CBSE Class 12 Chemistry Processes Of Isolation Of Elements Notes Set B

Chapter:6

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

CaCO₃  —→CaO+CO₂

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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