1. Electrochemistry-Corrosion Corrosion

2. Involves oxidation of metal; often returning them to their natural state (oxides or ores) Happens because the oxidation process is favorable Reduction potentials are less positive than that of oxygen gas So how can we make anything from metal and use it in air?

3. Corrosion of Iron Since E  (Fe 2+ ) < E  (O 2 ) iron can be oxidized by oxygen. Cathode O 2(g) + 4H + + 4e -  2H 2 O (l) Anode Fe (s)  Fe 2+ + 2e - Dissolved oxygen in water usually causes the oxidation of iron. Fe 2+ initially formed can be further oxidized to Fe 3+ which forms rust, Fe 2 O 3.xH 2 O(s). Oxidation occurs at the site with the greatest concentration of O 2. The presence of salt speeds up the process. Why?

4. Corrosion of Iron

5. Preventing the Corrosion of Iron To protect underground pipelines, a sacrificial anode is added. The water pipe is turned into the cathode and an active metal is used as the anode. Often, Mg is used as the sacrificial anode: Mg 2+ +2e -  Mg (s) E  red = -2.37 V Fe 2+ + 2e -  Fe (s) E  red = -0.44 V

6. Corrosion Preventing the Corrosion of Iron

7. Corrosion Layer of oxide protects the metal below Steel acts as a wire to conduct e - for Fe oxidation