Answer: Phenolphthalein was used as an indicator because it is colorless in neutral and acidic solutions and pink in basic solutions.
Step-by-step explanation:
Recall that in the lab we added enough of the base NaOH so that the indicator turned pink. Prior to the solution turning pink, the solution was acidic (HCl) → neutral. Furthermore, phenolphthalein is used as an indicator of basic solutions.
The equivalence/equilibrium point occurs at ph 7.
Phenolphthalein causes solutions to become pink around pH 8.2 (a basic pH). Therefore, we added slightly more NaOH than actually needed to neutralize the acid.