Question

phenolphthalein when acidic

Answer 1

Phenolphthalein adopts four different states in aqueous solution: Under very strongly acidic conditions, it exists in protonated form, providing an orange coloration. Under strongly acidic conditions, the lactone form is colorless. The singly deprotonated phenolate form (the anion form of phenol) gives the familiar pink color. In strongly basic solutions, phenolphthalein's pink color undergoes a rather slow fading reaction and becomes completely colorless above 13.0 pH. The rather slow fading reaction that produces the colorless InOH3− ion is sometimes used in classes for the study of reaction kinetics