Question

question 5 of 5
the ph indicator bromothymol blue is blue in an alkaline solution and yellow in an acidic solution. a slight increase in acidity, such as when co₂ gas is added, causes a solution with the indicator to change from blue to yellow.
a solution with the indicator would be most likely to turn from yellow to blue when which combination of factors exists?
a. yeast cells and sugar are placed in the solution.
b. water plants in the solution are placed under a bright lamp.
c. algae are placed in the solution and left in a dark room.
d. a person blows air into the solution through a straw.

Explanation:

Bromothymol blue changes from yellow (acidic) to blue (alkaline). Water plants under a bright lamp perform photosynthesis, which consumes \(CO_2\) (a source of acidity as \(CO_2 + H_2O
ightarrow H_2CO_3\)). Reducing \(CO_2\) (and thus \(H_2CO_3\)) increases the pH (makes the solution more alkaline).

• Option A: Yeast cells with sugar will ferment (anaerobic respiration) and produce \(CO_2\), which would make the solution more acidic (keep or turn it yellow).
• Option C: Algae in the dark will respire (produce \(CO_2\)), making the solution more acidic.
• Option D: Human breath contains \(CO_2\), which when bubbled into the solution will form \(H_2CO_3\) and make the solution more acidic.

Answer:

B. Water plants in the solution are placed under a bright lamp.