Corrosion in case of iron is known as rusting.
Rusting of iron
Rusting of iron refers to the formation of rust, a mixture of iron oxides, on the surface of iron objects or structures. This rust is formed from a redox reaction between oxygen and iron in an environment containing water. The rusting of iron is characterized by the formation of a layer of a red, flaky substance that easily crumbles into a powder.
The reaction taking place in the formation of rust is given below
Oxygen is a highly active oxidizing agent whereas iron is a reducing agent. Therefore, the iron atom immediately gives up electrons when exposed to oxygen.
The chemical reaction takes place as follows
Fe → Fe2+ + 2e–
The oxidation state of iron is further increased by the oxygen atom when water is present in the atmosphere
4Fe2+ + O2 → 4Fe3+ + 2O2-
The listed below acid-base reactions occur between the iron cations and the water molecules.
Fe2+ + 2H2O ⇌ Fe(OH)2 + 2H+
Fe3+ + 3H2O ⇌ Fe(OH)3 + 3H+
The hydroxides of iron are also formed from the direct interaction and reaction between the iron cations and hydroxide ions.
O2 + H2O + 4e– → 4OH–
Fe2+ + 2OH– → Fe(OH)2
Fe3+ + 3OH– → Fe(OH)3