Redox
Redox
- Oxidation and reduction always happen together — a redox reaction.
- Three ways to describe them:
- Oxygen: oxidation = gain of oxygen; reduction = loss of oxygen.
- Electrons: oxidation = loss of electrons; reduction = gain of electrons.
- Oxidation number: up in oxidation, down in reduction.
- Memory aid: OIL RIG — Oxidation Is Loss, Reduction Is Gain (of electrons).
Practice
In terms of electrons, oxidation is:
OIL RIG: Oxidation Is Loss of electrons, Reduction Is Gain.
Oxidation number rules
- An uncombined element = 0.
- A single-atom ion = its charge (so $\text{Na}^{+}$ is $+1$).
- The oxidation numbers in a compound add up to 0; in an ion they add up to the charge.
Agents and colour tests
- An oxidising agent oxidises another substance (and is itself reduced).
- A reducing agent reduces another (and is itself oxidised).
- Acidified potassium manganate(VII) is purple → fades to colourless when reduced.
- Potassium iodide (colourless) → red-brown iodine when oxidised.
Practice
An oxidising agent:
An oxidising agent oxidises something else, so it gains electrons and is itself reduced.
Practice
Acidified potassium manganate(VII) acting as an oxidising agent changes from:
As it is reduced, the purple manganate(VII) fades to colourless.
You've got it
Key idea
- redox: oxidation + reduction together; OIL RIG (Oxidation Is Loss, Reduction Is Gain of electrons)
- oxidising agent is itself reduced; reducing agent is itself oxidised
- colour tests: manganate(VII) purple → colourless; iodide → red-brown iodine