Activity Coefficients Of Aqueous Solutions Research Articles

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 CaCl 2 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.

Isopiestic determination of osmotic and activity coefficients of aqueous solutions of aliphatic polyols at 298.15 K

The osmotic coefficients of 1,2-butanediol (12BD), 1,3-butanediol (13BD), 1,4-butanediol (14BD), 2,3-butanediol (23BD), 1,2,4-butanetriol (124BT) and 1,2,3,4-butanetetrol (1234BT) in water were measured by the isopiestic method at 298.15 K. Experimental osmotic coefficients were used to calculate water activity, solute activity coefficients and the pairwise Gibbs energy coefficients for solute–solute interactions.

Correlation and prediction of osmotic coefficient and water activity of aqueous electrolyte solutions by a two-ionic parameter model

In this study, osmotic coefficients and water activities in aqueous solutions have been modeled using a new approach based on the Pitzer model. This model contains two physically significant ionic parameters regarding ionic solvation and the closest distance of approach between ions in a solution. The proposed model was evaluated by estimating the osmotic coefficients of nine electrolytes in aqueous solutions. The obtained results showed that the model is suitable for predicting the osmotic coefficients in aqueous electrolyte solutions. Using adjustable parameters, which have been calculated from regression between the experimental osmotic coefficient and the results of this model, the water activity coefficients of aqueous solutions were calculated. The average absolute relative deviations of the osmotic coefficients between the experimental data and the calculated results were in agreement.

Osmotic and activity coefficients of aqueous solutions of KCl at temperatures of 283.15, 288.15, 293.15 and 298.15 K: A new isopiestic apparatus

Osmotic coefficients of aqueous KCl solutions have been determined by the isopiestic method using standard NaCl reference solutions for comparison. Measurements were made at 283.15, 288.15, 293.15, and 298.15 K. A modified isopiestic apparatus is described. Equilibrium times ranged from 4 to around 15 days. The equilibrium molalities went up to 1.0 m. The average relative uncertainty of the observed water activities of the solutions was less than 0.005%. The activity and osmotic coefficients of KCl aqueous solutions at several temperatures are compared with literature data.

Osmotic and activity coefficients of aqueous solutions of KCl at temperatures of 283.15, 288.15, 293.15 and 298.15 KA new isopiestic apparatus

Osmotic coefficients of aqueous KCl solutions have been determined by the isopiestic method using standard NaCl reference solutions for comparison. Measurements were made at 283.15, 288.15, 293.15, and 298.15 K. A modified isopiestic apparatus is described. Equilibrium times ranged from 4 to around 15 days. The equilibrium molalities went up to 1.0 m. The average relative uncertainty of the observed water activities of the solutions was less than 0.005%. The activity and osmotic coefficients of KCl aqueous solutions at several temperatures are compared with literature data.

Modeling of Activity Coefficients of Aqueous Solutions of Quaternary Ammonium Salts with the Electrolyte-NRTL Equation

Ionic liquids (ILs) have been studied recently as potential “green” solvents because of their negligible vapor pressure. Modeling the phase behavior of such liquids with water and organic solvents and their partitioning between aqueous and organic phases is vital for an evaluation of their many potential uses. Unfortunately, phase behavior data for the popular imidazolium and pyridinium salts are still somewhat limited. However, a wealth of data exists for aqueous solutions of quaternary ammonium salts, a class of compounds that includes potentially interesting ILs. Therefore, as a first step toward modeling the phase behavior of IL solutions, we show how a conventional electrolyte model, the electrolyte nonrandom two-liquid (NRTL) model proposed by Chen et al. (AIChE J. 1982, 28, 588), can be applied to model activity coefficients of quaternary ammonium salts in water. This model requires two parameters per salt that must be fit to the experimental data. Particular attention is paid to computing these bi...

Water activity, osmotic and activity coefficients of aqueous solutions of Li 2SO 4, Na 2SO 4, K 2SO 4, (NH 4) 2SO 4, MgSO 4, MnSO 4, NiSO 4, CuSO 4, and ZnSO 4 at T=298.15 K

The water activities for aqueous solutions of Li 2SO 4(aq), Na 2SO 4(aq), K 2SO 4(aq), (NH 4) 2SO 4(aq), and sulphates MgSO 4(aq), MnSO 4(aq), NiSO 4(aq), CuSO 4(aq), and ZnSO 4(aq) were determined experimentally at a temperature of 298.15 K with a hygrometric method, at molalities in the range from 0.1 mol·kg −1 to saturation. The osmotic coefficients are calculated from these results. The coefficients of Pitzer’s model was used to fit the osmotic coefficients for each salt solution. These parameters were used to predict solute activity coefficients for the salts studied.

A new model for predicting activity coefficients in aqueous solutions of amino acids and peptides

A new two-parameter model based on the perturbation of a hard-sphere reference has been developed to correlate the activity coefficients of several amino acids and simple peptides in aqueous solutions. The hard-sphere equation of state used as the reference in the model was proposed recently by Ghotbi and Vera. The perturbation terms coupled with the reference hard-sphere equation of state are attributed to the dispersion forces and the dipole–dipole interactions. The Lennard-Jones and Keesom potential functions are used to represent the dispersion and dipole–dipole interactions, respectively. The results of the new model are compared with those obtained by other models. It is shown that the new model can more accurately correlate the activity coefficients of amino acids and peptides in comparison with the other available models in the literature. The model was also used to correlate the solubility of several amino acids in aqueous solutions. The results show that the model can accurately correlate the solubility of the experimental data over a wide range of temperatures with only two adjustable parameters. New values for Gibbs free energy change, Δ g, and enthalpy change, Δ h, of the solute, i.e., amino acid for transferring one mole of solute from a saturated solution to a hypothetical aqueous solution with an activity of one molal at temperature 298.15 K are also reported.

Water Activities and Osmotic and Activity Coefficients of Aqueous Solutions of Nitrates at 25°C by the Hygrometric Method

The thermodynamic properties of LiNO3(aq.), NaNO3(aq.), KNO3(aq.), NH4NO3(aq.), Mg(NO3)2(aq.), Ca(NO3)2(aq.), and Ba(NO3)2(aq.) have been determined at 25°C by the hygrometric method for molalities, ranging from 0.1 mol-kg−1 to saturation. From measurements of droplet diameters of reference solutions NaCl(aq.) or LiCl(aq.), the dependence of relative humidity on solute concentration was determined. The data on the relative humidity allow deduction of water activities and the osmotic coefficients at various molalities. Osmotic coefficient data are described by Pitzer's ion interaction model. The ion interaction parameters were also determined for each of the salts studied. With these parameters, the solute activity coefficients can be predicted. These results are used to calculate the excess Gibbs energy for these aqueous electrolyte nitrates. Our present results are compared with published thermodynamic data.

Determination of water activities, osmotic and activity coefficients in aqueous solutions using the hygrometric method

In the present study we use the hygrometric method for the determination of relative humidities of aqueous electrolyte solutions. The relative humidities of KCl(aq), Na2SO4(aq), and NaNO3(aq) have been measured for different molalities and at temperatures from (278.15 to 323.15) K. The data on the relative humidities allow the deduction of the water activities and the osmotic coefficients at the temperature of 298.15 K. The solute activity coefficients are also determined for the three salts using Pitzer’s model. The results obtained by this method are compared with those found in the literature.

The use of the N,N-diethyldodecanamide for actinide extraction in conjunction with liquid scintillation counting

The extraction properties of N,N-diethyldodecanamide in hydrochloric and nitric acid solutions for uranium, plutonium, thorium and americium have been investigated. As a primary step, the liquid scintillation performances of organic solutions of the amide have been studied revealing a moderate quenching and a lower energy resolution than HDEHP. Nitric acid, uranyl nitrate and thorium nitrate extraction systems have been modeled, taking into account the stoichiometric mean activity coefficients in aqueous solutions. A general protocol to analyse actinides (U, Th, Pu and Am) in soils in conjunction with liquid scintillation counting is proposed using this amide together with other extractants (TOPO, HDEHP).

Ionic Solutions in the Binding Mean Spherical Approximation: Thermodynamic Properties of Mixtures of Associating Electrolytes

Recent advances in the theory of electrolytic solutions are used to describe osmotic and activity coefficients for aqueous solutions of electrolytes. The thermodynamic properties and also the structure are described by an extension of the mean spherical approximation (MSA) that includes association. The association of ions of opposite charges is described using the BIMSA, based on the Wertheim formalism. As was done before, hydration effects are included using a concentration-dependent cation size and permittivity. The theory is used to study aqueous solutions of mixed salts at 25 °C. The procedure yields a very satisfying representation for a number of mixed salts with a common cation where no adjustable cross parameter is needed. For salts without a common cation, cross parameters are introduced.

Real Ionic Solutions in the Mean Spherical Approximation. 3. Osmotic and Activity Coefficients for Associating Electrolytes in the Primitive Model

Osmotic and activity coefficients for aqueous solutions of pure associating electrolytes are described by a MSA-like theory that includes the following effects: association (ion pairing or chemical) and solvation. The association of ions of opposite charges is described using the BIMSA, based on the Wertheim formalism. As for nonassociating electrolytes, the hydration is taken into account by introducing a cation size and permittivity that are allowed to vary with concentration. New expressions for the osmotic and activity coefficient are given that account for this variation. These equations have been applied to fit data for a variety of aqueous solutions of pure salts at 25 °C. About 80 new salts have been treated, including perchlorates, nitrates, hydroxides, and sulfates. For some solutions, good fits could be obtained up to very high concentrations, such as 25 mol kg-1 for ammonium nitrate and 34 mol kg-1 for potassium nitrite. Solutions of NaOH and nitric acid could be described to 10 mol kg-1. A description for sulfuric acid has been obtained at low concentration (below 0.1 mol kg-1). Another description has been made for high concentrations (between 6 and 28 mol kg-1) by using a chemically plausible model. In most cases the association constant is of the same order of magnitude as the literature value when available.

Prediction of infinite dilution activity coefficients in aqueous solutions by group contribution models. A critical evaluation

Based on an extensive database, the predictive accuracy of the ASOG and several UNIFAC-type models has been critically evaluated for infinite dilution activity coefficients in aqueous solutions. In general, all the models give rather poor results with mean relative deviations of 45–72% (except the cases where the relative deviations are higher than 100%), whereas the modified UNIFAC (Dortmund) performs well for most of higher polar compounds (e.g., ethanol, acetone, acetic acid) in water mixtures. The UNIFAC–LLE of Magnussen et al. may provide order of magnitude estimates for some lower polar compounds (e.g., aldehydes or 2-ketones with carbon number of 6–9), although it gives poor results for the higher ones. In the particular case of alkanes in water mixtures, the specially developed model of Hooper et al. provides comparatively fair results, but the predicted mean relative deviations of 36% are still large. In this work, an improved UNIFAC will be proposed by using mixture-type groups to account for the specially hydrophobic effects in systems including water, satisfactory results are obtained.

Critical evaluation of thermodynamics of complex formation of metal ions in aqueous solutions I. A description of evaluation methods

An important step for the reliable evaluation of the thermodynamics of aqueous complex species is the appropriate choice of a model for interpolation and extrapolation of experimental values of log K and Δ rH of complex formation reactions in different ionic media. Several models proposed for the representation of activity coefficients in aqueous solutions are briefly discussed. It has been shown that, at the present state of the art, with a small number of experimental determinations of limited accuracy, the Brønsted-Guggenheim-Scatchard specific interaction (SIT) model is the most suitable method for evaluating the values of log K° and Δ rH° at infinite dilution and for reproducing the dependence of log K and Δ rH on the ionic medium and concentration. The analytical expressions needed to represent the dependencies of log K and Δ rH of complex formation reactions have been derived on the basis of the SIT model. As an example of using the SIT model, the experimental data of water dissociation in different ionic media and concentrations have been critically treated to evaluate the values of log K° and Δ rH°, as well as the respective values of Δϵ for different ionic media. The application of the SIT model has also been demonstrated for the representation of CuO (cr) solubility and Cu 2+ hydrolysis in various ionic media.

Measurement and correlation of ion activity coefficients in aqueous solutions of mixed electrolyte with a common ion

Ion selective electrodes have been used to measure the activity coefficients at 298.2 K of individual ions in aqueous solutions of mixtures of NaCl and KCl up to 4 molal total chloride ion concentration, and of NaCl and NaBr up to 4 molal total sodium ion concentration. The experimental results show that the activity coefficient of an ion in the presence of different counterions depends on the nature and concentration of all counterions present in the solution. The results also show that the activity coefficients of the cations in an aqueous mixture are different from those of the anions. These effects can be considered as a corollary of the ion-ion and ion-solvent interactions. A modified form of the Pitzer's model, coupled with a mixing rule which distinguishes between the activity coefficients of the anion and the cation, has been used to correlate the experimental results.

Activity Coefficients of Aqueous Solutions of NaOH and KOH in Wide Concentration and Temperature Ranges

Up to now, there exist a quite wide temperature interval between 70 or 80 and 150 °C with no sufficiently reliable experimental data of mean activity coefficients for aqueous NaOH as well as KOH solutions. In order to fill this gap, it was tried to derive suitable correlation equations for this quantity in dependence on the molality (for NaOH in the range mNaOH = 2-25 mol kg-1, for KOH in the range mKOH = 2-18 mol kg-1) and temperature (in the range 0-200 °C for both kinds of solutions) on the basis of the available data of this quantity and with the use of the previously derived correlation equations for the water activity in aqueous solutions of NaOH and KOH under the same conditions. The comparison between the calculated and experimental data was discussed.

Role of Solvent Permittivity in Estimation of Electrolyte Activity Coefficients on the Basis of the Mean Spherical Approximation

A modified version of the model for electrolyte solutions based on the restricted version of the mean spherical approximation is applied to estimate mean ionic activity coefficients for aqueous solutions of the alkali metal halides. The modification involves using the actual dielectric permittivity of the solution rather than the permittivity of the pure solvent. In the case of sodium and potassium salts, fits between theory and experiment are possible over wide concentration ranges up to 2.5 M using one adjustable parameter, namely, the single effective ionic diameter. Limitations of the model, especially with respect to systems with weak ion pairing, are discussed.

Counterion binding to poly(allylammonium) cation

AbstractChloride ion activity coefficients in aqueous solutions of poly(allylamine) hydrochloride (PAA · HCl) have been determined both in the absence and the presence of simple salts. Without added salt, the activity coefficient depends on the polymer concentration. With added salt, the binding of added counterions by PAAH+ is evaluated from the release of chloride ion. The extent of interaction between counterions and PAAH+ at a given polymer concentration decreases in the order SO ≫ ClO > NO > Cl− > Br− > I−. This order of counterion selectivity agrees with the previous estimation of potentiometric titrations. The result shows that the hydration of the counterion, as well as its charge, plays an important part in counterion binding to the polyion.

Ionic activity coefficients in aqueous solutions of copper and lead nitrates

Ionic activity coefficients in aqueous solutions of copper and lead nitrates