RUSTING OF IRON
 
 
   When iron is exposed to air and moisture, its surface gradually corroded and converted in to a brown    mass. This brown mass is called rust and this phenomenon is known as rusting.
CAUSE OF RUSTING
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   The rusting of iron is due to the formation of hydrated iron (III) oxide (Fe2O3.H2O).
NATURE OF RUSTING
 
   Rusting is an electro-chemical process. Different parts of the surface of iron act as a cathode and anode.    Moisture on the surface of iron plays a role of electrolyte between cathode and anode.
HOW RUSTING TAKES PLACE
 
   At anode iron is oxidized to Fe+2 ions and forms precipitates of Fe(OH)2. These precipitates are then    oxidized in to Fe2O3.H2O which is known as rust.
ELECTROCHEMICAL CHANGES
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Fe ® Fe+2 + 2e-

Fe+2 + 2OH- ® Fe(OH)2

4Fe(OH)2 + O2 + 2H2O ® 4Fe(OH)3

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   DESCRIBE DIFFERENT METHODS TO PROTECT IRON FROM RUSTING?
CATHODE PROTECTION
 
   In this method any reactive metal such as Mg+2, Zn+2 or Al+3 which is more reactive than Fe+2 small    blocks of any of the above metals is connected to the iron objects such as pipes, when corrosion starts,    only more reactive element is corroded and iron is prevented from rusting.
USE OF OIL PAINT
 

   Large objects such as bridge or ship can be protected from rusting by using oil paints.

USE OF GREASE
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   Moving parts of machinery are protected from rusting by using grease or oils.

GALVANIZING METHOD
 
   Iron objects can be protected by thin layers of zinc from rusting. This process is called galvanizing.
TINNING
 
   In this process a thin layer of tin is coated over the iron object.
ELECTROPLATING
 
   We can protect rusting of iron by electroplating of nickel or chromium.
ALLOY FORMATION
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   Iron can also be protected from rusting by converting it in to alloys such as stainless steel.
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