The color change of a pH indicator is caused by the dissociation of the H⁺ ion from the indicator itself. Recall that pH indicators are not only natural dyes but also weak acids. The dissociation of the weak acid indicator causes the solution to change color.

Why does the indicator change color in a titration?

When the reaction is complete, that is, when there is no excess of acid or base but only the reaction products, that is called the endpoint of the titration. The indicator must change color at the pH which corresponds to that endpoint. The indicator changes color because of its own neutralization in the solution.

What is it called when the indicator changes color?

The equivalence point, or stoichiometric point, of a chemical reaction is the point at which chemically equivalent quantities of reactants have been mixed. ... The endpoint (related to, but not the same as the equivalence point) refers to the point at which the indicator changes color in a colorimetric titration.