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

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

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

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

• pH indicator
• Titration
• Le Chatelier's principle
• Carcinogen

References

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