In a titration, what indicates the endpoint?

In a titration, the endpoint is indicated by a color change of an indicator. During the titration process, an indicator is used to signal when the reaction between the titrant and the analyte is complete. This is often manifested as a distinct color change that occurs at or near the equivalence point, where the amount of titrant added is stoichiometrically equivalent to the amount of the substance being analyzed.

This color change allows the person performing the titration to visually assess when to stop adding titrant. The choice of indicator depends on the pH range of the titration. For example, phenolphthalein is commonly used in acid-base titrations due to its clear transition between acidic and basic conditions.

While the completion of a chemical reaction is an essential part of titration, it is the observable change that the indicator provides that directly signifies reaching the endpoint for practical purposes. Other factors such as temperature change or the volume of titrant used do not directly point to the endpoint; these measurements may provide supplementary information but do not serve as a definitive visual cue like the color change does.