Chemistry 12 · Chemistry · Lesson 6.1
Oxidation-reduction
- Level
- Grade 12
- Reading time
- 11 min reading
- Review
- Last reviewed 2026-09-03
- Standard
- Accuracy standard
- Errata
Abstract
Oxidation numbers and identifying redox.
What is oxidation and reduction (redox)?
Short answer
Oxidation and reduction are paired processes involving the transfer of electrons. Oxidation is the loss of electrons (its oxidation number increases); reduction is the gain of electrons (its oxidation number decreases). They always occur together in a redox reaction — the substance oxidized gives electrons to the substance reduced. A common memory aid is OIL RIG: Oxidation Is Loss, Reduction Is Gain.
Concept preview
What you will be able to do
- 01Assign oxidation numbers using the rules
- 02Identify what is oxidised and reduced
- 03Identify the oxidizing and reducing agents
The words oxidation and reduction once referred only to reactions with oxygen — a metal 'oxidised' when it gained oxygen and was 'reduced' when the oxygen was removed. Chemists later realised that the essential event is not oxygen at all, but the transfer of electrons. The modern definitions are: oxidation is the loss of electrons, and reduction is the gain of electrons. Because electrons must go somewhere, oxidation and reduction always happen together — a reaction in which they occur is called a redox reaction.
School Plan
Oxidation-reduction
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Related topics
Frequently asked questions
- What does OIL RIG mean?
- Oxidation Is Loss of electrons, Reduction Is Gain of electrons — a mnemonic for the direction of electron transfer.
- What is an oxidizing agent?
- The substance that gains electrons (is reduced) and thereby causes another substance to be oxidized.