- An indicator is a substance that undergoes a change when the endpoint of a titration is reached E.g.: acid indicators are used to single the end of acid-base titration.
- Indicators are organic weak acids or bases with complicated structures.
- The chemical substances which are used to indicate the endpoint during titration are called indicators.
Types of indicator:
Self-indicator: A substance is said to be self-indicator if it itself acts as an indicator in the titration. Example: KMnO4 acts as a self-indicator during the titration of Potassium permanganate (KMnO4) and oxalic acid (COOH)2.
Internal indicator: The indicator which is used within the solution is called internal indicator. Example: Methyl orange and phenolphthalein can act as an indicator in the acid-base titration.
External indicator: The indicator which is not added to the solution are called external indicator. Potassium Ferrocyanide K3[Fe(CN)6] can acts as external indicator during titration of ammonium or ferrous sulphate (FeSO4) with Potassium dichromate (K2Cr2O7).