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

 

   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