What is the purpose of adding phenolphthalein to your erlenmeyer flask prior to starting a titration?
a. the phenolphthalein acts as a color changing indicator to signal the endpoint of the reaction.
b. the phenolphthalein will change color once we have added the correct amount of base to our acid.
c. the phenolphthalein acts as an acid in the neutralization reaction.
d. the phenolphthalein acts as a base in the neutralization reaction.

a. The phenolphthalein acts as a color changing indicator to signal the endpoint of the reaction.

Explanation:

Phenolphthalein is an organic substance with chemical formula .

It is a substance commonly used in acid-base titrations to indicate the end point in the titration because phenolphthalein is colorless in acidic solutions but turns a purplish-pink color in basic solutions.

In this way it helps visually to notice when the final point of the titration has been reached.