Question

When alloy of silver and lead is rich in silver:
A. Cupellation process is used
B. Parke’s method is used
C. Pattinson’s method is used
D. Any of the above method can be used

Answer 1

Hint: In an alloy of silver and lead rich in silver we use the process of oxidation to remove the impurities of lead from silver. Parke’s method is generally used to remove impurities of silver from lead.

Complete step by step answer:
-Cupellation: Pb impurities present in Ag(silver) are removed by this method. The impure metal is heated in a couple or oral shaped crucible made of bone ash or cement and a blast of air passes over the molten mass. The impurities get oxidized with the blast of air.
-Parke’s method: It is a pyro metallurgical industrial process for removing silver from lead during the production of bullion. It is an example of liquid-liquid extraction. The process takes advantage of two liquid state properties of zinc.
-Pattinson’s process: It is a method for removing silver from lead. The process is dependent on the fact that lead which has least silver in it solidifies first on liquefaction. In practice several times crystallizations were required and silver content of the silver-rich melt could not be raised above $2\% $.
So, the correct answer is (A).

Additional Information: Native Silver is a rare element, although it exists as such. It is usually found in nature combined with other metals, or in minerals that contain silver compounds, generally in the form of sulphides such as galena (lead sulphide), or cerussite(lead carbonate). So, the primary production of silver requires the smelting and then Cupellation of argentiferous lead ores.
 Lead melts at ${327^ \circ }$, lead oxide at ${888^ \circ }$and silver melts at ${960^ \circ }$. To separate the silver, the alloy is melted again at a high temperature of ${960^ \circ }$ to ${1000^ \circ }$ in an oxidizing environment.

Note: Cupellation process is based on the principle that precious metals including gold, silver do not get oxidized while the base metals including zinc, copper, lead etc they react and form compounds when subjected to high temperatures. Thus both these metals are separated from each other.