Write the principle of the following :

(a) Zone refining

(b) Froth floatation process

(c) Chromatography

(a) Zone refining is based on the principal that the impurities are more soluble in the molten state(melt) than in the solid state of the metal. In other words, when the melt of an impure metal is allowed to cool, the pure metal crystallizes out while the impurities remain in the molten state(melt).

(b) Froth floatation process is widely used for the concentration of sulphide ores such as zinc blende(ZnS), copper pyrite (CuFeS₂), galena (PbS), etc. This is based upon the principal that the surface of the sulphide ores is preferentially wetted by the oils while that of gangue is preferentially wetted by the water.

(c) Chromatography is the most modern and versatile method for the separation, purification and testing the purity of elements and their compounds. This method is based upon the principle that the different components of a mixture are adsorbed to different extents on an adsorbent (the substance on which it is adsorbed).