An indicator is a chemical substance used in titrations to signal the endpoint of the reaction between the titrant and the analyte.
The function of an indicator in a titration is to change color when the solution being titrated has reached the equivalence point. This is important because the endpoint or equivalence point of a titration is the point at which the moles of the titrant added are stoichiometrically equal to the moles of the substance being titrated.
The purpose of using an indicator in a titration is to make it easier to detect the endpoint. The endpoint is often where the change of color occurs, signaling the reaction has come to completion.
Different indicators will change color at different pHs and each indicator has an associated pH range over which it changes color. The choice of indicator to use depends on the nature of the substance being titrated, as well as the titrant being used and the desired accuracy and precision of the results.
Overall, indicators are important to ensure accurate and precise results in a titration by signaling when the reaction has reached completion.