Redox indicator

A redox indicator (also called an oxidation-reduction indicator) is an indicator which undergoes a definite color change at a specific <a href="/facts/Electrode_potential/LfPpMt0u">electrode potential</a>.
The requirement for fast and reversible color change means that the oxidation-reduction <a href="/facts/Chemical_equilibrium/y8ToYXHp">equilibrium</a> for an indicator <a href="/facts/Redox_system/Pyd5RVcj">redox system</a> 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 classes of redox indicators:

<ul><li><a href="/facts/Metal_complex/1tCyeQUm">metal complexes</a> of <a href="/facts/Phenanthroline/WAKnx70S">phenanthroline</a> and <a href="/facts/Bipyridine/C2pcpnlb">bipyridine</a>. In these systems, the metal changes oxidation state.</li>
<li>organic redox systems such as <a href="/facts/Methylene_blue/NIo9Xaag">methylene blue</a>. In these systems, a proton participates in the redox reaction. Therefore, sometimes redox indicators are also divided into two general groups: independent or dependent on <a href="/facts/PH/RnSv8D7y">pH</a>.</li></ul>
The most common redox indicator are <a href="/facts/Organic_compounds/gqCNaN45">organic compounds</a>.
Redox Indicator example:
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.

Redox indicator open-in-new

Redox indicator