Activity coefficients of glycine in aqueous electrolyte solutions: experimental data for (H2O + KCl + glycine) atT = 298.15 K and (H2O + NaCl + glycine) atT = 308.15 K

Electrochemical cells with two ion-selective electrodes against a single-junction reference electrode were used to obtain the activity coefficients of glycine in aqueous electrolyte solutions. Activity coefficient data were presented for {H₂O  +  KCl (m_S)  +  glycine (m_A)}, and {H₂O  +  NaCl (m_S)  +  glycine (m_A)} atT =  298.15 K and T =  308.15 K, respectively. The results show that the presence of an electrolyte and the nature of its cation have a significant effect on the activity coefficient of glycine in aqueous electrolyte solutions and, in turn, on the method of separation from its culture media. The results of the mean ionic activity coefficients of KCl were compared with those values reported in the literature, which were obtained by the isopiestic method. It was found that the method applied in this study provides accurate activity coefficient data. The effect of temperature on the mean ionic activity coefficient of NaCl in presence of glycine was also investigated.     

Hygrometric determination of water activities,osmotic and activity coefficients of (NaCl + KCl)(aq) at T = 298.15 K

The purpose of this study is to present a model for the prediction of water activity in multicomponent aqueous solutions containing a common ion from available binary data. The hygrometric method has been used to measure relative humidities for the aqueous electrolyte mixture (NaCl  +  KCl)(aq) at total molalities ranging from 0.2 mol · kg ^− 1to saturation for different molal ratiosr of NaCl(aq) to KCl(aq) with r =  (0.2, 0.5, 1, 2, 3, and 4) at T =  298.15 K. The data obtained have been used to determine water activities and osmotic coefficients. The results show that the values of water activities and osmotic coefficients calculated with the proposed model are close to the experimental ones. This model is also compared with four other models (RS, Pitzer, RWR, and LS II) over the range of the studied total molalities. From the measurements, the activity coefficients of NaCl(aq) and KCl(aq) in the mixture have also been determined.     

Isopiestic studies on the saturated systems {H2O + BaCl2(sat) + NaCl + NH4Cl} and {H2O + BaCl2(sat) + mannitol(sat) + NaCl + NH4Cl} at the temperature 298.15 K: Comparison with the ideal-like solution model

Isopiestic measurements have been carried out at the temperature 298.15 K for two saturated aqueous solutions: {H₂O + BaCl₂(sat) + NaCl + NH₄Cl} saturated with barium chloride and {H₂O + BaCl₂(sat) + mannitol(sat) + NaCl + NH₄Cl} saturated with barium chloride and mannitol. Taking sodium chloride (aq) as reference solutions, osmotic coefficients of the aqueous solutions were determined. The experimental results are well represented by the ideal-like solution model.     

Water activities,osmotic and activity coefficients in aqueous chloride solutions atT = 298.15 K by the hygrometric method

Water activities of aqueous electrolyte solutions of HCl(aq), LiCl(aq), NaCl(aq), KCl(aq), CsCl(aq), NH₄Cl(aq), MgCl₂(aq), CaCl₂(aq), and BaCl₂(aq) have been determined at T =  298.15 K by the hygrometric method, and at molalities ranging from 0.2 mol · kg ^− 1to saturation. From measurements of droplets diameters of reference NaCl(aq) or LiCl(aq), the dependence of relative humidity on solute concentration was determined. The data on the relative humidities allow the deduction of water activities and the osmotic coefficients at different molalities. Osmotic coefficient data have been described by the ion interaction model of Pitzer. The ion interaction parameters were also determined for each of the studied salts. With these parameters, the solute activity coefficients can be predicted. Our present results have been compared with reported thermodynamic data.     

Effect of potassium chloride on diffusion of theophylline at T = 298.15 K

Ternary mutual diffusion coefficients measured by Taylor dispersion method (D₁₁, D₂₂, D₁₂, and D₂₁) are reported for aqueous solutions of KCl + theophylline (THP) at T = 298.15 K at carrier concentrations from (0.000 to 0.010) mol · dm^?3, for each solute. These diffusion coefficients have been measured having in mind a better understanding of the structure of these systems and the thermodynamic behavior of potassium chloride and theophylline in solution. For example, from these data it will be possible to make conclusions about the influence of this electrolyte in diffusion of THP and to estimate some parameters, such as the diffusion coefficient of the aggregate between KCl and THP.     

Activity coefficients of electrolyte and amino acid in the systems (water + potassium chloride + dl -valine) at T = 298.15 K and (water + sodium chloride + l -valine) at T = 308.15 K

The activity coefficient data were reported for (water  +  potassium chloride  + dl -valine) at T =  298.15 K and (water  +  sodium chloride  + l -valine) at T =  308.15 K. The measurements were performed in an electrochemical cell using ion-selective electrodes. The maximum concentrations of the electrolytes and the amino acids studied were 1.0 molality and 0.4 molality, respectively. The results of the activity coefficients of dl -valine are compared with the activity coefficients of dl -valine in (water  +  sodium chloride  + dl -valine) system obtained from the previous study. The results show that the presence of an electrolyte and the nature of its cation have a significant effect on the activity coefficient of dl -valine in aqueous electrolyte solutions.     

Viscosity studies of (l-alanine-, l-proline,l-valine,l-leucine + aqueous KCl/KNO3) solutions at different temperatures

Viscosity coefficients of (l-alanine-, l-proline, l-valine, l-leucine + 2.0 M aqueous KCl/KNO₃) solutions have been determined as a function of amino acid concentration at different temperatures: (298.15, 303.15, 308.15, 313.15, 318.15, and 323.15) K. The trends of variation of viscosity values with increase in the concentration of l-alanine, l-proline, l-valine, and l-leucine in 2.0 M aqueous KCl and 2.0 M aqueous KNO₃ solutions, and temperature have been ascribed to the solute–solvent interactions operative in the solutions.     

Isopiestic study of (calcium chloride + water) and (calcium chloride + magnesium chloride + water) atT = 313.15 K

The osmotic coefficients of aqueous calcium chloride solutions were experimentally determined atT =  313.15 K by the isopiestic method. Magnesium chloride served as the isopiestic standard for the calculation of osmotic coefficients. The molality range covered in this study correspond to about 0.1mol · kg ^− 1to 3.0mol · kg ^− 1. In addition, the osmotic coefficients of aqueous mixtures of calcium chloride and magnesium chloride were determined over the range of ionic strength levels of about 0.1mol · kg ^− 1to 9mol · kg ^− 1and at various mole fractions. The results obtained were correlated by the Pitzer equation.     

Investigation of 1-(2-carboxyethyl)-3-methylimidazolium chloride[HOOCEMIM][Cl] ionic liquid effect on water activity and solubility of l-serine at T = 298.15 K

Water activity measurements by the isopiestic method have been carried out on the aqueous ternary system of {l-serine + 1-(2-carboxyethyl)-3-methylimidazolium chloride[HOOCEMIM][Cl]} ionic liquid and the aqueous binary system of IL at T = 298.15 K and atmospheric pressure. The data obtained were used to calculate the vapor pressure and osmotic coefficient of solution as a function of concentration. The experimental results for the activity of water were accurately correlated with segment-based local composition models of modified NRTL and UNIQUAC. The fitting quality of the above models has been favorably compared with the NRTL and Wilson models. From these data, the corresponding activity coefficients have been calculated. For the same system, the solubility of the l-serine at various [HOOCEMIM][Cl] ionic liquid concentrations was measured at T = 298.15 K using the gravimetric method. A chemical model was employed to describe the dissociation equilibria of all amino acid species with hydrogen ions in water. Moreover, for l-serine, the chemical model indicated that the formation of cations is insignificant in the [HOOCEMIM][Cl] solution. Also the above local composition models were used to predict the solubility of l-serine in aqueous IL solutions. To provide information regarding (solute + solute) interactions, transfer Gibbs free energies (ΔG_tr) of amino acid from water to aqueous IL solutions have been determined.     

Phase equilibria of hydrogen sulfide and carbon dioxide simple hydrates in the presence of methanol, (methanol + NaCl) and (ethylene glycol + NaCl) aqueous solutions

This work aims at reporting the dissociation pressures of hydrogen sulfide and carbon dioxide simple hydrates in the presence of methanol, (methanol + NaCl) and (ethylene glycol + NaCl) aqueous solutions at different temperatures and various concentrations of inhibitor in aqueous solution. The equilibrium results were generated using an isochoric pressure-search method. These values are compared with some selected experimental data from the literature on the dissociation conditions of hydrogen sulfide and carbon dioxide simple hydrates in the presence of pure water to show the inhibition effects of the above mentioned aqueous solutions. Comparisons are finally made between our experimental values and the corresponding literature data. Some disagreements among the literature data and our data are found.     

The impact of uni-univalent electrolytes on (water + acetic acid + toluene) equilibria: Representation with electrolyte-NRTL model

The presence of salts can significantly alter the (liquid + liquid) equilibrium and extraction process. In this work, a study was conducted on the (liquid + liquid) equilibria of (water + acetic acid + toluene + sodium chloride or potassium chloride) at temperatures (288.2, 298.2 and 313.2) K. This chemical system, irrespective of salt, is frequently used in (liquid + liquid) extraction investigations. The selected salt concentrations in initial aqueous solutions were (0.9 and 1.7) mol · L⁻¹. The results show that salting-out effect of the salts was significant, so that an enhancement in the acetic acid distribution coefficient was achieved within (15.6 to 66.8)% with NaCl and within (2.5 to 37.6)% with KCl. Meantime, high separation factors were found at low temperatures and low solute concentrations. The electrolyte-NRTL model was satisfactorily used to correlate the phase equilibria. In this regard for each salt, the temperature dependent binary interaction parameters between components were calculated. The predicted tie-line mole fractions give root-mean square deviation (RMSD) values of only 0.0038 and 0.0045 for the systems containing NaCl and KCl, respectively.     

Thermodynamic properties of (NaCl + KCl + LiCl + H2O) at T = 298.15 K: Water activities,osmotic and activity coefficients

The water activities of aqueous electrolyte mixture (NaCl + KCl + LiCl + H₂O) were experimentally determined at T = 298.15 K by the hygrometric method at total ionic-strength from 0.4 mol · kg⁻¹ to 6 mol · kg⁻¹ for different ionic-strength fractions y of NaCl with y = 1/3, 1/2, and 2/3. The data allow the deduction of new osmotic coefficients. The results obtained were correlated by Pitzer’s model and Dinane’s mixing rules ECA I and ECA II for calculations of the water activity in mixed aqueous electrolytes. A new Dinane–Pitzer model is proposed for the calculation of osmotic coefficients in quaternary aqueous mixtures using the newly ternary and quaternary ionic mixing parameters of this studied system. The solute activity coefficients of component in the mixture are also determined for different ionic-strength fractions y of NaCl.     

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.     

Activities of Individual Ions From Infinite Dilution to Saturated Solutions

A new procedure, which provides a closer approximation for the junction potentials than the Henderson equation, is tested to reduce new emf data for the chloride ion in CsCl solutions and previously measured data for individual ions in aqueous solutions of KCl, NaCl, and NaBr. The liquid junction potential is calculated from numerical integration of its basic equation without assuming constant mobility or using concentrations instead of activities. The mean ionic activity coefficients of the salts, obtained from the activity coefficients of the individual ions, show good agreement with values reported in the literature. The activity coefficients of the individual chloride ion at 25°C in aqueous solutions of CsCl up to 3 molal and in KCl solutions were measured using a chloride ion-selective electrode. It has been confirmed that the activity of the chloride ion is equal to the activity of the cation in CsCl solutions and, contrary to the prediction of hydration theory, it is higher than the activity of the cation in aqueous KCl solutions. The New Hydration Theory has been developed to overcome the shortcomings of the older hydration theory and has been used to smooth the experimental activity coefficients of the individual ions in aqueous solutions and to extrapolate them up to the saturated solution.     

Volumetric and isentropic compressibility behaviour of aqueous solutions of (polyvinylpyrrolidone + sodium citrate) at T = (283.15 to 308.15) K

The apparent specific volumes and isentropic compressibilities have been determined for polyvinylpyrrolidone in aqueous solutions of sodium citrate by density and sound velocity measurements at T = (283.15 to 308.15) K at atmospheric pressure. The results show a positive transfer volume of PVP from an aqueous solution to an aqueous sodium citrate solution. For low concentrations of PVP, the apparent specific volumes of PVP in water increased along with an increase in the polymer mass fraction, while in aqueous sodium citrate solutions decreased along with an increase in the polymer mass fraction. For high concentrations of PVP, the apparent specific volumes of PVP in water and in aqueous sodium citrate solutions were independent of the polymer mass fraction. The apparent specific isentropic compressibility of PVP is negative at T = (283.15 and 288.15) K, which imply that the water molecules around the PVP molecules are less compressible than the water molecules in the bulk solutions. The positive values of apparent specific isentropic compressibility at T = (298.15, 303.15, and 308.15) K imply that the water molecules around the PVP molecules are more compressible than the water molecules in the bulk solutions. Finally, it was found that the apparent specific isentropic compressibility of PVP increases as the concentration of sodium citrate increases.     

Water activities of ternary mixtures of poly(ethylene glycol), NaCl and water over the temperature range of 293.15 K to 313.15 K

The improved isopiestic method has been used to obtain activities of water for aqueous solutions of poly(ethylene glycol) 400/NaCl at T = (293.15, 298.15, 303.15, 308.15, and 313.15) K. From these measurements, values of the vapour pressure of solutions were determined. The effect of temperature on the (vapour + liquid) equilibrium of {poly(ethylene glycol) + NaCl + H₂O} systems has been studied. It was found that the slope of the constant activity lines for water increased with increasing temperature. The results have been discussed on the basis of the effect of temperature on the hydrophobicity of the polymer. Also it was found that the vapour pressure depression for an aqueous (PEG + NaCl) system is more than the sum of those for the corresponding binary solutions. Furthermore, the segment-based local composition Wilson model has been used for the correlation of the experimental water activity data. The agreement between the correlation and the experimental data are good.     

Salt effects on the partition coefficients of phenol in two-phase mixtures of water and carbon dioxide at pressures from (8 to 30) MPa at a temperature of 313 K

Partition coefficients K_c of phenol between an aqueous solution containing different salts and a compressed CO₂ phase have been determined at T=313 K. For NaCl and (CH₃)₄NBr a pressure range from 8 MPa to around 30 MPa was investigated, for KCl and NaBr measurements were performed at a pressure of 22 MPa. The salt concentration has been varied between (0.25 and 3.0) mol·dm⁻³. With increasing pressure a rise in K_c is observed which typically is also found in systems free of salt. Salting-out was observed for the alkali salts, salting-in has been found for the ammonium salt, both effects increased with increasing salt concentration. From the concentration dependence of the K_c values Setschenow coefficients k_S have been derived. At p>10 MPa values are obtained as found in two phase mixtures of water with other organic solvents at ambient pressure. This conclusion was confirmed with both literature and own experimental data in the case of salting-out by NaCl as well as for the salting-in by (CH₃)₄NBr from measurements with phenol in (water + cyclohexane) at T=313 K.     

Interaction of biological buffers with electrolytes: Densities of aqueous solutions of two substituted aminosulfonic acids and ionic salts from T = (298.15 to 328.15) K

Biological buffers are of utmost importance for research in biological and clinical chemistry and in oceanography, but they may not be inert enough, thus interfering with the system under study. The N-[Tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid (TAPS) and N-[Tris(hydroxymethyl)methyl]-3-amino-2-hydroxypropanesulfonic acid (TAPSO) are useful zwitterionic buffers for pH control as standard buffers in the physiological region of pH 7.7 to 9.1 for TAPS and 7.0 to 8.2 for TAPSO, respectively. In this work, interaction between these zwitterionic compounds and electrolytes of potassium acetate (KAc), potassium bromide (KBr), potassium chloride (KCl), and sodium chloride (NaCl) were investigated through measuring the densities of these buffers in aqueous and in aqueous electrolyte solutions by a high precision vibrating tube digital densitometer from T = (298.15 to 328.15) K under atmospheric pressure. In this series of measurements, the aqueous samples were prepared with various concentrations of the zwitterionic buffers, up to saturated conditions, and over salt concentrations from (1 to 4) mol · dm^?3. The measured densities served to evaluate the cubic expansion coefficients, α(m, T) and the apparent molar volumes, V_?(m, T). An empirical equation was used to correlate quantitatively the experimental densities over the entire concentration ranges.     

Diffusion coefficients of nickel chloride in aqueous solutions of lactose at T = 298.15 K and T = 310.15 K

Binary mutual diffusion coefficients (interdiffusion coefficients) of nickel chloride in water at T = 298.15 K and T = 310.15 K, and at concentrations between (0.000 and 0.100) mol · dm^?3, using a Taylor dispersion method have been measured. These data are discussed on the basis of the Onsager–Fuoss and Pikal models. The equivalent conductance at infinitesimal concentration of the nickel ion in these solutions at T = 310.15 K has been estimated using these results. Through the same technique, ternary mutual diffusion coefficients (D₁₁, D₂₂, D₁₂, and D₂₁) for aqueous solutions containing NiCl₂ and lactose, at T = 298.15 K and T = 310.15 K, and at different carrier concentrations were also measured. These data permit us to have a better understanding of the structure of these systems and the thermodynamic behaviour of NiCl₂ in different media.     

Determination of stoichiometric dissociation constants of lactic acid in aqueous salt solutions at 291.15 and at 298.15 K

Equations were determined for the calculation of the stoichiometric (molality scale) dissociation constant, K_m, of lactic acid in aqueous salt solutions at 291.15 and 298.15 K from the thermodynamic dissociation constant, K_a, of this acid and from the ionic strength, I_m, of the solution. The salt alone determines mostly the ionic strength of the solutions considered in this study, and the equations for K_m were based on the single-ion activity coefficient equations of the Hückel type. New data measured by potentiometric titrations in a glass electrode cell at 298.15 K and the literature data obtained by Larsson and Adell with quinhydrone (qh) electrode cells at 291.15 K were used in the estimation of the parameters for the Hückel equations (HE) of lactate ions in NaCl and KCl solutions. The Harned cell data measured at 298.15 K by Nims and Smith were used to obtain the activity parameters for lactate ions in dilute LiCl, BaCl₂ and SrCl₂ solutions. The conductance data measured at 298.15 K by Martin and Tartar were used to determine the thermodynamic value of the dissociation constant of lactic acid. By means of the calculation method suggested in this study, K_m can be obtained almost within experimental error at least up to I_m of about 0.5 mol kg⁻¹ for lactic acid in NaCl and KCl solutions at the two temperatures considered. The K_m values obtained by this method were compared to those obtained by the calculation methods presented recently in the literature for a general treatment of thermodynamics of weak acids in NaCl and KCl solutions.