The electrolysis of some other solutions using inert electrodes
2 marks · EasyA student electrolyses an aqueous solution of potassium nitrate using inert electrodes.
State the name of the product formed at:
the cathode
the anode
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(a) hydrogen
(b) oxygen
Common mistakes: Potassium at the cathode (should be hydrogen); Nitrate at the anode (should be oxygen formed)
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Marking points
B1 (a) · 1 mark · States hydrogen (or correct formula, e.g., H2) as the product at the cathode.
B1 (b) · 1 mark · States oxygen (or correct formula, e.g., O2) as the product at the anode.
Worked solution
At the cathode, potassium ions (K⁺) and hydrogen ions (H⁺) are present. Hydrogen is less reactive than potassium, so hydrogen ions are reduced:
Product at the cathode: hydrogen.
At the anode, nitrate (NO₃⁻) and hydroxide (OH⁻) ions are present. Nitrate is not discharged; hydroxide is oxidised to form oxygen:
Product at the anode: oxygen.