Metal Extraction By Reduction Of Oxides (AQA GCSE Combined Science: Synergy: Physical Sciences): Revision Note
Exam code: 8465
Written by: Stewart Hird
Updated on
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Metal oxides
Metals react with oxygen in the air to produce metal oxides
metal + oxygen ⟶ metal oxide
Oxidation is a reaction in which:
Oxygen is added to an element or a compound
Reduction is a reaction in which:
Oxygen is removed from a compound
A common example is the reaction of red-brown copper metal with oxygen to produce black copper oxide:
copper + oxygen ⟶ copper oxide
2Cu + O2 ⟶ 2CuO
In this reaction, copper metal has been oxidised since oxygen has been added to it
Examiner Tips and Tricks
When asked to identify oxidation or reduction in a reaction, look for:
Oxidation: the substance that gains oxygen
Reduction: the substance that loses oxygen
Make sure you name the specific substance, not just say "the reactant."
Extraction of metals & reduction
Most metals are found in the Earth's crust as compounds, known as ores
This means that the metal must be chemically extracted from the ore
Unreactive metals such as gold and platinum are found as the uncombined element
These metals are described as native
They can be mined directly
The position of a metal in the reactivity series determines the method of extraction
Metals extraction method table
Metal | Extraction method |
|---|---|
Most reactive | |
Potassium | Electrolysis |
Sodium | |
Lithium | |
Calcium | |
Magnesium | |
Aluminium | |
Carbon | |
Zinc | Reduction with carbon |
Iron | |
Copper | |
Silver | Found as pure elements |
Gold | |
Least reactive | |
Extraction by reduction with carbon
Metals that are less reactive than carbon can be extracted from their oxide ores by reduction with carbon
This is a relatively inexpensive process because:
Carbon is cheap
Carbon can also be a source of the heat required for the reaction
Carbon removes the oxygen from the metal oxide:
metal oxide + carbon ⟶ metal + carbon dioxide
For example, zinc (a non-ferrous metal) can be extracted from zinc oxide:
2ZnO + C ⟶ 2Zn + CO2
In this reaction:
Zinc oxide is reduced because it loses oxygen
Carbon is oxidised because it gains oxygen
Examiner Tips and Tricks
A common mistake with metal extraction questions is to say that the metal is reduced. This is not correct because the compound is losing oxygen, so it is the compound that is reduced.
For example, ZnO + C ⟶ Zn + CO:
Zinc metal does not lose oxygen, so it is not reduced
Zinc oxide loses oxygen, so zinc oxide is reduced
Worked Example
Copper can be extracted from copper(II) oxide, CuO.
State the method used to extract copper from copper(II) oxide and explain why this method is suitable.
[2]
Write a balanced equation for this extraction.
[1]
Identify which substance is reduced in this reaction. Explain your answer.
[2]
Answers
Reduction with carbon [1 mark]
This is because copper is less reactive than carbon, so carbon can remove the oxygen from copper(II) oxide [1 mark]2CuO + C ⟶ 2Cu + CO2 [1 mark]
Copper(II) oxide is reduced [1 mark]
It loses oxygen to form copper metal [1 mark]
Extraction by electrolysis
Metals that are more reactive than carbon cannot be reduced by carbon
They are extracted by electrolysis
This is an expensive process because it requires large amounts of electricity
Worked Example
Explain why iron is not extracted by electrolysis.
[1]
Answer
Iron is not extracted by electrolysis because it is below carbon in the reactivity series [1 mark]
Examiner Tips and Tricks
You may be asked to explain why some metals are extracted by carbon reduction and others by electrolysis. The answer always comes back to the reactivity series!
If the metal is more reactive than carbon, carbon cannot remove the oxygen from its ore, so electrolysis is needed instead.
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