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Application of Electrochemical Cells Lesson 12

Application of Electrochemical Cells Lesson 12. Banana Watch. Application of Electrochemical Cells 1. Zn/C or LeClanche Cell Anode: Zn Anode Reaction: Zn → Zn 2+ + 2e - Cathode: C Cathode Reaction: Mn 4+ +1e - → Mn +3 Electrolyte: NH 4 Cl and MnO 2

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Application of Electrochemical Cells Lesson 12

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  1. Application of Electrochemical Cells Lesson 12

  2. Banana Watch

  3. Application of Electrochemical Cells 1. Zn/C or LeClanche Cell Anode: Zn Anode Reaction: Zn → Zn2+ + 2e- Cathode: C Cathode Reaction: Mn4+ +1e- → Mn+3 Electrolyte: NH4Cl and MnO2 InexpensiveNot rechargeableShort life

  4. Application of Electrochemical Cell 2. The Alkaline Cell Anode: Zn Anode Reaction: Zn → Zn2+ + 2e- Cathode: C Cathode Reaction: Mn4+ +1e- → Mn3+ Electrolyte: KOH and MnO2 More expensiveNot rechargeableLonger life

  5. Application of Electrochemical Cells 3. The Lead Acid Battery (Automobile) Anode: Pb Anode Reaction: Pb → Pb2+ + 2e- Cathode: PbO2 Cathode Reaction: PbO2 + HSO4- + 3H+ + 2e- → PbSO4 + 2H2 Electrolyte: H2SO4 Rechargeable Long life Large current

  6. Application of Electrochemical Cells • The Fuel Cell • Overall Reaction: H2 + ½O2 → H2O + energy • ExpensiveRequires fuelEnvironmentally friendly

  7. Nickel Cadmium Rechargable Cordless Phones

  8. Nickel Metal Hydride Rechargable

  9. Lithium Rechargable Cameras Laptops

  10. Corrosion of Iron Corrosion is oxidation: Fe(s)→ Fe2+ + 2e- Rust is initially Fe(OH)2 which dries to become Fe2O3.   There are three requirementsfor the corrosion of iron. Iron Water Oxygen Corrosion is spontaneous or an electrochemicalcell.

  11. Corrosion of Iron The anode reaction is the oxidation of Fe The cathode reaction is the reduction of O2 and H2O- outer circle of drop Cations to cathode and anions to anode Electrons flow from the anode to the cathode Anode Fe(s)→ Fe2+ + 2e- Cathode Water Drop 1/2 O2 + H2O + 2e- → 2OH- Fe2+ Fe2+ OH- OH- e- e- FeFeFe Fe(OH)2(s) Fe(OH)2(s) Iron Surface Rust- low solubility

  12. Methods of Preventing Corrosion Protective Coatings Paint Grease Electroplating Plastic

  13. Cathodic Protection Remember corrosion is oxidation Make iron the cathode of a cell, which is the site of reduction, oxidation cannot occur.

  14. Fe Nail in Water Attach a piece of Zn or Mg All lower than Fe. Cathode or Reduction Fe - - Zn Anode Zn → Zn2+ + 2e- Sacrificial anode - - - - - - Electrons flow from anode to cathode to protect the Fe

  15. Mg bracelets on a ship

  16. Cathodic Protection Remember corrosion is oxidation Make iron the cathode of a cell, which is the site of reduction, oxidation cannot occur. + - e- Scrap iron anode Fe(s)→ Fe2+ + 2e- Cathode No oxidation! 50 km Fe pipe How do we protect it from corrosion? Coat with plastic Make it the cathode or negative side of an electrolytic cell - - - - - -

  17. Make Fe the negative side of an electrolytic cell Cathodic Protection- red and H2 bubbles Unprotected nail- blue indicating Fe2+ Fe and Cu- not a good idea Add a piece of Zn to the Fe Cathodic Protection- red and H2 bubbles 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.

  18. BC Fast Ferry The Aluminum hull is protected by an electrolytic cell When it was first put to sea this system was not in operation. The Paint peeled off requiring a new multimillion dollar paint job.

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