Phenolphthalein
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![Synthesis of phenolphthalein:[14]](/Images/godic/202502/02/Phenolphthalein_Synthesis.svg1451.png")
Phenolphthalein /ˌfiːnɒlfˈθeɪliːn/ 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 acidic solutions and pink in basic solutions.