# Oxidation state and redox

Redox reactions move electrons. Oxidation is loss of electrons and reduction is gain. Oxidation state is the charge an atom would have if all bonds were ionic. Oxidation raises it, reduction lowers it.

Chemistry (university) · Part 04: Stoichiometry and reactions in solution · Card 8 of 9 · Last updated 2026-10-19

## Analogy

Passing a ball: the player who gives it away is oxidised, the player who catches it is reduced.

## Example

**Find Mn in MnO₄⁻**

O is −2, four O = −8
Total charge = −1
Mn + (−8) = −1
Mn = +7

## In practice

Rusting, burning, batteries and bleaching are all redox reactions.

## Practice

### Flashcards

- **What is the oxidation state of Mn in MnO₄⁻?** +7.
- **What does an oxidising agent do?** It takes electrons from another species and is itself reduced.

### Interview questions

**Balance the reaction of MnO₄⁻ with Fe²⁺ in acid and name the oxidising agent.**

- Write two half-reactions
- Balance O with H₂O and H with H⁺
- Match the electrons (5 for 1)
- MnO₄⁻ is the oxidising agent

## Questions people ask

### What do OIL RIG and LEO GER stand for?

These are memory aids. OIL RIG: Oxidation Is Loss, Reduction Is Gain, of electrons. LEO the lion says GER: Lose Electrons Oxidation, Gain Electrons Reduction. Both give the same rule: the species that loses electrons is oxidised, and the one that gains them is reduced.

### What are the oxidising and reducing agents?

The oxidising agent takes electrons and so is itself reduced. The reducing agent gives electrons and so is itself oxidised. In rusting, oxygen is the oxidising agent and iron is the reducing agent. The names describe the effect on the other substance.

## Related concepts

- [Balancing redox equations](https://studyvisually.com/learn/science/chemistry-university/chemistry-university-part-4/chemistry-university-part-4-concept-9)

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