BROMOTHYMOL BLUE (BTB) AND RESPIRATION
OVERVIEW: What kind of factors would affect how much carbon dioxide a person exchanges?
Background:
Bromothymol blue is an indicator that changes colors in the presence of acids and bases in the range of 6 to 7.5 pH. It will change as the student bubble his/her breaths through the solution, changing from blue to greens to yellows as the solution becomes more acidic. The student can compare how much carbonic acid (carbon dioxide dissolved in water) was produced before and after activity by titrating the indicator back to its original color using a weak NaOH solution.
Supplies/ Equipment:
Stock Bromothymol Blue (BTB)
2 Erlenmeyer flasks (250 ml)
1 small beaker (100 ml)
3 to 5 straws per student who tests
weak sodium hydroxide in a dropper bottle (.1 M NaOH)
graduated cylinder (100 ml)
2 label (masking tape and marker OR pencil able to write on flasks)
timer or clock with a second hand
safety eye wear
Safety:
Do not draw the BTB solution into your mouth.
MSDS:
Hypothesis:
If BTB is titrated to determine how much carbon dioxide is exhaled, the amount of CO2 will ______after exercise because ______
______.
Procedure:
1. Pour 200 ml of stock BTB into each flask. Label one before and one after.
2. Pour 50 to 100 ml of stock BTB into the small beaker. (This sample is what you will compare your titration to so you can determine when you have reached the end point.
3. The student being tested will blow through 3 to 5 straws for 1 minute. The student should not ingest the BTB! Place the straws in the solution, breath in through your nose and mouth but exhale only through the straws. The exhaled breath will bubble through the solution.
4. After one minute, drop by drop add NaOH to the sample. Count and record the number of drops.
Hint: Swirl after each drop to distribute the NaOH. When first added, the solution may be blue but upon sitting it will become more green.
Stop the addition when the solution matches the sample in the beaker and it stays the same color.
5. The student should jog in place for one minute.
6. Repeat step 3 and 4 immediately after the exercising.
Analysis:
Create your data table below:
Graphing:
Graph your data:Graph the % of change in your data and at least 4 other participants
Conclusion:
1. Was the hypothesis supported?
2. Data supports your answer to question 1?
3. What conclusion can you draw from your data?
4. Brainstorm other questions and inquiries can you conduct building on this activity.