Question

The colour of phenolphthalein in the pH range 8.0 – 9.8 is

• A. Pink
• B. Orange red
• C. Yellow
• D. Colourless

Answer 1

Answer:

A. Pink

• In the pH range of 8.0/8.2 to 9.8, phenolphthalein undergoes a transition from colorless to pink / magenta.

• Below pH 8.2: Colorless (Acidic to slightly basic environment)

• pH 8.2 – 9.8 / 10.0: Turns Pink / Magenta (Slightly basic to moderately basic environment)

• Above pH 10.0 / 12.0: Turns colorless again due to a structural transformation into a tri-anionic form in strongly alkaline environments