Zinc-Carbon Dry cell (1 Viewer)

[wrxsti]

my oxidation reaction for this is Zn -> Zn2+ + 2e-
im sure thats rite
but im not so sure about my reduction reaction ive got
2MnO2 + H2 -> Mn2O3 + H20 i had a much longer one but my teacher said this was sufficient, but in my textbook it has a longer and complex reaction... wud this be be sufficient :S

 

[xiao1985]

it would be... cept i am sure there are no H2 (g) involved... it's probably 2H +

 

[Forbidden.]

Type:
Leclanché or dry cell
Zn | (ZnCl₂), NH₄Cl | MnO₂, C
Silver button cell
Zn, ZnO | KOH (paste) | Ag₂O, Ag

Anode:
Zinc case
Zn(s) -----> Zn²⁺(aq) + 2e^-
Steel cap in contact with powdered Zinc
Zn(s) + 2OH^-(aq) -----> ZnO(s) + H₂O(l) + 2e^-

Cathode:
Carbon rod in contact with carbon & manganese dioxide (MnO₂)
NH₄⁺(aq) + MnO₂(s) + e^- -----> NH₃(aq) + MnO(OH)(s)
Steel case in contact with powdered Ag₂O
Ag₂O(s) + H₂O(l) + 2e^- -----> 2Ag(s) + 2OH^-(aq)

Electrolyte:
Paste of NH₄Cl, ZnCl₂ (Acidic electrolyte)
Paste of KOH (Alkaline electrolyte)

Cell voltage:
1.5 Volts
1.3 Volts

Uses:
Low drain appliances such as radios, torches, liquid crystal calculators and toys.
Watches, pacemakers, hearing aids
As cell discharges, concentrations do NOT change as reactants & products are solids.
[OH^-] in electrolyte does NOT change.
So, the voltage of this cell remains constant throughout its lifetime.

Cost and practicality:
They are afforable cells which can be used for many low-drain devices.

Environmental impact:
Zinc is harmless in small amounts
Ammonium salts is harmless
Carbon is harmless
Manganese(III) is readily oxidised to insolutble Maganese Oxide(IV)

Source(s):
http://www.ausetute.com.au/battery.html
Conquering Chemistry Third Edition