Metal Oxides
Revise Metal Oxides for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Metals react with oxygen to form metal oxides; oxidation is the gain of oxygen and reduction is the loss of oxygen.
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Topic overview
When metals react with oxygen they form metal oxides. This is an oxidation reaction, because oxygen is gained.
The general equation is metal + oxygen → metal oxide. Magnesium burns with a brilliant white flame to form white magnesium oxide, and copper heated in air forms black copper oxide.
Oxidation and reduction are opposites. Oxidation is the gain of oxygen; reduction is the loss of oxygen. When a metal oxide is reduced back to the metal, the oxygen is removed — which is exactly what happens during metal extraction.
Revision notes
Forming metal oxides
Metal + oxygen → metal oxide.
Magnesium + oxygen → magnesium oxide. Copper + oxygen → copper oxide. The more reactive the metal, the more vigorously it reacts with oxygen.
Oxidation and reduction in terms of oxygen
Oxidation is the gain of oxygen. Reduction is the loss of oxygen.
When magnesium forms magnesium oxide it has been oxidised. When copper oxide is heated with carbon and the copper is released, the copper oxide has been reduced.
Linking to extraction
Metals found as oxides in the Earth must be reduced to obtain the pure metal.
This is why the terms matter: extraction is a reduction reaction, and understanding oxidation in terms of oxygen is the foundation for it.
Key points
- Metal + oxygen → metal oxide.
- Forming a metal oxide is oxidation.
- Oxidation is the gain of oxygen.
- Reduction is the loss of oxygen.
- Magnesium oxide is white.
- Copper oxide is black.
Worked examples
Example 1
Write the word equation for magnesium reacting with oxygen. [2 marks]
Model answer
Magnesium + oxygen → magnesium oxide. Correct reactants (1 mark). Correct product (1 mark).
Example 2
Explain why the reaction of a metal with oxygen is described as oxidation. [2 marks]
Model answer
The metal gains oxygen during the reaction (1 mark), and oxidation is defined as the gain of oxygen (1 mark).
Example 3
Copper oxide is heated with carbon and copper is produced. Explain what has happened to the copper oxide. [2 marks]
Model answer
The copper oxide has lost its oxygen to the carbon (1 mark), so it has been reduced (1 mark).
Common mistakes
Saying oxidation is the loss of oxygen.
Oxidation is the GAIN of oxygen; reduction is the loss.
Forgetting to name the product correctly.
The product is a metal oxide, named after the metal.
Confusing which substance is reduced.
The substance that loses oxygen is reduced.
Saying all metals react equally with oxygen.
More reactive metals react more vigorously.
Exam tips
- Learn oxidation as gain of oxygen and reduction as loss.
- Write the general equation before substituting names.
- Identify which substance gains and which loses oxygen.
- Link this topic to metal extraction.
Key terms
- Oxidation
- The gain of oxygen in a reaction.
- Reduction
- The loss of oxygen in a reaction.
- Metal oxide
- A compound of a metal and oxygen.
- Oxidise
- To cause a substance to gain oxygen.
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Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.