Explain the reasons for the choice of materials and the design of the Downs' cell for the industrial production of sodium. Also, explain why large quantities of electricity are required.

a) The anode is made of graphite because graphite is inert and resistant to corrosion by the chlorine gas produced at the anode at high temperatures. Steel, being an alloy of iron, would react with chlorine and corrode.

b) The electrolytic products, molten sodium and chlorine gas, are separated by a steel gauze diaphragm (or baffle). This physical barrier prevents the highly reactive molten sodium from coming into contact with the chlorine gas, which would react explosively to reform sodium chloride. Molten sodium is also less dense and floats to a separate collection area.

c) Large quantities of electricity are required for this process because:

• The extraction of sodium from molten sodium chloride is an electrolytic process that requires a continuous supply of electrical energy to drive a non-spontaneous reaction.
• A large amount of energy is needed to break the strong ionic bonds in sodium chloride.
• The process operates at high temperatures (around $600^\circ\text{C}$) to keep $\text{NaCl}$ molten, which also consumes significant electrical energy.