The electrolysis of sodium chloride solution
3 marks · NormalAfter setting up an electrolytic cell with sodium chloride solution, a student predicts sodium metal will be produced at the cathode.
Use your knowledge of reactivity and the process of electrolysis to explain why this prediction is incorrect.
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.
Show answer
Also accept: Sodium is more reactive and stays in solution; hydrogen is less reactive and is discharged instead.; Because Na+ ions do not get reduced at the cathode as easily as H+ ions due to their higher reactivity.
Common mistakes: Claiming sodium is deposited at the cathode.
Show mark scheme and worked solution
Marking points
M1 · 1 mark · States sodium is more reactive than hydrogen.
M2 · 1 mark · Describes that the more reactive ion is less likely to be discharged/reduced at the cathode.
A1 · 1 mark · Explains hydrogen ions are reduced instead of sodium ions at the cathode, forming hydrogen gas not sodium metal.
Worked solution
Sodium is much more reactive than hydrogen, so sodium ions remain as ions in solution. More reactive metals are not easily reduced; less reactive ions (like H+) are reduced at the cathode. Thus, hydrogen ions gain electrons and form hydrogen gas, not sodium metal.