Why do indicators change colour at convenient points during a titration?

Apr 30, 2017

An indicator molecule is a large organic dye whose acidic and basic forms have distinctive colours. Usually you can discriminate between the colours when there is only a 10-fold difference in the concentration of the acid versus the base. In a titration this usually corresponds to less than $0.01 \cdot m L$ of added titrant, and this is equivalent to less than $\text{1 drop}$ of titrant.