Explain:
(i). Zone refining
(ii). Column chromatography.

Explanation

(i) Zone refining . This method is used for produacation of semiconductors and other metals of very high puity e.g. G.e Si. B, Ca and In .
it is based on the prinicple that impurites
are more soluble in the mothen state (Melt ) than in the solid state of the metal .
the impure metal in the form of bar is hearted at one end with a moving circular heater .As - the heater is slowly moved along the length of the rod, the pure metal crystallises out of the melt whereas the impurities pass into the adjacent molten zone Thi.s process is repeated several times till the impurites are completely driven to one end of hte rod which is then cut off and discarded
(ii) chromatogrophy , it is based on the principle that the different components of a misture are absorbed to different extens on an adsorbent .
in column chromatography , an adsorbent , such as alummina `(Al_92)O_(3))` or silica gel is packed in a colunm . this fonns the statioary phase . the mixture to be separated is dissolved in suitable solvent (mobile phase ) and applied to the column . the adsorbed componts are extracted (eluted) from the column with a suitable . solvent (eluent ) . the component which si more strongly adsorbed on the column takes longer time to travel through the colunm than a component which is weakly adsorbed . thus , the various components of the mixture are seperated asthey travel through adsorbent (stationary pase ).