Question

Why does the phenolphthalein pink color at the end point disappear?

Answer 1

The color fades because carbon dioxide from the air dissolves in the solution. When this happens, carbonic acid (a very weak acid) is formed. ... Well, when doing a titration like you describe, drops of base solution are added to an acidic solution containing the indicatorphenolphthalein.
hope it will help you

Answer 2

Phenolphthalein's pink colour at the end point disappears because the reaction brings some changes in the molecular structure of the phenolphthalein molecule.

Explanation:

• Phenolphthalein is an indicator which is used to test whether the solution is acidic or basic.
• It is used in acid-base titrations to detect the endpoint that shows the completion of the reaction.
• It is colourless in acidic/neutral solutions and turns pink in basic solutions.
• The pink colour appears in the ionised state of the Phenolphthalein molecule when the base is added.
• When the titration is done such that the reaction between the acid and base is complete, at that point, the ionised molecule changes into a neutral molecule and the pink colour disappears.

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