How do you use a pH indicator in titrations?

In titrations, a pH indicator is used to determine the endpoint by changing colour when the solution becomes neutral.

In a titration, a solution of known concentration (the titrant) is used to determine the concentration of an unknown solution (the analyte). The pH indicator is added to the analyte at the start of the titration. The titrant is then added slowly to the analyte while stirring until the indicator changes colour. This colour change indicates that the solution has reached the endpoint, or neutrality, which is the point at which the amount of titrant added is stoichiometrically equivalent to the amount of analyte present.

The choice of pH indicator is crucial as different indicators change colour at different pH levels. For example, litmus changes from red to blue around pH 7, while phenolphthalein changes from colourless to pink around pH 8.2. Therefore, the choice of indicator depends on the pH at the equivalence point of the titration.

The indicator should be chosen such that the colour change occurs at the pH of the equivalence point. For example, if the equivalence point of a titration is expected to be around pH 7, litmus would be a suitable indicator. If the equivalence point is expected to be around pH 8.2, phenolphthalein would be more suitable.

In some cases, a pH meter can be used instead of an indicator. This gives a more precise measurement of the pH at the equivalence point, but it is more time-consuming and requires more expensive equipment. However, for most GCSE level experiments, a suitable pH indicator will provide sufficiently accurate results.