Activity coefficients of single electrolytes in concentrated solutions derived from a quasi-lattice model

This paper describes a new model to calculate the mean activity coefficients of dissociated electrolytes in concentrated solutions. It is based on three assumptions: (i) a quasi-lattice arrangements of ions in solution; (ii) a contribution from ion-water interactions to the mean activity coefficients; (iii) a concentration dependence of the dielectric constant. The mean activity coefficients of thirteen strong electrolytes from moderately dilute solutions to saturated solutions are found to correlate well by this model. For dilute solutions, a limiting equation in which only ion-specific parameters are required is proposed. It is suggested that specific ionwater interactions might be the major source of the nonideality of strong electrolyte solutions at high concentrations.     

Activity coefficients of concentrated strong and weak electrolytes by a hydration equilibrium and group contribution model

A new speciation-based group contribution model for activity coefficients is proposed to estimate the equilibrium properties of aqueous solutions containing electrolytes. The chemical part of the model accounts for the hydration equilibrium of water and ions with the formation of ion n-water complexes in a single stage process; the hydration number n and the hydration equilibrium constant K are the two independent parameters in this part. The physical part of the model is the UNIFAC group contribution model for short-range interactions. Each ion is considered as a group. Long-range interactions are accounted for by a Pitzer contribution (Debye–Hückel theory). The model is compared with experimental data at 25 °C including water activity, osmotic coefficients, activity coefficients, and pH of binary diluted and concentrated electrolyte solutions (up to 20 mol kg⁻¹ for NaOH, 16 mol kg⁻¹ for HCl, etc.).     

Activity coefficients of electrolytes from the emf of liquid membrane cells. IV: Revised activity coefficients of lanthanum hexacyanoferrate(III)

Lanthanum ferricyanide is so far the only 3–3 electrolyte whose activity coefficients have been studied carefully; however, the results have been acknowledged to be inconsistent below 1×10^–4 mol-kg^–1. New measurements have been made with an improved cell, proving that the wrong trend was due to chemical interference in the original cell. The new cell makes it possible to reach dilution levels of the order of 4×10^–6 mol-kg^–1. The salt behaves radically unlike Debye-Hückel's predictions, but agrees with other more refined treatments of the hard sphere models without needing any further hypotheses, such as e.g., association. The revised values of the activity coefficients are reported.     

The reduction of Cr(III) in concentrated aqueous electrolytes at a DME: The influence of anions

The reduction of Cr(III) at a dropping mercury electrode is studied in the presence of highly concentrated NaCl, NaI and Na₂SO₄ solutions. Thermodynamic analyses of the interface in the supporting electrolyte solutions are also performed in order to account for the double-layer contributions to the reaction rates. The results can be rationalized better fi the relative surface excesses are corrected for the amount of adsorbed water and if the discharge plane is situated outside the OHP. The reactivities in NaI solutions are higher than those in NaClO₄ at the same concentration but they are equal when compared at the same water activity. Lower rate constants are observed in NaCl and Na₂SO₄ solutions, which are explained on the basis of ion-pair associations in the bulk of the solution.     

Activity coefficients of electrolytes in binary mixtures calculated using total molal quantities

Activity coefficients in binary mixed electrolytes are expressed in terms of the parameters from total molal quantities. Two versions of the calculations are presented and compared with the methods of Pitzer and Scatchard. For each method interrelations among the various parameters are examined. The system being tested is HCl+CoCl₂+H₂O at 25°C, for which new experimental data at low ionic strengths are included.     

Activity coefficients of hexaamminecobalt(III) oxalate and hexacyanoferrate(III) in aqueous solutions of higher valent electrolytes at 25°C

The solubilities of hexaamminecobalt(III) oxalate and hexaamminecobalt(III) hexacyanoferrate(III) in aqueous solutions of different 1-2, 2-1 and 2-2 electrolytes were measured at 25°C. The results have been used to evaluate the relative activity coefficient of the saturating salts.     

A molecular dynamics simulation of the electrical conductivity behaviors of highly concentrated liquid ammoniates NaIalphaNH(3): comparison with experimental measurements

In this paper, we present a molecular dynamics simulation study devoted to the calculation of the electrical conductivities of highly concentrated liquid electrolytes as a function of their dilution. As an illustration, we give the first such study of the ammoniate NaIalphaNH(3). The theoretical results are presented together with experimental data obtained at 293 K, and show that the calculated conductivities are in agreement with the experimental values in the whole salt dilution range provided that correlations between the species in the solution are taken into account. Indeed, the usual Nernst-Einstein relation is a crude approximation to calculate accurately the conductivities in such high concentrated electrolytes.     

Numerical values of individual activity coefficients of single-ion species in concentrated aqueous electrolyte solutions and the attempt of a qualitative interpretation on a model of electrostatic interaction

Individual activity coefficients of single-ion species can be achieved by the factorizing of a new concentration function for the mean activity coefficient to the required power applying a purely mathematical method. These single-ion activity coefficients, calculated in this manner, are listed for some aqueous strong electrolytes. The reasons for the magnitude and variation of the activity coefficients as a function of the concentration are, without a doubt, of complex nature. Activity coefficients have their meaning as practical values. In relation to the analytical concentration, the individual activity coefficients represent the macroscopic effectiveness of the single-ion species in solution an easy manner. However, with increasing deviations from Debye–Hückel conditions of an infinitely diluted electrolyte solution, a physically correct interpretation of the macroscopically visible activity coefficient is becoming more and more difficult, if not impossible to find. On the basis of a model of electrostatic interaction, an attempt has been made to create a qualitative interpretation of the individual ion activity coefficients in concentrated aqueous electrolyte solutions which were calculated applying the purely mathematical method by Ferse.     

Determination of diffusion coefficients of Cu(I) ions in concentrated perchlorate solutions

The diffusion coefficients of Cu(I) ions in concentrated aqueous Ca(ClO₄)₂ solutions have been determined from the limiting currents of anodic oxidation at the rotating disc electrode.

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Zur Bestimmung der Diffusionskoeffizienten von Cu(I)-Ionen in konzentrierten Perchloratlösungen (Kurze Mitteilung)

Zusammenfassung Diffusionskoeffizienten von Cu(I)-Ionen in konzentrierten wäßrigen Ca(ClO₄)₂-Lösungen wurden durch Messung der anodischen Grenzströme an der rotierenden Scheibenelektrode bestimmt.

     

State of the Tb(III) and Nd(III) ions in concentrated solutions of electrolytes of various types

An investigation of the state of terbium and neodymium ions in solutions of various supporting electrolytes was conducted using an analysis of the electronic absorption spectra of Nd(II) and the fluorescence spectra of Tb(III). The supporting electrolytes selected were the salts LiSCN, LiCl, MgCl₂, NaCl, and CsCl, the concentration of which was varied within wide limits. The neodymium and terbium chloride concentrations were kept constant in all the solutions and equal to 0.015 and 0.03 M, respectively. To eliminate the influence of hydrolysis on the experimental results, all the solutions were acidified with hydrochloric acid (0.1 M).St. Petersburg University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 2, pp. 105–111, March–April, 1993.     

Activity coefficients of electrolytes from the emf of liquid membrane cells. III: LaCl3, K3Fe(CN)6, and LaFe(CN)6

The activity coefficients of LaCl₃, K₃Fe(CN)₆, and LaFe(CN)₆ were measured down to about 1×10^–4, 3×10^–5, and 2×10^–5 mol-kg^–1 respectively, by means of cells with ion-exchange liquid membranes. In the diluted region, the trend of lanthanum chloride agrees with the Debye-Huckel theory and corroborates earlier findings in the literature relevant to more concentrated solutions, with minor systematic corrections of the _± values. K₃Fe(CN)₆ attains (rather than tends to attain) the Debye-Huckel limiting slope at1×10^–3 mol-kg^–1, and lanthanum ferricyanide in the diluted region shows negative deviations from the limiting law, similar to the ones predicted for large-sized, highly-charged ions in the diluted region by Bjerrum's, IPBE, and Mayer's theories. The behavior of LaCl₃ in the concentrated solutions proves that lanthanum ion drags along with it into the membrane many molecules of water which were then found to be twelve. Pitzer's theory best-fit coefficients that meet the experimental curves to be reproduced satisfactorily are reported.     

Modification of the Pitzer model to calculate the mean activity coefficients of electrolytes in a water-alcohol mixed solvent solution

The approach tested in this work consists in adapting the Pitzer model, initially designed for aqueous solutions of electrolytes, to the case of solutions with a mixed solvent, without systematically readjusting the coefficients. This modified model was applied successfully to the calculation of the mean activity coefficients of NaBr in the mixed solvent H₂O+MeOH, H₂O+EtOH and compared with the experimental values obtained from electrode potential measurements.General D dielectric constant - G ^ex excess Gibbs energy - I ionic strength - k Boltzman's constant - m _i molality - N _o Avogadro's number - n _w number of kilograms of water - R gas constant - T temperature (K) - T _c critical temperature - T _cm critical temperature of mixed solvent - x _i molar fraction - z _i ionic charge - electronic charge - osmotic coefficient - ± mean activity coefficient of electrolyte - number of moles of ions given by one mole of electrolyte - _M number of moles of cations given by one mole of electrolyte - _X number of moles of anions given by one mole of electrolyte - _W density of water Debye- Hückel Model A Debye-Hückel parameter - a distance of closest approach of ions in solution - B Debye-Hückel parameter Pitzer Model b numerical parameter of model - numerical parameter of model - ₁, ₂ numerical parameters of model, used in the case of 2:2 electrolyte - _MX ⁽⁰⁾ numerical parameter of electrolyte MX - _MX ⁽¹⁾ numerical parameter of electrolyte MX - _MX ⁽²⁾ numerical parameter of 2:2 electrolyte MX - C _MX numerical parameter of electrolyte MX - binary interaction parameter - ternary interaction parameter     

Diffusion in concentrated dispersions: a study with fiber-optic quasi-elastic light scattering (FOQELS)

A fiber-optic, quasi-elastic light-scattering instrument is described using single-mode fiber optical components, including a novel slanted exit face optode. The setup operates with homodyne signal detection. It enables the characterization of diffusion processes in concentrated dispersions up to volume concentrations of 50%.The performance of the instrument is exemplified with results obtained from latex spheres with diameters of 226 nm and 404 nm at volume fractions from =0.01 to =0.5. The correlation functions are analyzed according to the second order cumulants method and the Contin-procedure yielding an average and a distribution function of the short-time self-diffusion coefficient,D _eff ^s , respectively.At high ionic strength the concentration dependence ofD _eff ^s /D ₀ is found to be in close agreement with theoretical predictions based on a multi-body interaction model of hard spheres up to =0.45. With decreasing ionic strength the negative slope of the virial expansion tends to increase, presumably due to enhanced repulsive electrostatic interactions.The described technology offers new experimental means for on-line remote control sensing of particle size in concentrated disperse systems.Presented at the 34. Hauptversammlung der Kolloidgesellschaft e.v., Bochum, Oct. 1–4, 1989     

Evidence of solvation of aqueous electrolytes in a range from diluted to concentrated solutions

Parameters of solvation of strong electrolytes in aqueous solutions have been investigated based on literature data on their densities, thermal capacities, and rates of ultrasound propagation. By using appropriate thermodynamic equations, such quantitative parameters of solvation as hydration number (h), molar adiabatic compressibility of the hydrated forms (β _h V _h ), volume (V _1h ), and compressibility (β_1h ) of water in the hydrated shells of ions have been determined in the temperature interval from 278.15 to 323.15 K. It has been demonstrated that the h and β _h V _h values are temperature-independent within the studied interval and that electrostrictive compression near ions has a stronger effect on their structure than a simple change in pressure.     

Polarographic determination of diffusion coefficient values of In(III) in potassium chloride and nitrate supporting electrolytes

The diffusion coefficient values of In(III) in potassium chloride and potassium nitrate supporting electrolytes have been determined by polarography. Also, the half-wave potential, E(1/2), and the |E(3/4)-E(1/4)| values have been calculated. The results show ionic strength and chloride concentration effects on electrode kinetics in the reduction of In(III).     

Electrokinetic parameters of colloidal model systems: analysis and comparison between dilute and concentrated dispersions

In the last decades, the interest of many scientists has been focused on the atypical electrokinetic behavior of charged colloidal systems since several studies have shown, in most cases; it is not so ideal as expected. Particularly, two interesting phenomena have not been clearly explained yet. First, the zeta potential magnitude does not decrease monotonically with increasing ionic strength, as expected according to the Gouy-Chapmann model predicts. Second, the zeta potential obtained from different techniques shows discrepancies. More specifically, the zeta potential obtained from streaming potential is lower (in absolute value) than that measured through electrophoretic mobility. However, a recent work has pointed out that these discrepancies seem to disappear if certain conditions (related with the surface charge density) are satisfied. This work also revealed that unexpected results are found when the electric conductivity was used. Spherical polystyrene particles of appropriate particle size and charge density are employed as polymeric colloidal model in the present work. Common and adequate models are used to make clear and easy our theoretical analysis and its interpretation. To test the surface conductance and ionic mobility effects at the solid-liquid interface, both water medium and alcohol-water mixtures are used.     

Synthesis and oxygenation of a nickel(II) and zinc(II) dithiolate: an experimental and theoretical comparison

The diamino-dithiolato N2S2 ligand N,N'-bis-2-methyl-mercaptopropyl-N,N'-dimethylethylenediamine, H2bmmp-dmed), and its nickel (1) and zinc (2) complexes have been prepared and their reactivities with hydrogen peroxide investigated. Complex 1 yields a mixture of sulfenato (RSO-), 4, sulfinato (RSO2-), 3, and sulfonato (RSO3-), 5, products upon addition of H2O2. Products are separable by column chromatography. Stoichiometric addition of H2O2 to 2 yields an inseparable mixture. Excess peroxide addition results in oxygenation of the ligand to the disulfonate, 6, and decomplexation of zinc. Complexes 1, 2, and 3 and compound 6 have been investigated by X-ray crystallography, and their structures are reported. Density functional theory (DFT) calculations of 1 and 2 reveal significant sulfur p character in the HOMO of each complex. However, 1 also shows significant metal d character that is pi-antibonding with respect to the sulfur p orbitals. Complex 2 shows little metal character in the HOMO. Implications of the HOMO with respect to S-centered reactivity and metal ligand distances in S-oxygenated products are provided.     

Anomalous dependence on the diffusion coefficients of the ionic relaxation time in electrolytes

We show, by using a numerical analysis, that the dynamic toward equilibrium for an electrolytic cell subject to a step-like external electric field is a multirelaxation process when the diffusion coefficients of positive and negative ions are different. By assuming that the diffusion coefficient of positive ions is constant, we observe that the number of involved relaxation processes increases when the diffusion coefficient of the negative ions diminishes. Furthermore, two of the relaxation times depend nonmonotonically on the ratio of the diffusion coefficients. This result is unexpected, because the ionic drift velocity, by means of which the ions move to reach the equilibrium distribution, increases with increasing ionic mobility.