CBSE Class 12 Chemistry General Principles Process Of Isolation Of Elements Chapter Notes

                                                           Chemistry Ch 6: General Principles & Processes  Of Isolation of Elements Top concepts:

1. Minerals: The naturally occurring chemical substances in the earth’s crust which are obtained by mining are known as minerals. Metals may or may not be extracted profitably from them.

2. Ores: The rocky materials which contain sufficient quantity of mineral so that the metal can be extracted profitably or economically are known as ores.

3. Gangue: The earthy or undesirable materials present in ore are known as gangue.

4. Metallurgy: The entire scientific and technological process used for isolation of the metal from its ores is known as metallurgy.

5. Chief Ores and Methods of Extraction of Some Common Metals:                          

6. Steps of metallurgy:

   a. Concentration of ore

   b. Conversion of concentrated ore to oxide

  c. Reduction of oxide to metal

   d. Refining of metal

7. Concentration of ore: The process of removal unwanted materials like sand, clay, rocks etc from the ore is known as concentration, ore – dressing or benefaction. It involves several steps which depend upon physical properties of metal compound and impurity (gangue). The type of metal, available facilities and environmental factors are also taken into consideration.

8. Hydraulic washing (or gravity separation): It is based on difference in densities of ore and gangue particles. Ore is washed with a stream of water under pressure so that lighter impurities are washed away whereas heavy ores are left behind.

9. Magnetic separation: This method is based on the difference in magnetic and non – magnetic properties of two components of ore (pure and impure). This method is used to remove tungsten ore particles from cassiterite (SnO₂). It is also used to concentrate magnetite (Fe₃O₄), chromite (FeCr₂O₄) and pyrolusite (MnO₂) from unwanted gangue.

10. Froth Floatation Process: The principle of froth floatation process is that sulphide ores are preferentially wetted by the pine oil, whereas the gangue particles are wetted by the water. Collectors are added to enhance the non-wettability of the mineral particles. Examples are pine oil, fatty acids and xanthates are added to it. Froth stabilizers are added to stabilize the froth. Examples are cresols, aniline. If two sulphide ores are present, it is possible to separate the two sulphide ores by adjusting proportion of oil to water or by adding depressants.For example- In the case of an ore containing ZnS and PbS, the depressant used is NaCN. It selectively prevents ZnS from coming to froth but allows PbS to come with the froth.

11. Leaching (Chemical separation): It is a process in which ore is treated with suitable solvent which dissolves the ore but not the impurities.

12. Purification of Bauxite by Leaching: Baeyer’s process: