The electrolysis of some other solutions using inert electrodes
4 marks · NormalThe table shows part of the reactivity series and the likely product at the cathode during the electrolysis of an aqueous solution of the metal compound.
| Metal | Relative position (above/below H) | Product at cathode |
|---|---|---|
| Potassium | Above | Hydrogen |
| Copper | Below | ? |
| Sodium | Above | Hydrogen |
| Silver | Below | ? |
a) Complete the column for 'Product at cathode' for copper and silver.
b) Explain, using the reactivity series, why these products are formed for copper and silver.
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 — copper; Silver — silver · must show Correctly completed for both metals
(b) Because copper and silver are less reactive than hydrogen, their ions are preferentially discharged at the cathode, producing metal rather than hydrogen. · must show Both metals less reactive than hydrogen, Therefore the metal forms at cathode
Common mistakes: Saying hydrogen is formed for metals below hydrogen
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · 'Copper' correctly completed as 'copper'.
B2 (a) · 1 mark · 'Silver' correctly completed as 'silver'.
M1 (b) · 1 mark · States that copper and silver are less reactive than hydrogen.
A1 (b) · 1 mark · States that the metal ion is therefore discharged and metal is deposited at the cathode.
Worked solution
| Metal | Relative position (above/below H) | Product at cathode |
|---|---|---|
| Potassium | Above | Hydrogen |
| Copper | Below | Copper |
| Sodium | Above | Hydrogen |
| Silver | Below | Silver |
Copper and silver are below hydrogen in the reactivity series. Their ions are more easily reduced than hydrogen ions, so copper or silver is deposited at the cathode.