Here's what happens:
* Phenolphthalein in acidic solution: In acidic solutions, phenolphthalein exists in a colorless lactone form.
* Reaction with NaOH: When NaOH is added, the hydroxide ions (OH-) from NaOH react with the phenolphthalein molecule. The hydroxide ions remove a proton (H+) from the phenolphthalein molecule, causing it to deprotonate.
* Color change: This deprotonation results in the formation of a highly resonance-stabilized quinoid structure, which is pink in color.
Simplified Chemical Reaction:
* Phenolphthalein (colorless) + OH- (from NaOH) ⇌ Phenolphthalein anion (pink) + H2O
Important Notes:
* The reaction is an equilibrium reaction, meaning it can proceed in both directions.
* The color change is reversible. If you add an acid to the pink solution, the equilibrium shifts back towards the colorless form, and the solution turns colorless again.
* This reaction is the basis for using phenolphthalein as an indicator in acid-base titrations.
Let me know if you'd like a more detailed explanation or want to explore the structure of the molecules involved!
