Honours Specialist Chemistry

Honours Specialist Chemistry Concept Presentation

SCH4C Gr. 12 College Chemistry Qualitative Analysis: A Foundation for Lab Skills

Cora Burt Tuesday, July 13, 2010

Instructors: Janine Extavour, Marty Zatzman

1 Background Information Students selecting the 4C level of chemistry are likely more focused on the applications of chemistry rather than the abstract theories of chemistry. Therefore, by providing these students a solid practical foundation in qualitative analysis it may give students greater confidence in making connections in subsequent strands of chemistry.

This unit may be presented in a manner that promotes good lab practice as well as develop good lab skills which may be translated into valued technical career path. Thus, the approaches presented are designed to minimize confusion in the learning process as well as fostering the strengths of the individual learner.

Expectations The following expectations focus on the qualitative analysis lab skills required:

B2.3 investigate precipitation reactions and flame tests, using qualitative analysis instruments, equipment and techniques [PR, AI]

B2.4 conduct qualitative analysis of an unknown sample, using a flow chart and experimental procedures, including flame tests and precipitation reactions to determine the presence of metal ions [PR, AI]

B2.5 identify an unknown gas sample by observing its emission spectrum and comparing it to the spectra of known gases [PR, AI]

For the purposes of this document, the former two expectations (flame tests and precipitation reactions) will be the focus of discussion.

Misconceptions / Difficulties Few misconceptions are of note when discussing qualitative analysis with students. For the most part, students are expected to associate a qualitative observation with a metal cation from a specific chart of known facts. Therefore, the difficulties in this area may be embedded in ensuring the students are well versed in recording scientific data as well as how to use the charts to analyze their data.

By presenting the demonstrations of the qualitative tests up front, the students will have a visual representation of the task they are expected to carry out as well as a mental image available for reference when discussing the analysis of the tests.

2 The following points discuss areas which can be addressed to minimize misconceptions and / or to improve clarity. 1. Solution and Flame Colours

Misconception: Solution and Flame Colours are Similar for a Cation Associating ions to their appropriate solution and flame test colours is not a difficult task, nor is dispelling the misconception that colours of a solution will not necessarily be related to the results of a flame test. However, presenting these materials in a manner to maximize visual impact may improve student reception of the ideas presented.

• displays of all the powders and aqueous solutions that are available, within reason • conduct the flame test as a long-lasting methanol solution rather than a brief flash of colour from powder on a wire (instructions on page 4)

• if available, compare different coloured salts with a common ion (e.g. CuCl2 vs.

CuSO4)

Textbook Chart/Table Difficulties Most textbook charts and tables are organized in manners which are not necessarily intuitive to the user. For example, the colours are not arranged in a particular order or the colour descriptions are not clear for all readers).

Allow the students to remake their own charts in modalities which suit their own preferences of learning and utilization.

• limit the charts to a select number of ions to minimize the feeling of being overwhelmed • as a lab (instruction on page 4) promote good lab skills in which students produce their own chart of associating ions with their solution or flame test colours • allow students to assess the quality of their chart through testing of other substances

2. Precipitate Formation

Textbook Chart/Table Difficulties Students should be fairly familiar with the notion that mixing solutions do not always result in a chemical reaction. Similar with the previous analyses, helping the students read a solubility table is key to their success. Thus, investing the time to identify the

3 most student-friendly chart, which may differ student-to-student, or helping them determine the best method in which to use a chart is of great importance.

• identify a multitude of charts/tables and allow students to select their preference • limit the charts to a select number of ion types • other modalities (Solubility Song; www.hschem.org/Honors/CH04/SolubilityRulesSong.pdf) Teacher Preparation / Materials:

Flame Test Demo safety goggles watch glasses for each chemical tested squeeze bottle of methanol matches

¼ tsp of an assortment of ionic salts (e.g. LiCl, KCl, NaCl, CaCl2, BaCl2, SrCl2, CuCl2)  some of the more interesting colours may be on the TDSB banned list

Flame Test for Students (Nelson Chemistry 12 College Prep, p 23) safety goggles Bunsen burner nichrome test wire small samples of an assortment of ionic salts (see Flame Test Demo above)

Solubility Table Resources http://castlelearning.com/review/reference/chem%20table%20f.gif The solubility table presented in the link above lists rules for soluble compounds as well as for insoluble compounds. http://www.professormeyer.com/images/solubility%20chart.jpg The solubility table presented in the link above is a chart listing possible anions (across the top) and possible cations (down the left-hand side). The soluble or insoluble identification may be determined by finding the intersection of the column and row of the ions of interest.

Career Exploration Forensics  identification of unknown materials

4  association of unknowns to potential sources Fireworks  production of colourful pyrotechnic displays for entertainment purposes Food/Water Quality Analysis  contamination recognition  toxicity testing Astronomy indirect identification of atoms on celestial object Ministry Learning Lesson Progression Expecta Teaching Strategies Styles tions Supported 1. Review physical properties of B2.1 Group Thinking Concept Verbal, Visual Diagnostic – do I matter Map remember? • classify qualitative vs. quantitative

2. Examine display of solid and A1.8 Teacher Directed, Student Verbal, Visual Formative – using correct aqueous solutions of ionic salts Involvement terminology

3. Introduction to flame test B2.3 Teacher Demo Verbal, Visual Formative • career exploration discussion A1.2 Teacher Directed, Student Verbal, Visual Formative – asking 4. Pre-lab preparation Involvement questions for clarity 1. Review pre-lab preparation A1.2 Teacher Directed, Student Verbal, Visual Diagnostic – did I Involvement remember?

2. Conduct lab B2.3 Student Directed Visual, Formative – safety, good • students observing and A1.5 Kinesthetic lab skills, completion developing their own flame test A1.6 tables

3. Practice assessment A1.8 Student Directed Visual, Formative – did I • students assess the quality A1.9 Kinesthetic understand, what changes of their own flame test table are necessary 1. Review understanding of B3.2 Teacher Demo, Student Visual Formative precipitate formation Involvement

2. Introduction to solubility charts B2.2 Direct Instruction Visual, Musical Formative and informal lab to associate B2.3 chart with Student Inquiry Kinesthetic Formative – lab skills

5 Evaluation Methods

1. Standard pen & paper questions. (Inquiry)

2. Practical test with unknown samples. (Knowledge, Inquiry)

3. Describe (Communication) and/or demonstrate how to produce a multi-coloured fire log that would burn in a specific sequence. (Application)

Making Multi-Coloured Fire Logs (Nelson Chemistry 12 College Workbook, p31) safety goggles scissors string newspaper matches labeled beakers of various ion solutions

Produce a newspaper log by rolling lengths of newspaper and tying the ends with string. Soak the newspaper log in the desired solutions, allow drying of “log” in between solutions. Burn the log to examine results.

4. Identify potential ions in drinking water. (Inquiry, Application)

Annotated References

Shamai, R. and Stavy, R., (1986) Teaching an Introductory Course in Qualitative Analysis in Order to Enhance Learning General Chemistry, J. Chem. Educ., 63 (8), 707 This article was outlines a study conducted in the US school system which demonstrated that a solid foundation in qualitative analysis in chemistry may facilitate the ease in which students make connections in other fields of chemistry such as electrochemistry.

Davies, L., Di Giuseppe, M., Gibb, T., Sanader, M. and Vavitsas, A. (2004) Nelson Chemistry 12: College Preparation Teachers Resources, Toronto: Thomson Canada Limited This resource was helpful for indentifying some student misconceptions and offering teaching methods which could help in dispelling those misconceptions.

Burt, C., Rahman, M., Wang, G., Woodcock-Ashford, G. (2009) Retrieved July 10, 2010 from

6 This website contains a compilation of numerous other chemistry-related websites currently available on the web with a focus on supporting chemistry teachers.