Using Electrolysis to Extract Metals (AQA GCSE Chemistry): Revision Note
Extracting metals
Choosing methods for metal extraction
The position of the metal on the reactivity series determines the method of extraction
Higher placed metals (above carbon) have to be extracted using electrolysis as they are too reactive and cannot be reduced by carbon
Lower placed metals can be extracted by heating with carbon which reduces
Electrolysis is very expensive as large amounts of energy are required to melt the ores and produce the electrical current
The reactivity series of metals is shown below with the corresponding method of extraction
Extracting metals
Metal | Extraction method |
|---|---|
Most reactive | |
Potassium | Extracted by electrolysis of the molten chloride or oxide Large amounts of electricity are required, which makes this an expensive process |
Sodium | |
Lithium | |
Calcium | |
Magnesium | |
Aluminium | |
Zinc | Extracted by heating with a reducing agent such as carbon or carbon monoxide in a blast furnace A cheap process as carbon is cheap and can also be a source of heat |
Iron | |
Copper | |
Silver | Found as pure elements |
Gold | |
Least reactive | |
Examiner Tips and Tricks
Questions on this topic often ask you to explain why in some cases electrolysis is used and in other cases reduction by heating with carbon is used. Make sure you can explain when each process is used and why.
The extraction of aluminium
How is aluminium extracted?
Aluminium is a reactive metal, above carbon in the reactivity series
Its main ore, is bauxite, which contains aluminium oxide
Aluminium is higher in the reactivity series than carbon, so it cannot be extracted by reduction using carbon
Instead, aluminium is extracted by electrolysis
The electrolytic cell for extraction of aluminium
Diagram showing the extraction of aluminium by electrolysis
Bauxite is first purified to produce aluminium oxide, Al2O3
Aluminium oxide is then dissolved in molten cryolite
This is because aluminium oxide has a melting point of over 2000°C which would use a lot of energy and be very expensive
The resulting mixture has a lower melting point without interfering with the reaction
The mixture is placed in an electrolysis cell, made from steel, lined with graphite
The graphite lining acts as the negative electrode, with several large graphite blocks as the positive electrodes
Aluminium is produced at the cathode
Oxygen is produced At the anode
Why does the anode need to be replaced?
The carbon in the graphite anodes reacts with the oxygen produced to produce CO2
C (s) + O2 (g) → CO2 (g)
As a result the anode wears away and has to be replaced regularly
A lot of electricity is required for this process of extraction, this is a major expense
Examiner Tips and Tricks
Questions on this topic often ask you to explain why cryolite is used in the process so make sure you are able to explain its use, providing reasons for your answer.
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