Who this is for: Cambridge IGCSE Chemistry (0620) students who want electrolysis — ion movement, products at each electrode and predicting results — to become reliable marks instead of guesswork about which ion discharges.
What query it owns: how to understand and revise electrolysis in Cambridge IGCSE Chemistry.
Why this is safe: this page owns the electrolysis revision-guide angle, while Tutopiya’s Electrolysis subtopic page owns the learning resource and the free Electrolysis quiz owns the practice.

Electrolysis uses electricity to decompose ionic compounds. In Cambridge IGCSE Chemistry (0620), examiners test your ability to identify electrodes, predict products at the cathode and anode, and explain why certain ions discharge preferentially. This guide covers the syllabus rules, the reactivity series shortcuts for aqueous solutions, and the question types that appear every year.

Key takeaways

• Electrolysis decomposes an ionic compound using a direct current.
• Cathode (negative electrode): cations gain electrons — reduction.
• Anode (positive electrode): anions lose electrons — oxidation.
• In molten electrolytes, all ions are free to move and discharge.
• In aqueous solutions, H⁺ or OH⁻ may discharge instead of less reactive ions.

What is electrolysis in Cambridge IGCSE Chemistry?

Electrolysis is the decomposition of an ionic compound when molten or in aqueous solution, using electricity. Positive ions (cations) move to the cathode and gain electrons; negative ions (anions) move to the anode and lose electrons. The products depend on the ions present, whether the electrolyte is molten or aqueous, and the reactivity of any metal ions.

You can read the full explanation, cell diagrams and worked examples on Tutopiya’s Electrolysis subtopic page before you attempt questions.

The core ideas you must master

Idea	What it means	How the exam uses it
Cathode product	Metal or hydrogen gas forms	”State the product at the cathode.”
Anode product	Non-metal or oxygen gas forms	”Identify the gas at the anode.”
Molten vs aqueous	Aqueous adds H⁺ and OH⁻ from water	”Compare products in molten and aqueous NaCl.”
Reactivity rule	Less reactive metal discharges at cathode	”Predict products of CuCl₂(aq) electrolysis.”
Half-equations	Show electron transfer at each electrode	”Write the half-equation at the cathode.”

How to predict electrolysis products — step by step

1. Identify the electrolyte — molten or aqueous? List all ions present.
2. Cathode: if metal ion is more reactive than hydrogen, H₂ forms; otherwise metal deposits.
3. Anode: if halide ion present (Cl⁻, Br⁻, I⁻), halogen forms; otherwise O₂ from OH⁻.
4. Write half-equations with electrons on the correct side.
5. Balance atoms and charge in each half-equation.
6. Name products and link to electrode colours or gas tests if asked.

Once you have worked through a few, test yourself with the free Electrolysis quiz — it tells you fast whether the predictions have actually stuck.

Molten vs aqueous: which rules does the question want?

Electrolyte type	Cathode product	Anode product	Typical example
Molten ionic compound	Metal	Non-metal	Molten PbBr₂ → Pb + Br₂
Aqueous, reactive metal salt	Hydrogen	Halogen or oxygen	NaCl(aq) → H₂ + Cl₂
Aqueous, less reactive metal	Metal deposited	Oxygen or halogen	CuSO₄(aq) → Cu + O₂
Concentrated vs dilute	Same rules; concentration affects halogen vs oxygen	”Concentrated NaCl” vs “dilute NaCl”

Electrolysis in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical electrolysis stem
Predict	Name products at electrodes	”Predict the products of electrolysing molten aluminium oxide.”
Explain	Give reasons using ion movement	”Explain why copper is deposited at the cathode.”
Write	Half-equation with electrons	”Write the half-equation at the anode.”
State	Short factual answer	”State the ion that moves to the cathode.”
Describe	What happens in the cell	”Describe what happens during the electrolysis of brine.”

Worked exam-style stems (how to answer the wording)

1. “Predict the products formed at each electrode during the electrolysis of molten lead(II) bromide.” Cathode: lead (Pb²⁺ + 2e⁻ → Pb). Anode: bromine (2Br⁻ → Br₂ + 2e⁻). Mark-scheme reward: correct products linked to correct electrodes.
2. “During the electrolysis of aqueous copper(II) sulfate using inert electrodes, explain what is seen at the cathode.” Cu²⁺ is less reactive than H⁺, so copper ions are discharged. A pink-brown deposit of copper forms. Reward: reactivity rule applied + observation.
3. “Write the half-equation for the reaction at the anode during the electrolysis of dilute sulfuric acid.” 4OH⁻ → O₂ + 2H₂O + 4e⁻ (or 2H₂O → O₂ + 4H⁺ + 4e⁻). Reward: balanced equation with electrons on anode side.

When you can recognise the wording instantly, work the full set on the Electrochemistry topical past paper questions and the Electrolysis quiz to lock the method in.

How electrolysis connects to the rest of Electrochemistry

Electrolysis links to Hydrogen–Oxygen Fuel Cells — fuel cells reverse the idea by combining H₂ and O₂ to produce electricity. Electroplating and extraction of aluminium also use electrolysis principles. When you are ready to mix topics, the Cambridge IGCSE Chemistry resource hub lets you move straight from a weak subtopic into the next.

Common mistakes students make

• Swapping cathode (negative, reduction) and anode (positive, oxidation).
• Predicting metal deposition for reactive metals like sodium in aqueous solution — hydrogen forms instead.
• Forgetting that water provides H⁺ and OH⁻ in aqueous electrolysis.
• Putting electrons on the wrong side of half-equations.
• Confusing electrolysis (uses electricity) with cells (produce electricity).

When you need more support

If electrolysis predictions keep tripping you up — especially aqueous solutions and half-equations — work through the Electrochemistry topical past paper questions and the Electrolysis quiz to pinpoint the exact gap, then get focused help from a Cambridge IGCSE Chemistry tutor to fix it quickly.

Frequently asked questions

Is electrolysis hard in Cambridge IGCSE Chemistry? No — the rules are systematic. Marks are lost when students swap electrodes, ignore the molten vs aqueous distinction, or misapply the reactivity series.

How do I remember cathode vs anode? Cathode = negative electrode = cations arrive = reduction. Anode = positive electrode = anions arrive = oxidation.

Why is hydrogen produced instead of sodium in aqueous NaCl? Sodium is more reactive than hydrogen, so H⁺ ions from water are discharged at the cathode instead of Na⁺.

How do I revise electrolysis effectively? Learn the molten rules first, add aqueous rules with the reactivity series, then take the Electrolysis quiz. Practise half-equations separately until balanced.

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