What is the color change signal for the endpoint when using phenolphthalein indicator in a titration?

• A. Pink to colorless
• B. Colorless to pink around pH 8.2
• C. Yellow to blue
• D. Red to green

Answer: (B)

Phenolphthalein signals endpoint by a pH-driven color change: it stays colorless in acidic solutions and turns pink as the solution becomes basic, with the transition occurring around pH 8.2. In a titration, as you add base to the acid, the solution is initially colorless; once the equivalence point is passed and the pH rises above about 8.2, the indicator changes to pink and that pink color signals you’ve reached the endpoint. This matches the color change from colorless to pink around pH 8.2.