Battery :
Primary battery : o The reaction in a primary battery occurs only once . o
Ag < Hg < Cr < Mg < K
Battery :
Battery is a collection of two or more batteries connected in series .
It is of two types : 1 . Primary battery 2 . Secondary battery
Primary battery : o The reaction in a primary battery occurs only once . o
The battery becomes dead after used once and cannot be reused o Example of primary cell is dry cell and mercury cell . o
The dry cell consists of a zinc anode and the carbon ( graphite ) cathode surrounded by powdered manganese dioxide and carbon .
o
Fig . Dry cell
o The space between the two electrodes is filled by a soaking paste of ammonium chloride ( NH4Cl ) and zinc chloride ( ZnCl2 ).
Anode : Zn ( s ) ⎯ -- > Zn 2 + + 2e – Cathode : MnO2 + NH4 + + e – ⎯ -- > MnO ( OH ) + NH3
o At the cathode manganese is reduced from + 4 oxidation state to + 3 oxidation state .
As per the equation , Ammonia produced forms a complex with Zn 2 + giving rise to [ Zn ( NH3 ) 4 ] 2 + .
o The cell has a potential of nearly 1.5 V .