Question

The pink colour of phenolphthalein in alkaline medium is due to

Answer 1

Well, you could call it the phenolphthalein ion (anion), or maybe the α-(p)-hydroxyphenyl)-α-(4-oxo-2,5-cyclohexadien-1-ylidene)-o-toluate ion. At neutral pH, phenolphthalein has two phenolic (hydroxyphenyl) rings, and a cyclic ester (lactone). At moderately alkaline pH’s the lactone opens up, forming a carboxylate group, and one of the phenol rings deprotonates, leaving a phenolate. This doubly negative ion is the species responsible for the pink color. At even more alkaline pH (above 13), the second phenol deprotonates and the pink color disappears

Answer 2

Answer:

here's the answer:-

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 in equilibrium shifts to the right, leading to more ionization as H+ ions are removed.

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