Phenolphthalein is an acid-base indicator.

Store at room temperature.

For general use, you can prepare 0.5% solution in ethanol: water (1:1).

Phenolphthalein is an acid-base indicator. It is a colorless substance in any aqueous solution with a hydronium ion concentration greater than 5.0 × 10⁻⁹ M (pH < 8.3). In more basic solutions where the hydronium ion concentration is less than 5.0 × 10⁻⁹ M (pH > 8.3), it is red or pink.