Phenolphthalein is the best indicator to use in the titration of a weak acid with a strong base. Phenolphthalein is a colorless, weak acid with the chemical formula C20H14O4. It remains colorless in acidic solutions but when added to a strong base, it changes sharply at the equivalence point and dissociates to form pink anions. The formation of a pink color is a clear indication of the endpoint of titration.