Phenolphthalein is a chemical compound commonly used as a pH indicator in titrations. It is colorless in acidic solutions and turns pink in basic solutions, typically around a pH of 8.2 to 10.0. This property makes it useful in laboratories to determine the acidity or alkalinity of a solution. In addition to its role in chemistry, phenolphthalein has applications in medicine and biology. It was historically used as a laxative, but its use for this purpose has declined due to safety concerns. Today, it primarily serves as a teaching tool and a laboratory reagent.