Question -
Answer -
(i) Zone refining:
Thismethod is based on the principle that impurities are more soluble in the moltenstate of metal (the melt) than in the solid state. In the process of zonerefining, a circular mobile heater is fixed at one end of a rod of impuremetal. As the heater moves, the molten zone of the rod also moves with it. As aresult, pure metal crystallizes out of the melt and the impurities pass ontothe adjacent molten zone. This process is repeated several times, which leadsto the segregation of impurities at one end of the rod. Then, the end with theimpurities is cut off. Silicon, boron, gallium, indium etc. can be purified bythis process.
(ii) Columnchromatography:
Columnchromatography is a technique used to separate different components of amixture. It is a very useful technique used for the purification of elementsavailable in minute quantities. It is also used to remove the impurities thatare not very different in chemical properties from the element to be purified.Chromatography is based on the principle that different components of a mixtureare differently adsorbed on an adsorbent. In chromatography, there are twophases: mobile phase and stationary phase. The stationary phase is immobile andimmiscible. Al2O3 column is usuallyused as the stationary phase in column chromatography. The mobile phase may bea gas, liquid, or supercritical fluid in which the sample extract is dissolved.Then, the mobile phase is forced to move through the stationary phase. Thecomponent that is more strongly adsorbed on the column takes a longer time totravel through it than the component that is weakly adsorbed. The adsorbedcomponents are then removed (eluted) using a suitable solvent (eluant).
