lechance dry cell

• s

  A) MnO2

  B) carbon electrode

  C) positive terminal

  D) negative terminal

  E) Zn cover

  
• anode?

  Zn cover
• a

  A) metal cap

  B) Zn cover anode

  C) graphite cathode

  D) Paste of NH4Cl + ZnCl

  E) MnO2 + C

  
• anode rxn?

  Zn -> Zn2+ + 2e
• cathode rxn?

  2MnO2 (s) +NH4+ +2e = Mn2O3 + H2O
• reductant?

  Zn
• oxidant?

  MnO2
• Carbon rod?

  conduct path for electrons moving into cathode paste
• NH4Cl?

  salt bridge

  • provides H+ / P+ in MnO2 reduction
  • Acidic nature: cause Zn anode to form Zn2+ ; decrease shelf life
• disadvantages?

  limited shelf life - the Zn anode reacts spontaneously with NH4Cl in the electrolyte, causing case to corrode -> allowing the contents to leak out.

  NOT very efficient in producing electrical energy -> only the small fraction of the MnO2 near the cathode is actually reduced -> only a small fraction of Zn cathode is actually consumed as the cell discharges.