Question

Select the incorrect statement.
(A) When the lead –silver alloy is rich in silver, lead is removed by the cupellation process
(B) When the lead –silver alloy is rich in lead, lead is removed by park’s or pattinson’s process
(C) Zinc forms an alloy with silver, from which zinc is separated by distillation
(D) Zinc forms an alloy with silver, from which zinc is separated by distillation

Answer 1

Hint: An alloy contains more than one element and has the characteristics of both the metals and pure metal and alloy have different physical properties.
Lead is obtained from galena which contains the main impurity of silver.

Complete answer:
(A) Cupellation process is used to purify silver containing the impurity of lead. This process is used when impurity has greater affinity toward oxygen, while metal does not have does not react with oxygen.
$\begin{align}
& \text{Pb}\,\,\text{+}\,\,{{\text{O}}_{\text{2}}}\,\,\,\to \,\,\text{volatile}\,\text{oxide(PbO)} \\
& \text{Ag}\,\,\text{+}\,\,{{\text{O}}_{\text{2}}}\,\,\to \,\,\text{No}\,\text{reactio} \\
\end{align}$
(B) Parke’s or Pattinson's process is mainly used to remove silver metal from lead-silver alloy. In Parke's process lead-silver is heated in an iron pot and 1% zinc is added then cooled. $\text{Zn-Ag}$ Alloy get solidified and molten lead floats which get separated. In Pattinson’s process alloy of lead –silver containing more lead is heated and allowed to cool slowly and finally pure lead is separated.
(C) In parke’s process zinc form alloy with silver from which lead is separated out.
(D) Zinc and mercury are purified by distillation process under low pressure. Zinc forms alloy with silver from which zinc is separated by vacuum distillation process.

So, option (C) will be the right choice.

Note: Metal having low boiling point is refined by distillation process. Zinc, cadmium and mercury have low boiling point.
Cupellation is the chemical method of purification of metal.