The electrolysis of sodium chloride solution
2 marks · NormalState two reasons why hydrogen is produced at the cathode, and not sodium, in the electrolysis of sodium chloride solution.
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Also accept: Hydrogen is less reactive than sodium, so is discharged in preference to sodium.; Sodium ions are harder to reduce than hydrogen ions.; It is easier to add electrons to hydrogen ions than sodium ions.
Common mistakes: Confusing reasons with process at the anode.
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Marking points
B1 · 1 mark · Gives first correct reason: hydrogen is less reactive than sodium (or easier to reduce H+).
B2 · 1 mark · Gives second correct reason: sodium ion is harder to reduce/add electron to than hydrogen ion, or hydrogen is discharged in preference.
Worked solution
1) Hydrogen ions are less reactive than sodium ions, so are preferentially reduced at the cathode. 2) It is much more difficult to reduce (add electrons to) sodium ions than hydrogen ions, so sodium is not produced.