Question

Which of the following ion will move at the anode when molten lead bromide is used as an electrolyte?

• A. H⁺
• B. OH^-
• C. Pb²⁺
• D. Br ^-

Answer 1

The correct option is D

Br ^-

In the electrolysis of molten lead bromide, when the current is turned on, the positive ions (Pb${}^{2+}$) migrate towards the cathode. They take 2 electrons each and become neutral lead atoms. The negative ions (Br${}^{-}$) come in contact with anode, give an electron each and become bromine atoms. These two atoms combine to form bromine molecule (Br${}_2$).

Electrode reaction:

At the cathode: $P{b}^{2+}+2e^{-}\Rightarrow Pb$

At the anode: $B{r}^{-}-e^{-}\to Br$

$Br+Br\to B{r}_2$

The overall reaction: $PbB{r}_2\left(I\right)\to Pb\left(s\right)+B{r}_2\left(g\right)$