Aqueous salting-out effect of inorganic cations and anions on non-electrolytes

Abstract

The salting-out effects of 27 lithium, sodium, potassium, ammonium and magnesium salts and HCl on chloroform, benzene, chlorobenzene and anisole were characterized in aqueous solutions at 303 K by measuring the Henry’s law constants. The concentration of the salt solutions was 0.5 mol dm −3, i.e., similar to the salinity of sea water. The solubility change was described in terms of the Setschenow constant, K S(salt,solute). The highest salting-out effects were observed for the solutions of salts involving doubly charged anions, and the smallest for NO 3 - . The individual ionic Setschenow constants, K S(cation,solute) and K S(anion,solute), were determined by multilinear regression, using the assumption of additivity for the ions. Cl − was selected as the reference ion for calculation of the K S(ion,solute) values of the other ions. The estimations resulted systematically in significant positive K S(cation,solute) values, ranging from 0.13 ± 0.026 ( NH 4 + ) to 0.28 ± 0.032 (Mg 2+), which were hardly affected by the accompanying anion in solution, and only slightly affected by the non-electrolytes present. NO 3 - resulted in a slight salting-in effect: K S( NO 3 - ,solute) = −0.083 ± 0.019; the other anions displayed salting-out effect for all of the non-electrolytes studied, with K S(anion,solute) ranging between 0.090 ± 0.008 ( HCO 3 - ) and 0.21 ± 0.035 ( CO 3 2 - ).