As part of an industrial process to extract magnesium metal, a furnace melts magnesium chloride, MgCl2, and a direct current is passed through the molten compound using two inert electrodes. (a) State the products formed at the cathode and at the anode. [2] (b) Write ionic half-…

Answer: ((a)) Magnesium forms at the cathode; chlorine forms at the anode. ((b)(i)) Mg^2+(l) + 2e^- → Mg(l) ((b)(ii)) 2Cl^-(l) → Cl2(g) + 2e^- ((c)) Reduction occurs at the cathode (magnesium ions gain electrons); oxidation occurs at the anode (chloride ions lose electrons).. Part (a): Products at each electrode Molten magnesium chloride contains only two mobile ions: Mg^2+ and Cl^-. The cathode (negative electrode) attracts and discharges the positive Mg^2+ ions, forming magnesium. The anode (positive electrod…

IGCSE Chemistry 0620: Half-Equations for Molten Magnesium Chloride Electrolysis

Part (a): Products at each electrode

Molten magnesium chloride contains only two mobile ions: $\text{Mg}^{2+}$ and $\text{Cl}^-$ . The cathode (negative electrode) attracts and discharges the positive $\text{Mg}^{2+}$ ions, forming magnesium. The anode (positive electrode) attracts and discharges the negative $\text{Cl}^-$ ions, forming chlorine.

Part (b): Ionic half-equations

(i) At the cathode, each magnesium ion gains two electrons: $\text{Mg}^{2+}(l) + 2e^- \rightarrow \text{Mg}(l)$

Check: 1 Mg atom on each side; charge on the left is $(+2) + (2 \times -1) = 0$ , matching the neutral $\text{Mg}(l)$ on the right.

(ii) At the anode, two chloride ions each lose one electron and combine to form a chlorine molecule: $2\text{Cl}^-(l) \rightarrow \text{Cl}_2(g) + 2e^-$

Check: 2 Cl atoms on each side; charge on the left is $2 \times (-1) = -2$ , and on the right is $0 + (2 \times -1) = -2$ , so both atoms and charge balance.

Part (c): Oxidation and reduction

At the cathode, magnesium ions gain electrons. This is reduction. At the anode, chloride ions lose electrons. This is oxidation.

The two electrons released by the two chloride ions at the anode are exactly the two electrons gained by each magnesium ion at the cathode, so the half-equations balance with each other as well as individually.

Final answers

(a) Cathode: magnesium. Anode: chlorine.
(b)(i) $\text{Mg}^{2+}(l) + 2e^- \rightarrow \text{Mg}(l)$
(b)(ii) $2\text{Cl}^-(l) \rightarrow \text{Cl}_2(g) + 2e^-$
(c) Cathode: reduction. Anode: oxidation.