Ion Solvation in Polar Solvents

The most direct way of determining A G is by measuring the work associated with transferring the electrolyte from the gas phase, where the ions are infinitely far apart from one another, to the liquid solution. However, from a practical point of view, it is much simpler to solve this problem starting with the solid electrolyte. Consider a simple 1-1 electrolyte MX which dissolves in solvent S  

The Gibbs energy change associated with formation of the solution may be written as 

In order to remove the contribution to A iG° from the solid phase, values of this quantity are compared in two different solvents. If one imagines that the same salt is dissolved in two different solvents Si and S2, then one may estimate the Gibbs energy of transfer of MX according to the process 

The corresponding standard Gibbs energy change is called the Gibbs energy of 

AtrG° depends only on the differences in the interaction of the ions with the two solvents, the contribution from the solid phase having been lost in subtraction. 

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Ion solvation in polar solvents is also an important aspect of the subject matter considered here. This is traditionally studied by measuring the Gibbs energy and enthalpy of transfer of a variety of electrolytes from water to another polar solvent. Single ion quantities are then derived on the basis of the TATB assumption. Study of these quantities for simple monoatomic ions like the alkali metal cations and the halide anions leads to the conclusion that specific molecular properties, namely, Lewis acidity and basicity, are important in ion solvation. On the other hand, the dielectric permittivity, a non-specific bulk property. 

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