Question

Elemental Li and Na are prepared by electrolysis of a molten salt, whereas K, Rb, and Cs are prepared by chemical reduction.(a) In general terms, explain why the alkali metals cannot be prepared by electrolysis of their aqueous salt solutions.

Answer 1

It is impossible to use electrolysis for displacing alkali metals from their salt solutions by any other element because of their highly electropositive nature.

Because hydrogen ions discharge at the cathode instead of alkali metal ions due to the high discharge potential of alkali metals, the aqueous solutions of their salts cannot be employed for electrolytic extraction. However, alkali metals can be deposited by employing Hg as the cathode. The amalgam formed when the alkali metal and mercury mix is challenging to remove. Therefore, the only effective approach is the electrolysis of their fused salts, which are typically chlorides. Usually, another metal chloride is added to lower the temperature at which they fuse.

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