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:

Cathode:

MnO₂ + NH₄⁺ + e^-     MnO(OH) + NH3

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

Anode:

Zn    Zn²⁺ + 2e^-

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

Zn²⁺ + 2NH₃     [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 1.35 V and the cell reactions are as follows:

 

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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