CBSE Class 12 Chemistry notes and questions for Processes of Isolation of Elements Part B. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.
General Principles & Process of Isolation of Elements
Important Points :
1. The chemical substances in the earth’s crust obtained by mining are called Minerals.
2. Minerals, which act as source for metal, are called Ore. From ore metal can be obtained economically .
3. The unwanted impurities present in ore are called Gangue.
4. The entire process of extraction of metal from its ore is called Metallurgy.
5. Removal of gangue from ore is called Concentration, Dressing or Benefaction of ore.
6. Concentration by Hydraulic washing is based on the difference in gravities of ore and gangue particles.
7. Concentration by Magnetic separation is based on differences in magnetic properties of ore components. If either of ore or gangue is capable of attracted by a magnet field, then such separation is carried out.
8. Concentration by Froth Flotation Process is based on the facts that sulphide ore is wetted by oil & gangue particles are wetted by water.
9. Concentration by Leaching is based on the facts that ore is soluble in some suitable reagent & gangue is insoluble in same reagent. e.g. Bauxite ore contains impurities of silica, iron oxide & TiO2 .The powdered ore is treated with NaOH which dissolve Al & impurities remains insoluble in it.
Al2O3 +2NaOH + 3 H2O —→ 2 Na [Al(OH)4].
10. Calcination involves heating of ore in absence of air below melting point of metal. In this process volatile impurities escapes leaving behind metal oxide.
Fe2O3.xH2O —→Fe2O3 +xH2O
ZnCO3 —→ ZnO +CO2
CaCO3.MgCO3 —→ CaO + MgO + 2CO2
11. Roasting involves heating of ore in presence of air below melting point of metal in reverberatory furnace. In this process volatile impurities escapes leaving behind metal oxide and metal sulphide converts to metal oxide.
2 ZnS + 3 O2 —→2ZnO+2SO2
2PbS + 3 O2 2 —→ PbO +2 SO2
2 Cu2S + 3 O2 —→2Cu2O + 2 SO2
12. Reduction of metal oxide involves heating of metal in presence of suitable reagent Coke or CO2.
13. Reactions taking place at different zones of blast furnace in extraction of iron:-
(i) Zone of reduction:- Temperature range 250oC-700oC
3Fe2O3+CO —→ 2Fe3O4+CO2
Fe3O4+CO —→3FeO+ CO2
FeO +CO —→ Fe+ CO2
(ii) Zone of slag formation:- Temperature range 800oC-1000oC
CaO+SiO2 —→ CaSiO3, P4O10+10C —→ 4P+10CO,
SiO2+2C —→ Si+2CO, MnO2+2C —→ Mn+2CO
(iii) Zone of fusion: - Temperature range 1150oC-1350oC
CO2 + C —→2CO
(iv) Zone of fusion: - Temperature range 1450oC-1950oC
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