Science Buddies: "Ask an Expert"

I have tried to do this experiment using a Ph test kit but I do not seem to see any effective change in colour of the Ph solution before or after exercise. The time it took for the colour of the solution to change was instantaneous hence I could not show any difference in amount of carbondioxide exhaled after doing exercise as opposed to having done the test at rest (normal breathing rate). I would like to know the normal time it takes for colour change. I am getting a few seconds & it is same under all circumstances.

Hello sanil_gupta!

I haven't tried this specific experiment myself, but there are a few things that you might try:

If the color is changing too quickly, you might want to increase the volume of the solution in the respirometer. Since more indicator will be present overall, more carbon dioxide molecules will be needed to fully change the color, and it will take longer for the color to change.

Equivalently, you could also try to breathe into the tube more slowly. This would decrease the rate at which your carbon dioxide enters the respirometer, and thus (hopefully) extend the time of the color change to where you can see the difference.

Hope this helps-- if you have more questions, be sure to ask!