Oxidation and Reduction in Terms of Electrons and Oxygen — AQA GCSE Chemistry
Oxidation and reduction can be defined in two ways: in terms of oxygen, and in terms of electrons.
In terms of oxygen
- Oxidation is the gain of oxygen.
- Reduction is the loss of oxygen.
For example, when copper oxide reacts with carbon: 2CuO + C → 2Cu + CO₂ The copper oxide is reduced (loses oxygen) and the carbon is oxidised (gains oxygen).
In terms of electrons (Higher Tier)
- Oxidation Is Loss of electrons.
- Reduction Is Gain of electrons.
Remember the mnemonic OIL RIG.
For example, when magnesium reacts: Mg → Mg²⁺ + 2e⁻ (magnesium is oxidised — it loses electrons).
Redox reactions
A reaction where both oxidation and reduction happen is a redox reaction. One species loses electrons (oxidised) while another gains them (reduced) — the two always happen together.
Displacement reactions and the extraction of metals by reduction are good examples of redox reactions.
Exam tips
- Oxygen definition: oxidation = gain of oxygen, reduction = loss of oxygen.
- Electron definition: use OIL RIG (Oxidation Is Loss, Reduction Is Gain).
- In a redox reaction, oxidation and reduction occur together.
- Be able to identify which substance is oxidised and which is reduced.