How does Phenolphthalein acid base indicator work...and in what titrations should it be used for?

Question

How does Phenolphthalein acid base indicator work...and in what titrations should it be used for?

Answer 1

It changes pink when the acid becomes a base.

Acid-base titration.

Answer 2

Phenolthalein is a weak acid. Let us call it HPh. When you add  a solution of HPh to an acidic solution, the acid HPh does not ionise. Because the HPh molecule is colourless, the acidic solution is colourless. If yo now add a solution of a base (as in a titration) when all the acid has been neutralise, the HPh is able to dissociate

HPh <=> H+  +  Ph-

The Ph - ion is bright pink in clour, so the base solution becomes pink in colour. The ionisation of the HPh occurs at a pH above 8.3. The indicator is therefore used to titrate a strong base with a strong acid.

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