REDOX & Electrochemistry - LSU Chemistry

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<strong>REDOX</strong> 34Alkaline CellsGraphiteCathodeMoist Pasteof KOH,MnO 2 &graphitePorousseparatorZinc anodeThe simple replacement ofNH 4 Cl electrolyte with aKOH gel eliminates theproduction of the problematicNH 3 gas that occurs in theregular dry cell. This batteryhas much improved stabilityfor delivering electricalcurrent until all the reagentsare used up.Anode Rxn:Zn + 2OH − Zn(OH) 2 + 2e-Cathode Rxn:2MnO 2 + 2H 2 O2MnO(OH) + 2OH −Overall Rxn:Zn + 2MnO 2 + H 2 O 2MnO(OH) + Zn(OH) 2Eº = 1.5 V
<strong>REDOX</strong> 35Corrosion of Steel/IronO 2CathodeFe 2+ Fe 2+ O 2WaterSteelAnodeCathode: ½O 2 + H 2 O + 2e-Anode: Fe Fe 2+ + 2e-2OH −Sum: ½O 2 + Fe + H 2 O Fe(OH) 2Subsequent Redox rxn:4Fe(OH) 2 + O 2 + 4OH −RUST2Fe 2 O 3 • 4H 2 OThe presence of NaCl (salt) in the water makes it moreconductive to e- flow, making it easier for the O 2to oxidize theiron without having to come directly in contact with it.Instead it can react anywhere at the surface of the water drop.
Page 4: REDOX 4The key to being able to fig
Page 8 and 9: Let's do another balancing act:REDO
Page 10 and 11: REDOX 10To balance the rxn in basic
Page 12 and 13: REDOX 12c) Na 2 S 2 O 3 (aq) + NaOC
Page 14 and 15: REDOX 14To harness the intrinsic ch
Page 16 and 17: REDOX 16Measuring Cell Potentials (
Page 18 and 19: REDOX 18Voltage (or potential) repr
Page 20 and 21: REDOX 20To add these half-cell rxns
Page 22 and 23: REDOX 22Example: What is the potent
Page 24 and 25: REDOX 24Example: Zn metal reacts wi
Page 26 and 27: REDOX 26Example: What about the rea
Page 28 and 29: REDOX 28Problems: Calculate the cel
Page 30 and 31: REDOX 30Example: Calculate the pote
Page 32 and 33: REDOX 32Lead-Acid Storage BatteryAn
Page 36 and 37: Standard Reduction Potentials - 25
Page 38: REDOX 38Tables from Chemistry, 8 th

REDOX & Electrochemistry - LSU Chemistry

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