Enthalpic pair interaction coefficients of NaI–non-electrolyte in DMF solution at 25 °C. A comparison of electrolyte–non-electrolyte interactions in DMF and in aqueous solutions

Abstract

Dissolution enthalpies of NaI in dilute solutions of N-methylformamide, dimethyl sulphoxide, tetrahydrofuran, acetonitrile, acetone and isobutanol in N,N-dimethylformamide have been measured. From these data, the enthalpic pair interaction coefficients h_xy[(Na⁺+ I^–)–non-electrolyte] have been determined. The h_xy values for all investigated systems containing NaI are positive, in contrast to aqueous solutions, where they are both positive and negative. A comparison of appropriate data concerning the h_xy(electrolyte–non-electrolyte) values in water and in DMF solution indicates that in the former systems the unusual properties of water influence the analysed h_xy values to a great extent, while in the latter, the h_xy values mainly reflect the replacement of the solvent molecule by cosolvent molecules in the solvation region of the ions.