Molten zinc chloride is electrolysed using inert electrodes.
.1
Explain why the zinc chloride must be molten.
[2 marks].2
Name the product at the cathode.
[1 mark].3
Name the product at the anode.
[1 mark]Practice · AQA Combined Science 8464 · Chemistry Paper 1
GCSE chemistry electrolysis questions: AQA Combined Science worked practice
Six exam-style questions on electrolysis, from products at each electrode to Higher half equations. Each part shows the worked answer.
1 of 6
A student investigates what is produced when aqueous solutions of copper chloride and sodium chloride are electrolysed using inert electrodes.
Plan an investigation to find the products at each electrode for both solutions.
Include how you would identify any gases.
[6 marks]A student electrolyses a small volume of dilute copper sulfate solution with inert electrodes and weighs the cathode every 5 minutes.
.1
Describe the line of best fit the student should draw.
[2 marks].2
Explain why the mass of copper levels off.
[2 marks].3
Calculate the mean rate of copper deposition in the first 10 minutes, in g/min.
[1 mark].4
Name the gas produced at the anode.
[1 mark]In electrolysis of water containing an electrolyte, a student collects 24 cm³ hydrogen and 11 cm³ oxygen. The theoretical hydrogen:oxygen volume ratio is 2:1 under the same conditions.
.1
Calculate the oxygen volume expected from 24 cm³ hydrogen.
[2 marks].2
Calculate the shortfall in measured oxygen as a percentage of the expected volume.
[3 marks].3
Suggest a measurement issue that could account for the shortfall and a way to check it.
[2 marks]Aluminium oxide, , is electrolysed in molten cryolite.
.1
Write the half equation for the formation of aluminium at the cathode.
[1 mark].2
Write the half equation for the formation of oxygen at the anode.
[1 mark].3
Use the half equations to calculate how many moles of oxygen molecules form for every 4 moles of aluminium produced.
[2 marks]In the electrolysis of molten aluminium oxide, 0.12 mol of aluminium ions is discharged and 0.18 mol of oxide ions is discharged.
.1
Calculate the amount of electrons gained by the aluminium ions. Each aluminium ion gains three electrons.
[2 marks].2
Calculate the amount of electrons lost by the oxide ions. Each oxide ion loses two electrons.
[2 marks].3
Explain why the two electron totals must match in the circuit.
[1 mark]Learn each topic
- ElectrolysisLesson in GCSE Science Pro
- Redox and half equations (Higher)Lesson in GCSE Science Pro
Questions people ask
What forms at the cathode in aqueous electrolysis?
Hydrogen, unless the metal is less reactive than hydrogen (such as copper), in which case the metal forms.
What forms at the anode in aqueous electrolysis?
Oxygen, unless the solution contains halide ions, in which case the halogen forms (chlorine, bromine or iodine).
Why is aluminium oxide mixed with cryolite?
Cryolite lowers the melting point, so less energy is needed to keep the electrolyte molten. The carbon anodes react with the oxygen made and must be replaced.