Reactivity Series and Rusting

Reactivity Series of Metals

  • Metals have electrons in their outermost shell and form positive ions.
  • Reactivity is how easily a metal forms positive ions.
  • Reactivity Series (most to least reactive):
    • Potassium, Sodium, Lithium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Hydrogen, Copper, Silver, Gold.
  • More reactive metals displace less reactive metals in displacement reactions. Example: Mg+FeSO<em>4→MgSO</em>4+FeMg + FeSO<em>4 \rightarrow MgSO</em>4 + Fe, but Cu+FeSO4→Cu + FeSO_4 \rightarrow No reaction.

Rusting of Iron

  • Corrosion is the process by which metals are slowly broken down by reacting with substances in their environment.
  • Rusting is the corrosion of iron: Iron + Oxygen + Water → Hydrated Iron (III) Oxide.
  • The reaction is a redox reaction: Fe→Fe3++3e−Fe \rightarrow Fe^{3+} + 3e^- (oxidised), O2+4e−→2O2−O_2 + 4e^- \rightarrow 2O^{2-}(reduced).
  • Oxygen and water must be present for rust to occur.
  • Rust is a soft solid that flakes off, exposing fresh iron to further rusting.
  • Methods to prevent rusting:
    • Barrier methods: Paint, oil, grease, electroplating.
    • Sacrificial methods: Adding a more reactive metal like Aluminium or Zinc.
  • Galvanising: Coating iron with zinc; if scratched, zinc still protects by reacting with oxygen.