Question

How many metals are commercially purified by the Van Arkel method from the given metals? Ti, B, Zr, Pb, Hg.

Answer 1

The van Arkel method comes under the vapor phase refining method. The metals which are refined by this method belong to the d-block. Both metals belong to group 4.

Complete step by step answer:
Van Arkel's method comes under the vapor phase refining method.
Vapour phase refining: In this method impure metal is freed from impurities by first converting it into a specific volatile compound by heating it with a specific reagent at a lower temperature and then decomposing the volatile compound at some higher temperature which gives the pure metal.
Thus the two requirements are: the metal should form a volatile compound with a suitable reagent and the volatile compound should be easily decomposable.
Van Arkel method: This method is very useful for preparing ultra-pure metals by removing all the oxygen and nitrogen present in the form of impurities in certain metals like titanium and zirconium which are used in space technology. In this method, crude zirconium is heated in an evacuated vessel with iodine at 870 K and titanium is heated at 523 K. the covalent zirconium tetraiodide or titanium tetraiodide thus formed is easily separated. It is then heated at tungsten filament at 2075 K to give pure zirconium. Pure titanium is obtained by heating the volatile compound at 1700 K.
The reactions of the process are given below:
$\underset{impure}{\mathop Zr(s)}\,+2{{I}_{2}}\to Zr{{I}_{4}}\to \underset{pure}{\mathop Zr(s)}\,+2{{I}_{2}}$
$\underset{impure}{\mathop Ti(s)}\,+2{{I}_{2}}\to Ti{{I}_{4}}\to \underset{pure}{\mathop Ti(s)}\,+2{{I}_{2}}$

Hence, the metals refined by the van Arkel method are Zi and Ti.

Note: The volatile compound must be decomposable so that the recovery is easy. Mond process is also one method which comes under vapor phase refining. Ni (nickel) is purified by the Mond process. This process also follows the same steps.