Question

(a) Here is an electrode reaction:
Cu → Cu²⁺ + 2e.
At which electrode (anode or cathode) would such a reaction take place? Is this an example of oxidation?
(b) A solution contains magnesium ions (Mg²⁺), iron (II) ions (Fe²⁺) and copper ions (Cu²⁺). On passing an electric current through this solution which ions will be the first to be discharged at the cathode? Write the equation for the cathode reaction.
(c) Why is carbon tetrachloride, which is a liquid, a non-electrolyte?

Answer 1

(a) The given reaction takes place at anode. Yes, this is an example of oxidation. During electrolysis, copper loses two electrons and gets oxidised to copper ions.

(b) The placement of metallic ions in the electrochemical series influences the preferential discharge of ions at the respective electrode. The ion located lower in the electrochemical series gets discharged first at the respective electrodes instead of other ions placed ahead of it in the series. The solution contains magnesium, iron (II) ions and copper ions. Copper ions (located lower in the electrochemical series) gets discharged first at the cathode instead of magnesium or iron (II) ions placed higher in the series. The equation for the cathode reaction would be:
${\mathrm{Cu}}^{2+}+2{\mathrm{e}}^{-}\stackrel{\mathrm{r}\mathrm{eduction}}{\to }\mathrm{Cu}(\mathrm{coppe}\mathrm{r}\mathrm{m}\mathrm{e}\mathrm{t}\mathrm{a}\mathrm{l})$

(c) Carbon tetrachloride contains molecules of carbon tetrachloride. It does not ionise, as it lacks ions. Thus, even though carbon tetrachloride is a liquid, it is considered a non-electrolyte.