Sour Chemistry *

Teacher Version(.doc)

Student Version(.doc)

• Grade Level(s):  7th
• Primary Focus: Science; NC Standard Course of Study Areas: 7th 4.01, 4.02, 4.04, 4.08
  • (Key Concepts:  Acids and Bases, pH, neutralization and concentration)
• Secondary Focus: Math; NC Standard Course of Study Areas: 7th 1.02, 1.03, 4.01
  • (Key Concepts:  Time graph, percent, log and rate of change)
• Technology Focus Areas: Calculators, Probeware, Data Visualization; NC Standard Course of Study Areas: 7th 1.10, 2.02, 3.01, 3.02, 3.05
• Essential Question: Why does your stomach feel upset?  Which medicines work the best to make you stomach feel better?
• Summary of Activity:  Students will simulate the acidity of the stomach with diluted lemon juice and then use a pH meter to test how different stomach medications affect the acidity level.
• Cognitive Teaching Strategies: Students will make predictions as to the effect of different stomach medications on the pH level of the diluted lemon. With this information, students will determine whether the active ingredient in the medication alters the pH (i.e., is it an antacid) and at what rate.
• Materials:
  • TI-84 Plus Silver graphing calculator
  • EasyData application
  • EasyLink interface
  • Vernier pH sensor
  • Various stomach medications (Alka-Selzer® or equivalent/Tums® or equivalent)
• Pepto-Bismal® or equivalent
• distilled water
• lemon juice
• eye dropper
• clean disposable cup

Part I: Set-up

Figure 1. pH sensor set-up.

1. Set up the pH sensor. Refer to Figure 1 for a typical setup of the pH sensors prior to conducting the lab. Note that the pH sensor is in a small plastic storage bottle of buffer solution. This will have to be unscrewed just prior to collecting the pH data. The cap that is fit over the sensor can stay on the sensor during data collection by pushing it up.
   
2. Turn on the calculator. Connect the pH sensor, data-collection interface, and calculator.
   Set up EasyData for data collection.
3. Start the EasyData application, if it is not already running.
   1. Select  from the Main screen, and then select New to reset the application.
   2. Select  from the Main screen, then select Time Graph…
   3. Select  on the Time Graph Settings screen.
   4. Enter 0.5 as the time between samples in seconds.
   5. Select .
   6. Enter 200 as the number of samples and select . Data collection will last 100 seconds.
   7. Select  to return to the Main screen.

Part II: Test Stomach Medicine

1. Place about 125 mL of distilled water in a very clean cup. The cup must be clean to get good results.
2. Loosen the top of the pH storage bottle, and carefully remove the bottle. Slide the top of the bottle up the shaft of the sensor so that the bottle top is out of the way. Do not remove the top from the sensor shaft.
3. Rinse the tip of the pH sensor with distilled water in a separate cup.
4. Place the pH sensor in the water. One student will have to support it so the sensor does not fall and spill the cup.
5. Put 20 drops of lemon juice into the water. This will simulate an acid stomach. Stir gently with the sensor.
6. Have another student get ready to drop your medicine tablet (or measured dose of liquid) into the water.
7. As soon as one student presses   to begin data collection, the other student should drop the tablet (or pour the liquid medicine) into the water.
8. Data collection will run for 100 seconds. After collection ends, a graph of pH versus time will be shown.

Part III: Analyzing the Data

1. For most of the medicines, the graph should show pH values that increase rapidly at first and then level off.
2. Use  to move the cursor to the beginning of the graph and record on your data sheet the beginning pH value.
3. Use  to move the cursor to right and record the time when the pH value begins to increase rapidly. This will be an estimate. Record this value on your data sheet.
4. Use  to move the cursor to right and record the time when the pH value stops increasing. This will be an estimate. Record this value on your data sheet.
5. Use  to move the cursor back to the left and record the time when the pH value reaches approximately 95% of its maximum value. This will be an estimate. Record this value on your data sheet.
6. Once you are satisfied with the values you’ve recorded, press to return to the main screen

Part IV: Test Additional Medicines

1. If you want to repeat data collection, discard the solution and thoroughly rinse the cup.
2. Use additional distilled water to rinse the pH sensor.
3. Repeat the pH value recording and analysis, starting at Part 2, Step 1.
4. When you are done testing medicines, discard the solution in the cup, and rinse the cup. Finally, rinse the pH sensor with distilled water and replace the storage bottle on the pH sensor.

Instructional Strategies:

1. Groups of two or three work well for this lab. One student can hold the pH sensor and stir the solution. Another can start the data collection and/or put the medicine dose in the cup.
2. Depending on the medicine, you may decide that you need to run the data collection longer than 100 sec.
3. You can start off the lab with a discussion about what medicine students use when they have a stomach ailment.

Additional Resources for this Lesson:

1. Common pH values (from Jack Eden)
2. Acid-Base Chemistry (from WOW, Ohio State University) provides an example lab of testing the pH of other common household products.

Re-teaching and Enrichment Strategies:

1. This lab can be extended by talking about acid-base reactions and the basis for pH values. Further analysis can be done on the active ingredients of the stomach remedies and what makes some of these ingredients basic.

2. pH readings can be made of other common household products dissolved in distilled water. Students can determine whether they are acidic or basic. Use the resource links above as a starting point.

Data Collection and Analysis:

HYPOTHESIS:

DATA:

Medicine	Start pH	Time pH starts to rise	Time pH stops rising	Time pH reaches 95% of max value	Final pH

QUESTIONS:

1. Compare the starting pH across different medicine trials. Was it different? Would you expect it to be?
2. Compare the final pH across different medicine trials. Was it different? Would you expect it to be?
3. Subtract the time the pH reaches 95% of its maximum value from the time the pH starts to rise. Is this value different for different medicines?
4. Do all of the stomach medicines affect the pH of the lemon juice solution the same? Do they change the pH the same amount or at the same rate? Examine the active ingredient of the medicine and the form the medicine comes in to reach your conclusions. Also make use of observations of the reaction when the medicine was added to the lemon juice solution.
5. Based on your findings, do all stomach medicines provide relief by altering the pH of the stomach contents? How else might they provide relief?
6. Compare your results with those of other students.

DISCUSSION:

Why does your stomach feel upset?  Which medicines work the best to make you stomach feel better?

 

*Adapted from: * Brueningsen, C., Bower, B., Antinone, L., Kerner, E., Gastineau, J. E., & Cortez, W. (2005). Real World Math Made Easy: Explorations. Dallas, TX: Texas Instruments Inc.