Rusting of iron is an electrochemical phenomenon
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Rusting of iron is an electrochemical phenomenon. A certain site on the iron object acts as an anode.
(Fe(s)⟶Fe2+(aq)+2e )× 2(Fe(s)⟶FeX2+(aq)+2e )× 2
Electrons released at this spot go to another site on the object and reduce oxygen in presence of H+HX+ ions which are either obtained from water out from acidic substances in water:
H2O⟶H++OH−HX2O⟶HX++OHX−
CO+H2O⟶H2CO3CO+HX2O⟶HX2COX3
H2CO3⟶2H++CO32−HX2COX3⟶2HX++COX3X2−
This site behaves as cathode and reaction is
4H++O2+4e⟶2H2O4HX++OX2+4e⟶2HX2O
Therefore the overall reaction is :
2Fe(s)+O2+4e⟶2Fe2+(aq)+2H2O2Fe(s)+OX2+4e⟶2FeX2+(aq)+2HX2O
Now the ferrous ions are further oxidised by atmospheric oxygen to ferric ions which come out as rust in form of hydrated ferric oxides.
Fe2+(aq)+2H2O+12O2⟶Fe2O3+4H+(aq)
(Fe(s)⟶Fe2+(aq)+2e )× 2(Fe(s)⟶FeX2+(aq)+2e )× 2
Electrons released at this spot go to another site on the object and reduce oxygen in presence of H+HX+ ions which are either obtained from water out from acidic substances in water:
H2O⟶H++OH−HX2O⟶HX++OHX−
CO+H2O⟶H2CO3CO+HX2O⟶HX2COX3
H2CO3⟶2H++CO32−HX2COX3⟶2HX++COX3X2−
This site behaves as cathode and reaction is
4H++O2+4e⟶2H2O4HX++OX2+4e⟶2HX2O
Therefore the overall reaction is :
2Fe(s)+O2+4e⟶2Fe2+(aq)+2H2O2Fe(s)+OX2+4e⟶2FeX2+(aq)+2HX2O
Now the ferrous ions are further oxidised by atmospheric oxygen to ferric ions which come out as rust in form of hydrated ferric oxides.
Fe2+(aq)+2H2O+12O2⟶Fe2O3+4H+(aq)
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