Oxidation — Chemistry, 11–13 years
Oxidation is a chemical change in which a substance combines with oxygen or loses electrons. It can be rapid, like burning, or slow, like rusting.
What oxidation changes
In everyday chemistry, oxidation often means a substance reacting with oxygen. Iron can slowly become rust, and wood can rapidly become ash and gases when it burns. More generally, chemists also use oxidation for the loss of electrons, even when oxygen is not present.
Why oxidation is one idea
Rusting and burning look very different, so it is tempting to treat them as unrelated. Chemists wanted one idea for the common change: oxygen or another substance takes electrons from the material. This helps explain why both processes can damage materials, release energy or create entirely new substances.
Why iron rusts
Leave a clean iron nail in moist air for several days. Water helps oxygen reach the iron, and the iron atoms lose electrons as they react; oxygen and water become involved in forming hydrated iron oxides, called rust. The nail’s surface changes colour and becomes flaky, so this is a chemical change, not just wet iron.
Not every colour change is oxidation
A colour change can be a clue, but it does not prove oxidation. A dye may change colour when mixed or lit, and an indicator changes colour because of a reaction with acidity. It is reasonable to notice colour first; the safer question is whether a new substance has formed and what particles changed.
Protecting materials
Cars, bridges and tools are protected from oxidation with paint, oil, coatings or metals such as zinc. These layers keep water and oxygen away from iron. Oxidation is also useful: batteries use controlled electron-transfer reactions to produce electrical energy, so the same broad idea can harm or help depending on how it is managed.
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