Question

Bromothymol blue (BTB) is a chemical that can be used as an indicator of the pH of a solution. Because CO2 produces an acid in water, BTB can indirectly measure how much CO2 is present in a solution. When placed in solutions with neutral pH (little CO2), the solution appears green. In solutions with low pH (high CO2), the solution appears yellow.
A teacher performed a demonstration to investigate how photosynthesis and respiration cycle carbon and oxygen. She placed a few drops of BTB in a test tube containing distilled water. Because distilled water has a neutral pH, the solution appeared green. The teacher used a straw to blow into the solution, and the solution turned yellow. She then placed an aquatic plant into the test tube, covered it to keep it air tight, and placed it under a light for 24 hours.

What color would the solution in the test tube be after being in the light, and what would it be if it were then placed in the dark for 24 hours, and why?
A
Green after being placed in the light because the plant would remove CO2 by photosynthesis; yellow after being placed in the dark because the plant would release CO2 by respiration.

B
Yellow after being placed in the light because the plant would release CO2 by photosynthesis; green after being placed in the dark because the plant could not photosynthesize in the dark.

C
Green after being placed in the light because the plant would remove CO2 by photosynthesis; green after being placed in the dark because no CO2 would enter the tube since it is air tight.

D
Yellow after being placed in the light because the plant would release CO2 by photosynthesis; yellow after being placed in the dark because no CO2 could leave the tube since it is air tight.

Answer 1

Answer:

A. Green after being placed in the light because the plant would remove CO2 by photosynthesis; yellow after being placed in the dark because the plant would release CO2 by respiration.

Explanation:

According to this question, Bromothymol blue (BTB) is a chemical that can be used as an indicator of the pH of a solution. The presence or absence of CO2 in a solution decreases or increases the pH of the solution respectively.

- BTB appears green in a neutral pH i.e. little CO2

- BTB turns yellow in a low pH i.e. high CO2

Plants, in the presence of light, will perform photosynthesis and use CO3 as a reactant while in the dark, will perform cellular respiration and release CO2 as a waste product. Hence, in this case where an aquatic plant was placed into a test tube and covered it to keep it air tight.

- When placed under light for 24 hours, the aquatic plant will undergo photosynthesis and remove CO2 from the solution to make the solution appear GREEN due to neutral pH.

- When placed in the dark for 24 hours, the aquatic plant will undergo cellular respiration and release CO2 into the solution making the solution appear YELLOW due to low pH.