1. A colorless chemical compound used as an acid-base indicator that turns pink or red in basic solutions and remains colorless in acidic solutions.
Usage: chemistry; commonly used in laboratory titrations and pH testing
2. A laxative medication that was historically used to treat constipation by stimulating bowel movements.
Usage: medicine; largely discontinued in many countries due to safety concerns

Examples

• The chemistry student added phenolphthalein to the solution to determine its pH level.
• In the titration experiment, phenolphthalein changed from colorless to pink when the endpoint was reached.
• Phenolphthalein is a standard indicator used in acid-base laboratory work.
• The indicator phenolphthalein helps chemists identify when a solution becomes neutral or basic.
• Many over-the-counter laxatives once contained phenolphthalein before regulatory agencies restricted its use.