pH Indicator Definition

Red cabbage juice can be used to test the pH of common household chemicals.
Red cabbage juice can be used as a pH indicator of common household chemicals. From left to right, the colors result from lemon juice, natural red cabbage juice, ammonia, and laundry detergent. Anne Helmenstine

Definition: A pH indicator is a compound that changes color in solution over a narrow range of pH values.

Also Known As: acid-base indicator

Examples: Methyl red is a pH indicator used to identify pH values between 4.4 and 6.2.
Bromocresol green is a pH indicator used to identify pH values between 3.8 and 5.4.