AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
For example, copper can be obtained from solutions of copper compounds by…
Full specification wording
Alternative methods of extracting metals (HT only): For example, copper can be obtained from solutions of copper compounds by displacement using scrap iron or by electrolysis.
Copper is less reactive than iron, so iron can displace copper from a solution of a copper compound.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 7 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Copper is less reactive than iron, so iron can displace copper from a solution of a copper compound. If scrap iron is placed in copper sulfate solution, the iron atoms lose electrons and dissolve as iron ions, while copper ions gain electrons and form copper metal. The word equation is iron + copper sulfate → iron sulfate + copper, and the ionic equation is Fe + Cu²⁺ → Fe²⁺ + Cu. Scrap iron is cheap and often waste material, which makes this an economical method. Alternatively, electrolysis of a copper compound solution uses a direct current to reduce copper ions at the negative electrode, producing copper metal. Electrolysis can produce very pure copper and can be used when displacement is unsuitable, but it needs electrical energy. Both methods obtain copper from a solution of a copper compound rather than from copper ore directly.
What earns the marks
- Iron is more reactive than copper, so iron displaces copper from a solution of a copper compound.
- In displacement, iron atoms form iron ions and copper ions gain electrons to form copper atoms.
- The ionic equation Fe + Cu²⁺ → Fe²⁺ + Cu summarises the displacement reaction.
- Scrap iron is a cheap and readily available reducing agent, which is an economic advantage.
- Electrolysis of a copper compound solution reduces copper ions at the negative electrode to copper metal.
- Electrolysis requires electrical energy but can produce very pure copper.
Common mistakes and how to put them right
Writing that copper displaces iron from solution.
Put it right: Iron is more reactive, so iron displaces copper, not the reverse.
Confusing the direction of electron transfer in the ionic equation.
Put it right: Iron atoms lose electrons and copper ions gain electrons, as shown by Fe + Cu²⁺ → Fe²⁺ + Cu.
Stating that electrolysis works by displacement.
Put it right: Electrolysis uses electrical energy to bring about the reduction of copper ions, which is a different process from displacement by a more reactive metal.
Exam tips
- Quote the ionic equation with correct state symbols or ion charges when asked to explain the displacement.
- Compare the two methods in terms of cost, energy demand and purity of copper produced.
- Use the reactivity series to justify why iron, not silver, is chosen to displace copper.
Try the lesson
The start of the Alternative methods of extracting metals (HT only): For example, copper can be obtained from solutions of copper compounds by displacement using scrap iron or by electrolysis. lesson, made from checked teaching notes for this specification point.
Have a go first
Copper can be obtained from copper sulfate solution by adding scrap iron. What type of reaction takes place?
Listen
Copper is less reactive than iron, so iron can displace copper from a solution of a copper compound. If scrap iron is placed in copper sulfate solution, the iron atoms lose electrons and dissolve as iron ions, while copper ions gain electrons and form copper metal. The word equation is iron + copper sulfate → iron sulfate + copper, and the ionic equation is Fe + Cu²⁺ → Fe²⁺ + Cu. Scrap iron is cheap and often waste material, which makes this an economical method. Alternatively, electrolysis of a copper compound solution uses a direct current to reduce copper ions at the negative electrode, producing copper metal. Electrolysis can produce very pure copper and can be used when displacement is unsuitable, but it needs electrical energy. Both methods obtain copper from a solution of a copper compound rather than from copper ore directly. A strong answer earns marks for these points. Iron is more reactive than copper, so iron displaces copper from a solution of a copper compound. In displacement, iron atoms form iron ions and copper ions gain electrons to form copper atoms. The ionic equation Fe + Cu²⁺ → Fe²⁺ + Cu summarises the displacement reaction. Scrap iron is a cheap and readily available reducing agent, which is an economic advantage. A common slip: Writing that copper displaces iron from solution. Instead, iron is more reactive, so iron displaces copper, not the reverse. Exam tip: Quote the ionic equation with correct state symbols or ion charges when asked to explain the displacement.
Key words
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Displacement
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Redox and electron transfer
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Electrolysis of solutions
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Economic and environmental choices in metal extraction
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See every definition
- Displacement
- Iron is more reactive than copper, so iron displaces copper from a solution of a copper compound.
- Redox and electron transfer
- Iron atoms lose electrons and dissolve as iron ions, while copper ions gain electrons and form copper metal.
- Electrolysis of solutions
- A direct current is used to reduce copper ions at the negative electrode, producing copper metal.
- Economic and environmental choices in metal extraction
- Scrap iron is cheap and often waste material, which makes this an economical method, while electrolysis needs electrical energy.
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