Redox indicator

A redox indicator (also called an oxidation-reduction indicator) is an indicator which undergoes a definite color change at a specific electrode potential.

The requirement for fast and reversible color change means that the oxidation-reduction equilibrium for an indicator redox system needs to be established very quickly. Therefore, only a few classes of organic redox systems can be used for indicator purposes.

There are two common types of redox indicators:

Sometimes colored inorganic oxidants or reductants (Ex. Potassium permanganate, Potassium dichromate) are also incorrectly called redox indicators. They can’t be classified as true redox indicators because of their irreversibility.

Almost all redox indicators with true organic redox systems involve a proton as a participant in their electrochemical reaction. Therefore, sometimes redox indicators are also divided into two general groups: independent or dependent on pH.

at pH=0

at pH=7

Oxidized form

Reduced form

or Sodium 2,6-Dichlorophenol-indophenol

(syn. Indigodisulfonic acid

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