Salts with Added Nonelectrolytes

Of the few scattered studies of concentrated solutions of organic salts, Kenausis et were the first to propose an explanation in some detail on the basis of the system (n-C Hn NSCN with -xylene added. By use of the Walden product they showed that approximately one pair of ions was removed from conduction per molecule of xylene added at the two diverse temperatures of 52° and 90° and at concentrations as high as 0.3 mole fraction of xylene. They argue that the nonelectrolyte causes an asymmetry in the Coulomb field about the ions near the nonelectrolyte and induces pairing. From Seward s data on tetrabutylammonium picrate with butanol added, the amount of ion pair formation per molecule of added nonelectrolyte decreases with increasing dielectric constant of the bulk nonelectrolyte. 

Shortly thereafter Longo et published a note showing that the addition of nitrobenzene to this same salt caused a maximum to occur in the Walden product of the mixture. Since these data would imply greater dissociation in solution than in the salt, a different explanation was sought. 

Recently Lind and Sageman/ using the friction formalism of Section 2.4, examined a number of systems near the limit of the pure salt. The formalism of Laity for 1-1 electrolytes yields  

Because these variations in the anion-cation friction arise from correlations for which the present theory is inadequate, conductance measurements may prove a useful means for probing these very interesting correlational phenomena. 

Angell and C. T. Moynihan, in Molten Salts, Characterization and Analysis (G. Mamantov, ed.), pp. 315-375, Marcel Dekker, New York (1969). 

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Several salts with large anions or cations which are themselves very soluble in water result in salting in, i.e. solubilisation of nonelectrolytes. Sodium benzoate and sodium p-toluenesul-fonate are good examples of such agents and are referred to as hydrotropk salts-, the increase in the solubility of other solutes is known as hydrotropy. Values of k (in (moldm ) ) for three salts added to benzoic acid in aqueous solution are 0.17 for NaCl 0.14 for KCl and -0.22 for sodium benzoate. That is, NaCl and KCl decrease the solubility of benzoic acid, and sodium benzoate increases it. 

If one of the partners in a second-order reaction is not an ion, then in ideal solutions there will be little effect of added salts on the rate. The activity coefficient of a nonelectrolyte does not depend strongly on ionic strength the way that the activity coefficients of ions do. In a reaction with only one participating ion, it and the transition... 

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