Real and chemical solvation energies of individual ions in solution

On the basis of the proposed concept of real thermodynamic properties for individual ions in solution, the real thermodynamic properties of transport (resolvation) for various ions (sodium, potassium, chloride, bromide, and iodide) from water to mixtures of water with ethyl, n-propyl, and isopropyl alcohols, acetone, acetonitrile, dimethylsulfoxide, and dimethylformamide are determined by the method of Volta potential differences. Values of the chemical thermodynamic properties of transport of the ions under investigation are determined on the basis of previously calculated values of surface potentials of the solvents mentioned above. A comparative analysis of the values obtained is carried out, and characteristics of the solvation of ions of different sign are established as functions of their nature relative to the physicochemical and structural properties of the solvents. The satisfactory agreement of the data obtained on the basis of the total Gibbs energy of transport of the ions under investigation in the indicated solvents with literature data is the criterion of correctness for the scientific material presented in this paper.     

Application of Volta chains to determine ionic components of real and chemical Gibbs energies of transfer of individual ions from water to aqueous-organic solvents

The state of individual ions in individual and mixed solvents was described from the thermodynamic point of view using the method of Volta potential differences. This methodology provides a way of solving the problem of determination of thermodynamic characteristics of individual ions in solutions. The possibility of using the method of Volta potential differences to determine the ionic components of the real and chemical thermodynamic properties of individual ions in solutions and the surface potentials at gas-solution interface is substantiated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 1–6, January, 2007.     

The evaluation and use of properties of individual ions in slution

A critical examination is given of extra-thermodynamic methods for evaluation of properties of individual ions in solution. The ways in which such data may be applied, or are required in various problems concerning specific properties of electrolyte solutions and in the fields of kinetics, electrochemistry, colloid and interfacial chemistry, are outlined. Special attention is given to the problem of evaluation of individual ionic thermodynamic functions for the hydration of ions but, in some cases, corresponding data for nonaqueous solutions are available for discussion and are of interest in a comparative way. The reliability of the various methods is assessed and estimates of numerical values for various individual ionic functions are tabulated. The question of scales of individual ionic radii, on which some of the derived data depend, is also examined. The dependence of various properties for anions and for cations on ionic radius is discussed and data are plotted comparatively. It is shown that for most, but not all, properties, the values for anions are more sensitive to increasing ionic radius than are the values for cations. This behavior, as well as the exceptions, is of theoretical interest. The significance of ion-specific behavior at interfaces is considered and the importance of interactions between ions of like sign of charge is indicated.Presented at the Symposium on Electrolytes, University of Reading, September 13, 1977.     

Thermodynamics of individual ions in ethylene glycol-water solvents

A new equation, correlating the cell (or electrode) potential with the dielectric constant of the solvent, has been developed and used to compute the chemical contribution to the transfer thermodynamic quantities of individual ions in various solvents. The results show that the electrostatic contribution to the transfer free energies should in fact account for all the interactions between the charge on the ion and the overall charge on the solvent molecules, of which the Born contribution plays but a minor role. The thermodynamic properties of individual ions have been discussed in the light of ion-solvent interactions as well as the structural effects of the solvents on the transfer process.     

Electrochemical study of potassium and iodide ions resolvation in aqueous methanol mixtures

The results from the compensating voltage measurements of Volta circuits by the Kenrik method at 298.15 K were used to calculate the real primary media effect of potassium and iodide ions and real Gibbs energy of K⁺ and I⁻ transfer from water to aqueous methanol (MeOH) mixed solvent. The surface potential $\Delta \chi _{H_2 O}^{MeOH} $\Delta \chi _{H_2 O}^{MeOH} at non-aqueous solvent/gas interface was found. This value was used to calculate the chemical thermodynamic characteristics of the studied ions. The solvation features of the studied ions were revealed in the aqueous methanol mixed solvent.     

Resolvation thermodynamics of individual ions in water-ethanol mixtures at 298.15 K

The standard real and chemical thermodynamic characteristics of resolvation for magnesium ions in the water-ethanol mixtures of different composition were determined by their Volta potential differences at 298.15 K. Based on our analysis of these characteristics, the regularities and peculiarities of solvation of investigated ions in the mixed solvent were established. It was shown that the energies of ion resolvation in dependence on their crystallographic radii correspond to the series Ba²⁺< Ca²⁺ < Cd²⁺ < Cu²⁺ < Mg²⁺ < Al³⁺.     

Thermodynamics of Resolvation of Sodium and Potassium Ions in Water–Dimethylformamide

The real primary medium effect of sodium and potassium ions and the real Gibbs energy of transfer of these ions from water into a mixed water–dimethylformamide (DMF) solvent are determined using the method of Volta potential differences at 298.15 K. For DMF, the surface potential at the solvent/gas interface is found to equal –0.434 V. Based on this value, chemical thermodynamic characteristics of the ions are calculated. The thermodynamic characteristics for resolvation of cations are compared with those for anions in the mixtures under investigation obtained earlier.     

A new model for the activity coefficients of individual ions in aqueous electrolyte solutions

In this study, the individual ion activity coefficient in an aqueous solution is modeled with a new model. This model contains two physical significant ionic parameters regarding the ionic solvation and the closest distance of approach between ions in a solution. The present model was evaluated by the estimation of the individual activity coefficients of the ions of thirty electrolytes in aqueous solutions. The results showed that this model suitably predicts the individual ion activity coefficients in aqueous two-electrolyte solutions consisting of the binary pairs of electrolytes of NaCl, KCl, KBr and CaCl₂ in a temperature range from 298.15 to 243.15 K. The results by this model were compared to the literature values. The average absolute relative deviations of vapor pressures showed acceptable agreement between experimental data and the results of this model.     

Activity coefficients of sodium,potassium, and nitrate ions in aqueous solutions of NaNO3, KNO3, and NaNO3+KNO3 at 25°C

Ion selective electrodes have been used to measure the activity coefficients at 25°C of individual ions in aqueous solutions of NaNO₃ up to 3.5 molal, KNO₃ up to 3.5 molal and mixtures of NaNO₃ and KNO₃ up to 2.4 molal total nitrate ion concentration. The experimental results confirm that the activity coefficient of anion and cation in aqueous single electrolyte solutions of NaNO₃ and KNO₃ were different from each other over the whole range of concentrations studied. These effects are attributed to the ion-ion and ion-solvent interactions. The results also show that the activity coefficients of nitrate ions in the presence of sodium and potassium counterions do not depend significantly on the nature of the counterions present in the solution. The experimental data obtained in this study were correlated by a model proposed previously.     

Analysis of the thermodynamic characteristics of solvation of individual ions in ethanol using model concepts

Solvation of individual ions in ethanol are given by the sum of various contributions: electrostatic, cavity formation, interactions of ions with the solvent, and structural rearrangement of the solvent itself. An analysis of the influence of all these contributions on the temperature dependence of solvation of ions is presented.     

Effects of the nature and composition of the solvent on the thermodynamic characteristics of the individual forms of hydrogen adsorbed on the surface of porous nickel

The effects of the nature and composition of solvents on the thermodynamic characteristics of the adsorption states of hydrogen on nickel were studied. The adsorption can be described in terms of the thermodynamic model of a surface with a discrete nonhomogeneity for three individual forms of adsorbed hydrogen. The thermodynamic characteristics of the individual forms of hydrogen adsorbed on porous nickel from aqueous solutions of sodium hydroxide, dimethylformamide, methanol, and ethanol were determined.     

Transport of hydrated nitrate and nitrite ions through graphene nanopores in aqueous medium

Nitrate () and nitrite () ions are naturally occurring inorganic ions that are part of the nitrogen cycle. High doses of these ions in drinking water impose a potential risk to public health. In this work, molecular dynamics simulations are carried out to study the passage of nitrate and nitrite ions from water through graphene nanosheets (GNS) with hydrogen-functionalized narrow pores in presence of an external electric field. The passage of ions through the pores is investigated through calculations of ion flux, and the results are analyzed through calculations of various structural and thermodynamic properties such as the density of ions and water, ion–water radial distribution functions, two-dimensional density distribution functions, and the potentials of mean force of the ions. Current simulations show that the nitrite ions can pass more in numbers than the nitrate ions in a given time through GNS hydrogen-functionalized pore of different geometry. It is found that the nitrite ions can permeate faster than the nitrate ions despite the former having higher hydration energy in the bulk. This can be explained in terms of the competition between the number density of the ions along the pore axis and the free energy barrier calculated from the potential of mean force. Also, an externally applied electric field is found to be important for faster permeation of the nitrite over the nitrate ions. The current study suggests that graphene nanosheets with carefully created pores can be effective in achieving selective passage of ions from aqueous solutions.     

Electrochemical study of the properties of Nd(III) and Nd(II) ions in molten LiCl-KCl-CsCl eutectic and individual CsCl

The electrochemical behavior of NdCl₃ solutions in eutectic LiCl-KCl-CsCl and individual CsCl melts was studied on an inert molybdenum electrode at temperatures in the range 573–943 K. Cyclic and differential pulse voltammetry and potentiometry at zero current and the electromotive forces method were used. The cathode reduction of Nd(III) ions to the metal was found to occur as a sequence of two stages. The formed Nd(II) ions were unstable above 798 K and underwent disproportionation 3Nd(II) ? 2Nd(III) + Nd_(m) in the salt melts. The conventional standard redox potential of the Nd(III)/Nd(II) pair in a eutectic LiCl-KCl-CsCl melt was measured over a wide temperature range. The main thermodynamic characteristics of the reaction NdCl_2(m) + 1/2Cl_2(g) ? NdCl_3(m) were determined.     

Ionic components of the real and chemical Gibbs energy of transport of potassium and chloride ions from water to water-methanol mixtures

With the method of volta-potential differences at 298.15 K the ionic components of the standard real and chemical thermodynamic properties of the resolvation of potassium and chloride ions were determined in mixtures of water and methanol (MeOH). The value of the surface potential at the methanol/gas phase boundary (Δχ^MeOH = ?0.18 V) is obtained. The characteristics of the solvation of these ions in a water-methanol medium are identified, and a comparison with literature data for other nonaqueous mixtures is carried out.     

Insight from adsorption properties of Xylidyl Blue embedded hydrogel for effective removal of uranyl: Experimental and theoretical approaches

Applications of a hybrid material consisting of polyacrylamide (PAA) and Xylidyl Blue (XB) for the removal of uranyl ions from aqueous solutions has been investigated with all details. Adsorption experiments were performed at batch mode and constant temperature. Experimental parameters affecting adsorption process such as pH, initial uranyl concentration, time and temperature were studied on the removal of the uranyl ions. The isotherms assays were carried out with synthetic solutions and adsorption data were evaluated by using Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models. Morphological and chemical characterizations of new synthesized material were investigated by UV-VIS-NIR spectroscopy and SEM/EDX techniques and pH_pzc experiments. The results of the kinetic experiments are consistent with pseudo-second-order models and intra-particle diffusion models with a slightly better fit to the latter. Equilibrium was achieved within 3 h. The value of rate constant for adsorption process was calculated as 1.055 mol⁻¹ kg min⁻¹ at 318 K. The calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) indicated that the adsorption of uranyl ions onto XB@PAA was feasible, spontaneous and endothermic nature under the studied temperature. The developed material has also a potential as a sensor because its color turn from pink to red by adsorption of uranyl ions.     

The thermodynamic characteristics of resolvation of calcium and cadmium ions in aqueous-ethanolic mixtures

The real and chemical thermodynamic characteristics of resolvation of calcium and cadmium ions in water-ethanol mixtures were determined by measuring the compensation voltages of Volta circuits by the Kenrick method at 295.15 K. The Harkins method was used to substantiate the assumption of a constant surface potential at the nonaqueous solvent/gas phase interface starting with a certain nonaqueous component concentration.     

Thin-Layer Electrolytic Molybdenum Oxydisulfides for Cathodes of Lithium Batteries

Electrolytic molybdenum oxydisulfides are synthesized out of aqueous molybdate solutions containing sulfur in the presence of ions of Ni²⁺ with the aim of applying them as materials for ballastless cathodes of thin-layer lithium batteries. The physicochemical and structural properties of the synthesized compounds are studied profilometrically and by methods of thermal and x-ray diffraction analyses, absorption IR spectroscopy, and atomic force microscopy. Specific discharge characteristics, the chemical diffusion coefficient of lithium ions, the interaction parameter of intercalated ions, and the repulsion energy of intercalated ions in the process of intercalation and deintercalation of lithium ions in the synthesized materials are determined.     

The gibbs energies of transfer of calcium ions from water into water-acetone mixtures

Volta potential differences measured at 298.15 K were used to determine the real primary effect of the medium of calcium ions and the real Gibbs energy of transfer of Ca²⁺ from water into a mixed water-acetone (Me₂CO) solvent. The surface potential at the solvent/gas phase interface was found to be $\Delta \chi ^{Me_2 CO} = - 0.337V$ . This value was used to calculate the chemical thermodynamic characteristics of calcium ions. The thermodynamic characteristics of resolvation of the 2-1 electrolyte are compared with those obtained earlier for a 1-1 electrolyte.     

The special features of the solvation of the sodium,potassium, and bromine ions in water-methanol mixtures

The compensation potentials of Volta circuits were measured by the Kenrick method at 298.15 K to determine the real and chemical thermodynamic characteristics of resolvation of the potassium, sodium, and bromine ions in water-methanol mixtures and the surface potential at the gas phase/methanol interface Δχ^MeOH. The special features of the solvation of the ions in mixed water-methanol solvents were studied.     

Measurement of real free energies of transfer of individual ions from water to other solvents with the jet cell

Resolution of the activities of solutions of electrolytes into the individual ionic contributions cannot be carried out rigorously and requires the introduction of extrathermodynamic assumptions which have inherent uncertainties. The most commonly used approaches are basically similar in that they are based on the assumed solvent independence of the difference in the enthalpy or Gibbs energy of transfer of pairs of model solutes, e.g., tetraphenylarsonium and tetraphenylborate ions, or ferricinium ion and ferrocene. In this work we follow an alternative approach pioneered by Parsons involving measurement in the jet (Kenrick) cell of outer-potential differences between solutions of the same electrolyte in two solvents. These potential differences provide the real free energies of transfer of individual ions which, in turn, differ from the usual Gibbs energies of transfer by the work required to transfer the ion through the dipolar layers at the two solvent-gas interfaces. One objective of this work was to improve the reliability of real free energy of transfer measurements, which are experimentally demanding, to within ca. ±0.5 kJ-mol^–1 in order to match typical uncertainties in Gibbs transfer energies of electrolytes. This goal was met, in most instances, by careful evaluation of experimental parameters (particularly jet pressure). A major improvement over previous measurements was made by adding a supporting electrolyte which allowed stable potentials to be obtained at test electrolyte concentrations as low as 10^–4M. Real free energy changes are reported for the transfer of silver ion from water to methanol, ethanol, acetonitrile, propylene carbonate and dimethyl sulfoxide, as well as for the transfer of chloride ion from water to methanol and ethanol. Reliable data of this kind may lead to improved understanding of either the properties of the surfaces of solvents or the interactions of model solutes with solvents, depending on which of the two fields develops most.