1. B ATTERIES, FUEL CELLS & CORROSION [20.7-20.8]

2. S TANDARD REDUCTION POTENTIALS Place in order of increasing strength as oxidizing agents: Cl 2, Mg +2, Fe +2, Fe +3 1.36 ; -2.37; -0.44; 0.77 Good OA are easily reduced, largest positive reduction potential = best OA Mg +2 <Fe +2 <Fe +3 <Cl 2 Should you store a solution of copper nitrate in a tin can? Sn → Sn +2 +0.14v Cu +2 → Cu +0.34 v +0.48 volts Spontaneous reaction, the can will dissolve! 1. To rank oxidizing or reducing agents 2. To determine spontaneity & to choose for spontaneity

3. Oxidizing strength increases Easily oxidized (good RA) Reducing strength increases Easily reduced (good OA)

4. Q UICK PREDICTIONS WITH USE OF TABLE 1. Find reactant s and circle 2. Visualize or connect with line 3. If positive slope, nonspontaneous reaction 4. If negative slope, spontaneous reaction TRY IT! Ag + + Cu Zn + Cu +2 Ag + Cu +2

5. B ATTERIES : P ORTABLE, SELF CONTAINED ELECTROCHEMICAL POWER SOURCE THAT CONSISTS OF ONE OR MORE VOLTAIC CELLS. Lead storage/car batteries, six 2 V cells, uses sulfuric acid as electrolyte; density determines age of battery; recent batteries use electrodes of Ca and Pb alloy that inhibit electrolysis, so they are sealed.

6. D RY CELLS More productive in alkaline version; anode of zinc, cathode of graphite, paste of MnO 2 & NH 4 Cl Ag cell, Hg cell Nickel-Cadmium “rechargeable”

7. F UEL CELLS Reactants are continuously supplied

8. C ORROSION Iron-rusting, Fe 2 O 3 Silver-tarnishing, Ag 2 S Copper-CuCO 3, greenish “patina” Gold, silver, platinum- noble metals

9. The Problem When two dissimilar metals are connected in an electrolyte such as seawater, a corrosion cell is formed in which one metal becomes an anode and suffers corrosion, while the other metal becomes the cathode and remains preserved. Current flows through the electrolyte from the anode to the cathode, resulting in electrolytic corrosion. Anodic and cathodic areas exist on the surface of all steel structures due to slight variations in material composition, local stresses, differences in coating condition and the availability of oxygen. Ships' hulls, cargo tanks and submerged fixed structures are all vulnerable to corrosion (details).details www.wilsonwalton.com/zincoline.htm

10. PREVENTION *Coating the iron-paint, grease, galvanizing (zinc coating) zinc is more easily oxidized than iron *Cathodic protection-fuel tanks, pipelines with magnesium, ship hulls and titanium similar to galvanizing, sacrificial metal protects the iron with electron flow.

11. C ATHODIC PROTECTION High Capacity Aluminum Sacrificial Anodes for Shipping & Offshore Industries Aloline anodes are cast in low-iron high efficiency aluminum alloys. Aloline anodes are characterized by light weight and high amperage output. Features & Benefits Improved Corrosion Protection is provided by Aloline’s higher driving potential compared to zinc or aluminum/mercury alloys. Lower Cost per System is achieved because Aloline’s greater efficiency means fewer anodes are needed, saving on material and installation labor cos. www.wilsonwalton.com/zincoline.htm

12. Aluminum anodes mounted on steel jacket structure