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When metals react with oxygen they form metal oxides, and rust is iron oxide formed as iron oxidises in damp air. Free notes and 9 questions answered.
Metal Oxides and Oxidation Reactions is part of Reactivity of metals in GCSE AQA Higher Chemistry.
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When metals react with oxygen they form metal oxides, and rust is iron oxide formed as iron oxidises in damp air. Free notes and 9 questions answered.
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Use this lesson to stay inside Reactivity of metals while connecting the detail back to the wider Topic 4: Chemical changes topic.
Read the core explanations from Metal Oxides and Oxidation Reactions before testing yourself from memory.
Ever wondered why iron gates go rusty or why copper roofs turn green? It's all down to metals reacting with oxygen in the air. This isn't just about rust - it's a fundamental type of chemical reaction that affects every metal around us.
When metals meet oxygen, they don't sit there politely. They react to form completely new compounds called metal oxides. This process is happening right now to the metal objects around you - it is usually too slow to notice.
Picture a piece of magnesium ribbon. When you heat it in air, it burns with a brilliant white flame and produces a white powder. That powder isn't magnesium anymore - it's magnesium oxide, a completely different substance.
The general pattern is always the same: metal + oxygen → metal oxide. But here's what makes this special - we call this type of reaction oxidation because the metal is gaining oxygen.
If oxidation is gaining oxygen, then reduction must be the opposite - losing oxygen. This happens when we extract metals from their ores in industry.
Think about iron extraction. Iron ore contains iron oxide (Fe₂O₃). To get pure iron, we need to remove the oxygen - that's reduction. We use carbon monoxide to 'steal' the oxygen away from the iron oxide.
Here's the memory trick: OIL RIG - Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons). But for GCSE, remember to: oxidation = gain oxygen, reduction = lose oxygen.
Let's see how to write these reactions properly. The key is getting the formulae right and balancing the equation.
Worked example: Writing a Metal Oxidation Equation
Write the balanced equation for magnesium burning in oxygen.
Answer: 2Mg + O₂ → 2MgO
Notice how we needed 2 magnesium atoms to use up all the oxygen in one O₂ molecule. This is because each oxygen atom needs to pair with one magnesium atom to make MgO.
These reactions aren't just laboratory curiosities - they're happening all around us. Let's look at some examples you'll recognise.
Rusting: Iron slowly oxidises in damp air to form iron oxide (rust). The equation is: 4Fe + 3O₂ → 2Fe₂O₃. This is why cars rust and why iron needs protecting with paint or galvanising.
Copper roofs: Copper first oxidises, then reacts with carbon dioxide and moisture to form a green layer called verdigris (basic copper carbonate). This actually protects the copper underneath from further corrosion.
Burning fuels: When we burn petrol or gas, we're oxidising the fuel. The carbon in the fuel gains oxygen to form carbon dioxide.
Examiners love testing oxidation and reduction because students often get confused. Here's how to nail these questions every time.
Command word focus: If asked to 'explain why this is oxidation', you must mention that oxygen is being gained. If asked to 'describe what happens', focus on observations like colour changes and new products formed.
Exam precision note: In Metal Oxides and Oxidation Reactions - Metal oxides - Reactivity of metals, always identify the key chemical idea first, then link it to evidence, data, or an equation. A high-scoring GCSE answer names the particles involved, states what changes, and justifies the conclusion using correct scientific language. Where calculations are used, show each step with units and keep significant figures sensible. Finally, check that terminology matches AQA wording so your answer is unambiguous and mark-scheme friendly.
Oxidation of a metal means that oxygen is added and a metal oxide is formed. This can be recognised both from the word equation and from the observation that the product usually has a higher mass because oxygen from the air has combined with the metal.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Rust is iron oxide, formed when iron slowly oxidises in damp air. The equation is 4Fe + 3O₂ → 2Fe₂O₃, and rusting is an oxidation reaction because the iron gains oxygen.
Rusting is the slow oxidation of iron in damp air to form iron oxide: 4Fe + 3O₂ → 2Fe₂O₃. This is why iron needs protecting with paint or galvanising.
A metal oxide is a compound formed when a metal reacts with oxygen, containing metal atoms bonded to oxygen atoms. The general pattern is metal + oxygen → metal oxide; for example, magnesium burns in air to make magnesium oxide.
When metals react with oxygen they form metal oxides: metal + oxygen → metal oxide. This is oxidation because the metal gains oxygen; for example, magnesium burns with a brilliant white flame to form white magnesium oxide powder.
Iron can be protected from rusting with paint or by galvanising. These stop the iron slowly oxidising in damp air to form iron oxide, which is why cars rust if the iron is not protected.
When magnesium ribbon is heated in air, it burns with a brilliant white flame and produces a white powder, magnesium oxide. The magnesium gains oxygen, so it is oxidised: 2Mg + O₂ → 2MgO.
Copper roofs turn green because copper first oxidises, then reacts with carbon dioxide and moisture to form a green layer called verdigris (basic copper carbonate). This layer protects the copper underneath from further corrosion.
The balanced equation for magnesium burning in oxygen is 2Mg + O₂ → 2MgO. Two magnesium atoms are needed to use up both oxygen atoms in one O₂ molecule, giving 2 Mg and 2 O on each side.
Burning a fuel such as petrol or gas is an oxidation reaction, because the carbon in the fuel gains oxygen to form carbon dioxide. Oxidation is any reaction in which a substance gains oxygen.