Definition of Phenolphthalein

Glossary of Chemistry Terms

phenolphthalein in clear liquid makes pink

nemoris / Getty Images

Phenolphthalein is an organic compound often used as a pH indicator. Phenolphthalein turns pink in pH greater than 8.3 and colorless in acidic solutions.

The chemical formula for phenolphthalein is C20H14O4.