1. Electrochemical Cells
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
Inexpensive Not rechargeable Short 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 expensive Not rechargeable Longer 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
Expensive Requires fuel Environmentally 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) → Fe e-
Rust is initially Fe(OH)2 which dries to become Fe2O3.  
There are three requirements for the corrosion of iron.
Iron
Water
Oxygen
Corrosion is spontaneous or an electrochemical cell.

11. Corrosion of Iron Anode Fe(s) → Fe2+ + 2e- Cathode Water Drop 1/2
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) → Fe e-
Cathode
Water Drop
1/2
O2 + H2O
+ 2e-
→ 2OH-
OH-
Fe2+
Fe2+
OH-
Fe Fe Fe e- e-
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 Fe Cathode or Reduction - - Zn Anode - - - - - -
Attach a piece of Zn or Mg All lower than Fe. Fe
Cathode or Reduction - -
Zn Anode
Zn → Zn e-
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) → Fe e- -
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.