What are primary cells and explain its reactions?, Chemistry

This type of cells becomes dead over a period of time and the chemical reaction stops. They cannot be revitalized or used again. Some ordinary examples are dry cell, mercury cell, etc.

Dry cell: it is a compact form of Leelanche cell known after its discoverer. In this cell, anode consists of zinc container while cathode  is a graphite rod surrounded by powdered MnO2 and carbon. The space between the electrodes is filled with the paste of NH4Cl and ZnCl2. The arrangement is shown in the reaction taking place at the electrodes are given in their simplified from as follows:


MnO2 + NH4+ + e-   525_halides.png  MnO(OH) + NH3

(Oxidization state of Mn changes from + 4 to + 3)


Zn  525_halides.png  Zn2+ + 2e-

The zinc ions (Zn2+) so produced combine with ammonis liberated zinc (II) cation.

Zn2+ + 2NH3   525_halides.png  [Zn(NH3)2]2+

Dry cells do not have long life as NH4Cl which is acidic, corrodes the zinc container even if the cell is not in use. The cell potential of dry cells lies in the range 1.25 V to 1.5 V.

Mercury cell: it is miniature cell which finds a frequent use these days to supply energy for watches, video cameras, hearing aids and other compact devices. In mercury cell the anode is zinc-mercury and amalgam and the cathode is a paste of mercury (II) oxide and carbon electrolyte is a moist paste of KOH-ZnO

The operating voltage for mercury cell is 756_primaru cell.png1.35 V and the cell reactions are as follows:

1307_primary cell.png 

Such a cell shows constancy in its potential throughout its life.







Posted Date: 6/26/2012 2:07:05 AM | Location : United States

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