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Why are chemical indicators added during some titrations?

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A strip of pH paper rests on the rim of a container holding a yellow liquid, with a color comparison chart and several unused pH strips nearby. — chemical analysis Strip of pH paper resting on specimen, with a comparison chart.

Chemical indicators are added during titrations to provide a visible signal—typically a change in color or the formation of turbidity—that marks the end point of a chemical reaction.12

In a titration, the goal is to reach the equivalence point, where the titrant and the sample have reacted in a precise, known proportion. Because this point is not always inherently visible, an indicator is used to signal that the reaction is complete. These substances are effective because they possess a characteristic transition range; they change their physical appearance when the concentration of a specific chemical species, the acidity, or the oxidizing strength of the solution reaches a critical threshold.12

Indicators are chosen to be highly sensitive, allowing them to signal the end point at or very close to the equivalence point. When used in very low concentrations, they do not influence the reaction conditions, ensuring the accuracy of the chemical analysis.12