Phenolphthalein is a chemical compound with the formula C20H14O4 and is often written as "HIn" or "phph" in shorthand notation. Phenolphthalein is often used as an indicator in acid–base titrations. For this application, it turns colorless in acidicsolutions and pink in basic solutions. It belongs to the class of dyes known as phthalein dyes.
Phenolphthalein is slightly soluble in water and usually is dissolved in alcohols for use in experiments. It is a weak acid, which can lose H+ ions in solution. The nonionized phenolphthalein molecule is colorless, the protonated phenolphthalein ion is an orange, and the deprotonated phenolphthalein ion is fuchsia. When a base is added to a solution containing phenolphthalein, the equilibrium between the nonionized and the deprotonated states shifts in favor of the deprotonated state as H+ ions are removed from solution.
https://en.wikipedia.org/wiki/Phenolphthalein
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