Miscibility with and Solubility in Water

Aqueous solutions of electrolytes that dissociate into ions have been and are studied so extensively that it is natnral to enquire about the solutions of electrolytes in binary mixtures of water and cosolvents. Mixtures of nonaqueous solvents among themselves, although important for other purposes, have not received much attention when solutions of electrolytes are concerned. Therefore, this section deals only with binary mixtnres of water with cosolvents. Many of the solvents on the list are miscible with water at all proportions, whereas others exhibit limited, even rather low mutual solubility at ambient conditions. For these cases, solubility of water in the solvent, is larger than that of the solvent in water, x, on the mole fraction scale. Conversion to (approximate) values of the solubility on the molar scale is according to  

The approximation is due to neglecting the relatively small excess volume of mixing, V, of the two components. For water-miscible solvents, the maximal value of C3 is its value for the neat solvent, the reciprocal of its molar volume Sneat = 10(X)/(ys /Cm -mOl ). 

Related to the mutual solubility of solvents with water is their lipophilicity or hydrophobicity that can be described by (the logarithm of) their partition coefficient between n-octanol and water, log. The more hydrophobic a substance is, the larger 

The mutual solubilities and the distribution coefficients of solvents at 25 C are shown in Table 3.11 adapted from [3], and it is noted that the majority of solvents 

TABLE 3.11 Mole Fraction Solubilities of Solvents in Water, Xj, and of Water in Solvents, and the Logarithm of the Octanol/Water Partition Coefficients of the Solvents, log, at 25°C 

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