CW27-Met - CHM 2046/Myers Worksheet 27 March 22, 2010 1....

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CHM 2046/Myers Worksheet 27 March 22, 2010 1. The Corrosion of Iron. A major industrial problem is that iron rusts. The rusting process involves different reactions occurring at different places on a piece of iron. Consider a piece of iron dipping into a body of water, or possibly wet soil, with a plentiful supply of air above: In one region, where H 2 O is present, but not much O 2 , iron is oxidized to Fe+2, causing pitting of the object. This is called an anodic region . Elsewhere, often near the water air interface, O 2 is reduced to OH - . This is called a cathodic region . The Fe +2 and OH - ions migrate together, acting somewhat as a salt bridge. Additional ions in the water help speed the process. Formed initially is Fe(OH) 2 (s). If the supply of oxygen is limited, the Fe(OH) 2 is oxidized to black magnetite, a mixed oxide of Fe 2 O 3 + FeO = Fe 3 O 4 . This is the black coating observed when iron has been buried in the ground. If the supply of oxygen is plentiful, the Fe(OH) 2 is oxidized to Fe 2 O 3 , the familiar rust-red color seen almost everywhere that iron is exposed to the elements. 2.
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CW27-Met - CHM 2046/Myers Worksheet 27 March 22, 2010 1....

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