Hydration energies, dependence, different

The Dependence of Calculated Hydration Energies on Different Charge Sets... 

Although there is no bulk liquid with which adsorbed cations can be exchanged in the experiments made in atmospheres of controlled relative humidity, successive experiments can be made with different adsorbed cation populations, and it is found that the succession of dehydration steps varies with size and hydration energy of the cation (Posner and Quirk, 1964). There is also a dependence upon the type and extent of substitution in the aluminosilicate framework White (1958), for example, observed that two montmorillonites with the same cation-exchange capacity, loaded with the same cation, may have different water sorption and swelling properties. 

Figure 3.4. Dependence of the selectivity coefficient, Ks, on the difference in hydration energy of the two alkali metal cations undergoing exchange.

Since the experimentally determined osmotic coefficient appears to be smaller even than the molecular dynamics results, this indicates effects to be relevant that go beyond the model used for simulation. Most obvious candidates for this are the neglect of additional chemical interactions between the ions and the polyelectrolyte as well as solvation effects, i.e., interactions between the ions or the polyelectrolyte with the water molecules from the solution. It is for instance demonstrated in Ref. 46 that the osmotic coefficient also depends on whether one uses chlorine or iodine counterions. While one could certainly account for the different radii of these ions when computing the distance of closest approach entering the PB equation, the implications of the different hydration energies is much less obvious to incorporate and in principle requires very expensive all-atom simulations. 

The anion effect on BLM transport of metal salts was examined by Lamb et al, 46). From determination of the transport rates for different alkali metal salts by dibenzo-18-crown-6, it became clear that the rate of transport was strongly dependent on the co-transported anion. The relative fluxes of different potassium salts were related to the hydratation energy. Cations which are accompanied by a hydrophilic anion (-AGg. is large) show low fluxes, due to a decrease in the partitioning. A linear relation was obtained by plotting In J vs -AGg. of the anion. For transport through an SLM, a similar relationship was found 47). 

Standard electrode potentials and stability of different oxidation states of transition metal ions in aqueous solutions The stability of a particular oxidation state in solution can be explained in terms of its electrode potential which in turn depends upon enthalpy of sublimation, ionization energy and hydration energy. 

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