Abstract
The cation-exchange system potassium-alkaline earth metals (Mg , Ca , Sr and Ba) has been studied with a view of applying a uni-bivalent statistical thermodynamic treatment to such a system. Linear plots of [mathematical equation] against [mathematical equation] are obtained as predicted by a theoretical approach developed in these laboratories. From the slopes of these plots o, the additional energy associated with placing a pair of bivalent B2+ ions on adjacent sites in the exchanger has been derived, whilst from the intercepts of such plots at x[B]= 0 , the thermodynamic equilibrium constant In K[T] and the standard free energies of exchange DeltaG° have been derived. Application of the Van't Hoff Isochore has given the standard heats of exchange Deltaeq H° , these are in good agreement with those obtained from the more accurate calorimetric method. Finally, the standard entropies of exchange DeltaS° have been calculated. The results show that there is a linear relationship between DeltaG° and the radii of the hydrated ions, also that the interaction energy o is related to the sizes of the hydrated ions within the resin. Furthermore w is not dependent on temperature but is dependent on the external electrolyte concentration as might be expected.