Chemistry 2005 JAMB Past Questions - Question 7: concentrated solution containing H+, Cu²+, OH- and Cu was electrolyzed using platinum electrodes. The ion that will be discharged at the cathode is

Correct Answer

A

Explanation

In electrolysis, the ion that will be discharged at the cathode depends on the standard reduction potentials of the ions present. The standard reduction potentials are a measure of the tendency of an ion to gain electrons and be reduced.

Let's consider the ions you mentioned:

1. H⁺ (Hydrogen ion)
2. Cu²⁺ (Copper(II) ion)
3. OH⁻ (Hydroxide ion)

The standard reduction potentials for these ions are as follows:

1. H⁺ + e⁻ → ½H₂ (E° = 0.00 V)
2. Cu²⁺ + 2e⁻ → Cu (E° = +0.34 V)
3. 2H₂O + 2e⁻ → H₂ + 2OH⁻ (E° = -0.83 V)

The more positive the standard reduction potential, the more likely the ion will be reduced. In this case, Cu²⁺ has the highest standard reduction potential (+0.34 V). Therefore, copper ions (Cu²⁺) are most likely to be reduced at the cathode during the electrolysis of the solution. The reduction half-reaction at the cathode would be:

Cu²⁺ + 2e⁻ → Cu

So, copper will be discharged at the cathode.