This guide covers IGCSE Chemistry topic 5: electricity and chemistry (electrolysis). You will revise anode (positive; oxidation; anions attracted) and cathode (negative; reduction; cations attracted), molten vs aqueous electrolysis, and predicting products.

Key concepts to revise

• Electrolysis – Decomposition of a compound using electricity; ions move to electrodes; oxidation at anode, reduction at cathode.
• Anode – Positive electrode; anions (negative ions) attracted; oxidation (loss of electrons); e.g. O2 from oxide, halogen from halide.
• Cathode – Negative electrode; cations (positive ions) attracted; reduction (gain of electrons); e.g. metal or H2.
• Molten – Only the ions in the compound (e.g. molten NaCl: Na at cathode, Cl2 at anode). Aqueous – H+ and OH- from water; use reactivity series (H2 if metal above H).

Exam tips and command words

• State – What is formed at the anode and cathode for a given electrolyte (molten or aqueous).
• Describe – The movement of ions (cations to cathode, anions to anode); what happens at each electrode.
• Explain – Why a particular product is formed (e.g. in aqueous NaCl, H2 at cathode because Na is more reactive than H).
• Write – Half-equations for the reactions at anode and cathode.

Common mistakes

• Confusing anode (positive; oxidation) with cathode (negative; reduction). Remember: anode = oxidation.
• Saying “electrons flow to the cathode” (cations move to cathode; electrons are gained at cathode).
• Not stating that in aqueous electrolysis, water provides H+ and OH-; so H2 or O2 can form.

Revision checklist

• State what is formed at the anode and cathode for molten NaCl and for aqueous NaCl.
• Describe the movement of ions during electrolysis and what happens at each electrode.
• Write half-equations for the formation of O2 at anode and H2 at cathode (aqueous).
• Explain why in aqueous CuSO4, Cu is formed at cathode (Cu below H in reactivity series).

Next steps

Book a free trial with an IGCSE Chemistry tutor to practise electrolysis questions, or explore Tutopiya’s learning portal for more revision resources.