Preferential solvation number chloride

A method of prediction of the salt effect of vapor-liquid equilibrium relationships in the methanol-ethyl acetate-calcium chloride system at atmospheric pressure is described. From the determined solubilities it is assumed that methanol forms a preferential solvate of CaCl296CH OH. The preferential solvation number was calculated from the observed values of the salt effect in 14 systems, as a result of which the solvation number showed a linear relationship with respect to the concentration of solvent. With the use of the linear relation the salt effect can be determined from the solvation number of pure solvent and the vapor-liquid equilibrium relations obtained without adding a salt. 

The preferential solvation formed between salt and solvent molecules causes a salt effect on vapor-liquid equilibria. A method of prediction of salt effect based on the preferential solvation number was reported previously for the case in which salt was solved below the saturation level. The idea introduced in this chapter applies for salt solved in saturation. The alcohol-ester-calcium chloride system for which the preferential solvation was thought to be formed was examined. Specifically, calcium chloride dissolves readily in alcohol but only sparingly in ester. Thus, when calcium chloride is solved into alcohol-ester mixed solvent, the calcium chloride will form a preferential solvation with alcohol only. Methanol-methyl acetate, butanolr-butyl acetate, and methanol-ethyl acetate systems were selected for the mixed-solvent systems. 

Figure 5. Preferential solvation number in the methyl acetate-methanol-calcium chloride system at 1 atm (O), CaCl2 6 tot % (A), CaCl2 15 wt % (0), CaCl2 saturated (5).

As a cause of salt effect, the existence of a preferential solvate formed across salt and particular component in a solvent mixture is considered. Preferential solvation number was calculated for the alcohol-ester-cal-cium chloride system in which formation of preferential solvate was believed to exist. The preferential solvation number was found to be constant regardless of compositions of a solvent mixture. On the other hand, the solubility of salt into mixed solvent increased linearly against an increase of composition of the component which dissolved salt. This fact indicates that the entire dissolved salt contributes to the formation of solvation with the particular component in the mixed solvent. The author feels that the study should be continued in order to make the salt effect clear so that it will be possible to apply the above described idea to other systems also. 

NO3 anions are surrounded by four to five imidazolium cations. Chaumont, Engler and Wipff employed the same technique to examine the solvation of uranyl and strontium nitrates as well as uranyl chlorides in the same ionic liquids.As was observed in the previous study, the anions of the ionic liquids solvate the strontium and uranyl ions preferentially. Detailed radial distribution functions and coordination numbers were computed. This group has extended this work by making comparisons of computed solvation ordering with data from experimental spectroscopic studies. 

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