Electrolysis
Specification points
Electrochemistry
Describe some general ideas used in electrolysis as electrolysis being the breakdown of an
ionic compound, molten or in aqueous solution, by the passage of electricity
• the cathode is the negative electrode and the anode is the positive electrode
• inert electrodes such as platinum or carbon are used in electrolysis
Describe the products formed at the electrodes in the electrolysis:
• molten lead(II) bromide
• concentrated hydrochloric acid
• dilute sulphuric acid
• concentrated aqueous sodium chloride
• metals or hydrogen are formed at the negative electrode
• non-metals (other than hydrogen) are formed at the positive electrode)
• predict the products when a molten simple salt (e.g. sodium bromide, lead iodide) is
electrolysed
• Describe the transfer of charge during electrolysis to include the movement of electrons
in the metallic conductor, the removal or addition of electrons from the external circuit
at the electrodes and the movement of ions in the electrolyte
Describe the products formed at the electrodes:
• when the electrolyte is molten
• when the electrolyte is a solution in water
• when the electrolyte is a dilute or concentrated solution of a halide in water
• when a solution of copper sulphate in water is electrolysed using carbon electrodes
• when a solution of copper sulphate in water is electrolysed using copper electrodes
Describe electrolysis in terms of:
• the ions present
• the reactions at the electrodes
• write ionic equations
Describe in outline:
• the manufacture of chlorine and sodium hydroxide from a concentrated solution of
sodium chloride
• the electroplating of metals
• the uses of electroplating
• why copper is used in electrical cables
• why aluminium with a steel core is used in electrical cables
• why plastics and ceramics are used as insulators
Describe how we get metals from their ores:
• the manufacture of aluminium from aluminium oxide from bauxite including the role of
molten cryolite and the reactions at the electrodes
Independent Study suggestions
1. Look at the specification points above – use the textbook pages (102-111 and 200-201) or the revision
guide pages (48-53) to make a few notes/spider diagram/revision cards
2. Have a go at the questions in the revision guide on pages 54-56 and mark yourself – answers in the
back
3.
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Watch the Fuse School short 3-4 minute explanation videos for any areas you need more help with:
Electrolysis of molten compounds: https://www.fuseschool.org/topics/67/contents/365
Electrolysis of brine: https://www.fuseschool.org/topics/67/contents/379
Purifying copper: https://www.fuseschool.org/topics/67/contents/378
Aluminium extraction: https://www.fuseschool.org/topics/65/contents/1201
Uses of aluminium: https://www.fuseschool.org/topics/65/contents/1050
Recycling metals: https://www.fuseschool.org/topics/65/contents/334
4. Can you do this question? - Chlorine is made by the electrolysis of concentrated aqueous sodium
chloride. Describe this electrolysis. Write ionic equations for the reactions at the electrodes and name
the sodium compound formed. [5 marks]
Answer:
hydrogen and chlorine / H2 and Cl2 (1)
sodium hydroxide / NaOH / Na+OH– (1)
2H+ + 2e → H2 / 2H+ → H2 – 2e (1)
2Cl– → Cl2 + 2e / 2Cl– – 2e → Cl2 (1)
Hydrogen / H2 / H / H+ at cathode and chlorine / chloride / Cl2 / Cl / Cl– at anode (1)
5. Can you do this question - Describe the extraction of aluminium from alumina. Include the electrolyte,
the electrodes and the reactions at the electrodes [6 marks]
Answer: