The chemical substances which are used to indicate the end point during titration are called indicators.
Types of indicator:
- Self indicator: A substance is said to be self indicator if it itself acts as a indicator in 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 acts as indicator in acid base titration.
- External indicator: The indicator which are not added to the solution are called external indicator. Potassium Ferro cyanide K3[Fe(CN)6] can acts as external indicator during titration of ammonium or ferrous sulphate (FeSO4) with Potassium dichromate (K2Cr2O7).