Show — 5 marks
A manufacturing company uses electrolysis to extract copper from impure copper ore. They use an electrolytic cell with an impure copper anode, a pure copper cathode, and copper sulfate solution as the electrolyte. The process is essential for producing high-purity copper for electrical wiring.
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(a) Show that the impure copper anode decreases in mass during electrolysis.
[2 marks]
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(b) Show the equation for the reaction occurring at the cathode during this process.
[2 marks]
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(c) Show why less reactive impurities (such as silver) fall to the bottom of the electrolytic cell as 'anode mud' rather than being oxidized.
[1 mark]
Show mark scheme
- (a) At the anode, copper atoms lose electrons (are oxidized) / Cu → Cu²⁺ + 2e⁻
- (a) As copper ions leave the anode, the anode decreases in mass
- (b) Cu²⁺ + 2e⁻ → Cu
- (b) Copper ions are reduced at the cathode / electrons are gained
- (c) Less reactive metals are not oxidized / do not lose electrons as readily as copper / remain as impurities and fall to the bottom
State — 3 marks
A student carries out an electrolysis experiment using copper sulfate solution with copper electrodes. An electric current is passed through the solution for several minutes.
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(a) State what happens to the mass of the positive electrode (anode) during electrolysis.
[1 mark]
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(b) State the name of the electrode where reduction occurs during electrolysis.
[1 mark]
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(c) State two factors that would increase the rate of electrolysis in this experiment.
[1 mark]
Show mark scheme
- (a) The mass decreases / the anode dissolves / copper is removed from the electrode
- (b) The cathode (negative electrode)
- (c) Any two from: increase the current / increase voltage / increase temperature / increase concentration of electrolyte / decrease distance between electrodes
State — 3 marks
A student carries out an electrolysis experiment using copper sulfate solution with copper electrodes. A direct current power supply is connected to the electrodes, and the student observes changes at both the positive and negative electrodes during the experiment.
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(a) State the name of the electrode connected to the positive terminal of the power supply.
[1 mark]
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(b) State what is observed at the negative electrode during the electrolysis of copper sulfate solution with copper electrodes.
[1 mark]
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(c) State why the copper electrode connected to the positive terminal gradually decreases in mass during this electrolysis.
[1 mark]
Show mark scheme
- (a) Anode (1 mark)
- (b) Copper is deposited/plated on the electrode OR the electrode becomes coated/covered with copper OR copper metal forms (1 mark)
- (c) Copper atoms are oxidised/lose electrons and form copper ions which dissolve into solution OR copper is oxidised to Cu²⁺ ions (1 mark)
Suggest — 5 marks
A jeweller uses electrolysis to coat a steel ring with a thin layer of silver. The steel ring is placed in a solution of silver nitrate. A silver electrode is used as the anode and the steel ring acts as the cathode. A direct current power supply is connected to complete the circuit.
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(a) Suggest why a silver electrode is used as the anode rather than an inert electrode such as platinum.
[2 marks]
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(b) During the electrolysis, silver ions are reduced at the cathode. Write the ionic equation for this reduction reaction.
[1 mark]
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(c) Suggest two ways the jeweller could increase the thickness of the silver coating on the steel ring.
[2 marks]
Show mark scheme
- (a) The silver electrode dissolves/oxidises to provide silver ions
- (a) This replenishes the silver ions in the solution so the plating process can continue efficiently
- (b) Ag⁺ + e⁻ → Ag (accept: Ag⁺(aq) + e⁻ → Ag(s))
- (c) Increase the current/potential difference supplied
- (c) Increase the time of electrolysis
Calculate — 2 marks
A company uses electrolysis to purify copper for making electrical cables. During this process, a current of 4 A is passed through copper sulfate solution for 20 minutes. Copper ions from the solution are deposited as pure copper metal at the negative electrode.
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(a) Calculate the total charge, in coulombs, that passes through the solution. Use the equation: charge = current × time
[1 mark]
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(b) 0.1 g of copper is deposited when 300 C of charge passes through the solution. Calculate the mass of copper deposited during the 20 minutes.
[1 mark]
Show mark scheme
- (a) charge = 4 × (20 × 60)
- (a) = 4800 C
- (b) 4800 ÷ 300 = 16
- (b) 0.1 × 16 = 1.6 g
GCSE Perfect