1. CORROSION
Iron Oxidation
Fe (s) → Fe2+ (aq) + 2e-
2e- + ½O2 (g) + H2O (l) → 2OH- (aq)
Ɛºox = V
Ɛºred = V
Fe (s) + ½O2 (g) + H2O (l) → Fe2+ (aq) + 2OH- (aq)
Ɛº = V
Aluminum Oxidation
2Al (s) + 1½O2 (g) + 3H2O (l) → 2Al3+ (aq) + 6OH- (aq)
Ɛº = V
EXP 19-1 (of 5)

2. Al oxidizes rapidly to Al2O3
Al2O3 adheres to the Al, forming a protective coating so the underlying Al is not oxidized
Fe oxidizes too (although not as fast)
Fe2O3 does not adhere to the Fe, it flakes off exposing more Fe, which oxidizes, etc.
Fe will eventually corrode away O2
H2O O2
H2O
EXP 19-2 (of 5)

3. To prevent iron corrosion (1) Paint (2) Layer with Tin
(3) Layer with Zinc (Galvanizing) O2 O2
H2O
H2O O2
H2O
Fe (s) → Fe2+ (aq) + 2e-
Zn (s) → Zn2+ (aq) + 2e-
Ɛºox = V
Ɛºox = V
Fe is prevented from being oxidized because Zn is more active – it gets oxidized instead
EXP 19-3 (of 5)

4. To prevent iron corrosion (1) Paint (2) Layer with Tin
(3) Layer with Zinc (Galvanizing) O2
H2O
Fe (s) → Fe2+ (aq) + 2e-
Sn (s) → Sn2+ (aq) + 2e-
Ɛºox = V
Ɛºox = V
Sn only prevents Fe from being oxidized by covering it
With Zn, the Fe does not even have to be covered
EXP 19-4 (of 5)

5. SACRIFICIAL METAL – A metal that oxidizes more readily than another when the two are electrically connected
Mg blocks (Ɛºox = 2.37 V) are attached to the hulls of ships, oxidize instead of the Fe, and are easily replaced after they have completely oxidized
EXP 19-5 (of 5)