A reducing agent (or reductant) is a substance that donates electrons to another substance, causing that other substance to be reduced (gain electrons). At the same time, the reducing agent itself is oxidised (loses electrons).
Think of it like a generous friend who gives away their candies (electrons) to help another friend get a candy (be reduced). The generous friend ends up with fewer candies (is oxidised).
In chemical notation: \$e^-\$ is the electron that is transferred.
| Reducing Agent | Oxidised Form | Typical Reaction |
|---|---|---|
| Na (sodium) | Na⁺ | \$2\text{Na} + 2\text{H}2\text{O} \rightarrow 2\text{NaOH} + \text{H}2\$ |
| H₂ (hydrogen gas) | H⁺ | \$2\text{H}2 + \text{O}2 \rightarrow 2\text{H}_2\text{O}\$ |
| C (carbon) | CO₂ | \$C + \text{O}2 \rightarrow \text{CO}2\$ |
🔁 Remember: Reducing agent = electron donor = oxidised in the reaction.
When you see a redox reaction, look for the species that changes its oxidation state from lower to higher. That species is the reducing agent. Write the oxidation numbers before and after to confirm.
Use the mnemonic “LEO the lion says GER”:
🧪 Practise balancing a few redox equations to get comfortable.