Phenolphthalein
Phenolphthalein is a chemical compound often used as a pH indicator in titrations. For this purpose, it turns colorless in acidic solutions and pink in basic solutions. It belongs to the class of compounds known as phthaleins.
Chemical Properties[edit]
Phenolphthalein is a weak acid, which can lose H+ ions in solution. The phenolphthalein molecule is colorless, and the phenolphthalein ion is pink. When a base is added to the phenolphthalein, the molecule ⇌ ions equilibrium shifts to the right, leading to more ionization as H+ ions are removed. This is predicted by Le Chatelier's principle.
Uses[edit]
Phenolphthalein is used in toys, for example as a component of disappearing inks, and is used in some forensic blood tests. The compound is also commonly used in various laboratory settings for titrations of acid-base reactions.
Health Effects[edit]
Phenolphthalein has been used for over a century as a laxative, but is not sold in the U.S. because it is carcinogenic. It was also used in over-the-counter products, such as Ex-Lax, until 1999, when the FDA reclassified the drug as "not generally recognized as safe and effective".
See Also[edit]
References[edit]
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Phenolphthalein structure
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Sample of solid phenolphthalein
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Phenolphthalein very low pH 2D skeletal
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Phenolphthalein low pH 2D skeletal
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Phenolphthalein mid pH 2D skeletal
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Phenolphthalein high pH 2D skeletal
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Phenolphthalein orange very low pH 3D balls
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Phenolphthalein colourless low pH 3D balls
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Phenolphthalein red mid pH 3D balls
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Phenolphthalein colourless high pH 3D balls
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Phenolphthalein in concentrated sulfuric acid
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Phenolphthalein at pH 9
