Ion exclusion principles

Let us consider aluminum sulfate and sulfuric acid solutions in a Donnan membrane cell divided into two chambers by a cation-exchange membrane that aUows only cations to migrate from one side to the other but rejects any passage of anions according to Donnan s co-ion exclusion principle. At equihbrium, the electrochemical potential of aluminum (Al ) ion (/i) in the electrolyte solution on the left hand side (LHS) of the membrane will be the same as that in the electrolyte solution on the right hand side (RHS) i.e.. 

Amount of co-ions (anions) in the membrane is negligibly small compared to its ion-exchange capacity, i.e., Donnan co-ion exclusion principle is valid. 

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