How does a standard AA battery (Zinc-Carbon dry cell) work? 🧐
An ususal AA battery consist of a zinc anode (as a case) and a graphite cathode (a central carbon rod) surrounded by a paste of powdered manganese (IV) oxide and carbon, and also a paste of ammonium chloride as electrolyte. A fibrous fabric separates the two electrodes, and a metal cap in the center of the cell conducts electricity to the outside circuit.
Rmb redox reaction in A-Level Chemistry?
At the anode (oxidation):
zinc loses electrons to form zinc ions
Zn(s)→Zn2+ +2e−
the electrolyte:
the paste of ammonium chloride (NH4Cl) reacts according to the following half-reaction:
2NH4(aq)+2e−→2NH3(g)+H2(g)
At the cathode (reduction):
manganese (IV) oxide is reduced to a manganese (III) compound when reacting with Hydrogen gas produced by ammonium chloride
2MnO2(s)+H2(g)→Mn2O3(s)+H2O(l)
the combined reaction at the cathode:
2NH4(aq)+2MnO2(s)+2e-→Mn2O3(s)+2NH3(g)+H2O(l)
the overall reaction is therefore:
Zn(s)+2MnO2(s)+2NH4(aq)→Mn2O3(s)+H2O(l)+Zn2+2NH3(g)
What is a dry cell?
A dry cell has the electrolyte immobilized as a paste, with only enough moisture in it to allow current to flow. Unlike a wet cell, a dry cell can operate in any orientation without spilling, as it contains no free liquid. This versatility makes it suitable for portable equipment.
Another example of a dry-cell battery is the alkaline battery. Alkaline batteries are almost the same as zinc-carbon batteries, except that the electrolyte used is potassium hydroxide (KOH) rather than ammonium chloride. In some more modern types of so-called “high-power” batteries that have a much lower capacity than standard alkaline batteries, the electrolyte ammonium chloride is replaced by zinc chloride.
Drafted by Eunice Wong (Chemistry)
References:
https://commons.wikimedia.org/wiki/File:Zincbattery_(1).png