Exhaling Carbon Dioxide Mini-Lab
Objective: What is the relationship between exercise and the amount of carbon dioxide that you exhale?
Background Info: Bromothymol Blue is a dye that indicates the presence and concentration of an acid. When it
is in the presence of an acid it turns more and more yellow depending on how acidic the solution is.
When carbon dioxide is added to normal water it becomes acidic
Materials:
 2 250 mL Erlenmeyer flasks
 Bromothymol blue solution (0.1% solution), 30 mL
 2 straws
 Timer
 Graduated cylinder
 Paper towels
Procedure:
1. Label one beaker “Control” and the other “Experimental”.
2. Fill each flask with 15 mL of the Bromothymol Blue solution.
Be careful, the solution will stain your skin ad clothing.
3. Look at the color of the solution at the start of the experiment (if you have a camera handy, you can
take a picture of it).
Part 1: Exhaling at rest:
Place one of the straws into the “Experimental” flask and gently blow through the straw into the
solution.
Be sure to exhale only. DO NOT suck the solution through the straw.
5. As soon as you begin exhaling, your partner should begin timing.
6. Stop exhaling as soon as the solution changes to a pH of about 6.0
7. Record the amount of time needed to change the color of the solution in the table below:
Part 1Data:
Time taken to change color when resting (seconds)
4.
Part 2: Exhaling after exercising:
8. Empty out the “experimental” flask in the sink and rinse it with water a few times.
9. Refill the “experimental” flask with 15 mL of the Bromothymol Blue solution.
10. Have the person who exhaled in Part 1 exercise for at least two minutes by running in place, doing
jumping jacks, or squat thrusts (anything that will increase your heart rate without needing to move
around the room)
11. Redo steps 4-7 from Part 1 and record your results in the table below:
Part 2 Data:
Time taken to change color when resting (seconds)
Continued on back
Analysis Questions: Answer the questions below after conducting your experiment.
1. How did exercising affect the amount of time it took for the solution to change color?
(1 points)
2. In this experiment, what were the dependent and independent variables?
(2 points)
Independent Variable:
Dependent Variable:
3. In part 2, what variables did you need to control? How did you control each of these variables?
You need to give at least four control variables
(2 points)
4. Why was there an increased amount of carbon dioxide being exhaled in part 2?
You need to construct your answer in paragraph form (like writing a “Reasoning” section of your lab
reports).
You need to explain the increased amount of carbon dioxide as it relates to cellular respiration and
exercise on a cellular level.
(10 points)