phenolphthalein phe·nol·phthal·ein (fē'nōl-thāl'ēn', -thāl'ē-ĭn, -thā'lēn', -thā'lē-ĭn)
A white or pale yellow crystalline powder that is used as an acid-base indicator and as a laxative.
A white or pale-yellow, crystalline powder used as an indicator for acid and basic solutions. In solutions that are either neutral or basic, it is colorless, while it is pink or red in solutions that are alkali. It is also used as a laxative and in making dyes. Chemical formula: C20H14O4.