Zinc -carbon Battery

Introduction :
Zinc -carbon battery is also called as dry cell or dry battery.  Zinc -carbon battery is a battery which is packaged in zinc that can  serves as both a negative terminal and a container.  Zinc -carbon battery was developed from wet Leclanche cell.   In Zinc-carbon battery carbon rod or the graphite rod is the positive terminal which is surrounded by manganese dioxide and carbon powder mixture.   Zinc chloride and aluminium chloride solution is used as an electrolyte.  The original ammonium chloride variety is improved by Zinc chloride cells.  They are commonly termed as “General purpose” batteries.   These are the primary batteries.

Construction of Zinc -carbon Battery :

Figure:   Cross section zinc-carbon battery.
The above figure is the cross sectional picture of zinc-carbon battery.
The zinc can is the container in the zinc-carbon battery which is the negative terminal which contains a layer of NH₄Cl with aqueous paste of ZnCl₂ separated by a paper layer from a mixture of manganese oxide and a powdered carbon which is packed around the carbon rod.The carbon rod is slightly porous which allows to escape out the accumulated gas retaining the water for the electrolyte. The ratio of manganese dioxide and carbon powder in the cathode paste affects the cell’s characteristics. If the carbon powder is more then there will be decrease in the internal resistance but the capacity is improved by more manganese dioxide.
Reactions involved in zinc-carbon battery:
In a zinc- carbon battery, the zinc container which is a negative terminal. Here zinc undergo oxidation as follows,
Zn(s) → Zn²⁺(aq) + 2 e^-.
A graphite rod which is surrounded by a powder containing manganese (IV) oxide is the positive terminal. Here the manganese (IV) oxide mixed with the carbon which increases the electrical conductivity. The reaction is as follows,
2MnO₂(s) + H₂ (g) → Mn₂O₃(s) + H₂O(l) , here H₂ is obtained from ammonium salt.
2NH₄⁺(aq) + 2 e^- → H₂(g) + 2NH₃(aq)
In this reaction, the manganese is reduced from an oxidation station (+4) to (+3).
The overall reaction of the zinc carbon battery is
Zn(s) + 2MnO₂(s) + 2NH₄⁺ (aq) → Mn₂O₃(s) + Zn(NH₃)₂²⁺(aq) + H₂O(l).

Advantages of Zinc-carbon Battery:

They are least expensive primary batteries.
The power drain is not too high.
Disadvantages of zinc-carbon battery:
These zinc-carbon batteries are not rechargeable which must be discarded.
Applications of zinc-carbon battery:
They are least expensive so they are used in remote controls, flashlights, clocks, transistor radios and many more.