Answer:
Questions: Explain why Phenol red is a good indicator of photosynthesis? Phenol red turns red in basic (and neutral) solutions: photosynthesis should remove CO2 (carbonic acid) and increase pH (red).
Step-by-step explanation:
In this lab, you will use phenol red as an indicator to show whether CO2 is being consumed or produced in a reaction within plants.
It is well known that in the presence of light plants perform photosynthesis. It is less well understood that at the same time plants are also performing cell respiration. To demonstrate this we will determine whether CO2 is consumed or produced as elodea (anacharis) is placed in either a light or dark environment. The change in CO2 will be detected by the pH indicator phenol red.
Think about the chemical equations for respiration and photosynthesis. Which one releases CO2 causing an increase and which one uses up CO2which will cause a decrease?
Phenol red is yellow under acidic conditions (high H ion concentration), pink under basic or alkaline conditions (low H ion concentration) and orange under neutral conditions. A change in CO2 will cause a directly proportional change in H ion.
If the CO2 concentration decreases, the H ion concentration will also decrease and the solution will change to pink, becoming basic.
If the CO2 concentration increases, the H ion concentration will also increase and the solution will change to yellow, becoming acidic.
Neutral solutions of phenol red will be orange.