Application of Electrochemical Cells Lesson 12
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Transcript of Application of Electrochemical Cells Lesson 12
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Application ofElectrochemical Cells
Lesson 12
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Banana Watch
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Application of Electrochemical Cells
1. Zn/C or LeClanche Cell
Anode: ZnAnode Reaction: Zn → Zn2+ + 2e-
Cathode: CCathode Reaction: Mn4+ +1e- → Mn+3 Electrolyte: NH4Cl and MnO2
Inexpensive Not rechargeable Short life
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Application of Electrochemical Cell
2. The Alkaline Cell
Anode: ZnAnode Reaction: Zn → Zn2+ + 2e-
Cathode: CCathode Reaction: Mn4+ +1e- → Mn3+ Electrolyte: KOH and MnO2
More expensive Not rechargeable Longer life
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3. The Lead Acid Battery (Automobile)
Anode: PbAnode Reaction: Pb → Pb2+ + 2e-
Cathode: PbO2
Cathode Reaction: PbO2 + HSO4- + 3H+ + 2e- → PbSO4 + 2H2
Electrolyte: H2SO4
Rechargeable Long life Large current
Application of Electrochemical Cells
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Application of Electrochemical Cells
4.The Fuel Cell
Overall Reaction: H2 + ½O2 → H2O + energy
Expensive Requires fuel Environmentally friendly
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Nickel Cadmium
Rechargable
Cordless Phones
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Nickel Metal Hydride
Rechargable
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Lithium
Rechargable
Cameras
Laptops
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Corrosion of Iron
Corrosion is oxidation: Fe(s) → Fe2+ + 2e-
Rust is initially Fe(OH)2 which dries to become Fe2O3.
There are three requirements for the corrosion of iron.
IronWaterOxygen
Corrosion is spontaneous or an electrochemical cell.
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Fe Fe Fe Fe2+Fe2+OH- OH-
Fe(OH)2(s) Fe(OH)2(s)
Corrosion of Iron
Rust- low solubility
e- e-
+ 2e-
Cathode
Fe(s) → Fe2+ + 2e- Anode
Water Drop
Iron Surface
→ 2OH- O2 + H2O 1/2
Cations to cathode and anions to anode
The anode reaction is the oxidation of Fe
The cathode reaction is the reduction of O2 and H2O- outer circle of drop
Electrons flow from the anode to the cathode
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Methods of Preventing Corrosion
Protective Coatings PaintGreaseElectroplatingPlastic
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Cathodic Protection
Remember corrosion is oxidation
Make iron the cathode of a cell, which is the site of reduction, oxidation cannot occur.
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Fe Nail in Water
Attach a piece of Zn or Mg All lower than Fe.
Zn Anode
Fe
Zn → Zn2+ + 2e-
Sacrificial anode
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Electrons flow from anode to cathode to protect the Fe
Cathode or Reduction--
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Mg bracelets on a ship
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Cathodic Protection
Remember corrosion is oxidation Make iron the cathode of a cell, which is the site of reduction, oxidation cannot occur.
50 km Fe pipe How do we protect it from corrosion?
Coat with plasticMake it the cathode or negative side of an electrolytic cell
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Scrap iron anode Fe(s) → Fe2+ + 2e-
+
Cathode No oxidation!- -- -- -
e-
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Solution is NaCl, K3Fe(CN)6, and phenolphathalein. Corrosion of Fe will show as blue- reaction with K3Fe(CN)6. Cathodic protection will reduce water and show as bubbles and pink.
Make Fe the negative side of an electrolytic cell
Cathodic Protection- red and H2 bubbles
Add a piece of Zn to the Fe
Cathodic Protection- red and H2 bubbles
Unprotected nail- blue indicating Fe2+
Fe and Cu- not a good idea
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The Aluminum hull is protected by an electrolytic cellWhen it was first put to sea this system was not in operation.The Paint peeled off requiring a new multimillion dollar paint job.
BC Fast Ferry