Edexcel IGCSE Chemistry · Spec 2.22C-2.24C
Extraction of Metals
How metals are extracted from their ores, linked to the reactivity series.
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Extraction of Metals
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Explained
Extracting metals, and why the method depends on reactivity
Most metals are not found as the pure element. They are locked into compounds called ores, usually oxides, and extracting the metal means removing the oxygen or supplying electrons. Which method works depends entirely on where the metal sits in the reactivity series relative to carbon.
Metals below carbon
Zinc, iron, copper and the metals below them can be extracted by heating their oxide with carbon. Carbon is more reactive, so it takes the oxygen from the metal oxide.
The metal oxide loses oxygen, so it is reduced. The carbon gains oxygen, so it is oxidised. Both happen together, which makes this a redox reaction, and saying so is often worth a mark in itself.
Iron is extracted this way in a blast furnace, using coke as the source of carbon.
Metals above carbon
Aluminium, magnesium, calcium, sodium, lithium and potassium cannot be extracted with carbon, because carbon is less reactive than they are and cannot take the oxygen away from them.
These metals are extracted by electrolysis instead. Electricity supplies the electrons that the metal ions need in order to become metal atoms, which is reduction by a different route.
Electrolysis is far more expensive, because melting the compound and passing a large current through it both take a great deal of energy. That cost is the reason aluminium was once more valuable than gold, and the reason recycling it saves so much.
Metals below hydrogen
Gold and silver are so unreactive that they occur naturally as the metal itself. No extraction is needed, only physical separation from the rock around them.
What examiners say about this topic
Principal examiner reports for Edexcel International GCSE Chemistry record a precise error. Many candidates correctly identified electrolysis as the method of extraction, but then lost the mark by referring to the electrolysis of aqueous sodium chloride.
Extraction requires the molten compound, not a solution. In a solution the water is also present and is discharged in preference to a reactive metal, so no metal is produced. Write molten, and say so explicitly.
Aluminium in more detail
Aluminium comes from bauxite, which is purified to aluminium oxide. The oxide is dissolved in molten cryolite, which lowers the melting point and therefore lowers the energy needed and the cost.
Aluminium forms at the negative electrode, because the positive aluminium ions are attracted there and gain electrons. Oxygen forms at the positive electrode, where it reacts with the carbon electrodes, so those burn away and must be replaced periodically. That replacement is a standard question and the answer is that reaction.
Spec 2.22C-2.24C
What you need to know
- Link the extraction method to reactivity
- Describe extraction by reduction with carbon
- Explain why reactive metals need electrolysis
Active recall
Quick check
Answer each question before opening the answer.
How does a metal's reactivity decide how it is extracted?
Metals less reactive than carbon are extracted by reduction with carbon; metals more reactive than carbon are extracted by electrolysis.
Why is gold found as the pure metal in the ground?
It is very unreactive, so it does not react to form compounds.
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