NCERT Class XII Chemistry
Chapter - General Principle of Process of Isolation of Elements
Questions with Solutions
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Question : 8
Total: 31
Write chemical reactions taking place in the extraction of zinc from zinc blende.
Solution:
Concentration : When zinc blende is used, the powdered ore isconcentrated by froth-floatation process.
Roasting : The concentrated ore is heated in excess of oxygen at about 900°C. Zinc sulphide is oxidised to zinc oxide. If some of the ore is oxidisedto zinc sulphate, it also decomposes at 900°C into ZnO.
2 Z n S + 3 O 2
2 Z n O + 2 S O 2
Z n S + 2 O 2
Z n S O 4
For roasting, a reverberatory furnace may be used.
Reduction : The principal reaction that takes place during reduction is theconversion of the oxide into the metal with the help of carbon.
Z n O + C
Z n + C O
Electrolytic refining : Purification of zinc is done by electrolytic refiningusing pure Zn as cathode and impure Zn as anode. The electrolyte isZ n S O 4
Reaction at cathode: Z n 2 + ( a q ) + 2 e − → Z n ( s )
Reaction at anode :2 H 2 O ( l ) → O 2 ( g ) + 4 H + ( a q ) + 4 e −
Z n S O 4
Roasting : The concentrated ore is heated in excess of oxygen at about 900°C. Zinc sulphide is oxidised to zinc oxide. If some of the ore is oxidisedto zinc sulphate, it also decomposes at 900°C into ZnO.
For roasting, a reverberatory furnace may be used.
Reduction : The principal reaction that takes place during reduction is theconversion of the oxide into the metal with the help of carbon.
Electrolytic refining : Purification of zinc is done by electrolytic refiningusing pure Zn as cathode and impure Zn as anode. The electrolyte is
Reaction at cathode:
Reaction at anode :
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