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CBSE Class 12th Chemistry Notes for Chapter 6 General Principles And Processes Of Isolation Of Elements

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   UNIT 6 GENERAL PRINCIPLES AND PROCESSES OF ISOLATION OF ELEMENTS

 

  • Ores are the minerals in which the metals are present and they can be extracted in a commercially feasible way.

 

  • Ores of the metal are associated with many impurities. Removal of these impurities to certain extent is achieved in concentration steps.

 

  • The concentrated ore is then treated chemically for obtaining the metal. The reducing agents used are carbon, CO or even some metals.

 

  • In these reduction processes, the thermodynamic and electrochemical concepts are used.

 

  • The metal oxide reacts with a reducing agent; the oxide is reduced to the metal and the reducing agent is oxidized.

 

  • In the two reactions, the net Gibbs energy change is negative.

 

  • The metals obtained by usual methods still contain minor impurities which are further removed by the process of refining.

 

  • Some metals and their extraction:
    • Aluminium:
      • Ore: Bauxite (Al2O3.xH2O) , Cryolite (Na3AlF6)
      • Extraction: Electrolysis of Al2O3 dissolved in molten Na3AlF6
    • Iron:
      • Ore: Haematite (Fe2O3) , Magnetite (Fe2O4)
      • Extraction: Reduction of the oxide with CO and coke in blast furnace
    • Copper:
      • Ore: Copper pyrites ( CuFeS2) , Copper glance (Cu2S) , Malachite (CuCO3.Cu(OH)2) , Cuprite (Cu2O)
      • Extraction: Roasting of sulphide partially and reduction
    • Zinc:
      • Ore: Zinc blende or Sphalerite (ZnS) , Calamine (ZnCO3) , Zincite (ZnO)
      • Extraction: Roasting followed by reduction with coke

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