How does phenolphthalein change with pH?

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Detailed Solution

Phenolphthalein is a chemical indicator used to determine whether a solution is acidic or basic. It changes color depending on the pH level of the solution.

Color Behavior

Acidic to Neutral (pH below 8.2): Phenolphthalein is colorless in this range because the molecule remains in its lactone form (a closed structure).
Basic (pH 8.2 to 13): Phenolphthalein turns pink or magenta. This happens when the molecule loses a hydrogen ion (deprotonation), causing a structural change that creates a colored quinoid form.
Strongly Basic (pH above 13): The pink color disappears and the solution becomes colorless again due to another structural change in the molecule.

Use in Experiments

Because of these clear color changes, phenolphthalein is widely used as a pH indicator in titrations, especially when working with strong bases.

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