Written by the Fiveable Content Team • Last updated September 2025
Verified for the 2026 exam
Verified for the 2026 exam•Written by the Fiveable Content Team • Last updated September 2025
Definition
Phenolphthalein is a chemical compound often used as an indicator in titrations. It is colorless in acidic solutions and turns pink in basic solutions.
A substance that changes color depending on the pH of the solution it's in. Phenolphthalein is one type of acid-base indicator, just like how a traffic light is one type of road signal.
pH Scale: A measure of acidity or alkalinity of water soluble substances. It's like our "road map" that tells us what color our "traffic light" (phenolphthalein) should be.
Alkaline Solution (Basic Solution): A solution with a pH greater than 7. When phenolphthalein enters this territory, it turns pink - just like how a traffic light turns red to signal drivers to stop!