Question

(i) Name the method of refining of metals such as Germanium.
(ii) In the extraction fo $Al$, impure ${Al}_2{O}_3$ is dissolved in conc. $NaOH$ to form sodium aluminate and leaving impurities behind. What is the name of this process?
(iii) What is the role of coke in the extraction of iron from its oxides?

Answer 1

(i) Zone refining method is used for the purification of semi-conductor metals such as Germanium. This method is based on the principle of fractional crystallization that is the difference in solubilities of impurities in a molten and solid state of metal.

(ii) The name of the process is Bayer process, where bauxite ore is heated in a pressure vessel along with a sodium hydroxide solution at a temperature of 150 to 200 C. At these temperatures, the aluminium is dissolved as sodium aluminate and impurities left behind.

(iii) Coke is cheap and provides both the reducing agent for the reaction and also the heat source. The coke burns in the blast of hot air to form carbon dioxide - a strongly exothermic reaction. This reaction is the main source of heat in the furnace in the extraction of iron from its oxides.