I. Teacher Notes & Guidelines

SOTM LAB: B 2M 11/23/99

I. TEACHER NOTES & GUIDELINES

TITLE OF LAB: UNDERSTANDING pH (B2)

DEVELOPERS OF THE LAB: Sally Cross JD867, Angela Flanagan JD883, Patrick Hancock JD892, Fran Kallman JD724, David Moss JD594, Sibylle Tulve JD746, Christine Zamenick JD589, SOTM Staff.

OVERVIEW OF THE LAB: DESCRIPTION: Though this activity does have students utilize conventional test papers and indicators for acids and bases, the focus is on the utilization of the computer and an electronic pH probe to obtain more accurate and precise pH readings. The teacher provides the solutions to be tested, and leads the students into their own inquiries about acids and bases. Again, the emphasis will be on the use of the electronic equipment to gather precise pH readings. From this activity it is anticipated that the role of acids and bases in the ecosystem will be investigated, and further activities and inquiries will evolve.

CURRICULUM CONSIDERATIONS: The teacher background information presented here supports the topics of environmental science, the water cycle, and pollution. However, the lab activity and inquiry themselves are also appropriate when studying digestion, chemistry, or types of solutions.

SAFETY CONSIDERATONS: 1. Solutions are not to be tasted, touched, or smelled. 2. No solutions are to be mixed without the instructor’s permission. (Although the

solutions used in this lab are generally harmless, it must be stressed to students that indescriminate mixing of chemicals may result in injury.) 3. Safety goggles are to be worn. 4. Glassware safety protocol should be followed. 5. Electrical safety protocol should be followed. 6. The pH sensor probe is to be rinsed with distilled water and dried with a kimwipe before and after each sampling.

BACKGROUND INFORMATION

A. SCIENTIFIC VIEWPOINT: *an acid is a substance that increases the hydrogen ion concentration in a solution *a base is a substance that decreases the hydrogen ion concentration in a solution *pH scale is a measure of the hydrogen ion concentration ranging in value from 0-14 *a solution of pH 3 is not twice as acidic as a solution with pH 6, but a thousand times more acidic (each whole # change in pH value is equal to a factor of 10) *buffers are substances that minimize the change of pH when adding an acid or a base to a substance *most biological fluids are within the range pH 6 to pH 8 (there are a few exceptions including the human stomach’s digestive juice with a pH of about 1.5) *human blood normally maintains a pH of 7.4 due to the presence of buffers; a person cannot survive for more than a few minutes if the blood pH drops to 7.0 or rises to 7.8

*normal, uncontaminated rain has a pH of 5.6 because of CO2 which combines with water to form carbonic acid *Acid precipitation refers to rain, snow, or fog that is more acidic than pH 5.6; this is a result of sulfur oxides and nitrogen oxides (released from the combustion of fossil fuels by factories and automobiles) combining with water in the atmosphere *acid precipitation is harming both terrestrial and freshwater ecosystems *the pH of soil affects the solubility of minerals; some mineral nutrients are washed out of the topsoil while other minerals (such as aluminum) reach toxic concentra- tions; both have a negative impact on the plant life *the pH of lakes and ponds has been lowered by the leaching of certain minerals from the soil by acid rain, having an adverse affect on many species of fish, amphibians, and aquatic invertebrates; acidity may kill water plants, deform fish, and prevent fish eggs from developing; some lakes at higher elevations in the Adirondacks have a pH less than 5.0 and fish have completely disappeared *acid precipitation can be reduced through industrial controls and antipollution devices; there is some evidence that sulfur oxide emissions have decreased by as much as 30% since 1985

B. COMMON MISCONCEPTIONS: Misconceptions about acids and bases will be ascertained by pre-lab brainstorming, small group discussions, and class discussions identified and described within.

OBJECTIVES: At the conclusion of this lab activity, students will be able to: 1. identify acids and bases based on their pH 2. use indicators to identify acids and bases 3. work with computers to take pH measurements 4. demonstrate the neutralization of an acid and a base 5. understand the relationship between acids, bases, and the pH scale 6. design and perform a simple neutralization reaction

EQUIPMENT/MATERIALS PROVIDED BY SOTM:

laptop computers kimwipes computer interfaces magnetic stirrers/ hot plate (and stir bars) pH probes possibly extension cords/ power strips buffer solutions of pH 4, 7, and 10 wash bottles surge protectors optional: magnetic stir plates spinbars

PROVIDED LOCALLY: pH test papers red litmus paper blue litmus paper phenolphthalein paper wash bottles with distilled water (1 for each station) collection vessel for waste water (1 for each station) 50 mL beakers (one for each solution X how many stations to be set up) 100 mL beaker with distilled water (1 for each station) 100 mL graduated cylinders (1 for each station) medicine droppers (1 for each station) paper towels electrical outlets (each lab station requires 2 outlets) safety goggles unknown solutions to be tested (acids= lemon juice, orange juice, tomato juice, vinegar, club soda, pickle juice, sauerkraut juice, rainwater; bases= lime water, liquid soap, liquid detergent, shampoo, milk of magnesia, baking soda solution)

ADVANCE PREPARATION: 1. Prepare acid/ base solutions (quantity to be determined by the teacher). 2. Label each 50 mL beaker with the name of the acid/base solution it will contain, then fill each beaker to the desired level. 3. Set up each lab station with the following: -test papers of all types -50 mL beakers of the solutions to be tested -100 mL beaker of distilled water -one wash bottle of distilled water -collection vessel for waste water -paper towelling -kimwipes -laptop computer -computer interface -pH probe -electric power supply with 2 outlets 4. Begin soaking the pH probes in the beaker of distilled water. Preferably overnight. 5. Refer to the General Procedure for Starting Science Workshop with Library. 6. For Item 4 select “biology” 7. For Item 5 select “b04_buff.sws 8. Close the “Experiment Notes” window 9. Click on Display menu and on New Digits 10. On the B04 line of the setup window, click on the box next to the X to view the interface screen. 11. Double click on the box with pH in it.

12. Using a sample of buffer at pH 10 for high value and one of pH 4 for low value, set the high and low value readings. This is accomplished by inserting the probe into the solution, clicking the “Read” button, and typing in the proper pH value in the first box on the line. Remember to rinse off the probe between all solutions and wipe off the probe with a Kimwipe. 13. When finished, click on “OK”. All probes in the classroom should read the same values, if the procedure was followed correctly.

II. PRE-LAB

EXERCISE TO ELICIT STUDENTS’ PRIOR KNOWLEDGE AND MISCONCEPTIONS

This is designed to elicit students’ prior knowledge and misconceptions regarding acids, bases, and pH.

Divide class into groups of three or four students. In a five to seven minute time frame, have the students brainstorm any knowledge and ideas they may have concerning acids, bases, and/or pH. One student will record the group’s information. No information that is offered is discounted.

After this period of time, teacher leads a class discussion by asking each small group, in turn, to give one fact from its list. From these offerings, the teacher constructs a class list (either on the board or, ideally, on large sheets of paper) and continues in this manner until no group can offer any additional facts or input.

From this master list, teacher will guide discussion about any thoughts that students have expressed about acids, bases, and pH. Teacher may want students to copy down those ideas shared through this class discussion in their notebooks. The master list will also be kept available for future reference.

DISCUSSION OF PRECONCEPTIONS: Any preconceptions that students bring forth during this teacher-led discussion will become the basis for the student-generated inquiry labs/experiments/activities that will follow. This pre-lab activity will allow students to formulate and share ideas that will be supported or refuted by their own experiments.

III. EXPLORATION OF SCIENTIFIC PRINCIPLE & INTRODUCTION OF EXPERIMENTAL PROTOCOL

The purpose of this activity is to introduce students to the use of conventional pH indicators and scientific instrumentation using computer-interfaced technology to show enhanced methods of obtaining similar information. It will allow students to see similarities and differences in obtaining scientific data and it will provide some practical knowledge regarding characteristics of acids and bases.

PROBLEM: How can the pH value of substances be determined?

EXPERIMENT AND TECHNICAL OPERATION OF EQUIPMENT:

This activity will consist of several parts. In Part I, students will familiarize themselves with the equipment and the types of data they will be getting as they test acids and bases and determine pH. They will be given substances whose pH values are known so that they can learn what types of results to expect. In Part II, they will use the information gained in Part I to guide them as to what they can expect for their results. In Part III, they will be given an acid and be asked to neutralize it to ascertain how a neutral solution can be obtained.

Part I. Finding the pH of “known” solutions

Materials (local ): pH paper, red litmus paper, blue litmus paper, phenolphthalein paper, wash bottle with distilled water, container for used water, 50 mL beakers for each solution, paper towels Materials from SOTM: laptop computer with pH sensor, buffer solutions of known pH value (one acid, one base, one neutral), kimwipes

Procedure: 1. Find the pH of the solution marked “acid” by using each of the indicators and the pH sensor. Record the information in the chart. For the red and blue litmus paper and the phenolphthalein, record the color. For the pH paper and the pH sensor, record the numerical value for the pH. For the pH sensor, give the pH reading accurate to one decimal point. 2. Repeat step 1 for the solution marked “base.” 3. Repeat step 1 for the solution marked “neutral.”

Substance pH paper Red litmus Blue litmus Phenolphthalein pH sensor acid base neutral

QUESTIONS: Base your answers to the following questions on the data in your table.

1. What results do you expect from your indicators for a neutral solution?

2. What results do you expect from an acidic solution?

3. What results do you expect from a basic solution?

Part II. Finding the pH of “unknown” solutions.

Materials (local): (solutions whose pH values are unknown may include the following): lemon juice, orange juice, tomato juice, vinegar, club soda, pickle juice, sauerkraut juice, rainwater, lime water, liquid soap, liquid detergent, milk of magnesia, baking soda solution, shampoo, pH paper, red litmus paper, blue litmus paper, phenolphthalein paper, 50 mL beaker for each unknown solution, wash bottle with distilled water, container for waste water, paper towels

Materials from SOTM: laptop computer with pH sensor, kimwipes,

Procedure: 1. Following the same procedure used for Part I (Finding the pH of known solutions), record the results for all of the unknown solutions. 2. List each of the solutions whose pH values are unknown on the chart below. Be sure to record the pH values for the sensor readings to one decimal point.

Substance pH paper Red litmus Blue litmus Phenolphthalein pH sensor

3. Based on the pH you recorded for each solution that you tested, write the name of each substance on the correct location on the pH scale below. Make a mark where the solution would be located based on the results you obtained and then label that mark.

0------1------2------3------4------5------6-----7-----8-----9-----10-----11-----12-----13-----14

Part III. Neutralizing an acid.

Materials (local): dilute (1:30) vinegar, baking soda solution (50 mL), 100 mL beaker, graduated cylinder, medicine dropper, paper towels

Materials from SOTM: laptop computer with pH sensor, magnetic stirrer, stirring bar

1. Place 20 mL of the dilute vinegar solution in the 100 mL beaker. 2. Using the laptop computer with the pH sensor, find the pH of the dilute vinegar. Record this value on the chart. 3. Place the beaker containing the vinegar on the magnetic stirrer and gently put in the stirring bar. Turn on the stirrer so it is slowly stirring the vinegar. 4. While the vinegar is being stirred, add 20 drops of the baking soda solution to

the vinegar with the medicine dropper. Note any changes in the pH value. Record this pH value on the chart. (Make sure the baking soda stays in suspension by stirring it frequently.) 5. Continue in this manner until the pH of the vinegar solution becomes 7.0 (neutral). Record all information on the chart.

Number of drops added pH value 0 (starting pH) 20 40 60 80 100 120 140 160 180 200

6.Use the information from the previous chart to graph the changes in the pH value as you conducted your activity.

13 12 11 10 9 8 7 6 5 4 3 2 1 0 pH/ 20 40 60 80 100 120 140 160 180 200 220 drops

Discussion Questions:

1. What is neutralization?

2. What type of solution must be added to an acid in order to neutralize it?

3. How do you suppose a base is neutralized?

IV. ELABORATION OF SCIENTIFIC PRINCIPLE: INQUIRY-BASED STUDENT INVESTIGATION

PROBLEM: By now each of you has gained knowledge about acids, bases, and pH. If you think back to the first day and the list of “facts” gathered from the class, you will be able to analyze each statement made as a student more educated about acids, bases, and pH.

But there is still much to learn. What would you like to learn about acids, bases, and pH? You will be working independently researching and experimenting on a topic of your choosing. What will it be? Give it some thought, then state your idea in the form of a problem.

Problem Statement: ______

______

HYPOTHESIS OR PREDICTION: 1. What will you need to research on the computer or in the library about your topic?

______

2. You are required to incorporate an experiment to test or support your idea, or to gather information about your topic. You are to use the materials used in the practice lab, or you may be bringing in other supplies from home (with teacher’s permission). How will you incorporate an experiment into your investigation? What will you test? Give some thought, then identify your ideas below.

______

3. Check off which of the following you will be using in your experiment:

____laptop computer with Science Workshop program ____printer ____computer interface and pH probe ____pH test paper ____red/ blue litmus paper STOP... SUBMIT FOR TEACHER SIGNATURE Other Materials:

SAFETY CONSIDERATIONS:

EXPERIMENTAL DESIGN: Include in your procedure all steps, types of data to be collected, and graphs, charts and tables to be created.

APPROVAL AT CHECKPOINTS

STUDENT EXPERIMENT ON ACIDS, BASES, pH

PURPOSE OF THE EXPERIMENT STEPS IN PERFORMING THE EXPERIMENT TEACHER COMPONENT

MATERIALS SUPPLIED

SAFETY CONSIDERATIONS

EXPECTATIONS OR PREDICTIONS

TYPES OF DATA TO BE COLLECTED

CHARTS, TABLES, GRAPHS TO BE CREATED TEACHER SIGNATURE:

PLAN FOR DATA COLLECTION & ANALYSIS Use the space below to draw a final copy of any data table, chart, or graph that you will use to represent the data collected during your experiment, or as a result of your experiment.

CONDUCTING THE EXPERIMENT While you are conducting the experiment, the teacher will monitor your work and initial the following items.

____student gathered all materials before beginning the experiment ____student measured and labeled all solutions to be used ____student handles materials and equipment in a responsible manner ____student follows safety protocol for glassware, unknown chemicals, and electrical power ____student is able to explain and describe his procedure as the experiment progresses ____student records observations and data as the experiment progresses ____student asks for assistance from teacher if needed ____student ends experiment at the appropriate time and in the appropriate manner ____student returns materials and supplies to their proper place ____student returns laptop computer, interface, and pH probe to the original condition ____student cleans up materials used ____student cleans up work station

TEACHER SIGNATURE:

ANALYSIS OF DATA In the space below, provide a written analysis of the data collected during your experiment. Refer back to your data table, graph, etc. Take a few minutes to review what you recorded and remember your experiment. Then begin your written analysis. Remember to express yourself in a way that demonstrates your understanding. Do not assume the reader understands what you mean. You will present your analysis to the class at a future date.

TEACHER SIGNATURE:

DISCUSSION OF RESULTS COMPARE Visit with 2 other students in your class. During your visit you are to discuss their experiment and your experiment in the following way: -briefly describe what each of you was investigating about acids, bases, or pH -identify what you hoped to learn by completing your experiment -identify whether or not you did get the information you were after, and were the results what you expected? -discuss together whether your results are something that can apply to all similar acids or bases, or whether your results are unique to the substances you used -offer support and words of encouragement to your partners

PERSUADE

RELATE

V. EVALUATION

POST-LAB SURVEY OF STUDENT’S CONCEPTIONS Re-form into your original 3 person group to discuss the original class list about acids, bases, and pH. Take 5 minutes to revisit what was written and come to a group consensus about the accuracy of each statement. Identify what part or parts of each sentence are true or false. Select one person from your group to participate in the class discussion that will follow.

TRADITIONAL Complete each sentence with a word, phrase, or number. 1. Acids have a pH of ______to ______. 2. Strong acids have a pH close to ______. 3. Weak acids have a pH close to ______. 4. Bases have a pH of ______to ______. 5. Strong bases have a pH close to ______. 6. Weak bases have a pH close to ______. 7. A neutral solution has a pH of ______. 8. To neutralize an acid ______. 9. To neutralize a base ______. 10. As a base is added to an acid, the pH number ______.

ALTERNATIVE THE GUEST SPEAKER

You are a visiting guest speaker at a school of fish in a freshwater lake in upstate New York. The young fish are about to begin a unit on acid rain and how it is changing their environment. You, as the expert, are at the school to explain to the young fish what acid rain is, where it comes from, how they can recognize it, what changes have taken place in their environment since you were a young fish, what changes they can expect to see in the future if steps are not taken to reduce the current acid rain problem, and so on. Since these are young fish that might be easily frightened, be sure to conclude on a positive note for them to leave feeling hopeful. What steps are being taken by humans to reduce or solve this problem of acid rain.

Requirements: 5 minute presentation to the class, in the role of the guest speaker Creation of 2 visual aids such as a poster, overhead transparency, or model. These are to support your presentation, but are to be designed for young fish, so design accordingly.

Grading Rubric:

5 Excellent Presentation: Presentation explains the meaning of acid rain, where it comes from, how students can recognize it, what changes have occured in their environment, what future changes might occur, etc. A “happy ending” is provided to reduce young fish stress syndrome. 2 visual aids were presented: age appropriate, educational, accurate, and neat.

4 Good Presentation: Presentation is age appropriate and includes 2 visual aids, but student fails to address 1 or 2 key points that were required.

3 Adequate Presentation: Presentation is age appropriate, but is lacking 2 or more key points, and visual aids need refinement.

2 Inadequate Presentation: Presentation is not age appropriate; visual aids are not age appropriate.

1 Presentation Gives False Information: Demonstrates a lack of understanding of acid rain and the impact on the environment. Visual aids provide little information of value. Student does, however, get up in front of peers.

0 Student absent/ Student Does Not Present

*This material is based upon work supported by the National Science Foundation under Grant No. ES1 9618936. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.