Ion Association According to the MSA

In the treatment of ionic activity coefficients according to the MSA it was emphasized that the finite size of the ions is an important factor in estimating their Gibbs energy. Accordingly, the work done to introduce an additional ion to the solution 

For the case of symmetrical electrolytes with ion pairing, the electrolyte activity is given by 

Finally, the experimentally available activity coefficient is (y )gxp where 

Given values of a and the activity coefficient is calculated in the following way. Initially assuming a, = 1, the value of (y )gs is estimated using equations (3.11.3) and (3.11.4) with the values of Cg and a. Now equation (3.11.2) may be solved for a, given The process is repeated using the new estimate of until successive estimates of agree to the required precision. 

Results of such an analysis for the MgS04 system are shown in fig. 3.11. The best values of a and for this system are 610 pm and 185LmoP, respectively. On the basis of dielectric relaxation experiments, the permittivity of MgS04 solutions as a function of electrolyte concentration is given by 

---