Oxidising and Reducing Agents
An oxidising agent oxidises another substance and is itself reduced (gains electrons, oxidation state decreases). A reducing agent reduces another substance and is itself oxidised (loses electrons, oxidation state increases).
Key Definitions
| Term | What It Does | What Happens to It |
|---|---|---|
| Oxidising agent | Causes oxidation in another species | Gets reduced (gains e-) |
| Reducing agent | Causes reduction in another species | Gets oxidised (loses e-) |
Example: Halogen Displacement
Cl2(aq) + 2Br-(aq) → 2Cl-(aq) + Br2(aq)
Identifying Agents in Halogen Reactions
In halogen displacement \(\text{Cl}_2 + 2\text{Br}^- \rightarrow 2\text{Cl}^- + \text{Br}_2\):
- \(\text{Cl}_2\) is reduced (\(0 \rightarrow -1\)) → oxidising agent.
- \(\text{Br}^-\) is oxidised (\(-1 \rightarrow 0\)) → reducing agent.
Writing Half-Equations
Constructing Oxidation and Reduction Half-Equations
Oxidation: \(2\text{Br}^- \rightarrow \text{Br}_2 + 2\text{e}^-\)
Reduction: \(\text{Cl}_2 + 2\text{e}^- \rightarrow 2\text{Cl}^-\)
Naming the Full Reagent Species
When asked to name an oxidising or reducing agent, always state the entire compound or ionic species (e.g. \(\text{KMnO}_4\) or \(\text{MnO}_4^-\)), not just the central atom (\(\text{Mn}\)).
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