Final answer:
Phenolphthalein is the indicator used to monitor pH changes in this lab, as it changes color sharply at the equivalence point of a titration, especially in strong acid-strong base reactions.
Step-by-step explanation:
The indicator used in this lab to monitor the pH change is phenolphthalein. Phenolphthalein is one of several acid-base indicators commonly used to signal the endpoint of a titration by a color change. When the solution is acidic or neutral, phenolphthalein is colorless, but it turns pink or red as the solution becomes basic, with a pH greater than 8.3. The sharp color change from colorless to pink at the equivalence point makes phenolphthalein particularly useful for titrations involving strong acids and strong bases, where the equivalence point occurs at a relatively high pH.