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LAB in Interdisciplinary, Indicators. Last updated June 15, 2017.

Summary

In this lab students will observe how increased carbon dioxide levels lead to a build-up of acidic conditions.

Grade Level

Middle and High School

Objectives

By the end of this lab, students should be able to

  • Determine the effects of exercise on CO2 levels.
  • Identify the source of the extra CO2.
  • Explain how increased CO2 levels affects the acidity of a solution.

Chemistry Topics

This lab supports students’ understanding of

  • Acids & Bases
  • Indicators
  • pH
  • Cellular respiration

Time

Teacher Preparation: 15-30 minutes

Lesson: 60 minutes

Materials (per group)

  • 1 large test-tube (small beaker can be substituted)
  • 1 - 10mL graduated cylinder
  • 2 straws
  • Bromothymol blue solution
  • Water
  • Timer
  • Paper towels

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
  • When working with acids, if any solution gets on students’ skin, they should immediately alert you and thoroughly flush their skin with water.
  • MSDS for Bromothymol Blue

Teacher Notes

  • Students should already have a basic background of pH, acids, bases
  • Model how the lab prior to the students doing the lab.
  • Students should work in pairs and switch roles throughout:
    • Exerciser: produces data by either running in place or doing jumping jacks.
    • Data-Recorder: sets up test-tube(s) for exerciser, times exercise, collects data.
  • Reference video for color change
    • Blue: basic/neutral solution
    • Yellow/green: acidic solution
  • Differentiation:
    • Higher level: Your higher-achieving students could be in a larger group of 3-4. The students could collect the data of the class and compare average times for boys vs. girls (would require the use of a double-bar graph)
    • Lower-level: groups of three with roles
      • Exerciser: produce the data
      • Timer: time the exerciser
      • Data-recorder: collect the data

For the Student

Background

Nearly every cell in your body contains mitochondria. The mitochondria are usually referred to as the “power houses” of the cell because they produce ATP, which is cellular energy. The equation for this process is shown below:

C6H12O6 + 6O2 → 36ATP + 6H2O + 6CO2

To produce this energy, cells must do cellular respiration. One product of cellular respiration is carbon dioxide (CO2). As cells produce CO2, it is moved from the cells to the blood stream. From there, it is transported to the lungs, where is gets exhaled.

We can measure how quickly your body is doing cellular respiration by measuring how quickly CO2 is produced and exhaled. Bromothymol blue is a chemical indicator that will be used to help us do this. Indicators are chemicals that change color as the pH of a solution changes. It is yellow in acidic solutions (pH:0-6) and blue in basic or neutral solutions (pH:7-14).

When carbon dioxide is dissolved in water, is combines with some of the water molecules to produce carbonic acid. This acid has a pH of ~5.7, which causes the solution to become more acidic as more CO2 is dissolved in the water. Today you will measure your cellular respiration rates both before and after exercise by exhaling into a test tube containing water and bromothymol blue!

Investigation Question

How does exercise affect a person’s rate of cellular respiration?

Hypothesis

Make a hypothesis statement below. Be sure to justify it with reasoning.

Pre-lab Questions

  1. Write the equation for cellular respiration. Draw a circle around the reactants and a box around the products.
  2. How will bromothymol blue be used in this experiment? What would happen if it were not used?
  3. How is breathing related to cellular respiration?

Materials

  • 1 large test-tube
  • 1 - 10mL graduated cylinder
  • 2 straws
  • Bromothymol blue solution
  • Water
  • Timer
  • Paper towels

Safety

  • Safety goggles and lab aprons must be work when handling chemicals in the lab.
  • Wash your hands thoroughly before leaving the lab.
  • When working with acids and bases, if any solution gets on your skin immediately rinse the area with water.
  • DO NOT DRINK THE SOLUTIONS TODAY
  • Clean-Up
    • Solutions can be dumped down the drain.
    • Make sure you clean up any spills on your table and/or on the floor.
    • All straws and paper towels can be thrown in the trashcan.
    • Test-tubes must be rinsed out and put back in the test-tube rack.
    • Goggles and aprons must be returned as they were received.

Procedure

Test-Tube Set Up

  1. Put on your safety equipment.
  2. Obtain a clean test tube.
  3. Using a graduated cylinder, measure 5mL of water. Then, pour the water into the test-tube.
  4. Add two drops of bromothymol blue to the test tube.

Resting Cellular Respiration Rate

  1. Measure your resting heart rate.
    • Have your partner set a timer for 15 seconds.
    • Count the number of heart beats you feel for 15 seconds.
    • Multiply that number by 4 to get your beats per minute.
    • Record that value in Data Table 1 under “resting heart rate.”
  2. Place a straw in the test tube.
  3. Have your partner start the timer.
  4. SLOWLY exhale through the straw, into the test tube. Take your mouth off of the straw to inhale between exhales so that you do not accidentally inhale the liquid. Continue to exhale until the color of the solution changes from blue to yellow (not green!)
  5. Record the time it takes for the solution to change color in Data Table 2 under “resting cellular respiration rate.”
  6. Rinse out your test-tube.
  7. While you exercise for two minutes, your partner should set-up your test-tube again.

Exercising Cellular Respiration Rate

  1. Measure your exercising heart rate
    • Have your partner set a timer for 15 seconds.
    • Count the number of heart beats you feel for 15 seconds.
    • Multiply that number by 4 to get your beats per minute.
    • Record that value in Data Table 1 under “exercising heart rate.”
  2. Place a straw in the test tube.
  3. Have your partner start the timer.
  4. SLOWLY exhale through the straw, into the test tube. Continue to exhale until the color of the solution changes from blue to yellow (not green!)
  5. Record the time it takes for the solution to change color in Data Table 2 under “exercising cellular respiration rate.”
  6. Rinse out your test-tube.
  7. Repeat the entire experiment, switching roles with your partner.

Data

Data Table 1: Heart Rates

Partner Name

Resting heart rate

Exercising heart rate

Data Table 2: Cellular Respiration Rates

Partner Name

Resting Cellular Respiration Rate

Exercising Cellular Respiration Rate

Analysis

Exercise and Heart Rate

  1. Create a bar graph that compares your heart rate before and after exercise.Lab exhalingacid graph
  2. Explain your graph. How did exercise affect your heart rate?

Exercise and Cellular Respiration

  1. Create a bar graph that compares your cellular respiration rate before and after exercise.Lab exhalingacid graph
  2. Explain your graph. How did exercise affect your cellular respiration rate?
  3. Does your data show that you produce more or less CO2 with exercise?

Conclusion

  1. Did your body need more oxygen or less oxygen to produce energy? How did your body compensate for this need?
  2. What would happen if your cellular respiration rate increased but your heart rate did not? How might the pH of your blood be affected?
  3. Why is it important to take deep breaths instead of shallow breaths while exercising?