* Phenolphthalein as an indicator: Phenolphthalein is an indicator, meaning it changes color in the presence of an acid or a base. It's a weak acid itself.
* Color change: In a basic solution like sodium hydroxide, phenolphthalein turns pink. This color change is a visual indication of the solution's pH.
* No new substance formation: The phenolphthalein molecules don't change their chemical structure when they come in contact with sodium hydroxide. They simply change their conformation, causing the color change.
In summary:
* The color change is a physical property change, not a chemical change.
* The phenolphthalein molecules remain the same, only their arrangement and energy levels change.
Therefore, adding phenolphthalein to sodium hydroxide is a physical change.
