Redox Indicator Definition

This is the chemical structure of 2,2'-bipyridine.
This is the chemical structure of 2,2'-bipyridine, a redox indicator. Brian Derksen/PD

Definition: A redox indicator is an indicator compound that changes color at specific potential differences.

A redox indicator compound must have a reduced and oxidized form with different colors and the redox process must be reversible.

Examples: The molecule 2,2'-Bipyridine is a redox indicator. In solution, it changes from light blue to red at an electrode potential of 0.97 V.