Question

Read the following description of Tube #2:

Tube #2 contains:

Bromothymol blue (BTB)
Carbon dioxide
Exposed to light
Elodea present
Initially yellow-green in color
After 24 hours, Tube #2 is now blue in color. In 1-2 sentences explain why.

Answer 1

Tube #2 changed from yellow-green to blue due to the presence of Elodea, which is a photosynthetic plant. In the presence of light, the Elodea consumed carbon dioxide through photosynthesis, reducing the concentration of carbonic acid in the solution, which led to an increase in pH and a resulting color change in bromothymol blue from yellow-green to blue.