Question

Give reason. For extracting some metals displacement reactions are used in place of carbon to obtain metal from their oxides.

Answer 1

The metals high up in the reactivity series are very reactive. They cannot be obtained from their compounds by heating with carbon. 

For example, carbon cannot reduce the oxides of sodium, magnesium, calcium, aluminum, etc., to the respective metals. 

This is because these metals have more affinity for oxygen than carbon. These metals are obtained by electrolytic reduction. 

For example, sodium, magnesium and calcium are obtained by the electrolysis of their molten chlorides. The metals are deposited at the cathode (the negatively charged electrode), whereas, chlorine is liberated at the anode (the positively charged electrode). The reactions are –

At cathode Na+ + e– → Na
At anode 2Cl– → Cl2 + 2e–

Similarly, aluminum is obtained by the electrolytic reduction of aluminum oxide.