Concentrated sodium chloride solution is electrolysed with inert electrodes. Name the product at the cathode and at the anode, and explain the cathode product.
[3 marks]
Total for this question: 3
Chemistry required practicals
Electrolysis of aqueous solutions
AQA 4.4 · RP3
GCSE Chemistry (8462) · Required practical 3 — method, variables, the marks examiners report students losing.
Board and spec code confirmed against AQA 8462 · registry checked 2026-07-17How this checking works
Investigate what is produced at each electrode when aqueous solutions are electrolysed using inert electrodes.
Apparatus
- Electrolysis cell / small beaker
- Two inert graphite electrodes
- Low-voltage dc power supply
- Solutions (e.g. copper(II) sulfate, sodium chloride)
- Small test tubes, lit splint, glowing splint, damp litmus paper
Method
- 1Half-fill the cell with the solution; stand two inert graphite electrodes in it, not touching each other.
- 2Connect the electrodes to the dc power supply (one to +, one to -).
- 3Invert a small test tube over each electrode to collect any gas produced.
- 4Turn on the supply and observe what forms at each electrode.
- 5Test the gases: lit splint (hydrogen gives a squeaky pop), glowing splint (oxygen relights it), damp litmus (chlorine bleaches it white).
- 6Note any metal deposit or colour change at the cathode.
Variables
Independent
The solution being electrolysed (or its concentration)
Dependent
The products formed at each electrode
Control
- Electrode material (inert)
- Voltage
- Time
- Volume of solution
Results & processing
- Record the product at the cathode (negative) and the anode (positive) for each solution.
- Cathode: the metal forms only if it is less reactive than hydrogen (e.g. copper) — otherwise hydrogen forms. Anode: a halogen forms if a halide is present, otherwise oxygen.
Where students lose marks
Confusing which electrode is which.
Fix: Cathode is negative and attracts positive metal/hydrogen ions; anode is positive and attracts negative ions (oxygen or a halogen).
Predicting sodium metal at the cathode from sodium chloride solution.
Fix: In solution, hydrogen forms because sodium is more reactive than hydrogen; the metal is only produced if it is less reactive than hydrogen (e.g. copper).
Using the wrong gas test.
Fix: Lit splint + squeaky pop = hydrogen; glowing splint relights = oxygen; damp litmus bleached white = chlorine.
Improve the method
- Use inert (graphite) electrodes so they don't react and change the products.
- Keep the voltage and time the same when comparing different solutions.
Try it — exam-style
Medium
ORIGINAL
Easy
ORIGINAL
Describe the test and result that confirms the gas produced at the anode is oxygen.
[1 mark]
Total for this question: 1
Questions are written in the style of past AQA papers — never copied from them.
Drill it properly
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