Question

Assertion: \[PbSi{{F}_{6}}+{{H}_{2}}Si{{F}_{6}}+Gelatin\] is taken as electrolyte in electrolytic refining of lead.
Reason: Discharge potential of \[P{{b}^{2+}}\] is less than H+.
(A)Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(B) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(C) Assertion is correct but the Reason is incorrect.
(D) Assertion is incorrect but the Reason is correct.

Answer 1

Hint: As per the Assertion, Electrolytic refining of lead is known as Betts electrolytic process. Lead is obtained from Bullion (non-ferrous compound) using an electrolyte. For this reason, discharge potential of an ion is the rate at which the ions tend to get reduced.

Complete answer:
Let us first see if the assertion is correct.
The assertion states that- \[PbSi{{F}_{6}}+{{H}_{2}}Si{{F}_{6}}+Gelatin\]is taken as electrolyte in electrolytic refining of lead.
According to Betts electrolytic process, which is used to obtain refined lead an electrolyte is used. The electrolyte used in this process is \[PbSi{{F}_{6}}\](Lead fluorosilicate) and \[{{H}_{2}}Si{{F}_{6}}\] (Hexafluorosilicic acid). The process takes place at \[45\text{ }{}^\circ C\text{ i}\text{.e }113\text{ }{}^\circ F\]. The cathodes are made of pure lead in thin sheets and the anode is generally of impure lead which has to be purified to which a potential of 0.5 volts is applied.
Gelatin is added to the electrolyte to smoothen the precipitate. Also it is quite inexpensive which makes it suitable for the refining process. 0.1% of gelatin is used in the electrolyte solution.
The electrolytic refining of lead is a very expensive method which provides high purity of lead. The lead obtained is mostly 99.999% pure.
Thus, we can conclude that the assertion stated is CORRECT.
Now, the reason is given as the Discharge potential of \[P{{b}^{2+}}\]is less than H+.
We know that the discharge potential is mainly dependent on the reduction potential. The reduction potential of an atom is the tendency to get reduced by gaining electrons. The reduction potential is directly proportional to the tendency to get reduced.
Higher SRP (Standard reduction potential) means that the positive ions will show lower discharge potential. So the SRP of \[P{{b}^{2+}}\]is -0.13 V and that of H+ is 0.00 V. SRP of \[P{{b}^{2+}}\]is less than H+.
This means, the discharge potential of \[P{{b}^{2+}}\] will be more than H+.
So, the reason stated is incorrect.

OPTION C- Assertion is correct but the Reason is incorrect.

Note:
To calculate the Discharge potential you must know the SRP values of the ions. The discharge potential is mainly affected by the concentration of the given ion in the electrolyte, nature of the electrodes, position of the ion in the electrochemical series and the relation between both the given ions in the electrochemical series.