Activity coefficients in mixed solvent electrolyte solutions

A brief, rigorous derivation is given for activity coefficients used in phase equilibruim calculations of multicomponents salts and solvents where an extended Debye—Hückel theory for long-range interactions is combined with short-range interaction effects using an excess Gibbs energy model, such as UNIQUAC. Calculations indicate only minor differences from approximate forms previously used for the salt effect on azeotropes.     

Ultimate high-frequency conductivity of solvent and electroconductivity of electrolyte solutions

The temperature curves of the ultimate high-frequency electroconductivity of water and acetonitrile were analyzed. The temperature curves of specific electroconductivity of aqueous 0.1 M sodium chloride solution and acetonitrile 0.1 M 1-butyl-3-methylimidazol trifluoromethane sulfonate were compared. The electroconductivity activation energy of solutions was found coinciding with the ultimate high-frequency electroconductivity activation energy of solvents within the experimental error. The specific electroconductivity of solutions was shown to increase at higher temperature in direct proportion to the ultimate high-frequency electroconductivity of solvents.     

New local composition model for electrolyte solutions: single solvent,single electrolyte systems

A new model for representation of the excess Gibbs energy of electrolyte solutions is proposed. The model is based on the Electrolyte nrtl model according to Chen. However, considerable modifications have been introduced. The new model contains four adjustable parameters per binary electrolyte–solvent system. A new local composition expression is used, in which an energy correction term has been introduced empirically, based on calculation results from statistical thermodynamics. The paper gives computed values of the new model parameters for 163 aqueous electrolyte systems at 298.15 K. The parameters were obtained by correlating data on molal mean ionic activity coefficients and osmotic coefficients from the open literature. A comparison of the performance of the model is made with the Chen model, and shows that the new model may be used to very high concentrations with very good accuracy. An investigation of the temperature dependence of the model parameters has been made for some electrolyte systems over a wide range of temperatures and concentrations. The results show a slight temperature dependence of two of the parameters, while the two other parameters may be assumed independent of the temperature.     

Infrared study of anion—solvent hydrogen bonding in formamide electrolyte solutions

A splitting of the ND stretching band of partly deuterated formamide has been found in perchlorate and tetrafluoroborate solutions. A continuous shift to lower frequencies has been observed for halide solutions. These effects are discussed in terms of the solvent separated ion pair model previously proposed for aqueous solutions.     

Quantitative estimation of the discontinuous function of the solvent in aqueous electrolyte solutions

The adiabatic compression method is used to determine quantitative solvation parameters such as hydration numbers h, the molar adiabatic compressibility of hydrated complexes β _h V _h , the volume V _1h and compressibility β_1h of water in ion hydration shells, and several other properties in the temperature range 278.15–323.15 K. Hydration numbers are used to determine the verified activity coefficient of the solvent, γ _R . The concentration dependence of the coefficient is shown to be a discontinuous function, with the discontinuity point corresponding to the complete solvation boundary.     

Structural parameters of the nearest surrounding of halide ions in the aqueous electrolyte solutions

Literature data and own experimental results on structural characteristics of the halide ions nearest surrounding in the aqueous electrolyte solutions under standard conditions has been summarized. Structural parameters like coordination number, interparticle distance, and ion association type have been discussed. It has been shown that in the halide ions series, from fluoride to iodide, the coordination number gradually increases from 6 to 8. In the same row, the coordination sphere stability decreases, this is reflected in more asymmetrical arrangement of water molecules of the nearest surrounding.     

Thermochemistry of electrolyte solutions

The results of calorimetric investigations of electrolyte solutions in the mixtures of water, methanol, N,N-dimethylformamide, and acetonitrile with numerous organic cosolvents are discussed with regard to the intermolecular interactions that occur in the solution. Particular attention is given to answer the questions how and to what extent the properties of the systems examined are modified by the cosolvent added and how much the properties of the cosolvent are revealed in the mixtures with the solvents mentioned above. To this goal, the analysis of the electrolyte dissolution enthalpies, single ionic transfer enthalpies, and enthalpic pair interaction coefficients as well as the preferential solvation (PS) model are applied. The analysis performed shows that in the case of the dissolution enthalpies of simple inorganic electrolytes in water–organic solvent mixtures, the shape of the dependence of the standard dissolution enthalpy on the mixed solvent composition reflects to a large extent the hydrophobic properties of the organic cosolvent. In the mixtures of methanol with organic cosolvents, the ions are preferentially solvated either by methanol molecules or by molecules of the cosolvent, depending on the properties of the mixed solvent components. The behavior of inorganic salts in the mixtures containing N,N-dimethylformamide is mostly influenced by the DMF which is a relatively strongly ion solvating solvent, whereas in acetonitrile mixtures, the thermochemical behavior of electrolyte solutions is influenced to a large extent by the properties of the cosolvent particularly due to the PS of cation by the cosolvent molecules.     

Hall voltage in electrolyte solutions

Abstract

Hall coefficient for CuSO₄ liquid electrolyte has been measured and found to be positive. Detection of Hall signal was limited to de methods although ac techniques were also investigated. The Hall coefficient increases with decreasing concentration of solute and for distilled water approaches 5 × 10⁵ cm³/coul. Calculations of H⁺ ion mobility using the two carrier expression for Hall coefficient show the charge carrier in a liquid electrolyte to be the H⁺ ion. Mobility of the proton in water is of the order of 1 cm² voltsec, which is near the value in ice     

Overcharging of nanoparticles in electrolyte solutions

Monte Carlo simulations are performed to investigate the effects of salt concentration, valence and size of small ions, surface charge density, and Bjerrum length on the overcharging of isolated spherical nanoparticles within the framework of a primitive model. It is found that charge inversion is most probable in solutions containing multivalent counterions at high salt concentrations. The maximum strength of overcharging occurs near the nanoparticle surface where counterions and coions have identical local concentrations. The simulation results also suggest that both counterion size and electrostatic correlations play major roles for the occurrence of overcharging.     

Thermochemistry of nonaqueous electrolyte solutions

Heats of solution and specific heats have been measured for NaI and KI in methanol at 25 and 50 for the full range of concentrations; the integral heat of solution of NaI or KI in methanol has a positive temperature coefficient, whereas the heats of solution of these salts and all strong electrolytes in water have negative temperature coefficients. The thermal capacity of an aqueous electrolyte is less than the sum of the thermal capacities of the components, whereas the result for methanol is the reverse. In addition, the integral heat of solution has a concentration coefficient much larger than that found for water, mainly because water has a dielectric constant about 2.5 times that of methanol. This leads to stronger interactions between ions in methanol, which contains ion pairs.     

Acidity of frozen electrolyte solutions

Ice is selectively intolerant to impurities. A preponderance of implanted anions or cations generates electrical imbalances in ice grown from electrolyte solutions. Since the excess charges are ultimately neutralized via interfacial (H(+)/HO(-)) transport, the acidity of the unfrozen portion can change significantly and permanently. This insufficiently recognized phenomenon should critically affect rates and equilibria in frozen media. Here we report the effective (19)F NMR chemical shift of 3-fluorobenzoic acid as in situ probe of the acidity of extensively frozen electrolyte solutions. The sign and magnitude of the acidity changes associated with freezing are largely determined by specific ion combinations, but depend also on solute concentration and/or the extent of supercooling. NaCl solutions become more basic, those of (NH(4))(2)SO(4) or Na(2)SO(4) become more acidic, while solutions of the 2-(N-morpholino)ethanesulfonic acid zwitterion barely change their acidity upon freezing. We discuss how acidity scales based on solid-state NMR measurements could be used to assess the degree of ionization of weak acids and bases in frozen media.     

Surface tension of electrolyte solutions

A simple analytic expression is derived for the excess surface tension of electrolyte solutions, which is in good agreement with the experimental data on NaCl in the concentration range up to as high as 1 M. This expression is consistent with the following two theories: (i) The recent theory of Levin and Flores-Mena (Europhys Lett (2001) 56:187), who demonstrated the important contribution of the formation of an ion free layer at the air–electrolyte solution interface, and (ii) the Onsager–Samaras theory (J Chem Phys (1934) 2:528) modified by taking into account the ion-free layer effect. It is shown that the excess surface tension consists of three parts: the contributions of the ion-free layer, the image interaction between the electrolyte ions and the ion-free layer, and the image interaction between the electrolyte ions and air.     

Thermochemistry of nonaqueous electrolyte solutions

Concentration curves δH_m=f(m) are presented for wide concentration ranges at 10 and 25? C; the shape of the curves is discussed.     

Osmotic coefficients of electrolyte solutions

In this paper, the osmotic coefficient, phi, of electrolyte solutions is considered. According to the Gibbs-Duhem equation, the calculation of phi follows from that of the mean activity coefficient, gamma, based on a pseudolattice approach recently proposed. For any given electrolyte, the whole range of concentrations providing gamma相似文献   

A view of electrolyte solutions

The uncertainties in the route to infinite dilution for 2–2 electrolytes are discussed in relation to the practical difficulties of determining the standard emf's of simple reversible cells containing ZnSO₄ in H₂O and D₂O solutions. These difficulties are due to uncertainties in the theory of highly charged ions in aqueous solution. Recent developments in theories of electrolytes, especially those for which numerical results are available, are critically evaluated for their accuracy and adaptability to changes in the solute potential. Simple refinements to the model (i.e., the solute potential) are described, and the changes are interpreted, in terms of the molecular interactions between sets or pairs of ions in the pure solvent. Recent work on the effect of solvent granularity and other molecular properties of the solvent (e.g., dipole moment) on the solute potential is reviewed.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.