In acid-base titrations the amount of the substance is determined by titrating it against a standard solution of acid or base. The chemical reaction involved in acid-base titration is called neutralization reaction.

To know the end point or the neutralization point, an indicator is used.

Common indicators used are organic compounds.

Indicator                                      Colour in                            Colour in

Basic Medium               Acidic Medium

Phenolphthalein                                  Pink                             Colourless

Methyl orange                                     Yellow                       Pink or red

Selection of indicator is made according to the solutions used for titration.

For strong acid and strong alkali titration phenolphthalein is the best choice.

For strong acid and weak alkali titration methyl orange suits the best.

Weak acid and strong alkali titrations phenolphthalein is most suitable.