Solubility of a Nonelectrolyte Due to Primary Solvation

It is easy to calculate this change of solubility so long as there are data available for the solvation numbers of the electrolyte concerned. Let it be assumed that the normal case holds true and that ions are solvated entirely by water molecules (i.e., the organic present is pushed out). Then recalling that 1 liter of water contains 55.55 moles, the number of water molecules left free to dissolve nonelectrolytes after the addition of ions is 55.55 - c n, where n, is the solvation number of the electrolyte concerned. 

Assuming that the solubility of the nonelectrolyte is simply proportional to the number of water molecules outside the hydration sheath, then 

Assume = 6, C = 1 M then from Eq. (2.137), (S/Sq) = 0.89. For comparison, with KCIO4 as electrolyte, and 2,4-dinitrophenol as nonelectrolyte, the corresponding experimental value is about 0.7. Some further effects must be taken into account. 

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