Oxidation and reduction — Chemistry, 14–17 years
Many reactions involve electrons moving from one substance to another. Tracking that movement explains rust, batteries and why two reacting substances can change in opposite ways.
An electron handover
In a redox reaction, one substance loses electrons and another gains them. Oxidation means losing electrons; reduction means gaining them. They always happen together, because an electron that leaves one place must arrive somewhere else. The two substances are called a redox pair.
Why track electrons?
Some reactions were first described only by visible changes, such as a metal becoming coated or a flame fading. That language did not explain what connected these cases. Electron transfer links them with one idea and helps predict which substance will donate electrons and which will accept them.
Zinc and copper ions
Place zinc metal in a solution containing Cu²⁺ ions. Zinc atoms lose two electrons: Zn → Zn²⁺ + 2e⁻, so zinc is oxidised. Each Cu²⁺ ion gains two electrons: Cu²⁺ + 2e⁻ → Cu, so copper is reduced. Overall, zinc replaces copper in solution and solid copper appears.
The names point opposite ways
People often mix up oxidation and reduction because “oxidation” sounds as if oxygen must be present. That is a reasonable link: oxygen commonly causes oxidation in everyday examples. But the broader test is electron movement: oxidation is loss, reduction is gain, even when oxygen is absent.
Batteries and rust
A battery separates oxidation from reduction so electrons travel through a wire and provide electrical energy. Rust is a less controlled redox process: iron loses electrons while oxygen and water help form iron oxides. The same core idea can therefore power a device or slowly damage a bridge.
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