What is phenylthalein?

Answer 1

Phenolphthalein is a chemical compound with the formula C20H14O4 (often written as "HIn" or "phph" in shorthand notation). Often used in titrations, it turns colourless in acidic solutions and pink in basic solutions. If the concentration of indicator is particularly strong, it can appear purple. In strongly basic solutions, phenolphthalein's pink colour undergoes a rather slow fading reaction and becomes colourless again. In other words, the molecule has four forms: {| ! Species | In H2In In2− In(OH)3− ! Structure ! Model ! pH | < 0 0−8.2 8.2−12.0 >12.0 ! Conditions | strongly acidic acidic or near-neutral basic strongly basic ! Colour | orange colourless pink to fuchsia colourless ! Image | The rather slow fading reaction that produces the colourless InOH3− ion is sometimes used in classes for the study of reaction kinetics. |}