(a) Write the principle of method used for the refining of germanium
(b) Out of PbS and `PbCO_(3)` (ores of lead), which one is concentrated by froth floatation process preferably ?
(c) What is the significance of leaching in the extraction of aluminium ?

Explanation

(a) Zone refining method is used for the refining of germanium.
Principle : This method is based upon the principle that the impurities are more soluble in the molten state than in the solid state of the metal
(b) PbS is concentrated by froth floatation process
(c) To remove the impurities like Silica `(SiO_(2))`, iron oxide `(Fe_(2)O_(3))`, leaching is carried out. During leaching, powdered bauxite ore is heated iwht conc. `NaOH` solution at `473 - 523` K.
`underset("Alumina")underset("Bauxite")(Al_(2)O_(3)(s)) + 2NaOH + 3H_(2)O overset(473 - 523)rarr underset("Sodium meta- aluminate")(2Na[Al(OH)_(4)])`
`underset("Silica")(SiO_(2)) + 2NaOH (aq) rarr underset("(Sodium Silicate)")(Na_(2)SiO _(3) + H_(2)O)`
Leaching leaves behind `Fe_(2)O_(3), TiO_(2)` and other impurities