Phenolphthalein is used as an acid or base indicator where, in contact or presence of acid, it will turn colorless and with a base, it will turn into a fuchsia color. It is also a component in universal indicator, a solution consisting of a mixture of pH indicators (usually phenolphthalein, methyl red, bromothymol blue, and thymol blue).

CAS Number 77-09-8
Empirical Formula (Hill Notation) C20H14O4
Molecular Weight 318.32

Phenolphthalein is another commonly used indicator for titrations, and is another weak acid.

Phenolphthalein Indicator, 1%. : Dissolve 1.0 g of phenolphthalein in 100 mL of alcohol (pH 8.0–10.0)

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