Question

Read the following description of tube #2:
Tube #2 contains:
Bromthymol 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

The change in color of tube #2 from yellow-green to blue indicates that the Elodea is photosynthesizing, consuming carbon dioxide (CO2) in the process. As CO2 levels decrease, the acidity of the solution reduces, resulting in a shift in the pH that causes the bromthymol blue indicator to turn blue.