Explain calcination and roasting with examples.

The process of heating an ore strongly in the presence of very limited quantity of air is called calcination. This method is used to convert carbonate ore into oxide, to remove moisture or water from the hydrated ores. Example: During the calcination carbon dioxide is removed from malachite ore. CuCO 3 . Cu OH 2 → 2 CuO + CO 2 g + H 2 O g The process of heating an ore strongly below its melting point in the presence of an excess of air is called roasting. It is mainly used to convert sulphide ore into oxide ore or sulphate ore. Example: Roasting of zinc blende. 2 ZnS + 3 O 2 → heat ( in air ) 2 ZnO + 2 SO 2 g

Explain zone refining method for the purification of metals.

Zone refining method is based on the principle that the impurities are more soluble in the melt than in the solid-state of the metal. In this method, the impure metal is cast into a thin bar. A circular mobile heater is fixed at on end of the rod of impure metal. One zone of the bar is melted by a circular mobile heater in the atmosphere of an inert gas like argon. At the heated zone, the metal melts and forms a molten zone or the melt. As the heater moves forward slowly, the pure metal crystallizes out of the melt and the impurities pass on into the adjacent molten zone. The process is repeated several times and the heater is moved in the same direction till the impurities are completely driven to one end of the rod. This end is finally cut off and discarded. Thus, we get completely pure metal by this method. This method is especially useful for producing semiconductors like germanium of very high purity.

How can copper be extracted from hydrometallurgical process.

Hydrometallurgical process is used when the ore contains lesser amount of copper. The crushed ore is exposed to air, and water is sprayed over it. The moist air converts copper sulphide to copper sulphate. Some ferrous sulphate is also formed. The sulphate so formed are extracted by water sprayed over a heap of the ore and the solution collected in the tanks below. The reaction taking place are, 2 FeS 2 + 7 O 2 + 2 H 2 O → 2 FeSO 4 + H 2 SO 4 2 Fe 2 S 3 + 11 O 2 + 2 H 2 O → 4 FeSO 4 + 2 H 2 SO 4 CuO + H 2 SO 4 → CuSO 4 + H 2 O Copper metal is recovered from the solution od copper sulphate by adding iron scrap to the solution. CuSO 4 + Fe → FeSO 4 + Cu Red ppt . The precipitated copper is washed with water and dried. It is further purified by the electrolytic method.

Explain with neat diagram the extraction of aluminium from molten alumina.

The alumina is dissolved in molten cryolite and is electrolysed in an iron tank lined inside with carbon. The molten cryolite Na 3 AlF 6 decreases the melting point and increases the electrical conductivity. The iron tank lined inside with carbon act as cathode. The anode consists of a number of carbon rods dipped in the fused electrolyte. During the electrolysis, aluminium is liberated at the cathode and gets collected at the bottom of tank from where aluminium is removed periodically. At cathode: 2 Al 3 + + 6 e - → reduction 2 Al l At anode: 3 O 2 - → oxidation 3 2 O 2 g + 6 e -

How is zinc extracted from zinc blende? Give chemical reaction.

Zinc is extracted from zinc blende as follows: i) The zinc blende ZnS ore is concentrated by froth flotation process. ii)The concentration of zinc blende is heated strongly below its melting point in the presence of air to convert into zinc oxide. 2 ZnS + 3 O 2 → ∆ 2 ZnO + 2 SO 2 ↑ iii) Zinc oxide is reduced to zinc by heating with coke at 1673 K . ZnO + C → 1673 K Zn + CO

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - General Principles and Processes of Isolation of Elements>Nagaland Board-2019>Q 4

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12th Nagaland Board

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Explain Mond’s process for extraction of nickel.

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