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Electrolysis

Key Stage 3

Meaning

A diagram showing an experimental setup to decompose Copper Chloride.

Electrolysis is a process where compounds are decomposed by an electrical current.

About Electrolysis

Electrolysis can be used to extract metals from minerals when the metal is more reactive than Carbon.

Key Stage 4

Meaning

Electrolysis is a process in which an ionic compound is decomposed by passing an electrical current through it.

NB: Electrolysis is a GCSE Chemistry Required Practical: Electrolysis of a Solution

About Electrolysis

In electrolysis two electrodes (an anode and a cathode) are placed in either a molten or aqueous ionic compound.
Electrolysis cannot happen in solids because the ions vibrate around fixed positions in a solid and are not free to move.
The positive ions are attracted to the negative electrode (cathode) and the negative ions are attracted to the positive electrode (anode).
When the negative ions reach the anode they lose electrons to become atoms or neutral compounds.
When the positive ions reach the cathode they gain electrons to become atoms. However, in aqueous solution if the metal ions are more reactive than Hydrogen then Hydrogen gas will be produced.
To describe an electrolysis reaction half equations are used.

Examples

Balanced Symbol Equation 2Li2O(l) → 4Li(l) + O2(g) CuCl2(aq) → Cu(s) + Cl2(g) 2H2O(l) → 2H2(g) + O2(g)
Half Equation at cathode Li+ + e- → Li Cu+2(aq) + 2e- → Cu(s) 2H+(aq) + 2e- → H2(g)
Half Equation at anode 2O-2 → O2 + 4e- 2Cl-(aq) → Cl2(g) + 2e- 4OH- → 2H2O(l) + O2(g) + 4e-

Electrolysis of Molten Ionic Compounds

The electrolysis of molten ionic compounds decomposes those ionic compounds in a liquid state.
The ionic compound must be heated and melted before electrolysis.
Non-metal ionic elements or compounds will be collected at the anode where they lose their extra electrons.
Metal ions will be collected at the cathode where they gain electrons.
ElectrolysisCell.png
A diagram showing the electrolysis of a molten ionic compound in an electrolysis cell.

Electrolysis of Aqueous Ionic Compounds

The electrolysis of aqueous ionic compounds decomposes those ionic compounds in solution.
The electrolysis of aqueous ionic compounds will produce Hydrogen gas if the the metal elements is more reactive than Hydrogen.
Non-metal ionic elements or compounds will be collected at the anode where they lose their extra electrons.
Metal ions less reactive than Hydrogen will be collected at the cathode where they gain electrons.
Metal ions more reactive than Hydrogen will displace Hydrogen atoms in the water after gaining [[electrons at the cathode. This causes Hydrogen gas to collect at the cathode.

References

AQA

Electrolysis, extraction of copper, pages 200, GCSE Combined Science Trilogy 2, Hodder, AQA
Electrolysis, page 117, GCSE Chemistry, Hodder, AQA
Electrolysis, pages 102-111, GCSE Chemistry; Third Edition, Oxford University Press, AQA
Electrolysis, pages 132, 133, 236, GCSE Combined Science; The Revision Guide, CGP, AQA
Electrolysis, pages 141- 147, GCSE Combined Science Trilogy; Chemistry, CGP, AQA
Electrolysis, pages 166-172, GCSE Chemistry, CGP, AQA
Electrolysis, pages 218-19, GCSE Combined Science Trilogy 1, Hodder, AQA
Electrolysis, pages 58, 59, 109, GCSE Chemistry; The Revision Guide, CGP, AQA
Electrolysis, pages 83, 130-1, 154-5, 333, GCSE Chemistry; Student Book, Collins, AQA
Electrolysis; aqueous solutions, page 102, GCSE Chemistry; Third Edition, Oxford University Press, AQA
Electrolysis; cell, pages 158-9, GCSE Chemistry; Student Book, Collins, AQA
Electrolysis; half equations, page 256, GCSE Combined Science Trilogy 1, Hodder, AQA
Electrolysis; half equations, pages 289-91, GCSE Chemistry, Hodder, AQA
Electrolysis; metal extraction, pages 118-19, GCSE Chemistry, Hodder, AQA
Electrolysis; metal extraction, pages 220-1, GCSE Combined Science Trilogy 1, Hodder, AQA
Electrolysis; of aqueous ionic compounds, pages 119-21, GCSE Chemistry, Hodder, AQA
Electrolysis; of aqueous ionic compounds, pages 221-3, GCSE Combined Science Trilogy 1, Hodder, AQA
Electrolysis; of aqueous solutions with inert electrodes, pages 162-3, GCSE Chemistry; Student Book, Collins, AQA
Electrolysis; of aqueous solutions, pages 145, 146, GCSE Combined Science Trilogy; Chemistry, CGP, AQA
Electrolysis; of aqueous solutions, pages 160-1, GCSE Chemistry; Student Book, Collins, AQA
Electrolysis; of aqueous solutions, pages 170, 171, GCSE Chemistry, CGP, AQA
Electrolysis; of lead bromide, page 142, GCSE Combined Science Trilogy; Chemistry, CGP, AQA
Electrolysis; of lead bromide, page 167, GCSE Chemistry, CGP, AQA
Electrolysis; of molten ionic compounds, pages 117-18, GCSE Chemistry, Hodder, AQA
Electrolysis; of molten ionic compounds, pages 156-7, GCSE Chemistry; Student Book, Collins, AQA
Electrolysis; of molten ionic compounds, pages 219-20, GCSE Combined Science Trilogy 1, Hodder, AQA
Electrolysis; of sodium chloride, page 146, GCSE Combined Science Trilogy; Chemistry, CGP, AQA
Electrolysis; of sodium chloride, page 171, GCSE Chemistry, CGP, AQA

Edexcel

Electrolysis, page 224-225, GCSE Combined Science, Pearson Edexcel
Electrolysis, pages 110-112, 118, GCSE Combined Science; The Revision Guide, CGP, Edexcel
Electrolysis, pages 133-141, 157, 158, 182, GCSE Chemistry, CGP, Edexcel
Electrolysis, pages 48-50, 56, 64, 111, GCSE Chemistry; The Revision Guide, CGP, Edexcel
Electrolysis, pages 80-81, GCSE Chemistry, Pearson, Edexcel
Electrolysis; aqueous solutions, pages 136-140, GCSE Chemistry, CGP, Edexcel
Electrolysis; half equations, pages 134, 135, GCSE Chemistry, CGP, Edexcel
Electrolysis; molten ionic substances, pages 134, 141, GCSE Chemistry, CGP, Edexcel
Electrolysis; of copper sulfate, page 50, GCSE Chemistry; The Revision Guide, CGP, Edexcel
Electrolysis; of metal ores, pages 157, 158, GCSE Chemistry, CGP, Edexcel
Electrolysis; products, pages 228-229, GCSE Combined Science, Pearson Edexcel
Electrolysis; products, pages 84-85, GCSE Chemistry, Pearson, Edexcel
Electrolysis; salt solutions, pages 228-229, GCSE Combined Science, Pearson Edexcel
Electrolysis; salt solutions, pages 84-85, GCSE Chemistry, Pearson, Edexcel

OCR

Electrolysis, pages 116-118, 137, 222, Gateway GCSE Combined Science; The Revision Guide, CGP, OCR
Electrolysis, pages 47-49, 77, 104, Gateway GCSE Chemistry; The Revision Guide, CGP, OCR
Electrolysis, pages 94, 122-127, 206, 210-211, 266-267, Gateway GCSE Chemistry, Oxford, OCR