<Tr> <Td_colspan="2"> Infobox references </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> </Tr> <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 . It belongs to class of dyes known as Pthalein dyes . </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>

What is the colour of phenolphthalein in hcl acid