Zdeněk Kodejš

Vapour pressures of very concentrated electrolyte solutions. IV: Measurements on {(1-x)(CH3)2SO+xKSCN} by a dew-point apparatus

Abstract The vapour pressure of water above {(1 − x)H2O + xKSCN} has been determined from dew-temperature measurements in the range 340 T K for 0.05

Vapour pressures of very concentrated electrolyte solutions III. Measurements on [(1−x)(CH3)2SO + x{(1−y)NH4NO3 + yLiNO3}] by a dew-point apparatus

Abstract The vapour pressure of dimethylsulphoxide above very concentrated solutions of NH 4 NO 3 , LiNO 3 , and their binary mixtures in (CH 3 ) 2 SO have been determined from dew-point measurements in the approximate range 327 T K . The results are treated on the basis of the Stokes-Robinson adsorption-hydration theory, which is found to be applicable over wide ranges of solvent activity a s , extending from the lowest experimental values a s ≈ 0.2 to 0.3, up to at least a s = 0.6. The structural and energetic parameters involved in the above theory, calculated for (ammonium nitrate + dimethylsulphoxide) and for (lithium nitrate + dimethylsulphoxide) are compared with those previously obtained for (calcium nitrate + dimethylsulphoxide) and with those for (ammonium nitrate + water) and (lithium nitrate + water). The strong interactions revealed for both Li + and NH 4 + with (CH 3 ) 2 SO bring both cations into the group of strongly solvated cations in such a good donor solvent as (CH 3 ) 2 SO, in agreement with previous suggestions in the literature. The existence of a caging effect of all the three cations Ca 2+ , Li + , and NH 4 + by (CH 3 ) 2 SO molecules in the whole experimental composition range might be expected. The dependences of the parameters on the mole fraction y of the solute mixture {(1− y )NH 4 NO 3 + y LiNO 3 } are discussed in relation to the trends previously observed for similar aqueous solutions.

Solution properties of water in molten AgNO3–LiNO3 mixtures as derived from vapour-pressure measurements on AgNO3–LiNO3–H2O melts

The results of extensive vapour-pressure measurements on highly concentrated aqueous solutions of AgNO3, LiNO3 and their binary mixtures in the temperature range 320 < T/K < 380 are treated by means of the Stokes–Robinson adsorption–hydration theory. The structural and energetic parameters in the theoretical equation are calculated after completing the set of measurable data for AgNO3–H2O melts with extrapolated data from the literature. Examination of the dependence of the adsorption–hydration energy on the composition of the nitrate mixture in the light of a previous theory for selective ionic hydration in such melts reveals the existence of an additional contribution to the predicted hydration energy of the AgNO3–LiNO3 melts. This excess hydration energy term is discussed in relation to the known positive excess free energy of mixing of anhydrous AgNO3–LiNO3 molten mixtures. In this way the dissolved water acts as a probe of the mixing features of the molten salts.

Theory of volumetric behaviour of hydrous melts. The systems LiNO3–H2O and NH4NO3–H2O

An equation for the dependence of the molar volume of a hydrous melt on its molar composition is derived on the basis of the concept of the apparent molar volume of water and from a previous calculation of the distribution of water molecules between sites near ions and sites near water molecules in the melt. The densities of LiNO3–H2O and NH4NO3–H2O liquid mixtures have been measured at 333 K over the composition ranges 0.05 < x(LiNO3) < 0.3 and 0.1 < x(NH4NO3) < 0.5, and have been used, together with literature data for the systems NH4NO3–H2O, (Li0.5K0.5)NO3–H2O, Ca(NO3)2–H2O and Cd(NO3)2–H2O, to test the validity of the derived equation and to calculate the values of the physical parameters involved.

Correlation of the solvation properties of water and dimethyl sulphoxide in metal nitrate–water and metal nitrate–dimethyl sulphoxide melts with the molecular properties of the constituents of the melts

The currently available thermodynamic data obtained by vapour pressure measurements on highly concentrated solutions of single-metal nitrates in water and in dimethyl sulphoxide are numerous and reliable enough to allow us to establish a correlation between the standard solvation free energy, ΔG°sv, of water and dimethyl sulphoxide in (undercooled) liquid nitrates and some of the molecular and ionic parameters which characterize the two molecules and the ionic constituents of the salts. To supplement the previously investigated systems, the system AgNO3–DMSO has been studied by vapour pressure measurements on a dew-point apparatus over the temperature range 330 < T/K < 375 with the salt mole fraction, x, ranging between 0.15 and 0.40. The widely used Stokes–Robinson adsorption–hydration theory has been employed to treat the experimental results and to calculate the values of ΔG°sv. Reasonable linear correlations have been found between ΔG°sv and a function relating the electrostatic cation–dipole interaction energy with physical parameters (charge numbers, ion–dipole distances), suggesting that solvation of both water and dimethyl sulphoxide in liquid nitrates is governed mainly by the cation–dipole electrostatic interaction energy. The roles of the dipole moments and of the donating abilities of the two molecules are pointed out and some suggestions are made concerning the contribution of other energetic and entropic factors to the solvation processes.

Volumetric Behaviour of Highly Concentrated Solutions of Salts in Non-Aqueous Solvents. The Systems Ca(NO3)2 + DMSO, LiNO3 + DMSO, and NH4NO3 + DMSO

The concentration dependences of the molar volume of highly concentrated solutions of Ca(N03)2, LiN03, and NH4N03 in dimethylsulphoxide have been investigated at 333.2 K over the composition ranges 0.05 < Xca(No3)2 < 0.26, 0.07 < .XunOj < 0.29, and 0.07 < Xnh.no, < 0.50. The experimental data are fitted by an equation previously derived on the basis of the concept of the apparent molar volume of solvent to test the applicability of the equation to such

Water solubility in molten-salt mixtures. A theory for selective ionic hydration

A statistical thermodynamic treatment based on the quasi-lattice model of molten salts is developed to explain the non-linear dependence of the enthalpy of transfer of water from liquid water to an infinitely dilute solution of water in a binary molten-salt mixture on the molar composition of the mixture. The derived equation is used to fit previously determined data for the enthalpy of transfer of water from liquid water to (undercooled) liquid LiNO3+ NH4NO3 mixtures in the whole composition range; a satisfactory fit is obtained for a reasonable choice of the values for the quasi-lattice coordination numbers of LiNO3 and NH4NO3. Literature data for the enthalpy of dissolution of water in molten LiNO3+ NaNO3 and LiNO3+ KNO3 mixtures are in qualitative agreement with the predictions of the present theory.