Anode: 2Fe (s) → Fe2+ (aq) + 4e-
The four electrons from anode move to cathode. Reduction take place in cathode .Oxygen dissolved in water is reduced to become water in cathode.
Cathode: O2 (g) + 4H+ (aq) + 4e-→2H2O (l)
When combine half-equation in anode and cathode,overall oxidation-reduction is:
2Fe (s) + O2 (g) + 4H+ (aq) → 2Fe2+ (aq) + 2H2O (l)
Fe2+ ions move out of the cathode then,it oxidizes to Fe3+ and contact with dissolved oxygen to form rust.
4 Fe2+ (aq) + O2 (g) + 4H2O (l) → 2Fe2O3 . x H2O(s) + 8H+ (aq)
Rusting will occur faster when there are acid and salt presences. 3 ways can reduce rusting which is
using protective coating, alloying and sacrificial protection. Protective coating is to prevent air and
water reaching in the surface of iron. We can use oil and grease for moving part of engine. Paint also
can use for the objects which are not easily to scratch such as gates and car. Then, plastic can use for
light item such as clothes hanger and wire fences. Besides that, alloying iron to stainless steel also
prevent rusting. Stainless steel is composed of chromium, carbon, iron and nickel. The chromium and
nickel provide a protective oxide coating so firming bonded to iron and no easily to remove. Other
way is sacrificial protection that is using more electropositive metal as sacrificial metal attached to
iron. This can explain by the more electropositive metal will act as anode which is oxidation occur site
protect less electropositive metal rusting. For example, iron attach to magnesium. Magnesium more
electropositive than iron because magnesium more tendency to lose electron.
