What is Van Arkel method of obtaining ultrapure metals ?

Explanation

The impure metal (Ti or Zr) is first converted into its volatile iodile by heating with ` I _2 ` at some low temperature. The volatile iodide thus formed is separated from impurities. It is decomposed at a suitable high temperature to give the pure metal. For example,
` underset (("Impure"))(Zr (s)) + 2 I _ 2 (g) overset(870 K ) to Zrl _ 4 (g) overset (2075 K ) underset ("W filament") to underset (("Pure"))(Zr(s)) + 2 I _ 2 (g) `