Rusting of iron occurs and the process of rusting

Describe the conditions under which rusting of iron occurs and explain the process of rusting

  • Corrosion: The degradation of a metal so that it loses strength and becomes unable to fulfill its intended purpose.
  • Rusting: The corrosion of iron to form hydrated iron (III) oxide, or rust.
  • Iron will rust when it is in contact with both oxygen and water.
  • Rusting is faster if the water involved contains an electrolyte, either an acid or a dissolved salt.
  • The rusting is accelerated if the iron is:
    • Impure.
    • In contact with a less active metal.
    • Under mechanical stress.
  • In the process of the rusting of iron:
    • The iron is the anode and is oxidized:
                            Fe → Fe2+ + 2e-
    • The reduction of oxygen occurs at the cathode:
                            O2 + 2H2O + 4e- → 4OH-
    • Electrons move from the anode to the cathode through the iron.
    • The anode and the cathode may be separated by some distance.
    • Insoluble iron (II) hydroxide is formed and the iron (II) ions are further oxidized to produce hydrated iron (III) oxide, or rust.