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Which of the following pairs of metals is purified by van Arkel method?
A
Ni and Fe
B
Ga and In
C
Zr and Ti
D
Ag and Au
Detailed Solution
The van Arkel method is a vapour phase refining method used to obtain ultra-pure Zr and Ti by removing oxygen and nitrogen present as impurities.
The crude metal is heated with iodine in an evacuated vessel to form the volatile tetraiodide: $Zr + 2I_2 \rightarrow ZrI_4$ (and $Ti + 2I_2 \rightarrow TiI_4$)
The tetraiodide is decomposed on a tungsten filament heated electrically to about 1800 K: $ZrI_4 \rightarrow Zr + 2I_2$
The pure metal deposits on the filament.
Ni is refined by Mond's process, Ga and In by zone refining, and Ag and Au by electrolytic methods.
Hence Zr and Ti are purified by the van Arkel method.
The crude metal is heated with iodine in an evacuated vessel to form the volatile tetraiodide: $Zr + 2I_2 \rightarrow ZrI_4$ (and $Ti + 2I_2 \rightarrow TiI_4$)
The tetraiodide is decomposed on a tungsten filament heated electrically to about 1800 K: $ZrI_4 \rightarrow Zr + 2I_2$
The pure metal deposits on the filament.
Ni is refined by Mond's process, Ga and In by zone refining, and Ag and Au by electrolytic methods.
Hence Zr and Ti are purified by the van Arkel method.