1. CORROSION Iron Oxidation Fe (s) → Fe 2+ (aq) + 2e - 2e - + ½O 2 (g) + H 2 O (l) → 2OH - (aq) Ɛ º ox =0.41 V Ɛ º red = 0.40 V Fe (s) + ½O 2 (g) + H 2 O (l) → Fe 2+ (aq) + 2OH - (aq) Ɛ º = 0.81 V Aluminum Oxidation 2Al (s) + 1½O 2 (g) + 3H 2 O (l) → 2Al 3+ (aq) + 6OH - (aq) Ɛ º = 1.71 V EXP 19-1 (of 5)

2. Al oxidizes rapidly to Al 2 O 3 Al 2 O 3 adheres to the Al, forming a protective coating so the underlying Al is not oxidized Fe oxidizes too (although not as fast) Fe 2 O 3 does not adhere to the Fe, it flakes off exposing more Fe, which oxidizes, etc. Fe will eventually corrode away O2O2 H2OH2O O2O2 H2OH2O EXP 19-2 (of 5)

3. O2O2 H2OH2O To prevent iron corrosion (1)Paint (2)Layer with Tin (3)Layer with Zinc (Galvanizing) O2O2 H2OH2O Fe (s) → Fe 2+ (aq) + 2e - Zn (s) → Zn 2+ (aq) + 2e - Ɛ º ox =0.41 V Ɛ º ox =0.76 V Fe is prevented from being oxidized because Zn is more active – it gets oxidized instead O2O2 H2OH2O EXP 19-3 (of 5)

4. To prevent iron corrosion (1)Paint (2)Layer with Tin (3)Layer with Zinc (Galvanizing) O2O2 H2OH2O Fe (s) → Fe 2+ (aq) + 2e - Sn (s) → Sn 2+ (aq) + 2e - Ɛ º ox =0.41 V Ɛ º ox =0.14 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 ( Ɛ º ox = 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)