Question

Explain why phenolphthalein is used as an indicator in acid-base titration.

Answer 1

Phenolphthalein is a weak organic acid. Its undissociated molecule (HPh) is colourless while its ion $\left(P{h}^{-}\right)$ is pink in colour. pH range of Phenolphthalein is $8-9.8$. In acid base titration phenolphthalein is used as indicator. As the concentration of $O{H}^{-}$ ions increases a little, solution turns pink from colourless giving its end point.