Phenolphthalein is one of the most common and important acid-base indicators used in chemistry laboratories, especially for titrations.
Phenolphthalein's chemical formula is C₂₀H₁₄O₄. It was discovered in 1871 by the famous German chemist Adolf von Baeyer.
Phenolphthalein changes colour depending on the pH of the solution:
(Note: In extremely strong bases, pH > 12, it can become colourless again).
Phenolphthalein is a weak organic acid.
It is widely used in titrations involving strong bases (like NaOH) and weak or strong acids (like HCl or CH₃COOH). The endpoint is indicated by the first appearance of a permanent pale pink colour.
The visual transition interval (pH range) of phenolphthalein is **8.2 to 10.0** (Colourless to Pink).
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