Jerry Braunstein

Isopiestic studies of very concentrated aqueous electrolyte solutions of LiCl, LiBr, LiNO3, Ca(NO3)2, LiNO3 + KNO3, LiNO3 + CsNO3, and Ca(NO3)2 + CsNO3 at 100 to 150°C†

Thermodynamic properties of aqueous salt solutions show marked changes when the water content is reduced below 4 to 8 mol of H 2 O per mole of salt, reflecting the gradual transition between aqueous electrolytes and molten salts. The enthalpy of vaporization of water rises from values near that of pure water to values characteristic of water at infinite dilution in molten salts. Water activities at high concentrations have been determined from precise isopiestic measurements of LiCl, LiNO 3 , LiBr, Ca(NO 3 ) 2 and several mixtures including (Li, K)NO 3 at 100 to 150°C. All show a region in which Stokes and Robinsons B.E.T. adsorption model of hydration can be fitted with physically reasonable energy parameters. For the system (Li, K)NO 3 + H 2 O, the difference between the energy of adsorption and energy of liquefaction, calculated with the model, is 0.7 kcal mol −1 , while the difference between the enthalpies of vaporization of water at infinite dilution in salt and of pure water is 0.8 kcal mol −1 .

On theAbraham equation for salt activities in concentrated solutions

SummaryIt is shown that the equations derived byVoigt andAbraham for the calculation of salt activities in concentrated solutions are equivalent and that they satisfy theGibbs-Duhem equation.ZusammenfassungEs wird gezeigt, daß die vonVoigt undAbraham zur Berechnung der Aktivitäten von Salzen in konzentrierten Lösungen hergeleiteten Gleichungen äquivalent sind und dieGibbs-Duhem-Beziehung erfüllen.

Nonideality and Association in Binary Mixtures of Molten Salts

Equations are derived for the composition dependence of activities to be expected in binary molten‐salt mixtures if association with ideal mixing of the associated and unassociated species is the cause of the deviations from ideality. Relations are derived between the association constants and the coefficients in the Margules expansion for binary mixtures of nonelectrolytes or of molten salts. Contrary to previous reports, the formation of the anionic associated species MgCl42− cannot account quantitatively for the observed deviations from ideality in alkali chloride–magnesium chloride mixtures.

Concentration dependence of correlation times from proton NMR relaxation in hydrous melts

Proton spin–lattice relaxation times (T1) for hydrous melts of Ca(NO3)2 containing 2.8, 4.0, 8.0, and 16.O moles H2O/mole salt (55.5 to 2.32 moles H2O/l) at temperatures between 290 and 390 K are analyzed in terms of intramolecular and intermolecular contributions. Rotational correlation times for water (τrot) are estimated from the relaxation rates in the high temperature (narrow line) region using intermolecular correlation times (τinter) estimated from melt viscosities or from diffusivities of protons or of dilute solute ions (Cd2+). The ratio τinter/τrot increases from about 2.5 in pure water to about 17 in the viscous melt Ca(NO3)2‐2.8 H2O, suggesting a much greater medium effect on translational than on rotational motion. An empirical relation was found that quantitatively correlates the dependence of the relaxation rate, varying over three orders of magnitude, with viscosity (or water diffusivity) and the volume concentration of water at all of the compositions and temperatures investigated.

Comment on dinuclear complex-ions in molten salts

Summary Graphical and computer evaluation of association constants in dilute molten reciprocal salt mixtures are compared in an attempt to explain agreement in the calculated values for K1 and K2 and discrepancies in calculated dinuclear association constants.