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How does a colour-changing indicator help find a titration end point?

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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.

A colour-changing indicator helps identify the end point of a titration by providing a visible signal that the reaction has reached or is very close to the equivalence point—the moment when the quantities of the reacting species are chemically equivalent.12

Because many chemical reactions do not produce a spontaneous colour change, a small amount of a chemical indicator is added to the analyte. These substances are designed to exist in different forms (such as acid/base or oxidized/reduced states) that possess distinct colours. As the titrant is added, the indicator remains in one state until the concentration of a specific chemical species reaches a critical threshold. At this transition range, the indicator shifts to its other form, resulting in a sharp, visible colour change.213

By observing this change, the analyst knows to stop adding the titrant. The volume added at this moment is recorded as the end point, which serves as a practical approximation for the equivalence point used in volumetric analysis calculations.12