The electrolysis of sodium chloride solution

2 marks · Hard

Write a balanced half-equation, including state symbols, for the reduction that takes place at the cathode during the electrolysis of sodium chloride solution. State the physical state of each species involved.

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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2H₂O(l) + 2e⁻ → H₂(g) + 2OH⁻(aq) (with state symbols)

Must show: All reactants and products shown with correct state symbols, Balanced equation

Also accept: 2H⁺(aq) + 2e⁻ → H₂(g)

Common mistakes: Missing state symbols; Unbalanced equation; Using Na⁺ instead of H⁺ or H₂O

Show mark scheme and worked solution

Marking points

M1 · 1 mark · Correct species and balanced equation written for the cathode half-equation (with H₂O or H⁺ as reactant)

A1 · 1 mark · All correct state symbols for every species in the equation

Worked solution

At the cathode, either water or hydrogen ions are reduced. With state symbols, the half-equation is:

Alternatively, using hydrogen ions from water splitting:

Both equations are fully balanced and use state symbols as required.