The electrolysis of some other solutions using inert electrodes

3 marks · Normal

Electrolysis of aqueous copper(II) nitrate solution was carried out using inert electrodes. No copper was deposited at the cathode.

Explain which products are formed at the cathode and anode, and why these products are formed.

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Cathode: hydrogen gas; Anode: oxygen gas. At the cathode, hydrogen is formed because copper ions are less likely to be discharged than hydrogen ions in aqueous solution. At the anode, oxygen is formed from hydroxide ions as nitrate ions are not discharged.

Must show: Product at cathode, Explanation for cathode product, Product at anode and explanation

Also accept: Hydrogen at cathode because copper is below hydrogen but not deposited in nitrate solution

Common mistakes: Stating copper is formed at the cathode; Stating nitrate is discharged at the anode

Show mark scheme and worked solution

Marking points

B1 · 1 mark · Correct product identified at cathode (hydrogen).

M1 · 1 mark · Explanation: hydrogen formed because copper is not discharged or H+ is preferentially discharged.

B2 · 1 mark · Correct product at anode (oxygen) and explanation: nitrate ions not discharged, so O2 is formed from OH-.

Worked solution

At the cathode, hydrogen gas is produced because copper ions are not discharged in this solution, so hydrogen ions are reduced.

At the anode, oxygen gas is produced because nitrate ions are not discharged and oxygen forms from hydroxide ions in the water.