Which one of the following electrolytes is used in Down's process of extracting sodium metal?
Which one of the following electrolytes is used in Down's process of extracting sodium metal?
$\mathrm{NaCl}+\mathrm{KCl}+\mathrm{KF}$
$\mathrm{NaCl}$
$\mathrm{NaOH}+\mathrm{KCl}+\mathrm{KF}$
$\mathrm{NaCl}+\mathrm{NaOH}$
Solution
Sodium metal is manufactured by the electrolysis of fused sodium chloride mixed with $\mathrm{KCl}$ and $\mathrm{KF}$.
On electrolysis
At iron cathode.
$\mathrm{Na}^{+}+e^{-} \longrightarrow \mathrm{Na}(s)$ (metallic sodium)
At graphite anode
$2 \mathrm{Cl}^{-} \longrightarrow \mathrm{Cl}_2(g)+2 e^{-}$
$\mathrm{NaCl}$ melts at $800^{\circ} \mathrm{C}$. It is difficult to attain and maintain its melting point. So, $\mathrm{KCl}$ and $\mathrm{KF}$ are mixed to lower the melting point of $\mathrm{NaCl}$ to about $600^{\circ} \mathrm{C}$. $\mathrm{KCl}$ and $\mathrm{KF}$ are themselves not electrolysed under the voltage conditions used for sodium.