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A-Level Redox, electrode potentials and electrolysis: worked solution
2 marks. Full working, one step per line.
Question
In Kolbe electrolysis, carboxylate ions couple at the anode with loss of CO2: 2R-CO2- -> R-R + 2CO2 + 2e-; electrolysing sodium ethanoate gives ethane at the anode. Suggest the products formed at the cathode and construct the overall equation for the electrolysis of sodium ethanoate.
Worked answer
At the anode ethanoate ions couple: 2CH3CO2- -> C2H6 + 2CO2 + 2e-. At the cathode, in aqueous solution water is reduced (Na+ is not discharged), giving hydrogen gas and hydroxide ions: 2H2O + 2e- -> H2 + 2OH- Adding the two electrode processes (electrons cancel) and including the spectator Na+ ions: 2CH3CO2Na + 2H2O -> C2H6 + 2CO2 + H2 + 2NaOH
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This question is part of A-Level Redox, electrode potentials and electrolysis, in A-Level H2 Chemistry.
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