The electrolysis of sodium chloride solution
3 marks · EasyDuring the electrolysis of sodium chloride solution, a student notices the solution near the cathode becomes alkaline.
Name the ion that increases in concentration near the cathode.
Write the half-equation that shows the production of hydrogen gas at the cathode.
Explain why the increase of this ion causes the solution to become alkaline.
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) Hydroxide ion (OH⁻)
(b) 2H₂O(l) + 2e⁻ → H₂(g) + 2OH⁻(aq)
(c) Because OH⁻ ions make solutions alkaline/high pH.
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Marking points
B1 (a) · 1 mark · Identifies hydroxide ions (OH⁻) as increasing.
B1 (b) · 1 mark · Writes the correct half-equation: 2H₂O(l) + 2e⁻ → H₂(g) + 2OH⁻(aq).
B1 (c) · 1 mark · Explains increase in OH⁻ ions makes solution alkaline/high pH.
Worked solution
a) Hydroxide ion (OH⁻) is the ion that increases. b) 2H₂O(l) + 2e⁻ → H₂(g) + 2OH⁻(aq) c) Because hydroxide ions cause a solution to be alkaline.