Question

Lead obtained from galena ore (PbS) by air reduction or carbon reduction process contains base metal (Cu, Bi, As, Sn, Zn) as impurities. The removal of the impurity of Ag from the commercial lead is called:
A.Desilverization of lead
B.Softening process
C.Bett’s electrolysis
D.Cupellation

Answer 1

Hint: Try to recall that lead obtained from galena contains silver and many base metals as impurity and removal of silver is done by Parke’s process. Now by using this you can easily find the correct option from the given ones.

Complete step by step solution:
It is known to you that lead is obtained from galena ore by self reduction. The lead obtained by self reduction contains base metals like copper, silver, zinc as impurities.
The removal of the impurities of Ag from the commercial lead is called desilverisation of lead and is done by Parke’s process. Thus, Parke’s process is the desilverisation of lead.
In Parke’s process, the commercial lead, which contains Ag as impurities, is melted in iron pots and 1% of Zn is added to it. The molten mass is thoroughly agitated. Since, Ag is about 300 times more soluble in Zn than in Pb, most of the Ag present in the commercial lead as impurity mixes with Zn, to form Zn-Ag alloy.
When the whole is cooled, two layers are obtained. The upper layer contains Zn-Ag alloy in the solid state, while the lower layer has lead in the molten state.
The lead obtained after removing most of Ag from it by Parke’s process, is called desilverised lead.
 Therefore, from above we can conclude that option A is the correct option to the given question.

Note:
It should be remembered to you that the lead obtained by desilverisation contains the impurities like Zn, Au, Sb, etc. These metal impurities are removed from desilverised lead by Betts electrolytic process.
Also, you should remember that in the cupellation method, lead present in silver is removed by the cupellation process.