Question

How does one ascertain that a chemical reaction has happened when NaOH is added to phenolphthalein solution?

Answer 1

Phenolphthalein:

1. Phenolphthalein is an indicator.
2. It is a chemical which changes its color depending on whether it meets an acid or a base.
3. It turns Pink/Purple if it meets something basic, such as Ammonia(${\mathrm{NH}}_3$); it stays colorless if it meets an acid like Hydrochloric acid ($\mathrm{HCl}$) or a neutral substance like water.
4. The Sodium hydroxide ($\mathrm{NaOH}$), which is a base, when mixed with Phenolphthalein, turns the solution pink.

Therefore, by seeing the change in color of the solution(Pink/Purple), one can ascertain that a chemical reaction has happened when $\left(\mathrm{NaOH}\right)$ is added to phenolphthalein solution.