The electrolysis of copper(ii) sulfate solution using inert electrodes
5 marks · HardA student performs the electrolysis of copper(II) sulfate solution using inert electrodes. Answer the following questions about the products at the electrodes.
State the product formed at the cathode.
State the product formed at the anode.
Describe how you can identify the product formed at the anode during the electrolysis.
What would you observe on the cathode after the electrolysis has run for a few minutes?
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Copper (Cu); or copper metal; · must show Copper identified as product
(b) Oxygen (O2); or oxygen gas; · must show Oxygen identified as product
(c) Bubbles of gas at the anode; test the gas with a glowing splint – it relights, showing the presence of oxygen. · must show Effervescence/bubbles at anode, Test: relights glowing splint = oxygen
(d) A pink-brown or reddish layer of copper forms on the cathode. · must show Pink-brown/reddish copper metal deposited
Must show: Copper at the cathode, Oxygen at the anode, Correct test or observation for oxygen, Correct observation for cathode
Also accept: Accept 'oxygen gas'/'O2' for anode; accept identification with 'relights a glowing splint.'
Common mistakes: Stating hydrogen at the cathode; Stating sulfate at the anode
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly identifies copper metal as the product at the cathode.
B2 (b) · 1 mark · Correctly identifies oxygen gas as the product at the anode.
M1 (c) · 1 mark · Describes observation of bubbles or effervescence at the anode.
A1 (c) · 1 mark · Explains testing of gas at the anode with a glowing splint and correct conclusion (relights = oxygen).
B3 (d) · 1 mark · Correctly states that a pink-brown/reddish layer of copper is deposited on the cathode.
Worked solution
a) Product at the cathode is copper (Cu).
b) Product at the anode is oxygen (O₂) gas.
c) Bubbles of gas are seen at the anode. The gas can be tested by holding a glowing splint at its mouth; if it relights, this confirms the presence of oxygen.
d) After a few minutes, a pink-brown or reddish layer of copper metal will be seen deposited on the cathode.