<P> Phenolphthalein is a chemical compound with the formula C H O and is often written as "HIn" or "phph" in shorthand notation . Phenolphthalein is often used as an indicator in acid--base titrations . For this application, it turns colorless in acidic solutions and pink in basic solutions . </P> <P> Phenolphthalein is slightly soluble in water and usually is dissolved in alcohols for use in experiments . It is a weak acid, which can lose H ions in solution . The phenolphthalein molecule is colorless, and the phenolphthalein ion is pink . When a base is added to the phenolphthalein, the molecule ⇌ ions equilibrium shifts to the right, leading to more ionization as H ions are removed . This is predicted by Le Chatelier's principle . </P> <P> Phenolphthalein's common use is as an indicator in acid - base titrations . It also serves as a component of universal indicator, together with methyl red, bromothymol blue, and thymol blue . </P> <P> Phenolphthalein adopts four different states in aqueous solution: Under very strongly acidic conditions, it exists in protonated form, providing an orange coloration . Between strongly acidic and slightly basic 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 In (OH) ion is sometimes used in classes for the study of reaction kinetics . </P>

When phenolphthalein is used as the indicator in a titration of an hcl