O Level / IGCSE Chemistry chapter 4: Electrochemistry MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
24 exam-style questions on Electrochemistry, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Which substance could not be formed at the anode during electrolysis?
A
chlorine
B
oxygen
C
bromine
D
hydrogen
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Answer: D. Metals and hydrogen form at the cathode, because they come from positive ions gaining electrons. Non-metals other than hydrogen, such as chlorine, oxygen and bromine, form at the anode.
2. Dilute sulfuric acid is electrolysed with inert electrodes. What is the ratio of the volume of gas at the cathode to the volume at the anode?
A
1 : 1
B
1 : 2
C
2 : 1
D
4 : 1
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Answer: C. Hydrogen at the cathode (4H+ + 4e− → 2H2) and oxygen at the anode (4OH− → O2 + 2H2O + 4e−): two volumes of hydrogen for every one of oxygen.
3. During the electrolysis of molten zinc chloride, how is charge carried through the wires of the external circuit?
A
by electrons, moving from the anode through the power supply to the cathode
B
by zinc ions, moving towards the cathode
C
by chloride ions, moving towards the anode
D
by electrons, moving from the cathode through the electrolyte to the anode
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Answer: A. In the wires, charge is carried only by electrons, which flow from the anode, through the power supply, to the cathode. Ions carry the charge inside the electrolyte; electrons do not pass through the electrolyte.
4. What is the ionic half-equation for the reaction at the anode during the electrolysis of molten sodium chloride?
A
Cl2 + 2e− → 2Cl−
B
Na → Na+ + e−
C
2Cl− → Cl2 + 2e−
D
Na+ + e− → Na
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Answer: C. At the anode negative ions lose electrons (oxidation): 2Cl− → Cl2 + 2e−.
5. Concentrated aqueous copper(II) chloride is electrolysed using carbon electrodes. What forms at each electrode?
A
anode: chlorine; cathode: hydrogen
B
anode: chlorine; cathode: copper
C
anode: copper; cathode: chlorine
D
anode: oxygen; cathode: copper
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Answer: B. Copper is less reactive than hydrogen, so Cu2+ ions are discharged at the cathode as copper. With a concentrated chloride, chlorine forms at the anode.
6. Why are metal objects such as taps and cutlery electroplated?
A
to raise their melting point so they can be used at high temperatures
B
to make them magnetic so that they attract other metal objects
C
to make them lighter and cheaper to transport around the world
D
to improve their appearance and resistance to corrosion
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Answer: D. A thin layer of a metal such as chromium or silver gives a shiny finish and protects the metal underneath from corrosion.
7. Solid sodium chloride does not conduct electricity, but molten sodium chloride does. Why?
A
the molten salt contains free electrons
B
the solid has no ions in it
C
molecules of sodium chloride split up into atoms when it melts
D
in the solid the ions are held in fixed positions, but in the melt the ions can move
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Answer: D. Both the solid and the melt are made of Na+ and Cl− ions. Only when the lattice breaks down on melting can the ions move to the electrodes and carry charge.
8. Dilute sulfuric acid is electrolysed for a long time using carbon electrodes. What happens to the concentration of the sulfuric acid?
A
it decreases, because sulfate ions are discharged at the anode
B
it decreases, because hydrogen ions are discharged at the cathode
C
it stays the same, because no ions are used up
D
it increases, because the hydrogen and oxygen formed come from water
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Answer: D. Hydrogen (cathode) and oxygen (anode) are produced in a 2 : 1 ratio, so overall water is decomposed. The acid stays in a smaller volume of water and becomes more concentrated; sulfate ions are not discharged.
9. Aqueous copper(II) sulfate is electrolysed using copper electrodes. Which half-equation shows the reaction at the anode?
A
Cu2+ + 2e− → Cu
B
4OH− → O2 + 2H2O + 4e−
C
Cu2+ → Cu + 2e−
D
Cu → Cu2+ + 2e−
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Answer: D. With a copper anode, the anode itself is oxidised: copper atoms lose electrons and go into solution as Cu2+. Oxygen forms only when the anode is inert, and Cu2+ + 2e− → Cu is the cathode reaction.
10. A molten binary compound is electrolysed with inert electrodes. A grey metal forms at the cathode and a pale yellow-green gas forms at the anode. Which compound was electrolysed?
A
zinc chloride
B
lead(II) bromide
C
potassium iodide
D
copper(II) oxide
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Answer: A. The yellow-green gas is chlorine, so the compound must be a chloride: molten zinc chloride gives zinc and chlorine. Lead(II) bromide gives red-brown bromine, potassium iodide gives iodine vapour and an oxide gives oxygen.
24, each with the answer and a short explanation, across 1 topics: Electrolysis. Every chapter test draws ten of them, so you can take it many times.
Is the O Level / IGCSE Chemistry chapter 4 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
