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.