Batteries

Question 1

Leclanche cell

Answer 1

• commonly used in transistors, clocks
• cell potential is 1.5V

Anode: Zinc container
Cathode: Graphite rod, with MnO2 + C (black)
Electrolyte: NH4Cl+ZnCl2 paste

Reactions:
Zn —-> Zn2+ +2e
MnO2 + NH4+ —> MnO(OH)+ NH3
NH3 +Zn—> [Zn(NH3)]2+

Question 2

Mercury cell

Answer 2

• for low current devices like watches and hearing aids
• cell potential is 1.35V; lasts long as no ions involved

Anode: Zn(Hg)
Cathode: HgO+C
Electrolyte: KOH+ZnO

Reactions:
Zn(Hg)—> ZnO +H2O
HgO+H2O—> Hg

Question 3

Pb storage battery

Answer 3

Anode: Pb
Cathode: Grid of Pb packed with PbO2.
Electrolyte: 38% of H2SO4

Reactions (decharging):
Pb +SO42- —>PbSO4 +2e-
PbO2 +SO42- + 4H+ +2e- —–> PbSO4 +H2O

Question 4

Ni-Cd cell

Answer 4

Cd+Ni(OH)3 —> CdO+ Ni(OH)2

Question 5

Fuel Cell

Answer 5

• fuels like hydrogen, methanol, methane
• used in Apollo space program

Electrodes: Carbon electrodes with Pt catalyst
Electrolyte: NaOH
H2+4OH- —> 2H2O +4e-
O2+ 4e- +2H2O —> 4OH- +