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Elemental Li and Na are prepared by electrolysis of a molten salt, whereas K, Rb, and Cs are prepared by chemical reduction.

In general terms, explain why the alkali metals cannot be prepared by electrolysis of their aqueous salt solutions,

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a) Alkali metals cannot be prepared by electrolysis of aqueous solutions because H+H^+ ions have a more positive standard reduction potential\textbf{standard reduction potential} than alkali metals.

Na++eNaEo=2.71VK++eKEo=2.93V2H++2eH2Eo=0.00V\begin{gather*} Na^+ + e^- \rightarrow Na \hspace{1cm} E^o = -2.71 V\\ K^+ + e^- \rightarrow K \hspace{1cm} E^o = -2.93V\\ 2H^+ + 2e^- \rightarrow H_2 \hspace{1cm} E^o = 0.00V \end{gather*}

So, the reduction of H+H^+ on the cathode is more favorable than the reduction of alkali metals. Alkali metals can be obtained by electrolysis only from molten salts (KCl(l)KCl(l), NaCl(l)NaCl(l), etc.).

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