153.

Describe the principle involved in each of the following processes.

(i) Mond process for refining of Nickel.

(ii) Column chromatography for purification of rare elements.

Mond process for refining of Nickel is based on the principle that nickel is heated in the presence of carbon monoxide to form nickel tetracarbonyl, which is a volatile complex.

Ni + 4CO  Ni(CO)₄

                      (Nickel tetracarbonyl)

Then, the obtained nickel tetracarbonyl is decomposed by subjecting it to a higher temperature (450 - 470 K) to obtain pure nickel metal.

Ni(CO)₄          Ni + 4CO
(Nickel tetracarbonyl)    nickel

(ii) Column chromatography is based on the principle that different components of a mixture are differently adsorbed on an adsorbent. In it, there are two phases: mobile phase and stationary phase. The stationary phase is immobile and immiscible example Silica gel(SiO₂) , Alumina gel(Al₂O₃) . Al₂O₃ column is usually used as the stationary phase in column chromatography. The mobile phase may be a gas, liquid, or supercritical fluid in which the sample extract is dissolved.

Then, the mobile phase is forced to move through the stationary phase. The component that is more strongly adsorbed on the column takes a longer time to travel through it than the component that is weakly adsorbed. The adsorbed components are then removed (eluted) using a suitable solvent (eluent).