Acid-Base Titration Indicators
- An acid-base indicator is a dye that changes colour when pH changes.
- An indicator is actually a Brønsted-Lowry conjugate acid-base pair in which the acid is a different colour to the base.
- The endpoint of a titration is when the indicator changes colour during a titration.
- The equivalence point1 of an acid-base reaction is when the amount of acid and of base is just sufficient to cause complete consumption of both the acid and the base.
At the equivalence point neither the acid nor the base is in excess.
At the equivalence point neither the acid nor the base is the limiting reagent.
- The pH of the solution at the equivalence point depends on the relative strength of the acid and strength of the base used in the titration.
- An appropriate indicator for an acid-base titration will change colour at the same pH as the equivalence point of the acid-base reaction.
That is, the endpoint of the titration as indicated by the indicator must be the same as the equivalence point of the acid-base reaction.