Definition of Phenolphthalein

Glossary of Chemistry Terms

phenolphthalein in clear liquid makes pink

nemoris / Getty Images

by Anne Marie Helmenstine, Ph.D.
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.
Updated July 03, 2019

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.