Question

Assertion: Desilverisation of lead is done by Parke’s method.
Reason: When the lead-silver alloy is poor in silver, zinc is added to molten ore.
(a) Both assertion and reason are correct and the reason is the correct explanation for the assertion.
(b) Both assertion and reason are correct and the reason is not the correct explanation for the assertion.
(c) Assertion is correct but the reason is incorrect.
(d) Assertion is incorrect but the reason is correct.

Answer 1

A pyrometallurgical method in which during the process of production of bullion, the silver is extracted from lead by the property of liquid-liquid extraction. The solubility of silver in zinc is 3000 times more than the solubility of silver in lead.

Complete step by step answer:
A pyrometallurgical method in which during the process of production of bullion, the silver is extracted from lead by the property of liquid-liquid extraction and the process is called the Parkes process. This process relies on the advantage of two liquid-state properties of zinc.
The two advantages of using zinc are that first, it is immiscible with lead, and the other is that the solubility of silver in zinc is 3000 times more than the solubility of silver in lead. So, when the zinc is added to the silver-lead alloy, zinc being is soluble in silver forms a solution while zinc is insoluble lead, so the lead remains as a separate layer. Now, this solution of silver-zinc is heated until zinc evaporates leaving pure silver.
So, the correct answer is an option (a) Both assertion and reason are correct and the reason is the correct explanation for the assertion.

Additional information: There is another process from which the silver is extracted from lead. This process is based on the fact that even when the lead has the least amount of silver, on cooling the silver will crystal out first but this is poorer, so the remaining liquid has a higher content of silver. This method is useful but it cannot be raised above 2% for separating the silver from the lead, so Parke’s method is followed.

Note: The process was invented in 1850. Gold is also a noble metal and it can also be extracted into pure form by the same process. This process was not used in the United States because of the low native production of lead.