Acid-base indicator

An acid-base indicator is a dye or mixture of dye that marks the end-point of the titration. The indicator has a sudden and obvious color change at the pH corresponding to the end-point of the titration. A good indicator must have the following properties:

  • The color change must be easily detected.
  • The color change must be rapid.
  • The indicator works by reacting with one (or both) of the solutions used in the titration, which is why the volume of indicator used should be small.
  • For accuracy, the pKin of an indicator must be close to the pH at the equivalence point of the reaction.

The logarithmic acid dissociation constant (pKin) determines the pH at which the indicator changes color (end-point).

Read more about various types of acid-base indicators here.