Electrolyte solutions that unmix to form two liquid phases. Solutions in benzene and in diethyl ether

Abstract

Some simple solutions of electrolytes in solvents of low dielectric constant exhibit a miscibility gap corresponding to the co-existence of two liquid phases. An explanation is given in terms of electrical forces among ion pairs. An approximation to the effect of these forces is based on the interaction of a simple ion pair with an ideal dielectric having the dielectric constant of the solution. The dielectric constant as a function of composition is measured for NH4FeCl4 in (C2H5)2O, which unmixes, and is found to be consistent with the theory, as are other less complete dielectric constant data for other unmixing solutions. However, the observed osmotic coefficients of these solutions approach unity much more slowly with increasing dilution than one deduces from the simple theory, a discrepancy which seems to be due to pairwise association of ion pairs in the real solutions.