Question

Name the gas that evolved when the following are electrolyzed :
(i) Molten lead bromide
(ii) Concentrated hydrochloric acid
(iii) Acidulated water

Answer 1

Molten lead bromide:

1. During the electrolysis process, the electrolyte molten lead$\left(II\right)$ bromide $PbB{r}_2$ (l) offers a high concentration of lead (II) ions $P{b}^{2+}$and bromide ions $B{r}^{-}$ to conduct the current.
2. Remember that melting an ionic compound weakens the strong ionic bonding, allowing the ions to travel freely and conduct the electric current.
3. The products of electrolyzing lead bromide are lead metal and Bromine gas.

Concentrated hydrochloric acid:

1. The reaction of concentrated hydrochloric acid in cathode and anode during electrolysis is given below:

At cathode: $2{\mathrm{H}}^{+}\left(\mathrm{aq}\right)+2{\mathrm{e}}^{-}\to {\mathrm{H}}_2\left(\mathrm{g}\right)$

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

Hence, Chlorine is evolved at the anode.

Acidulated water:

1. When acidulated water or dilute sulhouric acid is electrolyzed, oxygen gas is produced at the anode. OH travels towards the anode because it is negatively charged (positively charged electrode).
2. ${\mathrm{SO}}_4^{2-}$, $O{H}^{-}$, and $H+$ are the ions present in the solution.
3. The $+ve$charge goes towards the cathode, whereas the$-ve$charge moves towards the anode.

At cathode:

$2{\mathrm{H}}^{+}\left(\mathrm{aq}\right)+2{\mathrm{e}}^{-}⟶H_2\left(g\right)$

At anode:

$$\begin{gathered} {\mathrm{OH}}^{-}\left(aq\right)-{\mathrm{e}}^{-}⟶\mathrm{OH}\left(aq\right) \\ 4OH\left(aq\right)\to 2H_{2}O\left(l\right)+O_2\left(g\right) \end{gathered}$$

Hence, Oxygen is evolved at the anode.
The gas evolved when Molten lead bromide is electrolyzed is Bromine.
The gas evolved when Concentrated hydrochloric acid is electrolyzed is Chlorine.
The gas evolved when Acidulated water is electrolyzed is Oxygen.