Question

Giving a suitable example, describe Van Arkel method for the purification of metals.

Answer 1

This method is useful for removing all nitrogen and oxygen impurities found in some metals, such as Zr and Ti. In an evacuated vessel, iodine is used to heat the impure metal. Heating causes the formation of metal iodide. Since it is more covalent, the metal iodide volatilises.

\[\ce{\underset{(Impure)}{Zr} + 2I2 -> ZrI4}\]

\[\ce{\underset{(Impure)}{Ti} + 2I2 ->[320-500 K] TiI4}\]

After the metal iodide breaks down, it is electrically heated on a tungsten filament to produce pure metal that settles on the filament.

\[\ce{ZrI4 ->[1800 K][Tungsten filament] \underset{(Pure)}{Zr} + 2I2}\]

\[\ce{TiI4 ->[1700 K][Tungsten filament] \underset{(Pure)}{Ti} + 2I2}\]