Electrolysis of specific substances
Cambridge IGCSE Chemistry (0620) · Unit 4: Electrochemistry · 12 flashcards
Electrolysis of specific substances is topic 4.2 in the Cambridge IGCSE Chemistry (0620) syllabus , positioned in Unit 4 — Electrochemistry , alongside Electrolysis and Hydrogen-oxygen fuel cells. In one line: Electrolysis is the breakdown of an ionic compound, in molten or aqueous state, by the passage of electricity.
This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical).
The deck below contains 12 flashcards — 1 definition, 4 key concepts and 7 identification cards — covering the precise wording mark schemes reward. Use the definition card 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 breakdown of an ionic compound, in molten or aqueous state, by the passage of electricity.
What the Cambridge 0620 syllabus says
Official 2026-2028 specThese are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.
- State State that a hydrogen–oxygen fuel cell uses hydrogen and oxygen to produce electricity with water as the only chemical product
- Describe Describe the advantages and disadvantages of using hydrogen–oxygen fuel cells in comparison with gasoline/petrol engines in vehicles Supplement
Define electrolysis.
Electrolysis is the breakdown of an ionic compound, in molten or aqueous state, by the passage of electricity.
Why is graphite used as an electrode in electrolysis?
Graphite is used because it is inert and conducts electricity. Inert means it doesn't react with the electrolyte or the products of electrolysis. It allows electrons to flow.
Write the half-equation for the formation of hydrogen gas at the cathode.
2H⁺ + 2e⁻ → H₂. This shows that hydrogen ions (H⁺) gain two electrons to form hydrogen gas (H₂).
What particles carry the electric current through the wires in an electrolytic cell?
Electrons carry the electric current through the wires. They flow from the power supply to the cathode and from the anode back to the power supply.
What particles carry the electric current through the electrolyte in an electrolytic cell?
Ions carry the electric current through the electrolyte. Positive ions (cations) move towards the cathode, and negative ions (anions) move towards the anode.
During the electrolysis of brine (concentrated NaCl solution), which gases are produced at the anode and cathode?
Anode: Chlorine; Cathode: Hydrogen. The sodium ions and hydroxide ions remain in solution, creating sodium hydroxide.
What is the chemical formula of the compound that is electrolyzed to extract aluminum?
Aluminium oxide (Al₂O₃). This is also known as alumina.
Why is cryolite mixed with aluminum oxide during the electrolysis of aluminum?
Cryolite serves as a solvent, lowers the operating temperature (reducing energy costs), and increases the conductivity of the electrolyte. This makes the process more efficient and economical.
Why do the carbon anodes need to be replaced periodically during the electrolysis of aluminum oxide?
The carbon reacts with the oxygen produced at the anode and forms carbon dioxide (CO₂). This gradually erodes the anode.
Write the balanced chemical equation for the overall reaction in a hydrogen-oxygen fuel cell.
2H₂ + O₂ → 2H₂O. Hydrogen gas reacts with oxygen gas to produce water.
Give two advantages of using hydrogen-oxygen fuel cells compared to gasoline/petrol engines in vehicles.
No carbon dioxide is evolved, reducing greenhouse gas emissions, and hydrogen-oxygen fuel cells are more efficient at converting chemical energy into mechanical energy.
What happens to the colour of the electrolyte during the electrolysis of copper(II) sulfate using inert electrodes?
The electrolyte gets lighter/fades/less blue. This is because the concentration of Cu²⁺ ions in the solution decreases as copper is deposited at the cathode.
Key Questions: Electrolysis of specific substances
Define electrolysis.
Electrolysis is the breakdown of an ionic compound, in molten or aqueous state, by the passage of electricity.
Tips to avoid common mistakes in Electrolysis of specific substances
- ● Name the charge carriers in each case: metals (electrons), ionic solutions (ions), covalent compounds (usually none).
- ● Review the conditions (UV light) and mechanism (free radical substitution) for the reaction between alkanes and chlorine.
- ● 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 of specific substances 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 of specific substances 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.
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