Common Ion Effect:
The process in which the ionization of weak electrolyte decreases (suppresses) by the addition of strong electrolyte is called Common Ion Effect.
Application of Common Ion Effect:
Purification of NaCl:
NaCl ⥨ Na+ + Cl- ( Weak Electrolyte)
HCl ⥨ H+ + Cl- ( Strong Electrolyte)
We can use common ion effect for the purification of NaCl. For this purpose hot saturated solution of NaCl will be prepared,which establish the following equilibrium.
NaCl ⥨ Na+ + Cl- ( Weak Electrolyte)
Now the HCl gas which is more ionizable is passed through this solution.It gives the following equilibrium.
HCl ⥨ H+ + Cl- ( Strong Electrolyte)
The concentration of the chloride ions (Cl-) will be considerably increased so the first equilibrium will be shift to the left.Solid NaCl will be settle down whereas impurities will be left behind.
