Electrolysis
Cambridge IGCSE Chemistry (0620) · Unit 4: Electrochemistry · 17 flashcards
Electrolysis is topic 4.1 in the Cambridge IGCSE Chemistry (0620) syllabus , positioned in Unit 4 — Electrochemistry , alongside Electrolysis of specific substances and Hydrogen-oxygen fuel cells. In one line: Electrolysis is the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current.
This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 confirm this is a high-yield topic: Cambridge has set undefined questions worth 440 marks here (about 7.0% of all Chemistry marks across those years).
The deck below contains 17 flashcards — 3 definitions, 9 key concepts and 5 identification cards — covering the precise wording mark schemes reward. Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.
Electrolysis
Electrolysis is the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current.
What the Cambridge 0620 syllabus says
2026-2028 syllabus, in our wordsWhat the syllabus expects you to be able to do in this topic, in plain English. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks. For the exact wording, see the official syllabus (PDF).
- Define Define electrolysis: breaking down an ionic compound, either molten or dissolved in water (aqueous), by passing an electric current through it.
- Identify Identify the parts of a simple electrolytic cell: (a) the positive electrode, called the anode; (b) the negative electrode, called the cathode; (c) the electrolyte, the substance (molten or aqueous) that is electrolysed.
- Describe Describe how charge is transferred during electrolysis, covering: (a) electrons moving through the external circuit; (b) electrons being lost or gained at the electrodes; (c) ions moving through the electrolyte. Supplement
- Identify Identify the products at each electrode, and describe what is observed, when the following are electrolysed with inert platinum or carbon/graphite electrodes: (a) dilute sulfuric acid; (b) molten lead(II) bromide; (c) concentrated aqueous sodium chloride.
- State State that at the cathode, metals or hydrogen are produced, while non-metals (except hydrogen) form at the anode.
- Predict Predict which product forms at each electrode when a binary compound is electrolysed in the molten state.
- State State that electroplating metal objects improves how they look and how well they resist corrosion.
- Describe Describe the method used to electroplate a metal.
- Identify Identify the electrode products and describe what is seen when aqueous copper(II) sulfate is electrolysed using copper electrodes, and also using inert electrodes of carbon/graphite. Supplement
- Predict Predict the products at each electrode when a halide compound is electrolysed as a dilute or a concentrated aqueous solution. Supplement
- Construct Construct the ionic half-equations for the anode reaction, showing oxidation, and for the cathode reaction, showing reduction. Supplement
Define electrolysis.
Electrolysis is the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current.
In an electrolytic cell, what is the anode and what is its charge?
The anode is the positive electrode in an electrolytic cell. It's where oxidation (loss of electrons) occurs.
In an electrolytic cell, what is the cathode and what is its charge?
The cathode is the negative electrode in an electrolytic cell. It's where reduction (gain of electrons) occurs.
What is the electrolyte in electrolysis?
The electrolyte is the molten or aqueous substance that undergoes electrolysis. It contains ions that are free to move and conduct electricity. An example is molten lead(II) bromide or aqueous sodium chloride.
Describe the movement of charge during electrolysis in the external circuit.
Electrons move in the external circuit from the power supply to the cathode and from the anode back to the power supply. This flow of electrons constitutes the electric current. These electrons are gained or lost by ions at the electrodes.
Describe the movement of charge during electrolysis within the electrolyte.
Ions move in the electrolyte. Positive ions (cations) move towards the cathode, and negative ions (anions) move towards the anode. This movement of ions carries the charge through the electrolyte.
What are the products of electrolysis of molten lead(II) bromide using inert electrodes?
At the cathode (negative electrode), molten lead is formed. At the anode (positive electrode), bromine gas is formed. Observation: Brown fumes are produced at the anode.
What are the products of electrolysis of concentrated aqueous sodium chloride using inert electrodes?
At the cathode (negative electrode), hydrogen gas is formed. At the anode (positive electrode), chlorine gas is formed. Observation: Bubbles of gas produced at both electrodes, pungent smell at the anode. The remaining solution is sodium hydroxide.
What are the products of electrolysis of dilute sulfuric acid using inert electrodes?
At the cathode (negative electrode), hydrogen gas is formed. At the anode (positive electrode), oxygen gas is formed. Observation: Bubbles of gas are produced at both electrodes. More hydrogen is produced than oxygen.
What type of substance is formed at the cathode during electrolysis?
Metals or hydrogen are formed at the cathode during electrolysis. This is because positive metal ions or H+ ions are attracted to the negative electrode and gain electrons (are reduced).
What type of substance is formed at the anode during electrolysis?
Non-metals (other than hydrogen) are formed at the anode during electrolysis. This is because negative non-metal ions are attracted to the positive electrode and lose electrons (are oxidized).
What is electroplating, and why is it done?
Electroplating is the process of coating a metal object with a thin layer of another metal using electrolysis. It is done to improve the appearance of the object and to increase its resistance to corrosion.
Write the ionic half-equations for the electrolysis of molten lead bromide.
At the cathode (reduction): Pb²⁺ + 2e⁻ → Pb
At the anode (oxidation): 2Br⁻ → Br₂ + 2e⁻
Lead is deposited as a silvery metal at the cathode. Bromine is released as a brown/orange gas at the anode.
Remember: cathode = reduction (gain electrons), anode = oxidation (lose electrons). The mnemonic is OILRIG (Oxidation Is Loss, Reduction Is Gain).
Why must an ionic compound be molten or dissolved in water for electrolysis to occur?
In a solid ionic compound, the ions are held in fixed positions in a lattice and cannot move. For electrolysis to work, the ions must be free to move towards the electrodes. Melting or dissolving in water breaks the lattice, allowing ions to move: cations migrate to the cathode and anions migrate to the anode.
What products form at each electrode during the electrolysis of concentrated sodium chloride solution (brine)?
At the cathode: hydrogen gas (H₂) — from the water, not sodium, because sodium is too reactive
At the anode: chlorine gas (Cl₂) — from the chloride ions
Sodium hydroxide (NaOH) remains in solution.
Test: hydrogen gives a squeaky pop with a lit splint; chlorine bleaches damp litmus paper.
Describe how to electroplate a steel spoon with silver.
1. The steel spoon is the cathode (negative electrode)
2. A piece of pure silver is the anode (positive electrode)
3. The electrolyte is silver nitrate solution (contains Ag⁺ ions)
4. When current flows, Ag⁺ ions move to the cathode and are deposited on the spoon
5. At the anode, silver atoms dissolve to replace the Ag⁺ ions in solution
This gives the spoon a thin, even coating of silver for improved appearance and corrosion resistance.
During the electrolysis of aqueous copper sulfate with copper electrodes, why does the mass of the anode decrease?
At the anode (copper electrode), copper atoms lose electrons and dissolve into the solution as Cu²⁺ ions:
Cu → Cu²⁺ + 2e⁻
This is oxidation, which removes copper from the anode, decreasing its mass. At the same time, Cu²⁺ ions from the solution gain electrons at the cathode and are deposited as copper, increasing its mass. The concentration of the solution stays the same.
Key Questions: Electrolysis
Define electrolysis.
Electrolysis is the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current.
What is the electrolyte in electrolysis?
The electrolyte is the molten or aqueous substance that undergoes electrolysis. It contains ions that are free to move and conduct electricity. An example is molten lead(II) bromide or aqueous sodium chloride.
What is electroplating, and why is it done?
Electroplating is the process of coating a metal object with a thin layer of another metal using electrolysis. It is done to improve the appearance of the object and to increase its resistance to corrosion.
Tips to avoid common mistakes in Electrolysis
- ● Name the charge carriers in each case: metals (electrons), ionic solutions (ions), covalent compounds (usually none).
- ● Master electrolysis of salts by drawing a diagram, labeling the ions present, and writing the half-equations at each electrode.
- ● When labelling electrolysis diagrams, double-check that your labels point to the correct part (anode, cathode, electrolyte). Review the process.
- ● When answering an electrolysis question, read carefully and be sure you're giving the product formed (e.g., hydrogen at the cathode) and not just naming the electrodes.
- ● During electrolysis, double-check the substance's state AND whether the product would react with water in aqueous solution.
More topics in Unit 4 — Electrochemistry
Electrolysis sits alongside these Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 0620 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Key terms covered in this Electrolysis deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
Related Chemistry guides
Long-read articles that go beyond the deck — cover the whole subject's common mistakes, high-yield content and revision pacing.
How to study this Electrolysis deck
Start in Study Mode, attempt each card before flipping, then rate Hard, Okay or Easy. Cards you rate Hard come back within a day; cards you rate Easy push out to weeks. Your progress is saved in your browser, so come back daily for 5–10 minute reviews until every card reads Mastered.
Study Mode
Space to flip • ←→ to navigate • Esc to close
You're on a roll!
You've viewed 10 topics today
Create a free account to unlock unlimited access to all revision notes, flashcards, and study materials.
You're all set!
Enjoy unlimited access to all study materials.
Something went wrong. Please try again.
What you'll get:
- Unlimited revision notes & flashcards
- Track your study progress
- No spam, just study updates