Chemical Changes in a Dry Cell Battery

Components

• The dry cell contains three main components, the anode, which is a metallic cylinder made of zinc or any alkaline into which cathode and the electrolytes are placed, the cathode, which is normally a rod-like structure located at the center of the dry cell battery. Carbon coated with manganese dioxide is usually used as cathode; and the electrolyte which is a moist mixture of plaster of Paris, zinc chloride and ammonium chloride. The major volume of the cell is taken up by the electrolyte.

Effect of Current on Chemicals

• When electricity is passed through these electrolytes via electrodes, such as the anode and cathode, chemical changes occur due to electrolysis. But a process opposite to that of electrolysis occurs in the case of dry cells. The dry cell chemicals are also involved in the reverse electrolysis process in which chemical energy gets converted to electrical energy. This phenomenon by which chemical reactions lead to the development of electric current acts as the basis for the development of dry cells.

Chemical Changes

• The chemical changes which take place at the individual electrodes and the electrolyte are as follows:

  At anode: Zinc oxidizes and produces two electrons

  Zn' Zn2 + 2 (e-)

  At cathode: Manganese dioxide reacts with hydrogen yielding manganese trioxide and water

  2MnO2 + H2 ' Mn2O3 + H2O

  At electrolyte:

  2NH4 + 2 ' H2 + 2NH3

  The overall chemical changes within a dry cell can be represented by the following equation:

  Zn+ 2MnO2 + 2NH4 (+) ' Mn2O3 + Zn (NH3)2 (2+) + H2O

  Here, there is a vertical slit through which the gases formed due to chemical changes escape.

Conclusion

• Even though a wide range of dry cell batteries are available, the most popularly used is the carbon zinc Leclanche cell due to its low manufacturing cost and because it is suitable for all applications, including wristwatches, transistor receivers and flashlights. Disadvantages includes higher chance of leakage, more sensitivity to impurities and poor low temperature performance. The design of dry cells, number of electrode plates and mode of powering the plates will vary with the manufacturer but the basic properties and the way of working remains the same.