Q.ii. Explain electrolysis of molten NaCl.

Step 1. The electrolytic cell for molten NaCl has two graphite electrodes dipped in the fused NaCl, connected to a DC battery.

Step 2. In the melt, Na+ and Cl- ions are freely mobile; under the applied potential, Cl- migrates to the anode and Na+ migrates to the cathode.

Step 3. At the anode, each Cl- gives up an electron (primary process, forming a neutral Cl atom), and pairs of Cl atoms then combine to Cl2 gas (secondary process): overall $2Cl^-(l)\rightarrow Cl_2(g)+2e^-$.

Step 4. At the cathode, each Na+ accepts an electron and is reduced to molten sodium metal: $2Na^+(l)+2e^-\rightarrow2Na(l)$.

Step 5. Adding the two half reactions gives the overall cell reaction: $2Na^+(l)+2Cl^-(l)\rightarrow2Na(l)+Cl_2(g)$.

Step 6. Results: pale-green Cl2 gas at the anode, molten silvery-white sodium at the cathode; since this decomposition is nonspontaneous, it occurs only because the battery's electrical energy forces it.

Describe the cell construction, ion migration, both half reactions and the overall reaction, from section 5.5.1.

• Confusing this with AQUEOUS NaCl electrolysis (which involves water and gives H2/NaOH instead of Na metal).
• Reversing which ion goes to which electrode (anions migrate to the anode, cations to the cathode, following the applied field).