The electrolysis of some other solutions using inert electrodes
3 marks · Easy| Solution | Cation(s) | Anion(s) |
|---|---|---|
| A | K^+ | Cl^- |
| B | Mg^{2+} | SO_4^{2-} |
| C | Cu^{2+} | NO_3^- |
For solution B, state the product at the cathode when electrolysed using inert electrodes.
For solution C, state the product at the anode when electrolysed using inert electrodes.
For solution A, explain why this gas forms at the cathode instead of the metal.
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(a) hydrogen
(b) oxygen
(c) Potassium is more reactive than hydrogen; so hydrogen is discharged instead of potassium.
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Marking points
B1 (a) · 1 mark · Correctly states 'hydrogen' for solution B cathode product.
B1 (b) · 1 mark · Correctly states 'oxygen' for solution C anode product.
B1 (c) · 1 mark · Explains correctly that potassium is too reactive, so hydrogen is produced.
Worked solution
a) For solution B (Mg2+ and SO4^2-), hydrogen forms at the cathode.
b) For solution C (Cu2+ and NO3^-), oxygen forms at the anode (since nitrate is not discharged).
c) Potassium is above hydrogen in the reactivity series, so hydrogen gas forms at the cathode.