JEE Main 2015 Chemistry - Principles and Processes of Isolation of elements by ednexa.com

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General Principles and Processes of Isolation of elements Exercises Q.1 What is difference between minerals and ores? Ans. Naturally occurring chemical substances in form of which the metals occur in free or combined state in earth crust along with impurities are known Minerals and obtained by mining e.g. Haematite Fe2O3Magnesite MgCO3. In Ores are the minerals which contain high percentage of metal and can be extracted from it e.g. Zinc blende ZnS, Dolamite MgCO3, CaCO3. So all the ores are minerals all minerals are not ores. Q.2 Which are the different methods used in metallurgy? Ans. The processes of extracting metals from their ores are different metallurgical process. There is no single universal method for extraction of pure metal. They are as below-
i) Pyrometallurgy ii) Hydrometallurgy iii) Electrometallurgy.
Q.3 What is Pyrometallurgy? Ans. In Pyrometallurgy process the ore is reduced at high temperature in presence of some reducing agent e.g. carbon, hydrogen, aluminium etc. Q.4 What is meaning of Hydrometallurgy? Ans. In Hydrometallurgy the ore is first treated with water to make aqueous solution of metal. This aqueous solution of metal compounds then reduced with suitable reducing agent. Q.5 Explain the following terms (i) Gangue (ii) Slag. Ans. Gangue- A sandy, earthy and other undesired impurities of the various substance present in ore e.g. presence of silica in haematite iron ore. Slag- A slag is easily fusible material. It is formed due to presence of gangue in the roasted or calcined ore. It combines with flux. In Iron metallurgy the CaO is flux which combines with silica (gangue) and forms easily fusible slag of calcium silicate (CaSiO3). Q.6 Which are the various steps involved in the extraction of pure metals from there ores? Ans. No single universal procedure is adopted for extraction of pure metal. Most common metallurgical operations are as follows –
1. Crushing and grinding of the ore.
2. Concentration of ores.
3. Conversion of ores in reducible oxides or other compound.
4. Reduction of ores to get impure metal.
5. Refining of crude impure metal.

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Q.7 Using an Ellingham diagram indicates the lowest temperature at which the ZnO can be reduced to Zinc metal by carbon. Write the overall reaction at this temperature. Ans. Ellingham diagram shows variation in standard Gibbs free energy change with temperature for the formation of oxide. The Ellingham diagram shows straight line upward slope with formation of oxide but in case of ZnO there is sudden change. Ellingham diagram helps in selecting suitable reducing agent. By seeing the Ellingham diagram the free energy formation (ΔfG˚) of CO from C becomes lower temperatures above 1120 K while that of CO2 from C becomes lower above 1323 K than (ΔfG˚) of ZnO. As (ΔfG˚) of CO2 from CO is always higher than of ZnO. So c can reduce ZnO to Zn but not CO. Thus Carbon is better reducing agent than CO for ZnO.
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