Application ofElectrochemical Cells

Lesson 12

Banana Watch

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

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

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

Application of Electrochemical Cells 

4.The Fuel Cell

 Overall Reaction: H2 + ½O2 → H2O + energy

Expensive Requires fuel Environmentally friendly

Nickel Cadmium

Rechargable

Cordless Phones 

 

Nickel Metal Hydride

Rechargable

 

 

Lithium

Rechargable

Cameras

Laptops 

 

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.

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

Methods of Preventing Corrosion

Protective Coatings PaintGreaseElectroplatingPlastic

Cathodic Protection

Remember corrosion is oxidation

Make iron the cathode of a cell, which is the site of reduction, oxidation cannot occur.

Fe Nail in Water

Attach a piece of Zn or Mg All lower than Fe.

Zn Anode

Fe

Zn → Zn2+ + 2e-

Sacrificial anode

-

-

-

-

-

-

Electrons flow from anode to cathode to protect the Fe

Cathode or Reduction--

Mg bracelets on a ship

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

-

Scrap iron anode Fe(s) → Fe2+ + 2e-

+

Cathode No oxidation!- -- -- -

e-

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

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