acid–base indicator

An acid–base indicator is a chemical substance that changes color depending on the acidity or alkalinity of a solution. It helps identify whether a solution is acidic (more hydrogen ions) or basic (fewer hydrogen ions). When added to a liquid, the indicator's color shifts at a specific pH level, providing a visual cue about the solution’s nature. For example, litmus paper turns red in acids and blue in bases. These indicators are essential in chemistry for testing and measuring pH levels accurately in various applications, from laboratory experiments to industrial processes.