The solubility data for sodium halides
(NaF, NaCl, NaBr, and NaI)
have been determined at 298.15 K in the ε-increasing mixtures
of water–formamide, water–N-methylformamide,
and water–N-methylacetamide. In all cases,
the solubility of the electrolytes was decreased significantly in
the presence of a cosolvent. The solubility of an electrolyte in a
given solvent depends on both the nature of the solvent (mainly the
polarity, dielectric constant, solvation, or preferential solvation
if the solvent is a mixture of solvents, etc.) and the properties
of the electrolyte (principally the size, the charge, and the possible
association of its ions). If the molality of saturation is not sufficiently
small, the ion–ion and ion–solvent interactions must
be considered. Although it was not the objective of this work, the
solubility values were qualitatively correlated with several properties
of the solvent and solute. Finally, a simple justification, which
was both qualitative and quantitative, was carried out.