Reduction Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Reduction.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

The gain of electrons by an atom, ion, or molecule, decreasing its oxidation state.

Grabbing electrons. The charge gets 'reduced' (becomes more negative).

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: OIL RIG: Reduction Is Gain of electrons — always paired with oxidation in a redox reaction.

Common stuck point: Reduction and oxidation always happen together—electrons have to go somewhere.

Worked Examples

Example 1

easy
In the reaction 2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}, identify which species is reduced.

Solution

  1. 1
    Oxygen goes from oxidation state 0 (in \text{O}_2) to -2 (in MgO).
  2. 2
    A decrease in oxidation number means the species has gained electrons.
  3. 3
    Therefore, \text{O}_2 is reduced: \text{O}_2 + 4e^- \rightarrow 2\text{O}^{2-}.

Answer

\text{O}_2\text{ is reduced (0 → -2)}
Reduction is the gain of electrons (RIG in OIL RIG). The substance that is reduced is the oxidizing agent because it takes electrons from the other reactant.

Example 2

medium
In a blast furnace, iron ore is reduced: \text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2. Identify the reducing agent.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
In the reaction \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu}, is copper being oxidized or reduced?

Example 2

medium
In the reaction \text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O}, which substance is reduced?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

electronion