The electrolysis of sodium chloride solution
3 marks · EasyThe table shows the tendency to gain electrons (ease of reduction) for some ions in decreasing order.
| Ion | Reduction Tendency |
|---|---|
| K^+ | Very difficult |
| Na^+ | Very difficult |
| Ca^2+ | Difficult |
| H^+ | Easier |
| Cu^2+ | Very easy |
A student electrolyses sodium chloride solution. Use the data to answer the following questions.
Suggest which ion, Na⁺ or H⁺, is more easily reduced at the cathode.
Which gas is formed at the cathode?
Explain why sodium metal does not form at the cathode, using the reduction tendency data.
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
(a) H⁺ (hydrogen ion) is more easily reduced.
(b) Hydrogen gas (H2)
(c) Because Na⁺ is very difficult to reduce, H⁺ (which is easier to reduce) gains electrons instead.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States H⁺ is more easily reduced than Na⁺.
B1 (b) · 1 mark · States hydrogen gas (H2) is the gas produced.
B1 (c) · 1 mark · Explains sodium ions are not reduced as it is harder for Na⁺ to gain electrons than for H⁺.
Worked solution
a) H⁺ is more easily reduced at the cathode. b) Hydrogen gas (H2) is formed at the cathode. c) Na⁺ is not reduced because it is much harder (very difficult) for it to gain electrons than for H⁺, as shown in the data.