Question

Give appropriate reasons for the following statements:
During electrolysis of molten lead bromide graphite anode is preferred to other electrodes.

Answer 1

We know that electrolysis is a process in which electrolytes break down on passing electrical energy through it. In this process, the free ions formed are attracted to the oppositely charged electrodes which are connected to a DC supply.

Complete step by step answer:
Let’s understand the anode and cathode in detail. Two electrodes namely cathode and anode are used in the process of electrolysis. The cathode is the electrode which is negatively charged and anode is the electrode which is negatively charged. So, in the process of electrolysis there is movement of positively charged ions towards the cathode and negatively charged ions towards the anode.

Now, come to the question. Here, we are asked the reason due to which graphite electrode is preferred as anode in electrolysis than other electrodes. Graphite is an allotrope of carbon and due to its inert nature it is used as anode in electrolysis of molten lead bromide. If other active electrodes are used then the bromide undergoes reaction with them.

Additional Information:
Let’s understand the electrolysis of molten lead bromide.
At cathode:

1. Lead ions $\left( {{\rm{P}}{{\rm{b}}^{2 + }}} \right)$ gain electrons from the electrodes to become lead atoms.
2. $\left( {{\rm{P}}{{\rm{b}}^{2 + }}} \right)$ ions discharged and molten grey colored globules of lead metal are formed below the electrolyte.
   Cathodic reaction is,
   ${\rm{P}}{{\rm{b}}^{2 + }} + 2{e^ - } \to {\rm{Pb}}$
   At the anode:
3. Bromide ions lose electrons to electrodes to become bromine molecules.
4. Bromine atoms combine to form bromine molecules that are an effervescence of red-brown bromine gas possessing a pungent odour.
   Anodic reaction is,
   $2{\rm{B}}{{\rm{r}}^ - } \to {\rm{B}}{{\rm{r}}_{\rm{2}}}\left( g \right) + 2{{\rm{e}}^ - }$

Note: Always remember that products of electrolysis depend on two factors, that is, nature of materials and types of electrodes. There are two sets of electrodes namely inert and active electrodes. Inert electrodes are those electrodes that do not participate in the electrode reaction such as graphite, gold, platinum etc. and active electrodes are those electrodes that participate in the electrode reaction such as copper, silver etc.