Situation 1:Bromthymol blue is an acid indicator that turns a yellow/green color when exposed to acids such as carbon dioxide. Describe what would happen over the course of 24 hours if you placed a water plant in a bromthymol blue solution and then added your breath to make the liquid turn yellow/green. The container is sealed tight and placed on a sunny windowsill for the entire 24 hours.

24 hours later

The plant absorbed the CO2 from your breath. Therefore the water returned to its blue color.

CO2

CO2

CO2

CO2

CO2

CO2

CO2

CO2

CO2

CO2

Situation 2:You repeat the procedures mentioned in situation #1, only now you have wrapped tin foil around the sealed container holding the plant. Describe what would happen over the course of 24 hours and why.

24 hours later

No color change because the plant did not receive sunlight and was not able to perform photosynthesis. It did not use CO2.

CO2

CO2

CO2

CO2

CO2

CO2

CO2

CO2

CO2

CO2

FOIL

Situation 3:You place a water plant in a solution with bromthymol blue but you do not add your breath. Therefore the solution has a blue color. As described above in #2 you wrapped the sealed container with tin foil. After letting the plant sit for 24 hours, you reexamine the solution and notice there is a yellow/green color to the bromthymol blue. Explain how this happened.

24 hours later

The plant must have released CO2 in order to change the water yellow. The plant releases CO2 by doing cellular respiration.

CO2

CO2CO2

CO2CO2

CO2CO2

FOIL