Question

In the Downs process, molten sodium chloride is electrolyzed to produce sodium. A valuable by product is chlorine. Write equations representing the processes taking place at the anode and at the cathode in the Downs process.

Short answer

Cathode: ${\mathrm{Na}}^{+}+{\mathrm{e}}^{-}\to \mathrm{Na}\left(\mathrm{l}\right)$

Anode: $2{\mathrm{Cl}}^{-}\to {\mathrm{Cl}}_2\left(\mathrm{g}\right)+2{\mathrm{e}}^{-}$

Step-by-step solution

Down’s process

Sodium or magnesium is prepared by an electrochemical method known as Down’s process by the electrolysis of sodium chloride or magnesium chloride. The apparatus used in this method is known as Down’s cell.

Step 2: Equations at cathode and anode

During the electrolysis of molten sodium chloride, sodium releases at the cathode, and chlorine release at the anode. Since the melting point of sodium chloride is very high, potassium chloride and potassium fluoride are used to decrease their melting point.

At the cathode, $\mathit{N}{\mathit{a}}^{\mathbf{+}}$ reduces to by gaining an electron.

${\mathrm{Na}}^{+}+{\mathrm{e}}^{-}\to \mathrm{Na}\left(\mathrm{l}\right)$

At the anode, the chloride ion loses two electrons to form chlorine.

$2{\mathrm{Cl}}^{-}\to {\mathrm{Cl}}_2\left(\mathrm{g}\right)+2{\mathrm{e}}^{-}$

The total reaction is given below:

${\mathrm{Na}}^{+}+2{\mathrm{Cl}}^{-}\to \mathrm{Na}\left(\mathrm{l}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)$