11.8-12.2

11.8-12.2 - Unwanted Redox chemistry corrosion Unwanted...

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1 Redox chemistry corrosion Unwanted 2Fe (s) 2Fe 2+ + 4e - -0.44 V anode +1.23 V cathode 4Fe (s) + 3 O 2 (g) 2Fe 2 O 3 (s) 4H 1+ + O 2 2H 2 O + 4e - 4Fe 2+ O 2 (g) O 2 (aq) 4Fe 3+ + 4e - +0.77 V anode Section 11.7 4Al (s) O 2 (g) O 2 (aq) Redox chemistry corrosion Unwanted 4Al 3+ + 12e - -1.66 V anode 4Al (s) + 3 O 2 (g) 2Al 2 O 3 (s) +1.23 V cathode 6H 2 O + 12e - Passivation: Protection of a reactive metal by the formation of an oxide layer. Section 11.7 12H 1+ + 3O 2 Patina (CuCO 3 ) Passivation Where did the CO 3 2- come from? H 2 O (l) + CO 2 (g) H 2 CO 3 (aq) H 2 CO 3 (aq) + H 2 O (l) H 3 O 1+ (aq) + HCO 3 1- (aq) HCO 3 1- (aq) + H 2 O (l) H 3 O 1+ (aq) + CO 3 2- ( aq) Section 11.7 Unwanted Redox chemistry corrosion Fe Zn Galvanization: Protecting one metal by sacrificing another more reactive metal. More reactive Fe 3+ (aq) Zn 2+ (aq) Zn (s) E Fe (s) O 2- (aq) O 2 (g) + 2e - Section 11.7 Redox chemistry Fe Zn More reactive Zn is galvanized on Fe Section 11.7 Coating that protects Fe Instead of: 4Fe (s) + 3O 2 (g) 2Fe 2 O 3 (s) 2ZnO(s) 2Zn(s) + O 2 (g) Main rxn is: © Lori Petrovich My Get-Rich-Quick Scheme: Passing off gold-plated material as solid gold Au 1+ (aq) + 1e 1- Au (s) +1.68 V Sn 2+ (aq) + 2e 1- Sn (s) -0.31 V 2Au 1+ (aq) + Sn (s) 2Au (s) + Sn 2+ (aq) Net Reaction: http://www.caswellplating.com/kits/goldpl8.htm Section 11.7
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2 Forcing a nonspontaneous reaction to take place by the application of a voltage. Electrolysis
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This note was uploaded on 03/30/2010 for the course CH 101 taught by Professor Bigham during the Fall '08 term at N.C. State.

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11.8-12.2 - Unwanted Redox chemistry corrosion Unwanted...

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