Indicator: definition in chemistry
Indicator: A substance that changes color to show a change in conditions, most often whether a solution is acidic or basic.
Most acid–base indicators are weak acids whose acid and base forms have different colors, so the color depends on the pH. Each indicator changes color over its own pH range, which is why chemists choose one that changes near the expected end point of a titration. Universal indicator is a mixture of several dyes that gives a range of colors across the whole pH scale.
Examples
- Litmus — red in acid, blue in base
- Phenolphthalein — colorless in acid, pink above about pH 8.2
- Methyl orange — red below pH 3.1, yellow above pH 4.4
- Red cabbage juice — a homemade indicator that changes from red to green