790 nm, 800 nm, 810 nm, 820 nm, and 830 nm.

Wavelength Absorbance

790

800

810

820

830

Do the absorbencies vary greatly in this 40 nm range?

104 Student Handout Colorful Transition Metals

Q8: Use your graph to estimate the absorbance at 660 nm, 670 nm, 680 nm, 690 nm, and 700 nm.

Wavelength Absorbance

660

670

680

690

700

Do the absorbencies vary greatly in this 40 nm range?

Q10: Did any of the known compounds have more than one peak? If so, which peak did you use for the optimum wavelength. Why?

105 Student Handout Colorful Transition Metals

Assessment

References

1. Burns, R. A. Fundamentals of Chemistry, 4th Ed.; Prentice Hall: Upper Saddle River, New Jersey, 2003; p 142.

106

Student Handout Spectrophotometric Determination of Cu2+

The Problem Branicoda Copper Mine is considering opening up a new mining site. The geologists feel that there are copper-rich ore bodies present at this new site.

Samples of these ores were sent to Etapula Laboratories to be tested for acid consumption and to determine the percentage of copper present in the ore. Etapula Laboratories determined that malachite and chrysocolla both leach extremely well with sulfuric acid, and that malachite consumes acid at a greater rate than chrysocolla,

The ore samples have previously been leached with sulfuric acid to bring Cu2+ (copper (II) ion) into solution. Etapula Laboratories has been given the challenge of determining the amount of copper present per gram of ore for malachite and chrysocolla.

Your Task As a chemical technician at Etapula Laboratories, you are responsible for taking the 2+ Cu (aq) (aqueous copper (II) solution) and determining the mass percent of copper present per gram of ore in the original ore body. To accomplish this task, you must

2+ • prepare Cu (aq) (aqueous copper (II) sulfate solutions) of known concentration (standards).

• measure the absorbance of each standard solution using a spectrophotometer.

• prepare a graph from this data that should be linear over the concentration range.

2+ • measure the absorbance of your unknown Cu (aq) (aqueous copper (II) solution).

2+ • use the graph to determine the concentration of the unknown Cu (aq) (aqueous copper (II) solution).

Materials

Per Team of 3-4 students Spectrophotometer (Spec-20 or Genesys-20) Cuvettes (6 or more) 20 mL of 5.00 g/L Cu2+ (aqueous copper(II) sulfate solution) 1 box Kim Wipes 6 Beakers or Test tubes to prepare dilutions 2 Burets, pipets, or graduated cylinders

107 Student Handout 2+ Spectrophotometric Determination of Cu

Safety and Disposal

As instructed by your teacher, follow appropriate safety procedures, including the use of personal protective equipment such as goggles and an apron.

Follow any additional disposal procedures as outlined by your instructor.

Using a Spectrophotometer

Absorbance as a function of concentration

Notes: There are two types of cuvettes. One type is rectangular and has two smooth sides and two rough sides. When inserting the rectangular cuvettes into the spectrophotometer, make sure that the smooth sides are placed front to back so that the beam shines through the smooth section. The other type of cuvette looks like a regular test tube, but they are not. The tubes have been carefully and precisely made to have a composition that is transparent to light of the visible range and a shape that is a constant 1 cm diameter, perfectly round.

Cuvettes must be handled with care, being sure to touch them only near the top, and to wipe off the outside with a piece of lintless paper (Kim Wipe) every time before putting it into the instrument. Cuvettes should be stored in wooden/ plastic test tube racks when

108 Student Handout 2+ Spectrophotometric Determination of Cu

not in use to prevent scratching. Students should not put these cuvettes in their lab drawers. Students who break cuvettes will be responsible for the cost of replacing them, so be careful!

In order to determine the concentration of your unknown you will need to make a graph that includes several known points. If this graph is linear, you will be able to take any point along the y-axis (absorbance) and determine is corresponding x-value (concentration).

You will need at least 5 data points on your graph. Since you only have one solution that has a known concentration (5.0 g/L Cu2+ (aqueous copper(II) sulfate), you will need to prepare at least 4 more solutions of known concentration. A solution can be made less concentrated by diluting it with solvent. In this laboratory activity, the solvent will be water.

The mass of the solute does not change when a solution is diluted. The concentration of the solution will change however, because more solvent is added. Think of a soccer team practicing in the gym on a rainy day. Think of this same team practicing outside on the soccer field. In which location are the players more concentrated (closer together)? Did we change the number of soccer players? No, we simply increased the amount of space for them to practice.

Since the mass of the solute is equal in both situations, we can use the following expression to determine the concentration of our diluted solutions.

mass of solute in grams Concentration in g/L = liters of solution

Rearranging this equation we determine that

 g  mass of solute (g) = Concentration   x liters of solution (L)  L 

mass = CּV

Since the mass of copper in the concentrated solution is the same as the mass of copper in the diluted solution, we can write the following expression for dilutions, substituting CּV for mass in each case.

mass (concentrated) = mass (diluted)

Cc Vc = Cd Vd

In this equation Cc and Vc are the concentration (g/L) and volume of the original solution,

and Cd and Vd are the concentration (g/L) and volume of the final solution after dilution.

109 Student Handout 2+ Spectrophotometric Determination of Cu

The concentration can be recorded in mass (grams, kilograms, etc.) per Liter or moles per Liter, as long as the same units are used consistently. The volume units can be either mL or L as long as they are also consistent.

Example: Dilute 5.00 g/L copper sulfate with water by taking 1.00 mL of 5.00 g/L sulfuric acid and adding it to water to make 10.00 mL of solution.

Given: Cc = 5.00 g/L CuSO4

Vc = 1.00 mL CuSO4

Cd = ?

Vd = 10.00 mL solution (1.00 mL CuSO4 + 9.00 mL H2O)

Calculation:

mass(concentrated) = mass(diluted)

Cc Vc = Cd Vd

(5.00g / L)(1.00mL) = (Cd )(10.00mL)

(5.00g / L)(1.00mL) (C )(10.00mL) = d (10.00mL) (10.00mL)

(5.00g / L)(1.00mL) = (C ) (10.00mL) d

5.00 g / L = Cd

Procedure

1. You will be determining the concentration of Cu2+ in the solution that was leached previously in the “Leaching Copper” lab. Refer back to this lab and record the mass of the original ore sample, the mineral that was leached, whether it was crushed or uncrushed, and the volume of sulfuric acid that was used to leach the ore.

2. Separately filter the crushed and uncrushed leached Cu2+ solutions. While the Cu2+ solutions are being filtered, proceed to step 3.

3. Obtain 20 mL of 5.00 g/L Cu2+ from your instructor.

4. Make a table in your lab book similar to Table I to record your data.

110 Student Handout 2+ Spectrophotometric Determination of Cu

Table I: Cu2+ Standards Volume Volume Total Solution 5.00 g/L Concentration H O Volume Absorbance label Cu2+ 2 (mL) (mL) (g/L) (mL) A B C D E F

5. Prepare a set of 5 standards by diluting the 5.00 g/L Cu2+ with measured amounts of

H2O. Several possible dilutions are shown in Table II. You might want to use this table as a reference, but may want to alter the volumes depending on the type of measuring devices you have available. For best accuracy, it is important to use pipettes or burets to measure volumes. Graduated cylinders can be used, but are not as accurate.

Table II: Possible Ratios for Dilutions Volume Volume Solution 5.00 g/L H O label Cu2+ 2 (mL) (mL) A 5.00 0.00 B 4.00 1.00 C 3.00 2.00 D 2.00 3.00 E 1.00 4.00 F 1.00 9.00

6. To prepare solution B, use a pipette or buret to transfer 4.00 mL of the 5.00 g/L Cu2+ into a small beaker or large test tube. Use a pipette or buret to transfer 1.00 mL of

H2O into the same beaker or test tube. Mix this solution by pouring it back and forth between a second test tube. Calculate the concentration of solution B and record this value in your table.

7. Prepare at least 4 more dilutions. Make sure that you record the actual volumes of 2+ 5.00 g/L Cu and H2O that were used. Calculate the concentration of each diluted sample and record those values in your table.

111 Student Handout 2+ Spectrophotometric Determination of Cu

8. With your 5 standards prepared, you are now ready to record the absorbance of each solution. Based on previous laboratory experiences, what is the optimum wavelength for copper compounds? Set the wavelength on the Spectrophotometer to this wavelength.

9. Refer back to the “Colorful Transition Metals” lab for directions on how to use the spectrophotometer. Use water as the blank. Record the concentration and absorbance for each dilution in your data table.

2+ 10. Measure the absorbance of your unknown crushed and uncrushed Cu (aq) solutions. Record these values.

Data Manipulation and Analysis

1. Prepare a properly labeled graph with absorbance (y-axis) as a function of concentration (x-axis).

2. Plot the data for the standards (at least five points total.) An example is shown in Graph I.

This sample graph contains Absorbance vs. Concentration data for a series of

NiSO4 (nickel (II) sulfate) standards. These data were collected using a Colorimeter and the procedure in Experiment 11 of "Chemistry with Computers" lab manual.1

Graph I: Sample Graph of Absorbance vs. Concentration for NiSO4 (nickel (II) sulfate).

3. Use a ruler or straight edge to draw the “best straight line” through the data points.

112 Student Handout 2+ Spectrophotometric Determination of Cu

4. Use your graph and the absorbance value of your copper ore solution to determine the concentration of your copper sample. An example of how to do this is shown in Graph II.

Graph II: Absorbance vs. Concentration for NiSO4 (nickel (II) sulfate). Linear Fit Line with interpolation to determine the concentration at a specific absorbance.

5. Obtain a 2.5 g/L Cu2+ sample from your instructor. Use your graph to determine the concentration of this known sample. Calculate the percent error.

accepted − experiment %Error = *100 accepted

6. Determine the percent of Cu2+ present per gram of crushed ore. You will need to convert the concentration to grams by multiplying by the volume of your solution in Liters. Show your work, with cancelled units.

7. Determine the percent of Cu2+ present per gram of uncrushed ore.

8. Prepare a table summarizing your results. Include crushed and uncrushed data for both malachite and chrysocolla. You will have to communicate with other lab teams to obtain data for the ore sample that you did not test.

9. When you are satisfied with your data and results, combine the crushed and 2+ uncrushed Cu (aq) (copper (II) sulfate) solutions into a single container. Cover the container and label “Your Name PLS – from Malachite” or “Your Name PLS – from Chrysocolla.” You will use this solution in future laboratory activities.

113 Student Handout 2+ Spectrophotometric Determination of Cu

Discussion and Conclusions

Find another pair of classmates to work with and discuss the following ideas. Make sure that you understand the procedures you have just performed. If you have questions, ask other classmates or your instructor.

Q1: What wavelength did you choose to perform your measurements?

Q2: What makes a wavelength “optimum” for a particular analysis?

Q3: You made 5.0 mL and 10.0 mL of the diluted solutions you used. Consider reasons for making so much when the cuvettes only require approximately 2.0 mL.

Q4: You created your graph by taking measurements of known Cu2+ concentrations. Your graph is only valid between your lowest and highest absorbance readings. What changes in procedure would need to be made if the absorbance value of your unknown was below your lowest standard? What if the unknown absorbance reading was above your highest standard?

Q5: Is the graph of your standards accurate and precise? Give evidence to support your statement.

Q6: Compare the concentration of your leached Cu2+ solutions with other teams.

Q7: Which ore sample had the highest concentration of Cu2+ per gram of ore?

Q8: Do you feel that there is enough copper in the ore to recommend opening a new mining site? If so, which mining site would you recommend starting with?

Assessment

Review the previous three labs (Properties of Copper Ore, Leaching Copper, and Colorful Transition Metals) to help complete this assessment activity.

Write a letter to the Mining Director at Branicoda Mines explaining the experimental method that you used to determine the amount of Cu2+ present per gram of crushed and uncrushed malachite ore, and amount of Cu2+ present per gram of crushed and uncrushed chrysocolla ore.

Include a statement with your recommendation as to which ore body would be best to mine first, and whether the ore should be crushed. In your letter, defend your recommendation.

114 Student Handout 2+ Spectrophotometric Determination of Cu

Name ______

Data Table & Results Table I: Cu2+ Standards Volume Volume Total Solution 5.00 g/L Concentration H O Volume Absorbance label Cu2+ 2 (mL) (mL) (g/L) (mL)

Q1: What wavelength did you choose to perform your measurements?

Q2: What makes a wavelength “optimum” for a particular analysis?

Q3: You made 5.0 mL and 10.0 mL of the diluted solutions you used. Consider reasons for making so much when the cuvettes only require approximately 2.0 mL.

115 Student Handout 2+ Spectrophotometric Determination of Cu

Q5: Is the graph of your standards accurate and precise? Give evidence to support your statement.

Q6: Compare the concentration of your leached Cu2+ solutions with other teams.

Q7: Which ore sample had the highest concentration of Cu2+ per gram of ore?

Q8: Do you feel that there is enough copper in the ore to recommend opening a new mining site? If so, which mining site would you recommend starting with?

Assessment

Review the previous three labs (Properties of Copper Ore, Leaching Copper, and Colorful Transition Metals) to help complete this assessment activity.

Include a statement with your recommendation as to which ore body would be best to mine first, and whether the ore should be crushed. In your letter, defend your recommendation.

116

Student Handout Purification Techniques

The Problem Leaching occurs when a dilute aqueous solution of sulfuric acid (raffinate) is sprinkled on stockpiles of low grade ore containing copper carbonates (azurite and malachite) and hydroxy-silicates (chrysocolla). The acid leaches the copper out of the ore where it moves into an aqueous solution. Unfortunately other metals, such as iron, are also 2+ leached out of the ore. This Cu (aq) (copper (II) sulfate solution), termed “pregnant leach solution” or PLS, is between 2.5 g/L and 4.0 g/L of copper and is contaminated with other metal ions.

Your Task You have been hired by Etapula Laboratories as a Chemical Technician. Branicoda Mining Operations has sent you a sample of pregnant leach solution from the Lincoln Mining Site. They want this sample tested to determine if Ag+ and Fe3+ are present. Your supervisor has also asked you to test the pregnant leach solution (PLS) from the previous Leaching Lab for the presence of Ag+ and Fe3+.

Branicoda Mining Operations has also requested that you determine a method of purifying the pregnant leach solution (PLS) in order to rid it of undesirable Fe3+ contaminants, which if left unchecked can affect the grade of plated copper.

Materials

Reagents and equipment per lab team. Buchner funnel and adaptor cone or other funnel Filter paper disks to fit the funnel 100-mL graduated cylinder 5 test tubes 150-mL beaker (2) 2+ Cu (aq) (copper (II) sulfate solution) (PLS) from previous Leaching Lab 2+ Cu (aq) (copper (II) sulfate solution) (PLS) from the Lincoln Site

Dropper bottle of 0.1 M Fe(NO3)3 (ferric nitrate)

Dropper bottle of 0.1 M AgNO3 (silver nitrate) Dropper bottle of 3M HCl (hydrochloric acid) Dropper bottle of 0.1 M KSCN (potassium thiocyanate)

20 mL of 5 g/L CuSO4 (copper (II) sulfate)

10 mL of 200 g/L H2SO4 (sulfuric acid) 10 mL of Barren Organic (10% Acorga M5850 in Penrico 170 ES diluent)

117 Student Handout Purification Techniques

Safety and Disposal

As instructed by your teacher, follow appropriate safety procedures, including the use of personal protective equipment such as goggles and an apron.

Use caution when working with 3 M HCl (hydrochloric acid) and 200-g/L H2SO4 (sulfuric acid). If spills occur, neutralize by sprinkling with baking soda and diluting with water. The

3 M HCl (hydrochloric acid) and 200-g/L H2SO4 (sulfuric acid) can be disposed of by diluting the acid into a large beaker containing water. The final concentration of the acid

should be 1M or less. Slowly add 1 M Na2CO3 (sodium carbonate) solution to the diluted acid while stirring. Flush the neutral mixture down the drain with a 20-fold excess of water.

Use caution when working with AgNO3 (silver nitrate). It is corrosive and can cause burns. It also leaves black marks on the skin.

Fe(NO3)3 (ferric nitrate) may be a skin irritant.

KSCN (potassium thiocyanate) is moderately toxic by ingestion. It will emit toxic fumes of cyanide if heated or in contact with concentrated acids.

CuSO4ּ5H2O (copper (II) sulfate pentahydrate) is a strong irritant to the skin and mucous

membranes. To avoid inhaling its dust, use CuSO4ּ5H2O only where there is adequate ventilation. It can be harmful or fatal if taken internally. If contact with the skin occurs, flush with running water. Wash your hands after use. Follow local ordinances for disposal of copper (II) salts. It is recommended that unused copper (II) sulfate solution be left to evaporate to dryness.

Follow any additional disposal procedures as outlined by your instructor.

Procedure Observations:

1. Obtain 20 mL of pregnant leach solution (PLS) that you saved from the Spectrophotometric Determination Lab. Describe the color and clarity of this solution.

2. Ask your instructor for 20 mL of the pregnant leach solution (PLS) that was sent from the Lincoln Site. Describe the color and clarity of this solution.

3. Obtain 10 mL of 200 g/L H2SO4 (aq) (sulfuric acid). Determine the pH of the three solutions using a pH meter or pH paper.

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Testing for Impurities

4. Your task is to determine the presence of Ag+ (silver ions) or Fe3+ (iron (III) ions) as impurities in either of the PLS solutions. The test for Ag+ is described below and labeled “Silver Test” The test for Fe3+ is described below and labeled “Iron Test.”

SILVER TEST: Prepare a reference solution containing Ag+ (silver ions) by

placing 2-3 mL of 0.1 M AgNO3 (silver nitrate solution) into a small test tube. You now have a solution you know has Ag+ present. Add 1-2 drops of 3M HCl (hydrochloric acid). What evidence confirms the presence of Ag+ (silver ions)?

Write the balanced chemical reaction that occurs between silver nitrate and hydrochloric acid.

a. Test the PLS from the Lincoln Site for Ag+ and record the results.

b. Test the PLS from your previous lab for Ag+ and record the results.

IRON TEST: Prepare a reference solution containing Fe3+ (iron (III) ions) by

placing 2-3 mL of 0.1 M Fe(NO3)3 (iron (III) nitrate) into a small test tube. You now have a solution that you know has Fe3+ present. Add 2-3 drops of 0.1 M KSCN (potassium thiocyanate). What evidence confirms the presence of Fe3+?

c. Test the PLS from the Lincoln Site for Fe3+ and record the results.

d. Test the PLS from your previous lab for Fe3+ and record your results.

Q1: Which impurities, if any, were present in the PLS from the Lincoln Site? Which impurities, if any, were present in your PLS?

Solubility

5. Some chemical substances are soluble in polar solvents such as water, whereas other chemical substances are soluble in organic solvents. To be able to develop a method of removing impurities from a Cu2+ solution by extraction, it is important 2+ to determine the solubility of Cu (aq) (copper (II) ions) in polar solvents such as 2+ water and sulfuric acid, and the solubility of Cu (aq) (copper (II) ions) in nonpolar organic solvents.

6. Obtain 20-mL of a stock solution of 5 g/L CuSO4 (aq) (copper sulfate solution) from

your instructor. Observe and record the color, clarity, and pH of the CuSO4 (aq). It is often helpful to pour the solution into a test tube and then hold it against a

119 Student Handout Purification Techniques

white background to observe color.

Q2: Based on your observations of CuSO4 (aq), what physical evidence can be used to determine if an aqueous solution contains Cu2+?

7. Transfer 3-mL portions of this stock solution into a five separate test tubes. Label the test tubes 1 - 5.

8. Keep the first test tube as a reference.

9. Add 3-mL of water to the second test tube. Cover the test tube with a stopper and shake for 30 seconds. Record your observations.

2+ Q3: Is Cu (aq) soluble in water? What is your evidence?

10. Add 3-mL of 200 g/L H2SO4 (aq) (sulfuric acid) to the third test tube. Cover the test tube with a stopper and shake for 30 seconds. Record your observations.

2+ 11. Is the Cu (aq) soluble in sulfuric acid?

12. Obtain 10-mL of Barren Organic (10% Acorga M5850 in Penrico 170 ES diluent) from your instructor. Record the color and clarity of the Barren Organic.

13. Add 3-mL of Barren Organic (10% Acorga M5850 in Penrico 170 ES diluent) to the fourth test tube. Cover the test tube with a stopper and shake for 30 seconds. Repeat shaking for an additional 30 seconds. Record your observations of both layers, paying careful attention to color and clarity. Compare to the color

and clarity of the CuSO4 (aq) and the color and clarity of the barren organic.

2+ 14. Is Cu (aq) soluble in barren organic? What is your evidence?

15. Pour off the organic layer of test tube #4 into a separate test tube and label as

test tube #5. Carefully add 3-mL of 200 g/L H2SO4 (aq) (sulfuric acid) to this fifth test tube. Cover the test tube with a stopper and shake for 30 seconds. Let the layers separate. Shake for an additional 30 seconds. Allow the layers to separate. Record your observations of both layers, paying careful attention to

color and clarity. Compare to the color and clarity of the CuSO4 (aq) and the color and clarity of the barren organic.

Q4: Describe the solubility of copper ions (Cu2+) in barren organic, water, and acidic solutions.

120 Student Handout Purification Techniques

Discussion and Conclusions

Share your results with other teams. Obtain data from at least two groups that have 2+ Cu (aq) (copper (II) sulfate solution) referred to now as PLS, that was obtained from the leaching of malachite and data from two groups that was obtained from the leaching of chrysocolla.

Q5: List any metal contaminants present in the pregnant leach solution (PLS) that was obtained through the leaching of malachite?

Q6: List any metal contaminants present in the pregnant leach solution (PLS) that was obtained through the leaching of chrysocolla?

Assessment

Part 1:

A sample of pregnant leach solution has been sent from the Lincoln site that has both 2+ 3+ 3+ Cu and Fe ions present. It has been found that at a pH above 2.3, Fe (aq) becomes 3+ soluble in barren organic. As the pH decreases to around 1.8, Fe (aq) becomes insoluble in barren organic. Write a statement that describes a process that would allow you to remove the Fe3+, which is present as a contaminant, from the PLS solution, which is

currently at a pH of 1.8. The CuSO4 (aq) must be in an aqueous solution when you are finished.

Part 2:

Trade statements with another person from a different lab group. Evaluate their proposed method of purifying the PLS. Is their proposal logical? Does it follow correct science? Do you feel that their method would work?

Part 3;

Test your proposal on a 3-mL sample of PLS from the Lincoln Site. Report your results.

121 Student Handout Purification Techniques

Name ______Data Table & Results

Observations

Solution Color Clarity pH

PLS (from personal leaching experiments) PLS (Lincoln Site)

200 g/L H2SO4 (aq) (sulfuric acid)

Testing for Impurities

SILVER TEST

Solution Observations and Conclusions

AgNO3 Reference PLS (Lincoln Site) PLS (Student) Write the balanced chemical equation for the reaction between silver nitrate and hydrochloric acid.

IRON TEST

Solution Observations and Conclusions

Fe(NO3)3 Reference PLS (Lincoln Site) PLS (Student) Q1: Which impurities, if any, were present in the PLS from the Lincoln Site? Which impurities, if any, were present in your PLS?

122 Student Handout Purification Techniques

Observations of CuSO4 (aq)

Solution Color Clarity

CuSO4 (aq)

Q2: Based on your observations of CuSO4 (aq), what physical evidence can be used to determine if an aqueous solution contains Cu2+?

Solubility of Cu2+ in the following reagents:

Test Tube Reagent Color Clarity

#1 CuSO4 (Reference)

Test Tube Reagent Observations Soluble, or Insoluble 2+ #2 Cu in H2O

2+ #3 Cu in H2SO4

2+ Q3: Is Cu (aq) soluble in water? What is your evidence?

Reagent Color Clarity

Barren Organic

123 Student Handout Purification Techniques

Test Tube Reagent Observations Soluble, or Insoluble #4 Cu2+ in Barren Organic

#5 Cu2+ in Barren Organic with 200 g/L

H2SO4 added

Q4: Describe the solubility of copper ions (Cu2+) in barren organic, water, and acidic solutions.

Share your results Share your results with other teams. Obtain data from at least two groups that have 2+ Cu (aq) (copper (II) sulfate solution) referred to now as PLS, that was obtained from the leaching of malachite and data from two groups that was obtained from the leaching of chrysocolla. List the names of the other group members you consult with.

Ore Sample Group Member Was Ag+ Present Was Fe3+ Present

Lincoln Site

Malachite

Chrysocolla

Q5: What metal contaminants were present in the pregnant leach solution (PLS) that was obtained through the leaching of malachite?

Q6: What metal contaminants were present in the pregnant leach solution (PLS) that was obtained through the leaching of chrysocolla?

124 Student Handout Purification Techniques

Assessment

Part 1:

3+ At a pH above 2.3, Fe (aq) is soluble in barren organic. As the pH decreases to around 3+ 1.8, Fe (aq) becomes insoluble in barren organic. Write a statement that describes a process that would allow you to remove Fe3+, which is present as a contaminant, from the

PLS solution which is currently at a pH of 1.8. The CuSO4 (aq) must be in an aqueous solution when you are finished.

Comments:

Evaluated by

Part 2:

Part 3;

Test your proposal on a 3-mL sample of PLS from the Lincoln Site.

Write a letter to the Director of Mines describing your results. In your letter outline a method of removing the Fe3+ from the Lincoln Site PLS, thus purifying it.

125

Name ______Date ______Chemistry of Extraction Access the following web site or use the CD to find answers to the following questions. http://teach2.eac.edu/pmcbride

Define the following terms: 1. barren organic

2. loaded organic

3. extraction settler

Answer the following questions:

The pregnant leach solution (PLS) is sent to the mixer where it is mixed with a non-polar, organic reagent in a kerosene-based solvent.

4. Which phase (layer) is most dense (organic or aqueous)?

5. What is the purpose of the settling tank? How long does it take for a drop of solution to travel from one end of the tank to the other?

6. What is the color of the Raffinate (aqueous layer) as it leaves the extractor? (Watch the video on Slide 2 of the extraction phase.) What physical evidence shows that Cu2+ is no longer in the aqueous phase?

126 Student Handout Chemistry of Extraction

7. Draw the structure of the organic reagent complexed with Cu2+. Circle the intermolecular hydrogen bonding that occurs.

8. What helps stabilize the copper/organic complex?

9. What ion in the aqueous phase exchanges places with the Cu2+ as it forms a complex with the organic reagent? Why are two organic reagents required for one Cu2+?

10. Look at the chemical equilibrium for the reaction between the organic phase and the aqueous phase as they are mixed together. According to Le Chatelier’s Principle, what phase will the Cu2+ be in at a pH above 2 (the pH of the leach solution)?

11. What chemical and concentration is added to the loaded organic to strip the copper so that it returns to the aqueous phase?

12. What are the two main purposes of solution extraction?

127

Student Handout Solution Extraction

The Problem Leaching occurs when a dilute aqueous solution of sulfuric acid (raffinate) is sprinkled on stockpiles of low grade ore containing copper carbonates (azurite and malachite) and hydroxy-silicates (chrysocolla). The acid leaches the copper out of the ore where it moves into an aqueous solution. Unfortunately other metals, such as iron, are also leached out of the ore. This copper solution, termed “pregnant leach solution” is between 2.5 g/L and 4.0 g/L of copper and is contaminated with other metals. For electroplating, the concentration of copper must be around 40 grams per liter and the copper must be in an aqueous matrix.

Your Task You have been hired by Etapula Laboratories as a Chemical Technician. An experimental team has designed a method of purifying and concentrating the pregnant leach solution (PLS). You have been assigned the task of determining if this method would be appropriate for the leach solutions coming from Branicoda Copper Mine.

Materials

Reagents and equipment per lab team. Spectrophotometer pH meter or pH paper 100-mL graduated cylinder 20 Fluid ounce water bottle or 125-mL Erlenmeyer flask 100 mL of the pregnant leach solution (PLS) from the “Spectrophotometric Determination” lab.

100 mL of 200 g/L H2SO4 (sulfuric acid) 100 mL of Barren Organic (10% Acorga M5850 in Penrico 170 ES diluent) Dropper bottle of 3M HCl (hydrochloric acid) Dropper bottle of 0.1 M KSCN (potassium thiocyanate)

Safety and Disposal

As instructed by your teacher, follow appropriate safety procedures, including the use of personal protective equipment such as goggles and an apron.

Use caution when working with 3 M HCl (hydrochloric acid) and 200-g/L H2SO4 (sulfuric acid). If spills occur, neutralize by sprinkling with baking soda and diluting with water. The

3 M HCl (hydrochloric acid) and 200-g/L H2SO4 (sulfuric acid) can be disposed of by

128 Student Handout Solution Extraction

diluting the acid into a large beaker containing water. The final concentration of the acid

should be 1M or less. Slowly add 1 M Na2CO3 (sodium carbonate) solution to the diluted acid while stirring. Flush the neutral mixture down the drain with a 20-fold excess of water.

Copper (II) sulfate pentahydrate is a strong irritant to the skin and mucous membranes. To avoid inhaling its dust, use copper (II) sulfate only where there is adequate ventilation. It can be harmful or fatal if taken internally. If contact with the skin occurs, flush with running water. Wash your hands after use. Follow local ordinances for disposal of copper (II) salts. It is recommended that unused copper (II) sulfate solution be left to evaporate to dryness.

KSCN (potassium thiocyanate) is moderately toxic by ingestion. It will emit toxic fumes of cyanide if heated or in contact with concentrated acids.

Procedure

1. Obtain a pH meter, and use it to record the pH of your malachite or chrysocolla pregnant leach solution.

2. Observe and record the color and clarity of the pregnant leach solution (PLS) and the Barren Organic (10% Acorga M5850 in Penrico 170 ES diluent).

3. Accurately transfer 40-mLs of barren organic to a 100-mL graduated cylinder. Next, using the same technique, transfer 40-mLs of the PLS (pregnant leach solution) to the same graduated cylinder

Q1: Would you consider the aqueous PLS and the barren organic to be miscible? Explain.

4. Pour the contents of the graduated cylinder into a 20-fluid ounce water bottle (a 250- mL Erlenmeyer flask can be used in place of the water bottle.) Screw the lid on the water bottle or stopper the Erlenmeyer flask.

5. If you use a stopper, put your finger over the stopper. Shake the contents for 20 shakes and then remove the lid to release any pressure that may build up. Repeat for 2 minutes, removing the lid every 20 shakes to relieve any pressure.

6. Pour the solution back into the 100-mL graduated cylinder. Record how long it takes for the two layers to separate.

7. Observe and record the color and clarity of the two layers.

129 Student Handout Solution Extraction

Q2: Where is the Cu2+ (copper (II) ions) at this point (aqueous or organic layer)? What is your evidence?

8. The aqueous layer is termed “raffinate.” Raffinate is the term used to describe the aqueous phase remaining after extraction of Cu2+ into the organic phase. The organic phase is termed “loaded organic.”

Q3: Why is the organic now called “loaded organic?”

9. Carefully separate the two layers into two separate containers. Pour off the top organic layer back into the water bottle or 250-mL Erlenmeyer flask. You may also use a beral pipet to remove the organic phase from the graduated cylinder..

10. Describe the color and clarity of the raffinate. Compare with the color and clarify of the original PLS. Save the raffinate for further studies.

11. Obtain 20 mL of 200 g/L H2SO4 (sulfuric acid). Add 10-mL of 200 g/L H2SO4 to the water bottle or Erlenmeyer flask containing the organic solution (now termed loaded organic).

12. Put the lid on the water bottle or stopper the flask. Shake the solution for 2 minutes. Remove the lid every once in a while to vent the flask. Let the solutions separate, shake for 30 more seconds, allow to separate, and shake a third time for 30 seconds.

13. Pour the solution into the 100-mL graduated cylinder. Record how long it takes for the two layers to separate.

14. Describe the color and clarity of the aqueous layer and the organic layer.

Q4. Has there been any transfer of copper between the two solutions? Explain.

15. Add an additional 10-mL of 200 g/L H2SO4 to the graduated cylinder.

16. Pour the entire mixture (60-mL) into the Erlenmeyer flask or water bottle. Replace the lid or stopper. Shake the solutions for 2 minutes. Remove the stopper every once in a while to vent the flask. Let the solutions separate, shake for 30 more seconds, allow to separate, and shake a third time for 30 seconds.

17. Pour the solution into the 100-mL graduated cylinder. Record how long it takes for the two layers to separate.

18. Pour the organic layer into a separate beaker and label it barren organic. The aqueous layer is now termed “rich electrolyte.” Pour the rich electrolyte into a beaker

130 Student Handout Solution Extraction

and label as such. Describe the color and clarity of this solution. The beaker containing the organic layer should be labeled “barren organic,’ and the beaker containing the aqueous layer should be labeled “rich electrolyte.” Save the rich electrolyte and any left over PLS for the electroplating lab.

19. Return the “barren organic” to your instructor.

Q5: Why is the organic layer now termed “barren organic”, and the aqueous layer now termed “rich electrolyte?”

Q6: Can the “barren organic” be reused. Explain.

20. Use a spectrophotometer and your graph from “Spectrophotmetric Determination” to measure the absorbance and subsequently determine the Cu2+ (copper) concentration of the PLS, the raffinate, and the rich electrolyte. You should have already determined the concentration of the PLS (Spectrophotometric Determination) from a previous lab, but it would be appropriate to take another absorbance measurement.

21. Test the rich electrolyte for Ag+ and Fe3+ (See Purification Techniques Lab).

Discussion and Conclusions

Chelation can be used to describe how the organic oxime molecule binds to the Cu2+ (copper (II) ion). The organic oxime molecule has been specially designed to capture the Cu2+ at the interface between the organic and aqueous phases. This organic molecule is selective for copper at pH values below 2.0. At higher pH values, other metal ions will also be “captured” by the organic molecule. An effective separation of the Cu2+ from other metal impurities must be accomplished at a pH between 1.5 – 1.8.

Figure 1 The process by which the organic molecule (a mixture of ketoxime and aldoxime) extracts the Cu2+ from the aqueous phase.

ORGANIC PHASE R R

CH3 H

OH N N OH 2+ OH Cu HO

ketoxime aldoxime

AQUEOUS PHASE

131 Student Handout Solution Extraction

ORGANIC PHASE

H O H

R O N

N OR

H3C O H

+ + AQUEOUS PHASE H H

Figure 1: Distribution of copper ions between the organic and aqueous phases.

Hydroxy Oximes used in Copper Recovery (Organic)

R = C9H19 or C12H25

Salicylaldoximes A = H

Ketoximes A = C6H5 or CH3

Q7: Look at the Acorga M-5850 Product Specifications Sheet. What is the Copper/Iron Selectivity?

Q8: Does your data agree with the time listed in the Product Specifications for the two layers to separate (phase disengagement)?

Q9: By describing the nature of the solutes and solvents present in solution and their intermolecular attractions, explain why one part of the oxime (organic molecule) is in the organic phase while the other part reaches into the aqueous phase. (This is similar to the chemistry behind how soaps work.)

Le Chatelier’s Principle states that if a stress is applied to a reversible system at equilibrium, the equilibrium shifts in the direction that will partially relieve that stress.1

Q10: Would you consider the occurrence with the organic and aqueous phases a reversible system? Explain.

132 Student Handout Solution Extraction

The general chemical equilibrium involved in this process is shown below. The “L” in the equation stands for “ligand” and represents the entire aldoxime or ketoxime molecule as shown in Figure 1.

2+ + 2 L-H (org) + Cu (aq) ' L2Cu (org) + 2 H (aq)

Q11: According to this equation which way would the equilibrium shift if you stressed the system by adding H+ (sulfuric acid)?

Assessment

Write a letter to your Supervisor at Etapula Laboratories. Describe the two purposes of the extraction process? Comment on how well these purposes have been attained. Explain in your letter how Le Chatelier’s Principle is applied in solution extraction and whether you feel that it is a good method to use on a large scale to purify and concentrate the pregnant leach solution (PLS).

133 Student Handout Solution Extraction

Acorga M-5850

PRODUCT SPECIFICATION Acorga solvent extraction reagents for the mining industry. PHYSICAL DATA Appearance Clear amber-colored liquid, free from visible impurities. Specific gravity, 25°C 0.96-0.98 Viscosity, cP at 25°C Not more than 400 Flash point, °C Not less than 62 (PMCC)

PERFORMANCE DATA

Copper uptake, g/l per v/o 0.55-0.59 Extract kinetics, approach to equilibrium at 25°C, % 15 sec Not less than 85 30 sec Not less than 95

Strip kinetics, approach to equilibrium at 25°C, % 15 sec Not less than 95

Copper extraction isotherm point at 25°C, g/l Organic Not less than 4.3 Aqueous Not greater than 1.6

Copper strip isotherm point at 25°C, g/l Organic Not greater than 2.1 Aqueous Not less than 33.0

Copper/Iron selectivity Not less than 2000

Phase disengagement, sec Extract Not more than 60 Strip Not more than 80

Complex solubility at 0°C, at 24 hours No precipitation

Testing carried out in accordance with the methods described in Acorga COPPER EXTRACTANTS: Standard Methods of Test.

"Solvent extraction reagents in the Acorga P-5000 and M-5000 series are the subject of patents and pending applications for patents in the name of Avecia Limited, in most countries where copper extraction is practiced. Acorga is a trademark, the property of Avecia Limited, England, a member of the Avecia Group of companies and it is the subject of registrations or pending applications for registration as a trade mark in most countries where copper extraction is practiced. Details of such patents, registrations and pending applications can be obtained on application to The Manager, Intellectual Property Group, Avecia Limited, Blackley, Manchester, M9 8ZS, England."

134 Student Handout Solution Extraction

Name ______Data Table & Results

Initial pH of PLS

Q1: Would you consider the aqueous PLS and the barren organic to be miscible? Explain.

Procedural Phases Time for Phase Step Disengagement (sec)

6 Barren Organic with PLS

13 Loaded Organic with Sulfuric Acid

19 Loaded Organic with Sulfuric Acid

Solution Color Clarity Absorbance Concentration

PLS

Barren Organic

Raffinate

Loaded Organic

Rich Electrolyte

Q2: Where is the Cu2+ (copper (II) ions) at this point (aqueous or organic layer)? What is your evidence?

135 Student Handout Solution Extraction

Q3: Why is the organic now called “loaded organic?”

Q4. Has there been any transfer of copper between the two solutions? Explain.

Q5: Why is the organic layer now termed “barren organic”, and the aqueous layer now termed “rich electrolyte?”

Q6: Can the “barren organic” be reused. Explain.

Q7: Look at the Acorga M-5850 Product Specifications Sheet. What is the Copper/Iron Selectivity?

Q8: Compare your data with the time listed in the Product Specifications for the two layers to separate (phase disengagement). Does your data fall within the specifications listed?

Q9: By describing the nature of the solutes and solvents present in solution and their intermolecular attractions, explain why part of the oxime (organic molecule) is in the organic phase and part of it reaches into the aqueous phase. (This is similar to the chemistry behind how soaps work.)

136 Student Handout Solution Extraction

Q10: Would you consider the occurrence with the organic and aqueous phases a reversible system? Explain.

2+ + 2 L-H (org) + Cu (aq) ' L2Cu (org) + 2 H (aq)

Q11: According to this equation which way would the equilibrium shift if you stressed the system by adding H+ (sulfuric acid)?

Assessment

137

Student Handout Electrochemistry Background

Electrowinning is the final step of a 3-step process that involves the conversion of commercial electrolyte into copper metal.

The Commercial Electrolyte is pumped through a series of cells in the tankhouse. Alternating plates of lead and stainless steal hang in the tankhouse. Each lead plate serves as the anode pole of an electric circuit. The stainless steel “blank” is the cathode. A direct current passes from the anode through the electrolyte, causing the copper ions in the electrolyte solution to plate onto the cathode. The electrolyte is now partially depleted of its copper and is termed “lean electrolyte.” The lean electrolyte is returned to the stripping process.

The net effects of electrowinning are copper metal at the cathode, oxygen gas at the

anode, and regenerated sulfuric acid in the solution. Oxidation of H2O to O2 occurs at the Lead Anode and reduction of Cu2+ to Cu0 occurs at the Stainless Steel Cathode resulting in elemental copper. These copper sheets are then mechanically separated from the stainless steel plates and prepared for sale.

138 Student Handout Electrochemistry

Discussion and Conclusions

The reactions occurring in the electrochemical cell are called oxidation/reduction reactions.

Oxidation occurs when there is an increase in the oxidation number of an element, which results from the loss of electrons.

Reduction occurs when there is a decrease (reduction) in the oxidation number of an element, which results from the gain of electrons.

Oxidation/Reduction (Redox) reactions always occur with both an oxidation and reduction. To determine which will be the oxidation and which will be the reduction we look at the standard reduction potentials. These values are for reductions. If the reaction is an oxidation, we reverse the sign of the standard reduction potential. For example:

According to the Activity Series and/or by laboratory experience we know that AgNO3 reacts with Copper metal according to the single-replacement reaction shown:

2 AgNO3 (aq) + Cu(s) → 2 Ag (s) + Cu(NO3)2 (aq)

We will now find out reasoning behind the activity series and why this reaction occurs as such.

We must first determine the oxidation number of each element.

Ag in AgNO3 (aq) has an oxidation state of +1.

Ag as a solid has an oxidation state of 0.

We can write the half cell reaction as: Ag1+ + 1e- → Ag0

Q1: Would the half reaction involving silver be considered an oxidation or a reduction?

0 2+ - We can write the other half cell reaction as: Cu (s) → Cu (aq). + 2e

Q2: Would the half reaction involving copper be considered an oxidation or a reduction?

139 Student Handout Electrochemistry

The half reactions for silver and copper are shown in Table 1.

Standard Reduction Potential, Acidic Solution E° (volts)

+ - Ag (aq) + e → Ag(s) 0.80

2+ - Cu (aq) + 2 e → Cu(s) 0.34

Table 1: Standard Reduction Potential in Aqueous Solution at 25 °C

We notice that the reaction with copper is an oxidation reaction, not a reduction reaction. We must reverse this reaction to write it as an oxidation. When we reverse a half reaction, we must change the sign of the standard reduction potential. We can then add the two values together to obtain the cell potential.

+ - Reduction Half Reaction Ag (aq) + e → Ag(s) 0.80

2+ - Oxidation Half Reaction Cu(s) → Cu (aq) + 2 e - 0.34

1+ 2+ Overall Reaction 2 Ag (aq) + Cu(s) → 2 Ag (s) + Cu (aq) 0.46

Ecell = 0.80 + (-0.34) = 0.46

An overall positive voltage signifies that the reaction will be spontaneous.

An industrial application of electrochemistry involves the electrowinning of copper. The half reactions possible in the electrolytic cell are shown in Table 2.

Standard Reduction Potential, Acidic Solution E° (volts)

2+ - Cu (aq) + 2 e → Cu(s) 0.337

+ - ½O2 (g) + 2 H (aq) + 2 e → H2O 1.229

Table 2: Standard Reduction Potential in Aqueous Solution at 25 °C

Both reactions are written as reductions. There must be an oxidation reaction occurring

for every reduction reaction. The value of E°(net) must be positive for a spontaneous

reaction. If the value of E°(net) is negative, the reactions would occur spontaneously in the

140 Student Handout Electrochemistry

opposite direction. If a reaction does not occur spontaneously, electricity can be applied to overcome the negative voltage and force the reaction to occur.

Now let’s look at the reaction of copper sulfate and water as it occurs in the electrolytic cell.

Reaction of Copper Sulfate and Water.

2+ - Cu (aq) + 2 e → Cu(s) 0.337

+ - H2O → ½O2 (g) + 2 H (aq) + 2e - 1.229

2+ + Cu (aq) + H2O → Cu(s) + ½O2 (g) + 2 H (aq) - 0.892 V

Q3: What do you notice about the net voltage of this reaction? Will this reaction happen spontaneously? Explain.

Q4: We want this reaction to occur as written so that we obtain metallic copper. How can we do this in the laboratory?

Q5: Write the two half-cell reactions and overall reaction so that the reaction is spontaneous.

141 Student Handout Electrochemistry

Name ______

Q1: Would the half reaction involving silver be considered an oxidation or a reduction?

Ag1+ + 1e- → Ag0

Q2: Would the half reaction involving copper be considered an oxidation or a reduction?

0 2+ - Cu (s) → Cu (aq). + 2e

Q3: What do you notice about the net voltage of this reaction? Will this reaction happen spontaneously? Explain.

2+ - Cu (aq) + 2 e → Cu(s) 0.337

+ - H2O → ½O2 (g) + 2 H (aq) + 2e - 1.229

2+ + Cu (aq) + H2O → Cu(s) + ½O2 (g) + 2 H (aq) - 0.892 V

Q4: We want this reaction to occur as written so that we obtain metallic copper. How can we do this in the laboratory?

Q5: Write the two half-cell reactions and overall reaction so that the reaction is spontaneous.

142

Name ______Date ______Chemistry of Electrowinning Access the following web site or use the CD to answer the following questions. http://teach2.eac.edu/pmcbride/copperpage.html

Define the following terms: 1. Rich electrolyte

2. Anode

3. Cathode

Answer the following questions:

The last stage of copper mining involves the electroplating of copper onto stainless steel blanks.

Electrowinning can be defined as “the deposition of copper metal from a copper-bearing solution by passage of an electric current (1).” Li K

4. Refer to the Activity Series of Metals (2) on the right. When a piece of copper wire Ca Na is submerged in an aqueous, colorless AgNO3 (aq) (silver nitrate) solution, shiny Mg crystals of silver from on the copper wire. The solution begins to turn a blue color as Al 2+ the copper metal is oxidized to Cu . When comparing two elements, the more Zn reactive elements on top will replace any of those elements underneath. Should Cr Fe copper replace silver according to the activity series? Cd Ni Sn Pb 5. Complete the following reaction: H2 Cu Hg Cu(s) + AgNO3 (aq) → Ag Au

143 Student Handout Chemistry of Electrowinning

2+ 6. Pb is used as the anode. Will Pb react directly with Cu (aq) (CuSO4 – rich electrolyte)? Write the reaction that would occur.

7. Write the balanced oxidation/reduction reaction that occurs at the anode and cathode during the electrowinning of copper.

8. Using standard reduction potentials, determine the overall potential.

9. Noting that a negative potential would result in the reverse reaction occurring and a positive potential would result in the reaction occurring spontaneously, explain why electricity must be applied to the cell.

References:

1. The Acorga Technical Library [CD-ROM]; Avecia Inc.: Wilmington, DE, 2000.

2. Burns, R. A. Fundamentals of Chemistry, 4th Ed.; Prentice Hall: Upper Saddle River, NJ, 2003; p 454.

144

Student Handout Electrowinning

The Problem Electrowinning at a Copper Mine means just what is says – winning copper through the use of electricity. The more common name is electroplating or electrodeposition, which is a technique used to deposit a metal, such as copper, onto the surface of another metal.

Branicoda Mining Operations is trying to determine an optimum concentration of commercial electrolyte to send to the tankhouse for electroplating. The pregnant leach solution (2.0 - 4.0 g/L) is sent to the Solvent Extraction facility to remove other metals such as iron. The stripping cycle usually produces a rich electrolyte around 48 g/L of copper. This solution is mixed with lean electrolyte coming from the tankhouse at 30 - 34 g/L to prepare a commercial electrolyte of 40-49 g/L.

A concern of the mine is the possibility of a power outage. Since electricity is used to plate the copper, a power outage would stop the process. The Mine is considering building a large-scale generator for backup power. Is a generator really necessary? Would there be any adverse affects resulting from a power outage, other than loss of revenue due to copper not being electroplated.

Your Task You began this series of laboratory activities with a copper-bearing mineral. You leached this mineral with sulfuric acid. Leaching dissolved the copper forming an aqueous copper (II) sulfate solution. Other metals, such as iron, were also leached. Solid impurities were removed through filtration. Most of the iron impurities, and other water-soluble substances were removed through the extraction process. The remaining copper (II) sulfate solution (electrolyte) is now ready for the final step, converting the copper (II) ion into copper metal.

Your final three tasks will be to:

• Obtain metallic copper through an electrowinning process.

• Use your background in chemistry and other resources to determine if a generator would be necessary in case of power failure.

• Report your findings to the Mining Commissioner.

145 Student Handout Chemistry of Electrowinning

Materials

100 mL of leached CuSO4 (copper (II) sulfate solution) (rich electrolyte) 100 mL graduated cylinder 250 mL beaker or polystyrene jar anode – lead strip cut to give 20 cm2 one-sided area. cathode – copper strip to give 20 cm2 one-sided area. power supply alligator clips

Safety and Disposal

As instructed by your teacher, follow appropriate safety procedures, including the use of personal protective equipment such as goggles and an apron.

Rich electrolyte contains 200-g/L H2SO4 (sulfuric acid). Use caution when working with

200-g/L H2SO4 (sulfuric acid). If spills occur, neutralize by sprinkling with baking soda and

diluting with water. The 200-g/L H2SO4 (sulfuric acid) can be disposed of by diluting the acid into a large beaker containing water. The final concentration of the acid should be

1M or less. Slowly add 1 M Na2CO3 (sodium carbonate) solution to the diluted acid while stirring. Flush the neutral mixture down the drain with a 20-fold excess of water.

Copper (II) sulfate pentahydrate is a strong irritant to the skin and mucous membranes. To avoid inhaling its dust, use copper (II) sulfate only where there is adequate ventilation. It can be harmful or fatal if taken internally. If contact with the skin occurs, flush with running water. Wash your hands after use. Follow local ordinances for disposal of copper (II) salts. It is recommended that unused copper (II) sulfate solution be left to evaporate to dryness.

Procedure

1. Obtain both a lead (Pb) and a copper (Cu) electrode from your instructor.

2. Weigh both the lead and the copper electrodes on an analytical balance. Record the mass of each.

3. Fill the cell (beaker or polystyrene cup) with 150 mL of rich electrolyte (copper (II) sulfate solution obtained from leaching).

4. Measure the height and width of the copper electrode that is below the solution. It might be easier to make a mark on the electrode at the solution/air interface, and then remove the electrode to measure its height.

5. Determine the surface area in cm2 of the part of the copper electrode that is

146 Student Handout Chemistry of Electrowinning

below water. (Hint: Area = length x width and you have two sides on each electrode.) Record the surface area.

6. The optimum current density for copper is 0.020 Amperes per square centimeter. If the current density is too high, flaking will occur on the cathode. Determine the amount of current that would need to be applied. Record this value.

7. Use a red wire to connect one bracket to the positive (red) terminal on the power supply. Use a black wire to connect the other bracket to the negative (black) terminal on the power supply as shown in Figure 1.

8. Just before starting the electroplating, slide the lead electrode into the bracket attached to the red wire. Slide the copper electrode into the bracket attached to the black wire. Make sure that the electrodes penetrate the same distance into the solution as previously done in Step 4 (See Figure 1).

Figure 1: Electrolytic Cell

9. Place the cell on a stirrer. Add a small stir bar. Turn on the stirrer so that the stir bar spins at a constant slow speed.

10. Turn on the Power Supply. Adjust the current (A) according to your calculations. Record the voltage (V). Record the time you began the electroplating. Wait 60 seconds to make sure that the current and voltage don’t increase tremendously. If there is no current reading, try connecting the wires to the top of the electrodes.

11. Set up a spectrophotometer to measure the absorbance of copper sulfate,

CuSO4.

12. Set the wavelength to the optimum wavelength for copper. If you did not determine the optimum wavelength for copper, ask your instructor for this value.

13. Follow the directions for using the spectrophotometer as done in previous labs.

14. Measure the absorbance of your rich electrolyte solution Return this solution back to the cell after taking your measurement. You will be taking measurements every 10 minutes during the experiment.

15. An absorbance vs. concentration graph was created in the Spectrophotometric 147 Student Handout Chemistry of Electrowinning

Determination Lab. You will use this same graph to determine the concentration of your electrolyte solutions. Make sure that you return every 10 minutes to take a measurement of your electrolyte solution.

16. After 10 minutes, use a pipet to draw out enough solution to measure the absorbance of the electrolyte on a spectrophotometer. Record the voltage and current as well. Adjust the current back to the calculated value if it has changed.

17. Repeat every 10 minutes until the concentration falls below 1 g/L copper, or 10 minutes before your class ends.

18. Turn off the power to the power supply and unplug it. The electrolyte is now termed lean electrolyte.

19. Draw out enough solution to do one last absorbance determination.

20. Your instructor will inform half of the teams to leave their electrolytic cell as is. This symbolizes a power failure. Return the following day and take an absorbance measurement to determine if the concentration of the electrolyte has changed.

21. The other half of the class will proceed by gently rinsing the electrodes several times with water by dipping them into a beaker of distilled water to remove any acid or copper sulfate solution. Hang the electrodes to dry. It is sometimes convenient to pour out the electrolyte solution from the cell into another beaker and then clamp the electrodes back into place allowing them to air dry.

22. Determine the mass of each electrode using an analytical balance.

Discussion

Q1: Determine the mass of copper deposited on the cathode from your mass measurements.

Q2: Use the change in Cu2+ concentration to calculate the mass of copper metal deposited at each 10-minute interval. Add these values to obtain a total mass of copper deposited for the entire experiment.

Q3: How do the values from Data Analysis Question 1 compare with the values from Question 2?

Q4: Write the two half reactions and combined reaction. Identify the anode and the cathode.

Q5: Did the voltage or current change as the reaction progressed? If so, how did it change?

Q6: What would happen in the electrolytic cell if the power were to go off?

148 Student Handout Chemistry of Electrowinning

Assessment

Summarize your results in the form of a letter to the Mine Commissioner responding to the tasks mentioned at the beginning of the lab. Report on the mass of metallic copper produced during the electrowinning process.

Use your background in chemistry, your experimental data, and any other resources to determine if a generator would be necessary in case of power failure. Report this recommendation to the Mine Commissioner.

149 Student Handout Chemistry of Electrowinning

Name ______Data Table & Results

Electrode Mass Mass Length Width Surface Current (Before (After Area required for Plating) Plating) Covered by electrowinning Solution

copper

lead

Time Current Voltage Absorbance Concentration Conc. (g/L) Cu2+ 2+ (Amps) (Volts) of Cu lost to plating g/L

Q1: Determine the mass of copper deposited on the cathode from your mass measurements.

150 Student Handout Chemistry of Electrowinning

Q2: Use the change in Cu2+ concentration to calculate the mass of copper metal deposited at each 10-minute interval. Hint: You will need to convert grams per liter to grams using the volume of rich electrolyte used. Add these values to obtain a total mass of copper deposited for the entire experiment.

Q3: How do the values from Data Analysis Question 1 compare with the values from Question 2?

Q4: Write the two half reactions and combined reaction. Identify the anode and the cathode.

Q5: Did the voltage or current change as the reaction progressed? If so, how did it change?

Q6: What would happen in the electrolytic cell if the power were to go off?

Assessment

151

APPENIDIX D

Instructor’s Manual

CHEMISTRY of COPPER MINING

By Phil Blake McBride

in partial fulfillment of his requirements

for the degree of Doctor of Philosophy

Department of Chemistry and Biochemistry

Miami University

Oxford, Ohio

2003

152

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Learning Cycle Teaching Method Activity Page Leaching Exploration Copper Bearing Minerals 154 Exploration Properties of Copper Ores 159 Exploration Leaching Copper 167 Concept Development Chemistry of Leaching (Website Activity) 175 Concept Development Colorful Transition Metals 177 Application Spectrophotometric Determination 185

Solution Extraction Exploration Purification Techniques 191 Concept Development Chemistry of Extraction (Website Activity) 200 Application Solution Extraction 202

Electrowinning Awareness Copper Replacement 209 Concept Development Electrochemistry 211 Concept Development Chemistry of Electrowinning (Website Activity) 214 Application Electrowinning 216

153 Awareness Activity Exploration X Concept Introduction Concept Application Instructor Notes Copper-Bearing Minerals

Students are provided with mineral samples of azurite [2CuCO3 · Cu(OH)2], chalcopyrite

(CuFeS2), chrysocolla (CuSiO3 · 2 H2O), and malachite [CuCO3 · Cu(OH)2]. Students study the mineral samples, determine the oxidation state of all elements in each formula, and calculate the percent by mass of copper present in each mineral.

Coaching and guided inquiry will be used as the students follow the examples to complete the given tasks.

Key Science Concepts

Chemistry • oxidation states • percent by mass • physical properties of matter

Other Science Concepts

Mathematics • solving simple algebraic equations with one variable.

Engineering and Technology

Prior Concepts and Skills Needed Materials

Per class, group, or student

azurite [2CuCO3 · Cu(OH)2]

chalcopyrite (CuFeS2)

chrysocolla (CuSiO3 · 2 H2O)

malachite [CuCO3 · Cu(OH)2] Safety and Disposal

It is your responsibility to review appropriate safety procedures with your students, including the use of personal protective equipment. No special disposal procedures are required.

154 Instructor Notes Copper-Bearing Minerals

Getting Ready

Have mineral samples of azurite [Cu3(CO3)2(OH)2], chalcopyrite (CuFeS2), chrysocolla

(CuSiO3 · 2 H2O), and malachite [Cu2(CO3)(OH)2] at each lab station. It is helpful to place the samples in a Ziploc Baggie.

Amethyst Galleries' Mineral Gallery (1) at http://mineral.galleries.com/minerals/by- name.htm is a good reference to obtain data for the minerals being studied.

Procedure Notes

Students become aware of four copper-bearing minerals that are present in the earth. They study these minerals, determine the oxidation state of each element, and determine the percent by mass of copper present in each mineral.

The instructor may want to work through the examples in the student handout before setting the students free to complete the tasks.

The formula for azurite is written two ways [Cu3(CO3)2(OH)2] and [2CuCO3 · Cu(OH)2] as

is malachite [Cu2(CO3)(OH)2] or [CuCO3 · Cu(OH)2]. Either formula is acceptable. Assessment Sample Data Table & Results

5. Description of Mineral

Mineral Formula Color Hardness Specific Gravity

Azurite Cu3(CO3)2(OH)2 Deep blue 3.5 – 4.0 3.7+

Chalcopyrite CuFeS2 Bright golden 3.5 – 4.0 4.2

Chrysocolla CuSiO3 - nH2O green-blue 2.0 – 4.0 2.0 - 2.3

Malachite Cu2(CO3)(OH)2 banded light 3.5 – 4.0 3.9+ and dark green

155 Instructor Notes Copper-Bearing Minerals

Mineral Description

Whitish-tan rock with clumps of blue crystals. Azurite, Cu3(CO3)2(OH)2 The blue crystals are easy to see. There are also some greenish moss-like crystals on the rock. Dirty gray, with yellowish-gold crystals. A black Chalcopyrite, CuFeS2 charcoal-like substance rubs off.

Clumpy turquoise and light blue crystals. Chrysocolla, CuSiO3 · 2 H2O

Dirty, light green or pale green crystals. Malachite, Cu2(CO3)(OH)2

6. List at least 2 different websites that you visited to obtain your information. Rank the sites on a scale of 1-5, with 5 being excellent, and 1 being poor.

Site Ranking

http://mineral.galleries.com/minerals/by-name.htm (1) 4 (Very Good)

http://webmineral.com/ (2) 3 (good)

7. Assign Oxidation States by writing the oxidation state of each element directly above that element.

2+ 4+ 2- 2- 1+ Cu3(CO3)2 (OH)2

2+ 2+ 2- CuFeS2

2+ 4+ 2- 1+ 2- CuSiO3 · 2 H2O

2+ 4+ 2- 2- 1+ Cu2(CO3) (OH)2

156 Instructor Notes Copper-Bearing Minerals

8. Percent of Copper by mass present in each formula.

Mineral Percent of Copper by Mass

Azurite, Cu3(CO3)2(OH)2 55.31% Cu

Chalcopyrite, CuFeS2 34.63% Cu

Chrysocolla, CuSiO3 · 2 H2O 36.18% Cu

Malachite, Cu2(CO3)(OH)2 57.48% Cu

Q1: Which minerals are oxides? Azurite, chrysocolla, and malachite are all oxide ores.

Which minerals are sulfides?

Chalcopyrite is a sulfide ore.

Q2: Rank the minerals according to the percent by mass of copper present.

Mineral Percent of Copper by Mass

Malachite, Cu2(CO3)(OH)2 57.48% Cu

Azurite, Cu3(CO3)2(OH)2 55.31% Cu

Chrysocolla, CuSiO3 · 2 H2O 36.18% Cu

Chalcopyrite, CuFeS2 34.63% Cu

Explanation

In the activity the students research four minerals that will be used throughout the Chemistry of Copper Mining laboratory activities. The students calculate the percent by mass of copper in each mineral. The students use this data in subsequent labs to determine the benefits of different ore bodies.

Addressing the National Science Education Standards

• 193-1: Atoms interact with one another by transferring or sharing electrons that are furthest from the nucleus. Copper bearing minerals are composed of compounds that

157 Instructor Notes Copper-Bearing Minerals

have both ionic and molecular bonding. • 196-4: The physical properties of compounds reflect the nature of the interactions among its molecules. Azurite and malachite both have similar chemical formulas, but azurite is blue and malachite is green. Malachite represents a later stage of oxidation, which results in its green color (1).

References 1. Amethyst Galleries, Inc. Amethyst Galleries’ Mineral Gallery.

http://mineral.galleries.com/minerals/by-name.htm (accessed June 2003).

2. Barthelmy, D. Mineral Database. http://webmineral.com/ (accessed June 2003).

158 Awareness Activity X Exploration Concept Introduction Concept Application Instructor Notes Properties of Copper Ores

This is the first activity in a series of activities that takes the students through the chemistry of copper mining and processing. Students study the physical characteristics of oxide and sulfide ores, specifically color and solubility. They conduct experiments to determine if copper ores can be leached with water and/or sulfuric acid. This is an exploration activity.

Key Science Concepts

Chemistry • physical properties • solubility (leaching)

Other Science Concepts • properties of minerals

Prior Concepts and Skills Needed

There are no prior concepts or skills needed for this activity.

Materials

Per lab team

50-mL of 7 g/L sulfuric acid (H2SO4) 20 g of each ore (azurite, chalcopyrite, chrysocolla, and malachite) magnifier (not required but useful) balance two 150-mL beakers 50-mL or 100-mL graduated cylinder

Safety and Disposal

It is your responsibility to review appropriate safety procedures with your students, including the use of personal protective equipment. Use caution when working with 7-g/L sulfuric acid. This is a 0.07 M solution, which is dilute, but should still be handled with caution. If spills occur, neutralize by sprinkling with baking soda and diluting with water. The 7-g/L sulfuric acid can be disposed of by neutralizing with 1 M sodium carbonate

(Na2CO3) solution and flushed down the drain with 20-fold excess of water.

159

Instructor Notes Properties of Copper Ores

Getting Ready

Preparation of 7-g/L sulfuric acid (H2SO4). NOTE: Always ADD ACID to water!

• Weighing Method: Weigh out 7 grams of concentrated sulfuric acid. Add the acid to 500-mL of distilled water in a 1-L volumetric flask. Continue filling the flask with water up to the 1-L mark.

• Volume Method: Measure 3.8 mL of concentrated sulfuric acid. Add the acid to 500 mL of distilled water in a 1-L volumetric flask. Continue filling the flask with water up to the 1-L mark.

Obtain mineral samples of azurite, chalcopyrite, chrysocolla, and malachite. Place some small specimens of each mineral, along with a larger specimen in a container such as a Ziploc baggie. Label each container with the mineral it contains. Each team will analyze one mineral sample.

For the assessment activity, a nice sample of each mineral must be available for observation. Place a nice, large single rock sample of azurite in a Ziploc baggie and label it Nietfeld Site. Place a nice, large single rock sample of chalcopyrite in a Ziploc baggie and label it Graham Site. Place a nice, large single rock sample of chrysocolla in a Ziploc baggie and label it Franklin Site. Place a nice, large single rock sample of malachite in a Ziploc baggie and label it Bonita Site.

Procedure Notes

The instructor will divide the class into teams of 3-4. Each team will identify someone as Laboratory Director, Scribe, Chemical Manager, and Spokesperson. The Laboratory Director is the leader in charge of the group. The Scribe records everything that occurs during the laboratory session. This record is the official record for the group and will be turned in for evaluation. The Chemical Manager retrieves any chemical substances needed from the instructor. The Spokesperson communicates the team results to other teams.

The Chemical Manager of each team is provided a container of a single mineral (azurite, chalcopyrite, chrysocolla, or malachite). If the class has less than 16 students, smaller teams can be formed or each team can work with two minerals. If the class is larger than 16 students, duplicates of each mineral can be used. It is important that all four minerals be tested.

The students make detailed observations about the mineral they are studying. They should include variations in color, texture, and any specific identifying features that would allow someone who has never seen the mineral to recognize it.

160 Instructor Notes Properties of Copper Ores

Students test the solubility of their specific mineral in water and 7-g/L sulfuric acid. The students should record at least six observations over a 48-hour period. The best time to make observations is before school, at lunch, during class, and after school, depending on when the class meets. Encourage the Laboratory Director of each team to divide up the observations so that each team member has the opportunity to make and record observations during the 48-hour period.

Assessment

The instructor has the option of having the students write in a laboratory notebook or completing the worksheets provided.

Sample Data and Results

Name of Mineral Sample azurite

Physical Characteristics

Whitish-tan rock with clumps of blue crystals. The blue crystals are easy to see. There are also some greenish moss-like crystals on the rock.

Name of Mineral Sample chalcopyrite

Physical Characteristics

Dirty gray, with yellowish-gold crystals.

Name of Mineral Sample chrysocolla

Physical Characteristics

Clumpy turquoise and light blue crystals.

Name of Mineral Sample malachite

Physical Characteristics

Dirty, light green or pale green crystals.

161 Instructor Notes Properties of Copper Ores

Results of Leaching with H2O

Leached with AZURITE CHALCOPYRITE CHYRSOCOLLA MALACHITE water Observations Observations Observations Observations

Date: 5/14/03 Clear solution with Clear solution with Clear solution with Dirty solution with rock in the bottom. rock in the bottom. rock in the bottom. rock in the bottom. Time: 11:00 am

Date: 5/14/03 Clear & colorless Clear & colorless Clear & colorless Dirt has settled to Time: 3:00 pm solution solution solution the bottom and the solution is clear & colorless.

Date: 5/15/03 Clear & colorless Clear & colorless Clear & colorless Clear & colorless Time: 7:30 am solution solution solution solution

Date: 5/15/03 Clear & colorless Clear & colorless Clear & colorless Clear & colorless Time: 11:00 am solution solution solution solution

Date: 5/15/03 Clear & colorless Clear & colorless Clear & colorless Clear & colorless Time: 3:00 pm solution solution solution solution

Date: 5/16/03 Clear & colorless Clear & colorless Clear & colorless Clear & colorless Time: 7:30 am solution solution solution solution

162 Instructor Notes Properties of Copper Ores

Results of Leaching with H2SO4

Leached with AZURITE CHALCOPYRITE CHYRSOCOLLA MALACHITE

H2SO4 Observations Observations Observations Observations

Date: 5/14/03 Clear solution with Clear solution with Clear solution with The solution rock in the bottom. rock in the bottom. rock in the bottom. began to fizz when Time: 11:00 am the acid was added.

Date: 5/14/03 Clear & colorless Clear & colorless The solution is a Dirt has settled to Time: 3:00 pm solution solution faint blue color. the bottom and the solution is greenish in color.

Date: 5/15/03 The solution is a Clear & colorless The solution is a The solution is a Time: 7:30 am light blue color. solution light blue color. green color with sediment on the bottom.

Date: 5/15/03 The solution is a Clear & colorless The solution is a The solution is a Time: 11:00 am light blue color. solution light blue color. green color with sediment on the bottom.

Date: 5/15/03 The solution is a Clear & colorless The solution is a The solution is a Time: 3:00 pm light blue color. solution light blue color. green color with sediment on the bottom.

Date: 5/16/03 The solution is Clear & colorless The solution is The solution is Time: 7:30 am blue. solution blue. green. There is a lot of sediment on the bottom.

163 Instructor Notes Properties of Copper Ores

Q3: Can your ore (mineral) be leached with water? Explain.

None of the minerals can be leached with water. The solution remained colorless and clear signifying that no copper sulfate was present.

Q4: Can your ore (mineral) be leached with H2SO4? Explain.

Azurite, chrysocolla, and malachite can all be leached with H2SO4. In each case, there was evidence that copper sulfate was present in solution due to the blue or green color of the solution. They are all oxide ores. The sulfide ore (chalcopyrite) cannot be leached with sulfuric acid.

D1: List the physical characteristics of azurite, chalcopyrite, chrysocolla, and malachite.

Mineral Physical Characteristics

azurite Whitish-tan rock with clumps of blue crystals. The blue crystals are easy to see. There are also some greenish moss-like crystals on the rock.

chalcopyrite Dirty gray, with yellowish-gold crystals.

chrysocolla Clumpy turquoise and light blue crystals.

malachite Dirty, light green or pale green crystals.

D2: Which of the ores (azurite, chalcopyrite, chrysocolla, and malachite) can be leached with water?

None of the minerals can be leached with water. The solution remained colorless and clear signifying that no copper sulfate was present.

D3: Which of the ores (azurite, chalcopyrite, chrysocolla, and malachite) can be leached

with 7 g/L H2SO4?

164 Instructor Notes Properties of Copper Ores

D4: Which of the ores (azurite, chalcopyrite, chrysocolla, and malachite) appears to react the fastest with sulfuric acid?

The malachite fizzed when the sulfuric acid was added. None of the others appeared to react at the beginning.

Letter:

H2SO4. Attach the letter to this page.

Dear Director:

According to our data, it appears that azurite, chrysocolla, and malachite can all be

leached directly with 7 g/L H2SO4 (sulfuric acid). However, none of the minerals leached with water. Malachite appeared to react the fastest with sulfuric acid.

After looking at the samples sent from Branicoda Mines, it appears that the Nietfeld site contains azurite, the Franklin site contains chrysocolla, and the Bonita site contains malachite. All three of these sites can be leached with sulfuric acid. However the Graham site contains chalcopyrite, which cannot be leached directly with sulfuric acid.

Thank you for the opportunity to conduct this research on your behalf.

Sincerely,

The Gila Team Members

Explanation

In the activity the class will recognize azurite by deep blue crystals, that are soluble in acid but insoluble in water, chalcopyrite by brass yellow crystals that are insoluble in acid and water, chrysocolla by light blue or blue-green crystals that are soluble in acid but insoluble in water, and malachite by green crystals often in masses that are soluble in acid with fizzing, but insoluble in water,

165 Instructor Notes Properties of Copper Ores

Information about each of the minerals used in this laboratory activity can be obtained at http://www.theimage.com/mineral/index.htm (1).

Azurite (Carbonate) Cu3(CO3)2(OH)2

Chalcopyrite (Sulfide) CuFeS2

Chrysocolla (Silicate) Cu4(OH)8(Si4O10) · n H2O

Malachite (Carbonate) Cu2CO3(OH)2

Azurite, chrysocolla, and malachite are all considered “oxide” ores and can be leached with sulfuric acid. Chalcopyrite is a “sulfide” ore that is insoluble in sulfuric acid and requires iron in addition to sulfuric acid for leaching.

In their letter to the Mining Director, the students should state that azurite, chrysocolla, and malachite can all be leached with sulfuric acid, and that the mining sites of Nietfeld (azurite), Franklin (chrysocolla), and Bonita (malachite) should be mined.

Addressing the National Science Education Standards

• 178-2: Students conduct experiments to determine which minerals can be leached with sulfuric acid. • 196-4: Students learn that oxide ores of copper have green or blue crystals and are soluble in sulfuric acid. They learn that sulfide ores are yellow in color and are insoluble in sulfuric acid.

• 164-5: Students communicate the results of their experiments to other groups and write a letter to the Director of Mines indicating their recommendation as to which sites should be leached with sulfuric acid.

References

1. Minerals. http://www.theimage.com/mineral/index.htm (accessed June 2003).

166 Awareness Activity X Exploration Concept Introduction Concept Application Instructor Notes Leaching Copper

This is the second activity in a series of activities that takes the students through the chemistry of copper mining and processing. Students leach malachite and chrysocolla with sulfuric acid. They conduct experiments to determine the benefits of crushing the ore. They measure the pH at specific times over a 48-hour period to determine whether sulfuric acid is consumed in the leaching of the ore. This is an exploration activity.

Key Science Concepts

Chemistry • pH • physical properties • sample preparation • solubility

Other Science Concepts • properties of minerals

Prior Concepts and Skills Needed

There are no prior concepts or skills needed for this activity.

Materials

Per lab team

200-mL of 7 g/L H2SO4 (sulfuric acid) This is 0.068 M. 20 g of the ore to be analyzed (chrysocolla or malachite) balance two 250-mL beakers watch glass or parafilm to cover beakers 100-mL graduated cylinder pH meter (preferred) or pH paper buffer solutions of 4, 7, and 10 for pH meter calibrations

Safety and Disposal

It is your responsibility to review appropriate safety procedures with your students, including the use of personal protective equipment. Use caution when working with 7-g/L

167

Instructor Notes Leaching Copper

sulfuric acid. This is a 0.068 M solution, which is dilute, but should still be handled with caution. If spills occur, neutralize by sprinkling with baking soda and diluting with water. The 7-g/L sulfuric acid can be disposed of by neutralizing with 1 M sodium carbonate

(Na2CO3) solution and flushed down the drain with 20-fold excess of water. Getting Ready

Preparation of 7-g/L sulfuric acid (H2SO4). NOTE: Always ADD ACID to water!

• Weighing Method: Weigh out 7 grams of concentrated sulfuric acid. Add the acid to 500-mL of distilled water in a 1-L volumetric flask. Continue filling the flask with water up to the 1-L mark.

• Volume Method: Measure 3.8 mL of concentrated sulfuric acid. Add the acid to 500 mL of distilled water in a 1-L volumetric flask. Continue filling the flask with water up to the 1-L mark.

Obtain mineral samples of chrysocolla and malachite. Each lab team will need approximately 10 grams of uncrushed chrysocolla or malachite, and 10 grams of crushed ore (the same type as the uncrushed).

Uncrushed ore: Place a single rock sample that weighs approximately 10 grams into a Ziploc baggie and label as uncrushed chrysocolla or malachite.

Crushed ore: Take several pieces of chrysocolla and wrap in an old piece of cloth. Wearing safety goggles, use a hammer to crush the large pieces into small chunks. Place approximately 15 gram samples of this ore into Ziploc Baggies and label each as crushed chrysocolla. Repeat for malachite.

You should now have Baggies containing uncrushed chrysocolla, crushed chrysocolla, uncrushed malachite, and crushed malachite. If you have a class of 24 students, you will have 6 teams, 3 teams that will work with uncrushed and crushed chrysocolla, and 3 teams that will work with uncrushed and crushed malachite. Adjust accordingly based on your class size.

For the pH measurements, a pH meter is easier to work with than pH paper. If a pH meter is used it should be calibrated and ready to use when the students arrive. Follow the manufacturer’s directions to calibrate the pH meter.

Procedure Notes

The instructor will divide the class into teams of 3-4. Each team will identify someone as Laboratory Director, Scribe, Chemical Manager, and Spokesperson. The Laboratory

168 Instructor Notes Leaching Copper

Director is the leader in charge of the group. The Scribe records everything that occurs during the laboratory session. This record is the official record for the group and will be turned in for evaluation. The Chemical Manager retrieves any chemical substances needed from the instructor. The Spokesperson communicates the team results.

The Chemical Manager of each team is provided a Ziploc Baggie containing a single rock sample of uncrushed ore that weighs approximately 10 grams and a Ziploc Baggie containing approximately 15 grams of crushed ore. Half of the teams will be given chrysocolla and half will be given malachite. It is important that both chrysocolla and malachite be tested.

Students make detailed observations about the mineral they are studying. They should include variations in color, texture, and any other specific identifying features. Students weigh their uncrushed ore sample. The ore is leached with 7-g/L sulfuric acid. The pH of this solution is measured at least six times over a 48-hour period. The students also weigh out a sample of crushed ore. This sample should be measured so that the masses of the crushed and uncrushed ore are identical (or very close). The students record the pH and the color and clarity of each solution at least six times over a 48-hour period. The best time to make observations is before school, at lunch, during class, and after school, depending on when the class meets. Encourage the Laboratory Director of each team to divide up the observations so that each team member has the opportunity to make and record observations during the 48-hour period.

If you have Vernier Logger Pro and pH meters or other data collection hardware and software you can have the pH meter take measurements every 30 minutes for 48 hours. You can connect two pH meters to the Logger Pro to take pH measurements of crushed and uncrushed ore simultaneously.

Assessment

The instructor has the option of having the students write in a laboratory notebook or completing the worksheets provided.

169 Instructor Notes Leaching Copper

Sample Data and Results

Name of Mineral Sample chrysocolla

Physical Characteristics

Clumpy turquoise and light blue crystals.

Name of Mineral Sample malachite

Physical Characteristics

Dirty, light green or pale green crystals.

Leaching chrysocolla with H2SO4 (5 days)

Leached with Crushed Uncrushed

7 g/L H2SO4 Observations pH Observations pH

Date: 5/14/03 Clear solution with rock 1.14 Clear solution with rock 1.09 Time: 3:00 pm in the bottom. in the bottom.

Date: 5/15/03 The solution is a faint 1.37 The solution is a faint 1.27 Time: 9:05 am blue color. blue color.

Date: 5/15/03 The solution is a light 1.44 The solution is a light 1.31 Time: 12:00 pm blue color. blue color.

Date: 5/15/03 The solution is a light 1.47 The solution is a light 1.35 Time: 3:46 pm blue color. blue color.

Date: 5/16/03 The solution is a light 1.62 The solution is a light 1.42 Time: 11:18 am blue color. blue color.

Date: 5/17/03 The solution is blue. 1.70 The solution is blue. 1.50 Time: 11:18 am

Date: 5/18/03 The solution is blue. 1.79 The solution is blue. 1.55 Time: 9:35 am

Date: 5/19/03 The solution is blue. 1.91 The solution is blue. 1.64 Time: 11:47 am

170 Instructor Notes Leaching Copper

Leaching malachite with H2SO4 (2 days)

Leached with Crushed Uncrushed

7 g/L H2SO4 Observations pH Observations pH Date: 5/14/03 The solution began to 1.46 The solution began to 1.07 Time: 11:00 am fizz when the acid was fizz when the acid was added. added.

Date: 5/14/03 There is a lot of brown 1.49 A brown sediment has 1.11 Time: 3:00 pm sediment on the bottom settled to the bottom of of the beaker. The the beaker. The solution solution is light green. is greenish in color.

Date: 5/15/03 The solution is a green 1.82 The solution is a green 1.53 Time: 7:30 am color with sediment on color with sediment on the bottom. the bottom.

Date: 5/15/03 The solution is a green 1.85 The solution is a green 1.58 Time: 11:00 am color with sediment on color with sediment on the bottom. the bottom.

Date: 5/15/03 The solution is a green 1.88 The solution is a green 1.64 Time: 3:00 pm color with sediment on color with sediment on the bottom. the bottom.

Date: 5/16/03 The solution is green. 2.07 The solution is green. 1.89 Time: 7:30 am There is a lot of There is a lot of sediment on the bottom. sediment on the bottom.

171 Instructor Notes Leaching Copper

Yes, you want the mass of the crushed and uncrushed ore to be as close as possible. If the two samples are not identical in mass, it is not possible to determine whether the results are due to particle size (crushed vs. uncrushed) or if they are simply the result of the samples being different masses.

Q2: Why must the beakers be covered?

The beakers are covered to prevent evaporation. If evaporation occurs, the concentration of ions in the solution will increase simply because water was removed.

Q3: Analyze your data and graph. What trends do you notice?

The pH of the malachite increased more quickly over the span of the two days as compared to the chrysocolla. Both solutions had an increase in pH.

Q4: Was acid consumed in the leaching of chrysocolla and/or malachite? Explain your evidence.

Acid was consumed in the leaching of both chrysocolla and malachite. This was evidenced by an increase in the pH of the solution over time.

Q5: What physical evidence do you have that copper was leached out of the ore body?

The chrysocolla solution turned from a colorless solution to a light blue solution, which is evidence that copper sulfate is present. The malachite solution turned from a colorless solution to a light green solution, which is evidence that copper was present in the solution.

Q6: Would it be beneficial to crush the ore before leaching? Explain.

At this point it would be difficult to say because we don’t know how much copper we have recovered from each solution. The pH seemed to rise at the same rate for both crushed and uncrushed.

172 Instructor Notes Leaching Copper

Letter:

Write a summary letter to the director of Mines stating your findings from this lab.

Dear Director:

According to our data, it appears that chrysocolla and malachite can both be

leached directly with 7 g/L H2SO4 (sulfuric acid).

Malachite appeared to react the fastest with sulfuric acid.

Based on our data, the pH of all solutions increased over time, which signifies that sulfuric acid is being consumed. Malachite consumes sulfuric acid at a faster rate than chrysocolla.

At this time, we are not prepared to state the benefits of crushing or not crushing the ore. We will do a further analysis to determine the amount of copper in each solution. We will then report back to you.

Thank you for the opportunity to conduct this research on your behalf.

Sincerely,

The Gila Team Members

Explanation

The minerals that react with sulfuric acid tend to be carbonates. One of the products of

this reaction is CO2 (carbon dioxide). The CO2 is released as bubbles and is visible evidence of the reaction (1).

2+ 2- CuCO3 + H2SO4 → Cu + SO4 + CO2(g) + H2O

In the activity the class will recognize that malachite fizzes (effervesces) when placed in sulfuric acid signifying that a chemical reaction is taking place. The reactions of Malachite and Chrysocolla with sulfuric acid are shown below: Notice that both reactions consume

acid, but that malachite produces CO2, which when released as a gas helps drive the reaction to completion.

173 Instructor Notes Leaching Copper

Malachite

2+ 2- CuCO3·Cu(OH)2 + 2H2SO4 → 2Cu + CO2(g) + 3H2O + 2SO4 -

Chrysocolla

2+ 2- CuO·SiO2 ·2H2O + H2SO4 → Cu + 3H2O + SO4 + SiO2

Addressing the National Science Education Standards

• 178-2: Students conduct experiments to determine if acid is consumed in the leaching of chrysocolla and malachite. • 185-3: Students use a pH meter and possibly a data collection system to measure and record the change in pH over time during the leaching of chrysocolla and malachite. • 186-4: Students plot their pH measurements on a graph, which helps them to visualize the consumption of acid in leaching. • 199-1: Students learn that a chemical reaction takes place during the leaching of chrysocolla and malachite.

• 201-3: Chrysocolla is a metal oxide that reacts with water to form cupric hydroxide, which then undergoes an acid/base reaction with sulfuric acid. • 201-3: Malachite is a metal carbonate that dissolves readily in sulfuric acid to produce carbon dioxide and water. • 164-5: Students communicate the results of their experiments to other groups and write a letter to the Director of Mines indicating their recommendation as to which sites should be leached with sulfuric acid.

References 1. Burns, R. A. Fundamentals of Chemistry, 4th Ed.; Prentice Hall: Upper Saddle River,

NJ, 2003; p 478.

174 Awareness Activity X Exploration Concept Introduction Concept Application Instructor Notes Chemistry of Leaching Copper Access the following web site or use the CD to answer the following questions. http://teach2.eac.edu/pmcbride

Define the following terms: 1. Leaching – the dissolution of a valuable metal from minerals into an aqueous solution.

2. Raffinate - The phase remaining after extraction of copper.

3. Run of Mine Ore – Ore that is obtained by blasting and then dumped on the leach fields with a dump truck.

4. Pregnant Leach Solution – The solution that comes off of the leach fields. It is now full (pregnant) of copper.

5. Hydrological Sink – A geological formation in which bedrock will not allow any aqueous solution to pass through it. The bedrock channels the aqueous solution to a valley where it is pumped out.

Answer the following questions:

Once the area has been blasted, shovels are moved into place and the loading of haul trucks begins for the haulage of ore to the leach stockpiles or the crusher.

1. Once the ore has been hauled to the stockpiles, the leaching begins. What chemical is fed through the driplines to begin the leaching? What is the concentration of this chemical.

7.0 g/L H2SO4 (sulfuric acid)

2. There are two different kinds of leach fields. One leach field uses haul trucks to bring in the ore. The other uses a conveyor belt. What is the main different between these two leach fields.

175

Instructor Notes Chemistry of Leaching Copper

The leach field that uses haul trucks to bring in the ore from blasting sites uses run of mine ore. The other leach field brings in ore that has been crushed and conglomerated to increase the ability of the ore to be leached.

3. Provide the name and formula for malachite, chrysocolla, azurite, and chalcopyrite. Identify each as an oxide or sulfide ore.

Name Formula Oxide or Sulfide

Azurite 2CuCO3·Cu(OH)2 Oxide

Chalcopyrite CuFeS2 Sulfide

Chrysocolla CuO·SiO2 ·2H2O Oxide

Malachite CuCO3·Cu(OH)2 Oxide

4. Approximately how many lifts are added each year?

One every 90 days or approximately 3 each year.

5. How long does it take for a drop of acid to run through the leach field and be collected?

Approximately 3 weeks.

6. How is the solution collected once it runs through the leach fields.

It hits bedrock and is funneled to a lake (hydrological sink). From there it is pumped to the SX plant.

7. Could leaching be done on copper ore if there was not a hydrologic sink? Explain.

Yes, but they would have to put a liner down to catch the pregnant leach solution and channel it to a holding pond.

8. What is the Cu2+ concentration as it comes off the leach fields?

2 g/L

9. Is the PLS a solution that only contains Cu2+? Explain.

No. It contains 4 g/L iron as well as other metals that leach with sulfuric acid.

176 Awareness Activity X Exploration Concept Introduction Concept Application Instructor Notes Colorful Transition Metals

Students are introduced to Spectrophotometry. They work in teams of 4, with each student assigned to determine the optimum wavelength of a specific transition metal. The team is given the task of identifying which transition metals are present in a waste sample from Transition Metallica.

The goals of the activity are:

• Teach the students how to use of a spectrophotometer.

• Help students understand the relationships between absorbance and wavelength.

• Use graphing to summarize results.

• Work as a team using a spectrophotometer to determine which transition metals are present in an unknown.

Exploratory learning and guided inquiry will be used in this laboratory activity.

Key Science Concepts

Chemistry • spectrophotometry • transition metal chemistry

Other Science Concepts

Mathematics • definition of slope • reading line graphs

Engineering and Technology

Prior Concepts and Skills Needed

Constructing and reading line graphs.

177

Instructor Notes Colorful Transition Metals

Materials

Per Team of 3-4 students 10-mL of 0.15 M Co(NO3)2 (cobalt (II) nitrate) 10-mL of 0.15 M Ni(NO3)2 (nickel (II) nitrate) 10-mL of 0.15 M Cu(SO4)2 (copper (II) sulfate) 10-mL of unknown waste sample 1 spectrophotometer (Spec-20 or Genesys-20, both work fine) 5-cuvettes

Safety and Disposal

It is your responsibility to review appropriate safety procedures with your students, including the use of personal protective equipment.

Cobalt (II) nitrate can be harmful if taken internally. Use caution when handling it. Solutions containing cobalt (II) ion should be collected and disposed of as heavy metals according to local regulations. Flinn Method #27f is an alternative to storing the waste for disposal.

Nickel (II) nitrate is slightly toxic. Avoid dispersing this substance; dispense with care;

strong oxidant. Nickel compounds are known carcinogens by inhalation of dust. LD50 1620 mg/kg. Flinn Method #27f is an alternative to storing the waste for disposal.

Copper (II) sulfate pentahydrate is a strong irritant to the skin and mucous membranes. To avoid inhaling its dust, use copper (II) sulfate only where there is adequate ventilation. It can be harmful or fatal if taken internally. If contact with the skin occurs, flush with running water. Wash your hands after use. Follow local ordinances for disposal of copper (II) salts. It is recommended that unused copper (II) sulfate solution be left to evaporate to dryness.

(The Flinn Scientific Chemical Catalog Reference Manual contains a complete description of a method for disposing of compounds of cobalt, nickel, and copper.)

Getting Ready

Prepare 0.15 M cobalt (II) nitrate, 0.15 M nickel (II) nitrate, and 0.15 M copper (II) sulfate.

Prepare a 50:50 volume % mixture of 0.15 M cobalt (II) nitrate and 0.15 M nickel (II) nitrate and label as Transition Metallica Waste Sample.

Show the students the Cuvettes and Kimwipes. Remind them of how different from a test tube a cuvette is and how it should be handled to prevent fingerprints and scratches.

Remind the students about heavy metal ion solutions. Give them directions for disposal

178 Instructor Notes Colorful Transition Metals

of the solutions.

Procedure Notes

Students work as a team using a spectrophotometer to determine the optimum wavelength of cobalt (II) nitrate, nickel (II) nitrate, and copper (II) sulfate. The team also works together to determines which transition metals are present in an unknown sample sent from Transition Metallica.

Before students go into the lab, the instructor should make sure that the students understand the nature of the task they are given. It would be helpful to review transition metals and their location on the periodic table. Ask lots of questions about what’s going on and what the data means as it unfolds.

Encourage students to use the directions and for each one in the team to watch and critique the others as they work so that the proper steps are followed. This will help alleviate frustration, which occurs when students forget to reset the blank to 100% T after each wavelength adjustment. Make sure that if your spectrophotometer has two filters that the filter is switched when the students get to 600 nm. This is a very common problem but is easily recognized because the spectrophotometer readout will be flashing.

Assessment

Sample Data Tables & Results

Formula of Compound Name of Compound Color of Compound

Co(NO3)2 Cobalt (II) nitrate Reddish / Pink

Ni(NO3)2 Nickel (II) nitrate Green

CuSO4 Copper (II) sulfate Blue

179 Instructor Notes Colorful Transition Metals

Sample Date of Wavelength and Absorbance for all compounds. Wavelength (nm) Absorbance Absorbance Absorbance Absorbance

Co(NO3)2 Ni(NO3)2 CuSO4 Waste Sample

350 .004 .033 .004 .062

400 .024 .395 .011 .258

450 .122 .035 .002 .126

500 .386 .003 .008 .208

550 .192 .014 .020 .099

600 .033 .055 .075 .059

650 .023 .152 .238 .111

700 .010 .173 .539 .121

750 .004 .158 .838 .113

800 .007 .080 .970 .070

850 .011 .037 .938 .044

900 .013 .027 .830 .039

950 .016 .036 .713 .048

The absorbance remains relatively constant when the absorbance is very low (at the front and rear of the peak) and at the highest point of the peak.

Q2: Inform your instructor what you consider to be the optimum wavelength for your compound? Explain how you made this determination.

The optimum wavelength is the wavelength where the absorbance is the greatest. At this point small deviations in wavelength have very little affect on the absorbance measurements.

180 Instructor Notes Colorful Transition Metals

Compound Color of solution Optimum Wavelength

Co(NO3)2 Reddish / Pink 510 nm

Ni(NO3)2 Green 395 nm

Cu(SO4)2 Blue 810 nm

Q6: What is the purpose of measuring the absorbance of a solution at different wavelengths?

The absorbance of a solution is measured at different wavelengths in order to determine the optimum wavelength (the wavelength of greatest absorbance).

Look at the Absorbance vs. Wavelength graph of CuSO4.

Q7: Use your graph to estimate the absorbance at 790 nm, 800 nm, 810 nm, 820 nm, and 830 nm.

Wavelength Absorbance

790 0.96

800 0.97

810 0.99

820 0.97

830 0.96

Do the absorbencies vary greatly in this 40 nm range?

NO, they vary very little, by only 0.03 nm, in this range.

181 Instructor Notes Colorful Transition Metals

Q8: Use your graph to estimate the absorbance at 660 nm, 670 nm, 680 nm, 690 nm, and 700 nm.

Wavelength Absorbance

660 .25

670 .35

680 .43

690 .48

700 .53

Do the absorbencies vary greatly in this 40 nm range?

Yes, the absorbance varies by over 0.25 nm within this range.

810 nm. The absorbance is greater at 810 nm and the slope is zero. If there is a slight fluctuation in wavelength, the absorbance readings will not be affected.

Q10: Did any of the known compounds have more than one peak? If so, which peak did you use for the optimum wavelength. Why?

Nickel (II) nitrate had two peaks. The peak with the highest absorbance was used for the optimum wavelength.

There would be two maximum wavelengths. Cobalt would still have maximum absorbance at 510 nm and Nickel would still have a maximum absorbance at 395 nm. A mixture of these two compounds would result in two peaks.

182 Instructor Notes Colorful Transition Metals

Explanation

In this activity, the students explore the effects of wavelength on absorbance. They identify the point of maximum absorbance and call this point the optimum wavelength. By graphing their results and comparing with their teammates, the students learn that each colored compound has a different optimum wavelength.

White light from a tungsten lamp goes through an entrance slit where it is split into a spectrum of colors by the diffraction grating. The instrument only allows light of a specific wavelength to pass through the exit slit. This wavelength of light enters the sample cell. If the solution does not absorb any of this light, the intensity is unchanged when it emerges form the sample. However, if the solution in the sample cell absorbs the light of this specific wavelength, the light emerging from the sample has a lower intensity. The detector measures the intensity of light. An amplifier strengthens the signal where it is then read on a display.

A red solution absorbs green and blue light (cyan), allowing the red light to pass through to the eye. Red solutions would absorb in the green/blue region of the spectrum and would have an optimum wavelength around 510 nm, as is the case with cobalt (II) nitrate. (1,2)

The students are able to determine that cobalt and nickel are present in the waste solution by comparing the spectra of known compounds with the unknown waste solution.

Addressing the National Science Education Standards

• 179-3: Use technology and mathematics to improve investigations and communications. Students plot absorbance vs. wavelength and find the area of zero slope and maximum absorbance.

183 Instructor Notes Colorful Transition Metals

• 185-3: Scientists rely on technology to enhance the gathering and manipulation of data. Students use a spectrophotometer to measure the absorbance at various wavelengths for specific transition metal compounds. They use the data to identify which transition elements are present in a waste sample.

• 215-3: Each kind of atom or molecule can gain or lose energy only in particular discrete amounts and thus can absorb and emit light only at wavelengths corresponding to these amounts. Cobalt, nickel, and copper compounds absorb light at different wavelengths. • 264-5: Communicate the Problem, Process, and Solution. Students write a letter to Transition Metallica communicating the process that they went through to identify the transition metals present in the waste sample.

References 1. Kotz, J. C., Treichel, P. M. Chemistry and Chemical Reactivity, 5th Ed.; Thomson

Learning: Untied States; 2003; pp 950-951.

2. Burns, R. A. Fundamentals of Chemistry, 4th Ed.; Prentice Hall: Upper Saddle River,

NJ, 2003; p 142.

184 Awareness Activity Exploration Concept Introduction X Concept Application Instructor Notes Spectrophotometric Determination of Cu2+

Students are given the task of determining the mass percent of copper present per gram of ore in the original ore body and reporting those results. To accomplish this task, the students

2+ • prepare Cu (aq) (aqueous copper (II) sulfate solutions) of known concentration (standards). • measure the absorbance of each standard solution using a spectrophotometer. • prepare a graph from this data that should be linear over the concentration range. 2+ • measure the absorbance of their unknown Cu (aq) (aqueous copper (II) solution). 2+ • use the graph to determine the concentration of the unknown Cu (aq) (aqueous copper (II) solution). • Write a letter to the Mining Director at Branicoda Mines explaining the experimental method that they used to determine the amount of Cu2+ present per gram of crushed and uncrushed malachite ore, and the amount of Cu2+ present per gram of crushed and uncrushed chrysocolla ore. The students include a statement with their recommendation as to which ore body would be best to mine first, and whether the ore should be crushed.

The instructor serves as a facilitator and should encourage the students to communicate amongst each other to respond to the given tasks.

Key Science Concepts

Chemistry • Concentration (molarity and mass percent) • Direct relationship between absorbance and concentration (Beer’s Law) • Physical separation of impurities by filtration • Preparing standards by dilution • Solutions and their behavior

Mathematics • reading line graphs • Direct relationship between two variables

185

Instructor Notes 2+ Spectrophotometric Determination of Cu

Prior Concepts and Skills Needed

The students should be familiar with the use of a spectrophotometer. They should have been introduced to the mole concept.

Materials

Per Team of 3-4 students Spectrophotometer (Spec-20 or Genesys) Cuvettes (6 or more) 20 mL of 5.00 g/L Cu2+ (aqueous copper (II) sulfate solution) 5 mL of 2.50 g/L Cu2+ (aqueous copper (II) sulfate solution) 1 box Kim Wipes 6 Beakers or Test tubes to prepare dilutions 2 Burets, pipets, or graduated cylinders

Safety and Disposal

It is your responsibility to review appropriate safety procedures with your students, including the use of personal protective equipment.

Copper (II) sulfate pentahydrate is a strong irritant to the skin and mucous membranes. To avoid inhaling its dust, use copper (II) sulfate only where there is adequate ventilation. It can be harmful or fatal if taken internally. If contact with the skin occurs, flush with running water. Wash your hands after use. Follow local ordinances for disposal of copper(II) salts. It is recommended that unused copper (II) sulfate solution be left to evaporate to dryness.

Getting Ready

Have spectrophotometers out and the power turned on before the students arrive.

It is helpful to have burets or pipettes at each lab station to save time.

5.00 g/L Cu2+ (aqueous copper (II) sulfate solution) is prepared by dissolving 4.911 g

CuSO4·5H2O (copper (II) sulfate pentahydrate) in 200 mL of H2O in a 250-mL volumetric

flask and then filling to the mark with H2O. This is sufficient for 1 class.

2.50 g/L Cu2+ (aqueous copper (II) sulfate solution) is prepared by diluting the 5.0 g/L Cu2+ in a 1:1 ratio with water. Take care to do this very accurately.

Procedure Notes

The students filter the Cu2+ solutions they prepared from the leaching of the crushed and uncrushed ore. While the filtration is in progress, the students make Cu2+ standards from

186 Instructor Notes 2+ Spectrophotometric Determination of Cu

a 5.00 g/L Cu2+ (aqueous copper (II) sulfate solution). The students apply solution chemistry by making dilutions. Students record the absorbance of the standards using a spectrophotometer in order to create a graph, which should be linear over the range of standards. They measure the absorbance of their crushed and uncrushed leach solutions and use the graph to determine the concentration of these solutions.

This lab is designed to bring closure to the leaching section of Copper Mining. The first few labs guided the students through a series of steps to obtain an aqueous Cu2+ solution from ore samples. In this lab, the students use Spectrophotometry to determine the mass percent of Cu2+ present in various ore samples.

The instructor should not answer any questions directly, but should encourage the students to work together to accomplish the task. Students will ask how to make the standards. Refer them to the written directions and examples.

If a buret is used to make the standards, the students will have a tendency to record whole numbers for their volumes. Encourage them to read the buret accurately to two decimal places.

Assessment Sample Data Table & Results Table I: Cu2+ Standards Volume Volume Total Solution 5.00 g/L Concentration H O Volume Absorbance label Cu2+ 2 (mL) (mL) (g/L) (mL) A 5.00 0.00 5.00 5.00 1.150 B 4.00 1.00 5.00 4.00 .845 C 3.00 2.00 5.00 3.00 .704 D 2.00 3.00 5.00 2.00 .438 E 1.00 4.00 5.00 1.00 .224 F 1.00 6.00 7.00 0.714 .135 G 1.00 10.00 11.00 0.455 .101 H 1.00 20.00 21.00 0.238 .060 I 1.00 30.00 31.00 0.161 .027

Q1: What wavelength did you choose to perform your measurements?

810 nm – The optimum wavelength for CuSO4.

187 Instructor Notes 2+ Spectrophotometric Determination of Cu

Q2: What makes a wavelength “optimum” for a particular analysis?

The optimum wavelength is the wavelength at which a compound has the greatest absorbance.

Q3: You made 5.00 mL and 10.00 mL of the diluted solutions you used. Consider reasons for making so much when the cuvettes only require approximately 2.0 mL.

It is easier to measure larger volumes, which results in better precision and accuracy. If a micropipet is available, smaller volumes would be appropriate.

If the absorbance value of the unknown fell below the lowest standard, more standards would need to be made that had lower absorbance. The unknown’s absorbance must fall between the standards.

If the unknown absorbance was higher than the standards, the unknown would need to be diluted. A 1:1 dilution would be an easy dilution to make. Add 5.00 mL of unknown to 5.00 mL of water and record the absorbance. If this absorbance falls within the range of the standards, record the concentration from the graph. You would then have to multiply the concentration by a factor of 2 to obtain the actual unknown’s concentration.

Q5: Is the graph of your standards accurate and precise? Give evidence to support your statement.

If the graph is linear, you have good precision. Accuracy is determined by the percent error of the known sample.

Q6: Compare the concentration of your leached Cu2+ solutions with other teams.

Ore Concentration % Cu2+ in Ore Concentration % Cu2+ in Ore Sample Crushed Sample Uncrushed Sample (g/L) (Crushed) (g/L) (Uncrushed) malachite 5.86 7.60 7.16 9.33

malachite 4.18 5.98 4.22 5.92

chrysocolla 3.25 3.28 1.35 1.36

chrysocolla 2.32 2.32 1.20 1.20

188 Instructor Notes 2+ Spectrophotometric Determination of Cu

Q7: Which ore sample had the highest concentration of Cu2+ per gram of ore?

Malachite appears to have the highest concentration of Cu2+ per gram of ore. This will vary depending on the quality of ore samples used.

Q8: Do you feel that there is enough copper in the ore to recommend opening a new mining site? If so, which mining site would you recommend starting with?

Yes, there is enough copper in the ore to recommend opening a new mining site. Recommendations as to mining site will depend on lab results. The Franklin and Bonita sites, which contain copper-rich ore bodies of chrysocolla and malachite, should be recommended.

Assessment

Review the previous three labs (Properties of Copper Ore, Leaching Copper, and Colorful Transition Metals) to help complete this assessment activity.

Include a statement with your recommendation as to which ore body would be best to mine first, and whether the ore should be crushed. In your letter, defend your recommendation.

The letter must include the experimental method, a neatly organized summary of lab results, and a recommendation that is defended by physical evidence. A bonus would be if the students mentioned the extra cost that would be involved in crushing the ore.

Explanation The students should see that Spectrophotometry is a reliable method for determining the concentration of Cu2+ in aqueous solution. Beer’s law states that for monochromatic radiation, absorbance is directly proportional to the path length b through the medium and the concentration c of the absorbing species. These relationships are given by A=εbc, where ε is a proportionality constant called the absorptivity (1). The proportionality constant ε and the path length b remain constant throughout the experiment resulting in a

189 Instructor Notes 2+ Spectrophotometric Determination of Cu

linear graph with slope ε b for a plot of Absorbance vs. Concentration. Addressing the National Science Education Standards

• 178-2: Design and conduct scientific investigation. Students design a method of making Cu2+ standards by dilution of a 5.00 g/L Cu2+ solution. They use these standards to determine the concentration of an unknown Cu2+ solution. • 179-3: Use technology and mathematics to improve investigations and communications. Students use a spectrophotometer to take absorbance measurements. They use algebra to calculate the concentration of their standards. They plot the standards to create a linear graph that is used to determine the concentration of an unknown Cu2+ solution. • 182-6: Communicate and defend a scientific argument. Students write a statement with their recommendation as to which ore body would be best to mine first, and whether the ore should be crushed. In their letter they defend their recommendations. • 185-3: Scientists rely on technology to enhance the gathering and manipulation of data. Students use a spectrophotometer to take absorbance measurement. • 186-4: Mathematics is essential in scientific inquiry. Students use algebra to determine the concentration of their standards. • 264-5: Communicate the problem, process, and solution. Students write a letter describing the process they used to determine which ore body would be best to mine. The students provide a recommendation and defend that recommendation.

References 1. Skoog, D. A., Holler, F. J., and Nieman, T. A. Principles of Instrumental Analysis, 5th

Ed.; Harcourt Brace & Company: Philadelphia, PA, 1998; p 139.

190 Awareness Activity X Exploration Concept Introduction Concept Application Instructor Notes Purification Techniques

2+ Students test the Cu (aq) (copper (II) aqueous) solutions they recently leached with sulfuric acid for impurities of iron and silver. They make solutions containing Ag+ (silver ions) and Fe3+ (iron (III) ions) to serve as references. The students test for the presence of Ag+ by adding a few drops of 3M HCl. They test for the presence of Fe3+ by adding a few drops of 0.1 M KSCN.

Students explore the solubility of Cu2+ (copper (II) aqueous solutions) in water, sulfuric acid, and barren organic (10% Acorga M5850 in Penrico 170 ES diluent).

The students work together to develop a method to remove Fe3+ impurities from their 2+ Cu (aq) solutions (PLS).

The goals of the activity are to • Test for the presence of Ag+ and Fe3+ 2+ • Determine the solubility of Cu (aq) (copper (II) aqueous) in water, sulfuric acid, and barren organic. 2+ + • Develop a method to purify a Cu (aq) (copper (II) aqueous), ridding it of Ag and Fe3+. • Evaluate a proposed solution from another team in terms of logic and correct science.

Key Science Concepts

Chemistry • Chemical Reactions • Solution Chemistry (solubility and miscibility)

Other Science Concepts

Mathematics

Engineering and Technology

Prior Concepts and Skills Needed

Double replacement reactions

191

Instructor Notes Purification Techniques

Materials

Dropper bottle of 0.1 M Fe(NO3)3 (ferric nitrate)

Dropper bottle of 0.1 M AgNO3 (silver nitrate) Dropper bottle of 3M HCl (hydrochloric acid) Dropper bottle of 0.1 M KSCN (potassium thiocyanate)

20 mL of 5 g/L CuSO4 (copper (II) sulfate)

10 mL of 200 g/L H2SO4 (sulfuric acid) 10 mL of Barren Organic (10% Acorga M5850 in Penrico 170 ES diluent)

Safety and Disposal

It is your responsibility to review appropriate safety procedures with your students, including the use of personal protective equipment.

Use caution when working with 3 M HCl (hydrochloric acid) and 200-g/L H2SO4 (sulfuric acid). If spills occur, neutralize by sprinkling with baking soda and diluting with water. The

3 M HCl (hydrochloric acid) and 200-g/L H2SO4 (sulfuric acid) can be disposed of by diluting the acid into a large beaker containing water. The final concentration of the acid

should be 1M or less. Slowly add 1 M Na2CO3 (sodium carbonate) solution to the diluted acid while stirring. Flush the neutral mixture down the drain with a 20-fold excess of water.

Use caution when working with AgNO3 (silver nitrate). It is corrosive.

Ferric nitrate (Fe(NO3)3 may be a skin irritant.

KSCN (potassium thiocyanate) is moderately toxic by ingestion. It will emit toxic fumes of cyanide if heated or in contact with concentrated acids.

Copper (II) sulfate pentahydrate is a strong irritant to the skin and mucous membranes. To avoid inhaling its dust, use copper (II) sulfate only where there is adequate ventilation. It can be harmful or fatal if taken internally. If contact with the skin occurs, flush with running water. Wash your hands after use. Follow local ordinances for disposal of copper

192 Instructor Notes Purification Techniques

(II) salts. It is recommended that unused copper (II) sulfate solution be left to evaporate to dryness.

The barren organic (10% Acorga M5850 in Penrico 170 ES diluent) can be reused numerous times. When it no longer functions properly, it should be stored in an organic waste bottle and disposed of by a hazardous waste team.

Getting Ready

Student PLS: 2+ Cu (aq) (copper (II) sulfate solution (PLS) comes from the Leaching Lab (students should have retained their solutions).

2+ Lincoln Site PLS: Cu (aq) (copper (II) sulfate solution

Mix 40 mL of 0.1 M Fe(NO3)3•9H2O with 50 mL of 5.0 g/L CuSO4 (aq) (Copper (II)

sulfate) Add 200 g/L H2SO4 (aq) dropwise to bring the pH down to 1.5.

Name / Formula / F.W. Concentration Amount /Liter solution

Ferric nitrate 0.1 M Fe(NO3)3•9H2O 40.4 g

Fe(NO3)3•9H2O 404.00

Silver nitrate 0.1 M AgNO3 17.0 g

AgNO3 169.87 Potassium thiocyanate 0.1 M KSCN 9.7 g KSCN 97.18 Copper (II) sulfate 5.0 g/L Cu2+ 19.65 g

CuSO4•5H2O 249.69 Hydrochloric acid 3 M 250 mL HCl 36.4 12.1 M Sulfuric acid 200 g/L 200 g or 108.7 mL

H2SO4 98.08 18.0 M Barren Organic (10% Acorga M5850 in Penrico 170 ES diluent) This can be ordered from Avecia, Metal Extraction Products, 3259 E. Harbour Drive, Suite 100, Phoenix, AZ 85034-7227 (602) 470-1446.

193 Instructor Notes Purification Techniques

Procedure Notes

Students filter their solution if this has not already been done. Filtering should have been done in the labs using the spectrophotometers.

As the students begin making reference solutions, join their group and ask questions to

ascertain whether they understand why they are making reference solutions of AgNO3

(silver nitrate) and Fe(NO3)3 (iron (III) nitrate). If they don’t, ask them leading questions to guide them to that understanding.

When the students begin testing the solubility of the PLS, reinforce the careful observations of color and clarity.

As students develop their method of purification, walk around and provide leading questions to guide them. As they read proposed processes from other teams, guide them to write critical, as well as positive comments.

194 Instructor Notes Purification Techniques

Assessment Data Table & Results

Observations

Solution Color Clarity pH

PLS (from personal leaching Blue Clear 1.85 experiments) PLS (Lincoln Site) Green Clear 1.80

200 g/L H2SO4 (aq) (sulfuric acid) Colorless Clear 0.75

Testing for Impurities

SILVER TEST

Solution Observations and Conclusions

AgNO3 White precipitate forms upon the addition of HCl. Reference PLS No precipitate is seen. (Lincoln Site) PLS No precipitate is seen. (Student) Write the balanced chemical equation for the reaction between silver nitrate and hydrochloric acid.

AgNO3 (aq) + HCl (aq) → AgCl ↓ + HNO3 (aq)

IRON TEST

Solution Observations and Conclusions

Fe(NO3)3 Reddish – brown color forms upon the addition of KSCN. Reference PLS Reddish – brown color forms upon the addition of KSCN. This 3+ (Lincoln Site) confirms that Fe is present in this solution. PLS The solution turns slightly yellow-green. Probably due to the mixing 3+ (Student) of the blue color with the yellow. No red color, so no Fe is present.

195 Instructor Notes Purification Techniques

Q1: Which impurities, if any, were present in the PLS from the Lincoln Site? Which impurities, if any, were present in your PLS?

Fe3+ was an impurity in the Lincoln Site. There was no Ag+ nor Fe3+ present in my PLS.

Observations of CuSO4 (aq)

Solution Color Clarity

CuSO4 (aq) Blue Clear

Q2: Based on your observations of CuSO4 (aq), what physical evidence can be used to determine if an aqueous solution contains Cu2+?

Aqueous solutions of Cu2+ all appear to have a blue color.

Solubility of Cu2+ in the following reagents:

Test Tube Reagent Color Clarity

#1 CuSO4 Blue Clear (Reference)

Test Tube Reagent Observations Soluble, or Insoluble 2+ #2 Cu in H2O Blue – One layer Soluble

2+ #3 Cu in H2SO4 Blue – One layer Soluble

2+ Q3: Is Cu (aq) soluble in water? What is your evidence?

2+ Cu (aq) is soluble in water and sulfuric acid? Both solutions remained blue and mixed.

Reagent Color Clarity

Barren Organic Yellow – Tan Cloudy

196 Instructor Notes Purification Techniques

Test Tube Reagent Observations Soluble, or Insoluble #4 Cu2+ in Barren The organic layer turned Soluble Organic dark brown. The lower layer appeared colorless.

#5 Cu2+ in Barren The organic layer became Insoluble in Organic with 200 lighter and the lower layer Organic but is

g/L H2SO4 added appeared light blue. soluble in H2SO4

Q4: Describe the solubility of copper ions (Cu2+) in barren organic, water, and acidic solutions.

The copper ions (Cu2+) are soluble in barren organic at a pH of 1.8. They are soluble in water, and also soluble in acidic solutions.

Share your results

Ore Sample Group Member Was Ag+ Present Was Fe3+ Present

Lincoln Site NO YES

Malachite Rae Lynn NO NO

Malachite Tom NO NO

Chrysocolla Michael NO NO

Chrysocolla Trudy NO NO

Q5: What metal contaminants were present in the pregnant leach solution (PLS) that was obtained through the leaching of malachite?

There were no metal contaminants present in the malachite PLS.

Q6: What metal contaminants were present in the pregnant leach solution (PLS) that was obtained through the leaching of chrysocolla?

197 Instructor Notes Purification Techniques

There were no metal contaminants present in the chrysocolla PLS.

Assessment

Part 1:

PLS solution which is currently at a pH of 1.8. The CuSO4 (aq) must be in an aqueous solution when you are finished.

Add barren organic in a 1:1 ratio with the PLS. Mix for 30 seconds. Allow the two layers to separate. Mix for an additional 30 seconds. Allow the two layers to separate. Drain off the aqueous layer, which is now void of Cu2+, or pour off the

organic layer. Take the organic layer and add 200 g/L H2SO4 (sulfuric acid). Mix for 30 seconds. Allow the two layers to separate. Mix for an additional 30 seconds. Allow the two layers to separate. Drain off the aqueous layer, which now contains the Cu2.

Comments:

Evaluated by

Part 2:

Part 3;

Test your proposal on a 3-mL sample of PLS from the Lincoln Site.

Write a letter to the Director of Mines describing your results. In your letter outline a method of removing the Fe3+ from the Lincoln Site PLS, thus purifying it.

198 Instructor Notes Purification Techniques

Explanation

The students recognize that the formation of a white precipitate upon the addition of + HCl(aq) is a positive test for Ag (silver ion). They should recognize that a reddish-brown

precipitate or reddish-brown solution forming upon the addition of KSCN(aq) is a positive test for Fe3+ (iron (III) ion).

The students should recognize that Fe3+ is present in the PLS from the Lincoln Site.

Organic (10% Acorga M5850 in Penrico 170 ES diluent) is a metal extraction product that is selective for Cu2+. At a pH > 1.5, Cu2+ is extracted from the aqueous phase into the

organic phase. As the pH is lowered below 1.5 by the addition of 200 g/L H2SO4 (aq), the organic extraction product releases the Cu2+, which transfers back into the aqueous phase.

Addressing the National Science Education Standards

• 178-2: Design and conduct scientific investigations. Students conduct investigations + 3+ to determine if Ag and Fe are present as impurities in a CuSO4 (aq) solution. • 188-6: Results of scientific inquiry, new knowledge and methods emerge from different types of investigations and public communication among scientists. Students use the results of their investigation to develop a process to purify their pregnant leach solution (PLS). They communicate their data and results to other teams. Other teams critically critique each student’s proposed process. • 199-1: Chemical reactions occur all around us, for example in health care, cooking, cosmetics, and automobiles. The chemical tests for presence of Ag+ and Fe3+ are chemical reactions. The transfer of Cu2+ between the organic and aqueous phase is chemical reaction in equilibrium. • 202-4: Chemical reactions can take place in time periods ranging from the few femtoseconds (10^-15 seconds) required for an atom to move a fraction of a chemical bond distance to geologic time scales of billions of years. The chemical tests for presence of Ag+ and Fe3+ are chemical reactions that occur instantly. • 261-2: Propose designs and choose between alternative solutions. Students propose a process to purify their pregnant leach solution (PLS). They evaluate other processes proposed by other teams.

References The Acorga Technical Library [CD-ROM]; Avecia Inc.: Wilmington, DE, 2000.

199 Awareness Activity X Exploration Concept Introduction Concept Application Instructor Notes Chemistry of Extraction Access the following web site or use the CD to find answers to the following questions. http://teach2.eac.edu/pmcbride

Define the following terms: 1. barren organic – A combination of the extraction reagent and solvent that is void of copper.

2. loaded organic - A combination of the extraction reagent and solvent that is loaded with copper by contacting it with the pregnant leach solution.

3. extraction settler – A large tank that allows the organic and aqueous phases to separate.

Answer the following questions:

The pregnant leach solution (PLS) is sent to the mixer where it is mixed with a non-polar, organic reagent in a kerosene-based solvent.

4. Which phase (layer) is most dense (organic or aqueous)? The aqueous phase is most dense.

5. It is the purpose of the settling tank? How long does it take for a drop of solution to travel from one end of the tank to the other?

The settling tank provides time for the organic and aqueous phases to separate. It takes about 12 minutes for a drop of solution to travel the length of the tank.

The Raffinate is a yellowish brown color. If copper was present, the raffinate would be blue.

200

Instructor Notes Chemistry of Extraction

7. Draw the structure of the organic reagent complexed with Cu2+. Circle the intermolecular hydrogen bonding that occurs.

H O H

R O N

N OR

H3C O H

8. What helps stabilize the copper/organic complex?

Hydrogen bonding, the two 5-member rings, and the two 6-member rings.

9. What ion in the aqueous phase exchanges places with the Cu2+ as it forms a complex with the organic reagent? Why are two organic reagents required for one Cu2+?

H+ in the aqueous phase exchanges places with the Cu2+. Cu2+ has a +2 charge and therefore needs two H+ ions to exchange with (one from each reagent).

At a pH above 2, the Cu2+ r will be in the organic phase.

11. What chemical and concentration is added to the loaded organic to strip the copper so that it returns to the aqueous phase?

200 g/L H2SO4 (sulfuric acid) is added to the loaded organic to strip the copper.

12. What are the two main purposes of solution extraction?

To purify and concentrate.

201 Awareness Activity Exploration Concept Introduction X Concept Application Instructor Notes Solution Extraction

The students follow a designed solution extraction method to purify and concentrate Cu2+. This is a guided inquiry lab that leads the students to understand some of the chemistry behind solution extraction.

The goals of the activity are to help students

• understand the role of intermolecular attractions on solubility. • experience Le Chatelier’s Principle as it applies to solution extraction. • evaluate a graph for information to solve a problem. • apply chemistry concepts and techniques learned in previous labs to accomplish the given tasks.

Key Science Concepts

Chemistry • intermolecular forces of attraction • Le Chatelier’s Principle • solution chemistry • mass transport across phase boundary

Other Science Concepts

Mathematics

Engineering and Technology

Prior Concepts and Skills Needed

Students should have discussed bond polarity and molecular polarity. They should be familiar with intermolecular attractions. It is helpful if they have discussed Le Chatelier’s Principle. They should be familiar with operating a spectrophotometer and graphing.

202

Instructor Notes Solution Extraction

Materials

Safety and Disposal

It is your responsibility to review appropriate safety procedures with your students, including the use of personal protective equipment.

Use caution when working with 200-g/L H2SO4 (sulfuric acid). If spills occur, neutralize by

sprinkling with baking soda and diluting with water. The 200-g/L H2SO4 (sulfuric acid) can be disposed of by diluting the acid into a large beaker containing water. The final

concentration of the acid should be 1M or less. Slowly add 1 M Na2CO3 (sodium carbonate) solution to the diluted acid while stirring. Flush the neutral mixture down the drain with a 20-fold excess of water.

Copper (II) sulfate pentahydrate is a strong irritant to the skin and mucous membranes. To avoid inhaling its dust, use copper (II) sulfate only where there is adequate ventilation. It can be harmful or fatal if taken internally. If contact with the skin occurs, flush with running water. Wash your hands after use. Follow local ordinances for disposal of copper (II) salts. It is recommended that unused copper (II) sulfate solution be left to evaporate.

Getting Ready

The students should have their Cu2+ (copper (II) sulfate) solutions from the Spectrophotometric Determination lab.

Name / Formula / F.W. Concentration Amount /Liter solution Sulfuric acid 200 g/L 200 g or 108.7 mL

H2SO4 98.08 18.0 M

203 Instructor Notes Solution Extraction

Procedure Notes

Students extract Cu2+ from their leach solution by adding Barren Organic (10% Acorga M5850 in Penrico 170 ES diluent). The organic mixture is specially designed specifically for Cu2+, and is selective for copper through a pH range of 1.5 – 1.8. After extracting the 2+ 2+ Cu into the organic phase, the students strip the Cu by adding 200 g/L H2SO4 (sulfuric acid). The addition of a concentrated, strong acid, lowers the pH resulting in the release of Cu2+ back into the aqueous phase.

Students apply the lab techniques they learned in the Spectrphotometric Determination laboratory activity to measure the absorbance of the Raffinate, PLS, and rich electrolyte. They use their previous graph and absorbance readings to determine the concentration of the Raffinate, PLS, and rich electrolyte. This guides them to realize where the Cu2+ is located at different stages of the extraction.

Don’t provide direct answers to any of the questions, but guide the students to an appropriate response. Students will ask how to work the spectrophotometer. Refer them back to their previous lab reports or handout.

The barren organic can be recycled for use in the next lab. The barren organic can be

brought back to the light tan color by adding additional amounts of 200 g/L H2SO4 (sulfuric acid).

Assessment

Sample Data Table & Results

Initial pH of PLS 3.2

Q1: Would you consider the aqueous PLS and the barren organic to be miscible? Explain.

No. There were two distinct phases (layers).

204 Instructor Notes Solution Extraction

Procedural Phases Time for Phase Step Disengagement (sec)

6 Barren Organic with PLS 18 sec

13 Loaded Organic with Sulfuric Acid 23 sec

19 Loaded Organic with Sulfuric Acid 24 sec

Solution Color Clarity Absorbance Concentration Cu2+ (g/L)

PLS Blue Clear 0.639 2.40

Barren Organic Tan Clear Possibly cloudy if it has been recycled.

Raffinate Colorless Clear 0.079 0.30

Loaded Dark Brown Cloudy Organic

Rich Electrolyte Blue Clear 0.821 3.09

Q2: Where is the Cu2+ (copper (II) ions) at this point (aqueous or organic layer)? What is your evidence?

The Cu2+ (copper (II) ions) are in the organic phase. The aqueous phase is colorless, and organic phase has turned a dark brown color.

Q3: Why is the organic now called “loaded organic?”

It is loaded with Cu2+ (copper (II) ions).

Q4. Has there been any transfer of copper between the two solutions? Explain.

The Cu2+ (copper (II) ions) have transferred back to the aqueous phase. This is evidenced by the blue color of the aqueous phase.

205 Instructor Notes Solution Extraction

Q5: Why is the organic layer now termed “barren organic”, and the aqueous layer now termed “rich electrolyte?”

The organic layer has lost its Cu2+, and is therefore barren. The aqueous layer has become rich in Cu2+, and is therefore termed rich electrolyte.

Q6: Can the “barren organic” be reused. Explain.

The barren organic can be reused. It is now barren of Cu2+ and can therefore be loaded again.

Q7: Look at the Acorga M-5850 Product Specifications Sheet. What is the Copper/Iron Selectivity? What does this mean?

2000:1 The organic reagent will select copper 2000 times for every time it picks up an iron.

Q8: Compare your data with the time listed in the Product Specifications for the two layers to separate (phase disengagement). Does your data fall within the specifications listed?

Specifications for Extraction is not more than 60 seconds. Mine took 18 seconds. Specification for Stripping is not more than 80 seconds. Mine took 24 seconds. My data falls within the specifications.

The –OH and N-O-H parts of the organic molecule are polar and therefore reach into the polar, aqueous layer. The aqueous layer contains Cu2+, which, being positively charged is attracted to the Nitrogen and Oxygen atoms, which have strong dipoles.

Q10: Would you consider the occurrence with the organic and aqueous phases a reversible system? Explain.

2+ + 2 L-H (org) + Cu (aq) ' L2Cu (org) + 2 H (aq)

This is a reversible system. By changing the concentration of H+ ions, the equilibrium can be made to shift left (Cu2+ in the aqueous layer) or right (Cu2+ in the organic layer).

206 Instructor Notes Solution Extraction

Q11: According to this equation which way would the equilibrium shift if you stressed the system by adding H+ (sulfuric acid)?

It would shift to the left (Cu2+ in the aqueous layer).

Assessment

Yes it is a good method for purifying and concentrating the Cu2+ solution.

Explanation

Students recognize that the presence of Cu2+ is evidenced by a blue color. They are able to notice the disappearance of blue color after mixing the PLS with barren organic. The also witness the barren organic change from a light tan to a dark brown in color. The dark brown color is indicative of Cu2+ now present in the organic phase. The students then add

200 g/L H2SO4 (sulfuric acid) to the organic phase. After mixing, the aqueous and organic phases separate resulting in a blue aqueous solution, signifying that the Cu2+ has been stripped out of the organic back into the aqueous phase.

207 Instructor Notes Solution Extraction

Addressing the National Science Education Standards

• 184-2: Scientists conduct investigations for a wide variety of reasons. The reason for this investigation is to test an extraction method for applicability. • 196-4: The physical properties of compounds reflect the nature of the interactions among its molecules. The Cu2+ moves back and forth between the aqueous and organic phases depending on the acid content (pH). • 201-3: A large number of important reactions involve the transfer of either electrons (oxidation/reduction reactions) or hydrogen ions (acid/base reactions) between reacting ions, molecules, or atoms. The chemical reaction:

2+ + 2 L-H (org) + Cu (aq) ' L2Cu (org) + 2 H (aq)

involves the transfer of hydrogen ions. • 263-4: Evaluate the solution and its consequences. Students evaluate the proposed method of Cu2+ extraction.

References 1. The Acorga Technical Library [CD-ROM]; Avecia Inc.: Wilmington, DE, 2000.

208 X Awareness Activity Exploration Concept Introduction Concept Application Instructor Notes Copper Replacement

A thin sheet of copper or copper wire is placed in a 0.1 M solution of silver nitrate. The solution is allowed to sit over the duration of the class, with the instructor taking time for the students to make observations.

Key Science Concepts

Chemistry • oxidation/reduction reactions

Other Science Concepts

Mathematics

Engineering and Technology

Prior Concepts and Skills Needed

Chemical Reactions

Materials

Reagents and equipment per class

• 0.1 M AgNO3 (silver nitrate) • Copper sheet or wire

Safety and Disposal

It is your responsibility to review appropriate safety procedures with your students, including the use of personal protective equipment.

Use caution when working with AgNO3 (silver nitrate). It is corrosive and can cause burns.

209

Instructor Notes Copper Replacement

Getting Ready

Introduce the students to the activity series.

Procedure Notes

Take a piece of copper wire or copper sheet and place it in a beaker of 0.1 M AgNO3 (silver nitrate). Allow the reaction to take place over time. During the class, take time every once in awhile to have the students make observations.

Assessment

This is an awareness activity. There is no formal assessment. The students are being introduced to oxidation/reduction reactions.

Explanation

According to the Activity Series and/or by laboratory experience we know that AgNO3 reacts with Copper metal according to the single-replacement reaction shown:

2 AgNO3 (aq) + Cu(s) → 2 Ag (s) + Cu(NO3)2 (aq) Addressing the National Science Education Standards

• 201-3: A large number of important reactions involve the transfer of either electrons (oxidation/reduction reactions) or hydrogen ions (acid/base reactions) between reacting ions, molecules, or atoms. The electrowinning of copper is an oxidation/reduction reaction. • 202-4: Chemical reactions can take place in time periods ranging from the few femtoseconds (10^-15 seconds) required for an atom to move a fraction of a chemical bond distance to geologic time scales of billions of years. The electrowinning of copper is an oxidation/reduction reaction that depends on applied voltage to occur. The rate of the reaction depends on the amount of voltage applied.

210 Awareness Activity Exploration X Concept Introduction Concept Application Instructor Notes Electrochemistry

This is a worksheet to teach the students electrochemistry and how it applies to the electrowinning.

Key Science Concepts

Chemistry • electrochemistry • oxidation/reduction reactions • standard reduction potential

Other Science Concepts

Engineering and Technology

Prior Concepts and Skills Needed

Oxidation/Reduction Reactions should have been discussed.

Materials

None

Safety and Disposal

No special disposal procedures are required.

Getting Ready Procedure Notes

Students review oxidation/reduction reactions and how they are applied to the chemistry of copper mining, specifically electrowinning.

Assessment

Q1: Would the half reaction involving silver be considered an oxidation or a reduction?

Ag1+ + 1e- → Ag0 is a reduction reaction because there is a gain of one electron. (GER) – Gain Electrons Reduction

211

Instructor Notes Electrochemistry

Q2: Would the half reaction involving copper be considered an oxidation or a reduction?

0 2+ - Cu (s) → Cu (aq). + 2e is an oxidation reaction because there is a loss of electrons. (LEO) Lose Electrons Oxidation

Q3: What do you notice about the net voltage of this reaction? Will this reaction happen spontaneously?

2+ - Cu (aq) + 2 e → Cu(s) 0.337

+ - H2O → ½O2 (g) + 2 H (aq) + 2e - 1.229

2+ + Cu (aq) + H2O → Cu(s) + ½O2 (g) + 2 H (aq) - 0.892 V

The net voltage is negative, so the reaction will not occur spontaneously as written.

Q4: We want this reaction to occur as written so that we obtain metallic copper. How can we do this in the laboratory?

We would have to apply a voltage of at least +0.892 V for this reaction to occur.

Q5: Write the two half-cell reactions and overall reaction so that the reaction is spontaneous.

2+ - Cu(s) → Cu (aq) + 2 e - 0.337

+ - ½O2 (g) + 2 H (aq) + 2e → H2O + 1.229

+ 2+ Cu(s) + ½O2 (g) + 2 H (aq) → Cu (aq) + H2O + 0.892 V

Explanation

Students should work together to review or learn about oxidation/reduction reactions and how to determine if they would occur spontaneously.

Addressing the National Science Education Standards

212 Instructor Notes Electrochemistry

oxidation/reduction reaction. • 202-4: Chemical reactions can take place in time periods ranging from the few femtoseconds (10^-15 seconds) required for an atom to move a fraction of a chemical bond distance to geologic time scales of billions of years. The electrowinning of copper is an oxidation/reduction reaction that depends on applied voltage to occur. The rate of the reaction depends on the amount of voltage applied. • 282-3: Humans use many natural systems as resources. Copper is a natural resource that exists in the form of minerals. Through several chemical reactions, copper compounds are transformed into elemental copper.

References 1. Tour Guide, Phelps Dodge Morenci, Inc.; pp 1-20.

213

Instructor Notes Chemistry of Electrowinning Access the following web site or use the CD to answer the following questions. http://teach2.eac.edu/pmcbride

Define the following terms: 1. Rich electrolyte – electrolyte that has the most amount of copper in it. This electrolyte is the result of stripping the copper from the loaded organic.

2. Anode – A negative electrode where oxidation occurs. It is usually made of lead or some lead alloy.

3. Cathode – The positive electrode where copper is plated. It is usually made of stainless steel.

Answer the following questions:

The last stage of copper mining involves the electroplating of copper onto stainless steel blanks.

Electrowinning can be defined as “the deposition of copper metal from a copper-bearing solution (1) by passage of an electric current.” Li K 4. Refer to the Activity Series of Metals (2) on the right. When a piece of copper wire is Ca Na submerged in an aqueous, colorless AgNO (silver nitrate) solution, shiny 3 (aq) Mg crystals of silver from on the copper wire. The solution begins to turn a blue color as Al the copper metal is oxidized to Cu2+. When comparing two elements, the more Zn Cr reactive elements on top will replace any of those elements underneath. Should Fe copper replace silver according to the activity series? Cd Ni YES. Copper is higher than silver on the activity series. Sn Pb

H2 5. Complete the following reaction: Cu Hg + Ag Cu(s) + AgNO3 (aq) → Ag + Cu(NO3)2 Au

214

Instructor Notes Chemistry of Electrowinning

2+ 6. Pb is used as the anode. Will Pb react directly with Cu (aq) (CuSO4 – rich electrolyte)? Write the reaction that would occur.

Pb + CuSO4 (aq) → Cu + PbSO4 (aq)

7. Write the balanced oxidation/reduction reaction that occurs at the anode and cathode during the electrowinning of copper.

2+ - Cu (aq) + 2 e → Cu(s) 0.337 (CATHODE)

+ - H2O → ½O2 (g) + 2 H (aq) + 2e - 1.229 (ANODE)

2+ + Cu (aq) + H2O → Cu(s) + ½O2 (g) + 2 H (aq) - 0.892 V

8. Using standard reduction potentials, determine the overall potential.

See above.

Electricity must be applied to overcome the negative potential. If electricity was not applied, the copper cathode would begin to dissolve. The lead would react with the

CuSO4 precipitating out copper, which would fall to the bottom of the tank house.

References:

1. The Acorga Technical Library [CD-ROM]; Avecia Inc.: Wilmington, DE, 2000.

2. Burns, R. A. Fundamentals of Chemistry, 4th Ed. Prentice Hall, Upper Saddle River, NJ, 2003; p 454.

215

Instructor Notes Electrowinning

Students set up an electrolytic cell with copper and lead electrodes. They measure the surface area of the electrodes to determine the optimum current to be applied. A

measure volume of approximately 170 mL of the CuSO4 (aq) (copper (II) sulfate solution) termed rich electrolyte is placed in the electrolytic cell and the current adjusted to the calculated value. The students take absorbance, current, and voltage measurements every 10 minutes during the class period.

Guided inquiry is the teaching method used in this laboratory activity.

Key Science Concepts

Chemistry • electrochemistry • solutions chemistry • surface area

Other Science Concepts • electricity (current & voltage)

Mathematics • calculation of surface area

Engineering and Technology

Prior Concepts and Skills Needed

Students should already be familiar with using the spectrophotometer.

Materials

100 mL of leached CuSO4 (copper (II) sulfate solution) (rich electrolyte) 100 mL graduated cylinder 250 mL beaker or polystyrene jar anode – lead strip cut to give 20-cm2 one-sided area. cathode – copper strip to give 20-cm2 one-sided area. power supply alligator clips

216

Instructor Notes Chemistry of Electrowinning

Safety and Disposal

It is your responsibility to review appropriate safety procedures with your students, including the use of personal protective equipment.

Rich electrolyte contains 200-g/L H2SO4 (sulfuric acid). Use caution when working with

200-g/L H2SO4 (sulfuric acid). If spills occur, neutralize by sprinkling with baking soda and

diluting with water. The 200-g/L H2SO4 (sulfuric acid) can be disposed of by diluting the acid into a large beaker containing water. The final concentration of the acid should be

1M or less. Slowly add 1 M Na2CO3 (sodium carbonate) solution to the diluted acid while stirring. Flush the neutral mixture down the drain with a 20-fold excess of water.

Copper (II) sulfate pentahydrate is a strong irritant to the skin and mucous membranes. To avoid inhaling its dust, use copper (II) sulfate only where there is adequate ventilation. It can be harmful or fatal if taken internally. If contact with the skin occurs, flush with running water. Wash your hands after use. Follow local ordinances for disposal of copper (II) salts. It is recommended that unused copper (II) sulfate solution be left to evaporate to dryness.

Getting Ready

Have the Power Supplies, electrolytic cells, electrodes, and spectrophotometers set up before the students arrive.

Procedure Notes

Students set up an electrolytic cell. They determine the optimum current for plating copper. The mass of the copper and lead electrodes are determined. The electrolytic cell is set up and the power turned on. The students measure the absorbance of the electrolytic solution every 10 minutes to observe the decrease in Cu2+ concentration. They also monitor the current and voltage.

Ten minutes before the end of class, half of the teams are instructed to turn off the power supply and make one more absorbance measurement. These teams leave their electrolytic cell connected. They return the following day and take an absorbance measurement to determine the effects of a power outage. The other half of the class pours out their electrolyte carefully washes the electrodes and leaves them hanging to dry. Mass measurements are taken on a later day to determine the mass of copper that was deposited on the electrodes.

The students must work together and share tasks at the beginning or the class will be half over before they begin the actual experiment. Encourage them to read ahead and be prepared when they arrive.

When the power is first turned on, it may take up to 20 V to bring the current to 0.5 A. The 217 Instructor Notes Chemistry of Electrowinning

current will increase quickly and the plating will occur too rapidly. Remind the students to watch closely during the first minute to ensure that the current remains at the calculated value.

Assessment Data Table & Results

Electrode Mass Length Width Depth Surface Area Current required Covered by for Solution electrowinning

copper 21.967 6.00 cm 1.90 cm 0.10 cm 24 cm2 .48

lead 23.597 6.00 cm 1.90 cm 0.10 cm 24 cm2

Time Current Voltage Absorbance Concentration Conc. (g/L) Cu2+ 2+ (Amps) (Volts) of Cu lost to plating g/L 8:16 0.5 .755 2.84

8:26 3.0 .697 2.62 .22

8:36 0.4 5.0 .423 1.59 1.03

8:46 0.6 4.9 .331 1.24 .35

8:56 0.6 4.9 .255 .959 .281

9:06 0.5 4.9 .192 .722 .237

9:16 0.5 4.9 .150 .564 .158

9:26 0.5 4.9 .099 .372 .192

9:36 0.5 4.9 .073 .274 .098

Total 2.57

Q1: Determine the mass of copper deposited on the cathode from your mass measurements.

22.752 – 21.967 = 0.785 g Cu deposited on the cathode.

218 Instructor Notes Chemistry of Electrowinning

(2.57 g/L) (0.170 L) = 0.437 g Cu2+

Q3: How do the values from Data Analysis Question 1 compare with the values from Question 2?

They are quite different. There are two possibilities. The copper was still moist when it was weighed. The copper had oxidized because it appeared to be more of a rust color than a shiny copper color.

Q4: Write the two half reactions and combined reaction. Identify the anode and the cathode.

2+ - Cu (aq) + 2 e → Cu(s) 0.337 (CATHODE)

+ - H2O → ½O2 (g) + 2 H (aq) + 2e - 1.229 (ANODE)

2+ + Cu (aq) + H2O → Cu(s) + ½O2 (g) + 2 H (aq) - 0.892 V

Q5: Did the voltage or current change as the reaction progressed? If so, how did it change?

The voltage and current stayed fairly constant after the first initial surge. The current did have a tendency to increase slightly over a 10-minute interval.

Q6: What would happen in the electrolytic cell if the power were to go off?

If the power went off the reaction would reverse. Cu(s) would be oxidized to Cu2+ resulting in the copper plates dissolving. This would be very costly.

Assessment

219 Instructor Notes Chemistry of Electrowinning

Dear Director:

We were able to successfully electroplate copper according to the stated procedure. Our copper did not plate evenly. It appears that the current may have been too high to begin with. It may be more beneficial to lower the current to plate a slower rate to produce a more uniform plating.

It is our recommendation that a backup generator be purchased. According to our research, if the power were to go off, the oxidation/reduction reaction occurring to produce copper metal would be reversed and the copper metal cathodes would begin to dissolve. This would result in a great loss of revenue to the company.

Thank you for the opportunity to conduct this research on your behalf.

Sincerely,

The Gila Team Members

Explanation

2+ The students will visibly see the blue color of the electrolyte (Cu (aq)) solution fade to a light blue, almost colorless, solution. If the voltage is set too high, the copper will not plate evenly, and this occurs in most cases. I have had a few students set the voltage low so that it plates slowly and evenly over several days. However, the main goal at this point is to allow the students to see the plating occur.

Voltage is required for this reaction to occur as the response to Q4 indicates. If voltage is not applied, the copper electrode will begin to dissolve.

Addressing the National Science Education Standards

• 186-4: Mathematics is essential in scientific inquiry. Students determine the surface area of part of the copper electrode that is exposed to the electrolyte. • 201-3: A large number of important reactions involve the transfer of either electrons (oxidation/reduction reactions) or hydrogen ions (acid/base reactions) between reacting ions, molecules, or atoms. The electrowinning of copper is an oxidation/reduction reaction. • 202-4: Chemical reactions can take place in time periods ranging from the few femtoseconds (10^-15 seconds) required for an atom to move a fraction of a chemical bond distance to geologic time scales of billions of years. The electrowinning of copper is an oxidation/reduction reaction that depends on applied voltage to occur. The rate of the reaction depends on the amount of voltage applied. • 282-3: Humans use many natural systems as resources. Copper is a natural 220 Instructor Notes Chemistry of Electrowinning

resource that exists in the form of minerals. Through several chemical reactions, copper compounds are transformed into elemental copper.

References The Acorga Technical Library [CD-ROM]; Avecia Inc.: Wilmington, DE, 2000.

221

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