Downs cell is used commercially to perform electrolysis of molten

Options

A. `NaCl`
B. `LiCl`
C. `KCl`
D. `RbCl`

Answer

A

Explanation

A Downs cell is a commerical electrochemical cell used to obtain `Na` metal by the electrolysis of molten sodium chloride. The cell is constructed to keep the products of the electrolysis separate, because they would otherwise react. Calcium chloride is added to the sodium chloride to lower the melting point from `801^(@)C` for `NaCl` to about `580^(@)C` for the mixture. (Remember that the melting point, or freezing point, of a substance is lowered by the addition of a solute). We obtain the cell reaction by adding the half-reaction:
`{:(Na^(+)(l)+e^(-) rarr Na(l)),(Cl^(-)(l) rarr (1)/(2)Cl_(2)(g)+e^(-)))/(Na^(+)(l)+Cl^(-)(l) rarr Na(l)+(1)/(2)Cl_(2)(g))`
A number of other reactive metals are obtained by the electrolysis of a molten salt or ionic compound. Lithium, magnesium, and clacium metals are all obtained by the electrolysis of the chlorides.
The first commercial preparation of sodium metal adapted the method used by Humphry Davy when he discovered the ele-ment in `1807`. Davy electrolyzed molten sodium hydroxide, `NaOH` whose melting point `(318^(@)C)` is relatively low for an ionic compound. The half-reaction are
Cathode: `Na^(+)(l)+e^(-) rarr Na(l)`
Anode: `4OH^(-)(l) rarr O_(2)(g)+2H_(2)O(g)+4e^(-)`
Many of the commercial uses of electrolysis involve aqueous solutions