Question

Phenolphthalein has often been used to monitor the progress of an acid-base neutralization reaction. what color will phenolphthalein be when there is an excess of acid present?

Answer 1

Phenolphthalein changes color in the range 8.3 – 10. It is very easy to spot the change as it is colorless in acidic (< 8.3) and pink in basic (> 10).

It will be colorless in excess of acid.

Answer 2

When there is excess of acid the phenolphtalein remains colorless

Step-by-step explanation:

Hello,

Since, phenolphthalein is naturally colorless, it turns pink in alkaline solutions above pH levels of 8.2 and continues to a bright purple in stronger alkalines since the phenolphtalein is ionized (see attached pictures). In spite of this, below pH levels of 8.2 phenolphtalein is colorless due to the formation of the C-O bond just next to the lower carbonyl group. In such a way, at low pH levels the ionization is shifted rightwards and above 8.2 is shifted leftwards, giving the evidence that when there is excess of acid the phenolphtalein remains colorless.

Best regards.