Chemical Reactions and Equations-III


CHEMICAL REACTIONS AND EQUATIONS-III

The effects of oxidation reactions in everyday life

CORROSION
The phenomenon due to which the surface of metal is attacked by air, water and chemicals present in the atmosphere (acids), is called corrosion.
Some common examples of corrosion:
                          i.    Rusting of iron – iron when reacts with moist air forms a layer of rust over its surface
          
          Fe + 3 O2 + 2 xH2O      2 Fe2O3. xH2O
                                      Hydrated iron (III) oxide (rust)
                ii.    Tarnishing of silver – silver is a least reactive metal, yet it reacts with hydrogen sulphide to form black layer of silver sulphide.

           2Ag      +     H2S                   Ag2S    +   H2
          Silver        Hydrogen                Silver
                            Sulphide               Sulphide
                 iii.  Green coating on the surface of copper – copper when exposed to air and moisture forms a green layer of basic copper carbonate.

           2Cu + O2 + CO2 + H2O       CuCO3 + Cu (OH)2
                                                       (Basic copper carbonate)
                                                               Green coating
1.      Necessary conditions for corrosion –
i.                    Presence of air
ii.                  Presence of water

2.      Effects of corrosion – corrosion causes damage to car bodies, bridges, iron railings, ships and to all objects made of metals.

3.      Methods of prevention –
i.                    By painting
ii.                  By greasing
iii.                By oiling
iv.                Galvanisation
v.                  Using alloys

Rancidity
        It is the process of oxidation fat and oil present in the food materials, which result into bad taste and foul smell.
1.   Methods to prevent rancidity
i.                    Using air tight containers
ii.                  Refrigeration
iii.                Flushing of nitrogen gas in chips packet
iv.                By adding antioxidants e.g. BHA and BHT



Prepared by Ms. Priti Maan                                                                Uploaded by Amit Manhas

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