Phenolphthalein (PT)

Phenolphthalein is a chemical compound with the formula C20H14O4. Often used in titrations, it turns colorless in acidic solutions and pink in basic solutions. If the concentration of indicator is particularly strong, it can appear purple. Phenolphthalein has been used for over a century as a laxative, but is now being removed from over-the-counter laxatives because of concerns over carcinogenicity. Phenolphthalein is used in a test to identify substances that are thought to be, or to contain, blood. This test is commonly known as the Kastle-Meyer test. A dry sample is collected with a swab or filter paper. First a few drops of alcohol, then a few drops of phenolphthalein and finally a few drops of hydrogen peroxide are dripped onto the sample. If the sample contains hemoglobin, it will turn pink. Phenolphthalein is synthesized by condensation of phthalic anhydride with two equivalents of phenol under acidic conditions.