Question

State the following during the electrolysis of molten lead bromide

(i) Ions present

(ii) product formed at the electrodes [cathode and anode]

Answer 1

(i) The ions present in it are ${\mathrm{Pb}}^{+2}$ and ${\mathrm{Br}}^{-}$.

(ii)At the Cathode

• The Reduction half reaction is taking place at the cathode
• The cathode is an electron donor hence the lead ions gain electrons from the cathode to form metallic lead ions.
• Product at the cathode: Lead. silver grey metal(lead) is deposited around the cathode

${\mathrm{Pb}}^{+2}+2{\mathrm{e}}^{-}\to \mathrm{Pb}$

At the anode

• The Oxidation half reaction is taking place at the cathode.
• Bromide ions give up electrons to the anode and then turn into neutral bromine atoms hence the neutral bromine atoms form covalent bromine molecules.
• Product at the anode: Bromine. Reddish-brown vapors are seen at the anode and then bromine vapors are evolved from the molten lead bromide.

$$\begin{gathered} {\mathrm{Br}}^{-}-{\mathrm{e}}^{-}\to \mathrm{Br} \\ \mathrm{Br}+\mathrm{Br}\to {\mathrm{Br}}_2 \end{gathered}$$