A dynamic equailibrium exists between ions and unionised molecules of the electrolyte in solution and law of mass action can be applied to this equilibrium also. Consider a binary electrolyte .
AB + aq « A+ (aq)+B ` (aq)
Initial concentration C o o
Conc. at equilibrium C(1- a ) C a C a Where a is the degree of dissociation
Where is dissociation constant. For a weak electrolyte, the value of is very small in comparision to 1.
Then, (1- a) » 1 or K=C a2 or a = Ö(K/C) or a= ÖKV
Where is the volume containing one mole of electrolyte.
Note : Ostwald’s dilution law is applicable only for weak electrolytes but fails completely in the case of strong electrolytes.
q All salts (except Cd Br2,Hh Cl2), mineral acids like HCl, H2 SO4 , HNO3 etc and bases like NaOH , KOH etc. are strong electrolytes.
q All organic acids (except sulphonic acids), inorganic acids like HCN , H3 BO3 etc. and bases like NH3 amines etc., are weak electrolytes.
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