Acid-Base Indicator

Definition

An acid-base indicator is a weak acid or weak base that exhibits color change as the concentration of hydrogen (H+) ions changes in an aqueous solution. They are used in titrations to signal when all reactants have reacted (equivalence point).

Analogy

Acid-base indicators are like traffic lights for chemists! Just as traffic lights use colors to tell drivers when to go, stop, or slow down, indicators use color to tell chemists when a reaction has reached its endpoint.

Related terms

pH: A measure of the hydrogen ion concentration in a solution; it indicates the acidity or alkalinity of a solution.

Titration: A technique where a solution of known concentration is used to determine the concentration of an unknown solution.

Equivalence point: The point in a titration at which enough titrant has been added to react exactly with the substance in solution being titrated.