Activity coefficient of an electrolyte solute

The activity coefficients of solute and solvent are of comparable magnitudes in dilute solutions of nonelectrolytes, so that Equation (17.33) is a useful relationship. But the activity coefficients of an electrolyte solute differ substantially from unity even in very dilute solutions in which the activity coefficient of the solvent differs from unity by less than 1 x 10 . The data in the first three columns of Table 19.3 illustrate the situation. It can be observed that the calculation of the activity coefficient of solute from the activity coefficient of water would be imprecise at best. 

As a reminder that the level of approximation in Equation (21) is the same as that of the Debye-Hiickel limiting law, the following example continues from this last result to the Debye-Hiickel expression for the mean ionic activity coefficient of an electrolyte solution. 

From Eqs. 10.3.8 and 10.4.1 and the electroneutrality condition v+z+=v-z, we obtain the following expression for the logarithm of the mean ionic activity coefficient of an electrolyte solute ... 

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