Finite-Ion-Size Model with Experiment

Comparison of the Finite-Ion-Size Model with Experiment 

After taking into account the fact that ions have finite dimensions and cannot therefore be treated as point charges, the following expression has been derived for the iogarithm of the activity coefficient  

How does the general form of this expression compare with the Debye-Hiickel limiting law as far as agreement with experiment is concerned To see what the extra term (1 -i- Bal does to the shape of the log/. versus I curve, one can expand it in the form of a binomial series 

Fig- 3.32. Procedure for recovering the ion size parameter from experiment and then using it to produce a theoretical log 4 versus / curve that can be compared with an experimental curve. 

The values of the ion size parameter, or distance of closest approach, which are recovered from experiment are physically reasonable for many electrolytes. They lie around 0.3 to 0.5 nm, which is greater than the sum of the crystallographic radii of the positive and negative ions and pertains more to the solvated ion (Table 3.9). 

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