An indicator was used to test a water solution with a pH of 12. Which indicator color would be observed?

An indicator was used to test a water solution with a pH of 12. Which indicator color would be observed?

• A. Colorless phenolphthalein
• B. Red litmus
• C. Pink phenolphthalein
• D. Colorless litmus

Answer: (C)

Indicators change color at specific pH ranges to show whether a solution is acidic or basic. A solution with pH 12 is strongly basic, so the indicator that responds to base by turning color will show that color. Phenolphthalein becomes pink once the pH is above about 8.2 and becomes a vivid pink in strongly basic solutions like pH 12. So the observed color for this indicator at pH 12 is pink. Red litmus would turn blue in a basic solution, not pink, so that option doesn’t match. Litmus paper in a basic solution is blue rather than colorless, and phenolphthalein would not be colorless at such a high pH.

Indicators change color at specific pH ranges to show whether a solution is acidic or basic. A solution with pH 12 is strongly basic, so the indicator that responds to base by turning color will show that color.

Phenolphthalein becomes pink once the pH is above about 8.2 and becomes a vivid pink in strongly basic solutions like pH 12. So the observed color for this indicator at pH 12 is pink.

Red litmus would turn blue in a basic solution, not pink, so that option doesn’t match. Litmus paper in a basic solution is blue rather than colorless, and phenolphthalein would not be colorless at such a high pH.