Electricity to the rescue

The idea

Metals high in the reactivity series, having more affinity for oxygen than carbon, cannot be obtained by heating with carbon; they are obtained by electrolytic reduction, the metal depositing at the cathode and chlorine at the anode from molten chlorides.

Carbon is not enough

Zinc oxide can be reduced with carbon. But sodium oxide cannot.

Why might carbon fail with very reactive metals?

• These metals hold on to oxygen more strongly than carbon does
• They contain no oxygen
• Carbon is too heavy

Electrolysis of molten chloride

Press Next step. This is a picture of an industrial process.

Pulled out by electricity

Metals at the top of the series have a stronger pull on oxygen than carbon has, so heating with carbon does not work. They are obtained by electrolytic reduction. When molten chlorides are electrolysed, the metal collects at the cathode and chlorine is given off at the anode.

Metals high in the reactivity series, having more affinity for oxygen than carbon, cannot be obtained by heating with carbon; they are obtained by electrolytic reduction, the metal depositing at the cathode and chlorine at the anode from molten chlorides.

Notes

Metals high in the series are obtained by electrolytic reduction: from molten chlorides, metal at the cathode and chlorine at the anode.

Check yourself

Why can carbon not reduce the oxides of sodium, magnesium, calcium and aluminium?

How are metals high in the reactivity series obtained?

In the electrolysis of molten sodium chloride, sodium is deposited at ...

Which gas is liberated at the anode in the electrolysis of a molten chloride?

• They have no oxygen. Their oxides do contain oxygen; the problem is that the metals hold on to it more strongly than carbon does.
• These metals have more affinity for oxygen than carbon has — correct. Yes!
• Carbon is more reactive than they are. The book says these metals have more affinity for oxygen than carbon.
• By heating alone. Heating alone is enough only for metals low in the series.
• By roasting. Roasting converts sulphide ores into oxides; it does not give these metals.
• By electrolytic reduction — correct. Yes!
• the cathode — correct. Yes!
• the anode. Chlorine is liberated at the anode, which is the positively charged electrode.
• both electrodes. Sodium goes to the cathode and chlorine to the anode.
• Hydrogen. Hydrogen is not produced; chlorine is liberated at the anode.
• Chlorine — correct. Yes!
• Oxygen. Oxygen is not produced from a molten chloride; chlorine is liberated at the anode.