Phenolphthalein Solution 1% in Ethanol, 500ml, BENDOSEN

Phenolphthalein adopts at least four different states in aqueous solution as a result of pH changes.[3] Under strongly acidic conditions, it exists in protonated form (HIn+), providing an orange coloration. Between strongly acidic and slightly basic conditions, the lactone form (HIn) is colorless. The doubly deprotonated (In2-) phenolate form (the anion form of phenol) gives the familiar pink color. In strongly basic solutions, phenolphthalein is converted to its In(OH)3− form, and its pink color undergoes a rather slow fading reaction[citation needed] and becomes completely colorless above 13.0 pH.