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.     

含锂水盐体系热力学性质研究:LiCl-MgCl~2-H~O体系渗透系数和活度系数的等压测定

25℃下,用等压法测定了单盐水溶液(浓度范围分别为0.5-19.8mol.kg^-1,0.3-6.0mol.kg^-1)以及混合水溶液(离子强度范围为0.6-19.4mol.kg^-1)的水活度和渗透系数,同时测定了LiCl的溶解度.该体系的实验等水活度线符合本工作推导出的Zdanovskii规则扩展式,用Gibbs-Duhem方程和改进的Mckay-perring方法计算了单盐和混合盐水溶液的活度系数.由本实验获得的渗透系数拟合了Pitzer单盐和混合作用参数,检验了Pitzer方程对该体系渗透系数、活度系数和溶解度预测的适用性.用Pitzer方程取本工作得到的参数计算的溶解度与文献实验值基本一致.     

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.     

Isopiestic determination of osmotic coefficients and evaluation of vapor pressures for solutions of calcium chloride and calcium nitrate in methanol at 298.15 K

The osmotic coefficients of calcium chloride and calcium nitrate in methanol have been measured by the isopiestic method at the temperature 298.15 K. Sodium iodide served as isopiestic standard for the calculation of osmotic coefficients. The Pitzer model and the self-consistent local composition (SCLC) model developed by Ananth and Ramachandran was used to fit each set of osmotic coefficients. The parameters from the fit were used to calculate the vapor pressures. The osmotic coefficient data are successfully correlated with these models, which provide reliable predictions of vapor pressures.     

Density and activity of pertechnetic acid aqueous solutions at T = 298.15 K

The previous isopiestic investigations of HTcO₄ aqueous solutions at T = 298.15 K are believed to be unreliable, because of the formation of a ternary mixture at high molality. Consequently, published isopiestic molalities for aqueous HTcO₄ solutions at T = 298.15 K were completed and corrected. Binary data (variation of the osmotic coefficient and activity coefficient of the electrolyte in solution in the water) at T = 298.15 K for pertechnetic acid HTcO₄ were determined by direct water activity measurements. These measurements extend from molality m = 1.4 mol · kg⁻¹ to m = 8.32 mol · kg⁻¹. The variation of the osmotic coefficient of this acid in water is represented mathematically. Density variations at T = 298.15 K are also established and used to express the activity coefficient values on both the molar and molal concentration scale. The density law leads to the partial molar volume variations for aqueous HTcO₄ solutions at T = 298.15 K, which are compared with published data.     

Hygrometric determination of the water activities and the osmotic and activity coefficients of (ammonium chloride + sodium chloride + water) atT = 298.15 K

The mixed aqueous electrolyte system of ammonium and sodium chlorides has been studied by the hygrometric method at the temperature 298.15 K. The relative humidities of this system were measured at total molalities from 0.3mol · kg ^− 1 to 6 mol · kg ^− 1for different ionic-strength fractions of NH ₄Cl with y =  (0.33, 0.50, and 0.67). The data obtained allow the deduction of new water activities and osmotic coefficients. The experimental results are compared with the predictions of the extended composed additivity model proposed in our previous work, the Robinson–Stokes, Reilly–Wood–Robinson, and Lietzke–Stoughton models. From these measurements, the new Pitzer mixing ionic parameters were determined and used to predict the solute activity coefficients in the mixture.     

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.     

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.     

The osmotic and activity coefficients of some guanidinium salts at 298.15 K

Osmotic and activity coefficients are reported for aqueous solutions of six guanidinium salts at (298.15 ± 0.01) K, and these coefficients are compared with those of other uni-univalent electrolytes. The results are consistent with previously reported spectral results that indicated hydrogen bonding of guanidinium ion with chloride ion in aqueous solutions.     

Diffusion of sodium alginate in aqueous solutions at T = 298.15 K

Taylor dispersion technique was used for measuring mutual diffusion coefficients of sodium alginate aqueous solutions at T = 298.15 K, by using as carrier stream solution both pure water and solutions of this polyelectrolyte at a slightly different concentration. The limiting values found at infinitesimal ionic strength, D⁰, were determined by extrapolating to c → 0. These studies were complemented by molecular mechanics calculations. From the experimental data, it was possible to estimate both the limiting conductivity and the tracer diffusion coefficient values for the alginate anion, and the hydrodynamic radius of the sodium alginate (NaC₆H₇O₆), as well as to discuss the influence of the kinetic, thermodynamic and viscosity factors on the diffusion of sodium alginate in aqueous solutions at finite concentrations. Thus, the aim of our innovative research is to contribute to a better understanding of the structure and the thermodynamic behavior of these polymeric systems in solution and supplying the scientific and technological communities with data on these important parameters in solution transport processes.     

Osmotic and activity coefficients in the binary solutions of 1-butyl-3-methylimidazolium chloride and bromide in methanol or ethanol at T = 298.15 K from isopiestic measurements

Osmotic coefficients of the binary solutions of two room-temperature ionic liquids (1-butyl-3-methylimidazolium chloride and bromide) in methanol and ethanol have been measured at T = 298.15 K by the isopiestic method. The experimental osmotic coefficient data have been correlated using a forth-order polynomial in terms of (molality)^0.5, with both, ion interaction model of Pitzer and electrolyte non-random two liquid (e-NRTL) model of Chen. The values of vapor pressures of above-mentioned solutions have been calculated from the osmotic coefficients. The model parameters fitted to the experimental osmotic coefficients have been used for prediction of the mean ionic activity coefficients of those ionic liquids in methanol and ethanol.     

Solubilities of imidazolium-based ionic liquids in aqueous salt solutions at 298.15 K

The solubilities of ionic liquids in the ternary systems (ionic liquid + H₂O + inorganic salt) were reported at 298.15 K and atmospheric pressure. The examined ionic liquids are [C₄mim][PF₆] (1-n-butyl-3-methylimidazolium hexafluorophosphate), [C₈mim][PF₆] (1-n-octyl-3-methylimidazolium hexafluorophosphate), and [C₈mim][BF₄] (1-n-octyl-3-methylimidazolium tetrafluoroborate). The examined inorganic salts are the chloride-based salts (sodium chloride, lithium chloride, potassium chloride, and magnesium chloride) and the sodium-based salts (sodium thiocyanate, sodium nitrate, sodium trifluoroacetate, sodium bromide, sodium iodide, sodium perchlorate, sodium acetate, sodium hydroxide, sodium dihydrogen phosphate, sodium phosphate, sodium tetrafluoroborate, sodium sulfate, and sodium carbonate). The effects of the cations and the anions of the ionic liquids and of the inorganic salts on the solubility of the ionic liquids in the ternary solutions were systematically compared and discussed.     

The mean activity coefficients of LaCl3 in dilute aqueous solution at 298.15 K

The electromotive forces of a symmetrical concentration cell with transference, Ag; AgCl|LaCl₃ (m*):LaCl₃ (m)|AgCl; Ag, were measured over the concentration range from 8.762 × 10⁻⁴ mol kg⁻¹ to 6.788 × 10⁻² mol kg⁻¹ at 298.15 K to obtain the mean activity coefficients of LaCl₃. The mean activity coefficient for reference solution at 298.15 K and the ion size parameter for LaCl₃ in the extended Debye–Hückel equation are evaluated by using an approach extrapolating concentration to unlimited dilution. A modified Debye–Hückel equation with new parameters has been established for the studied concentration range. A comparison is done of the thermodynamic data of LaCl₃ that are determined by this experiment with those reported by previous literatures, and evaluated by some models.     

Thermodynamic studies for aqueous solutions involving 18-crown-6 and alkali bromides at 298.15 K

Osmotic vapor pressure measurements have been carried out for three ternary systems, H₂O + 0.2 m 18-crown-6 + NaBr, H₂O + 0.2 m 18-crown-6 + KBr and H₂O + 0.2 m 18-crown-6 + CsBr at 298.15 K using vapor pressure osmometry. The concentration of salts was varied between 0.04 and 0.6 m. The measured water activities were used to calculate the activity coefficient of water, 18-crown-6 and mean molal activity coefficients of ions. The lowering of activity coefficients of one component in presence of other is attributed to the existence of host–guest type complex equilibria in solution phase. The Gibbs transfer free energies, which have been calculated using the activity data, were used to estimate the McMillan–Mayer pair and triplet interaction parameters and are compared with that of alkali chlorides reported recently by us using similar studies. The pair interaction parameters, g_NE (non-electrolyte–electrolyte interaction coefficient), are used to obtain the thermodynamic equilibrium constant values for 18-crown-6:M⁺ complexes, which on comparison with alkali chlorides indicate that the counter anions plays a definite role in stabilizing such complexes in solution phase. Sign and the magnitude of triplet interaction parameters (g_NNE or g_NEE) show that along with electrostatic interactions hydrophobic effects also play an important role in stabilizing the host–guest type complexes.     

Osmotic coefficients of dilute aqueous solutions of unsymmetrical cobalt-amine type salts at 0°C

The osmotic coefficients of dilute aqueous solutions of [Co(pn)₃]X₃ [pn=1,2-diaminopropane and X=Cl^–, Br^– and (NO₃)^–] and [Co(tn)₃]X₃ (tn=1,3-diaminopropane and X=Cl^– and Br^–) have been measured from 0.00 to 0.02 mol-kg^–1 at 0°C by the freezing point method. The results have been compared with those obtained from the numerical integration of the Poisson-Boltzmann equation.     

Isopiestic determination of the osmotic and activity coefficients of aqueous Lu2(SO4)3 at 25°C

Osmotic coefficients have been measured for aqueous Lu₂(SO₄)₃ solutions from 0.12402 to 0.89631 mol-kg^–1 at 25°C by use of the isopiestic method; these measurements extend into the supersaturated molality region. Since there was a lack of activity data for Lu₂(SO₄)₃ solutions at lower molalities, they were approximated by equating them to results for La₂(SO₄)₃ from freezing temperature depression measurements. The combined osmotic coefficients were then used to derive mean molal activity coefficients for Lu₂(SO₄)₃ solutions. The osmotic coefficients decrease to 0.307 as their minimum value and the mean molal activity coefficients decrease to 0.0069. When these activities were combined with our previously reported solubility of 0.6260±0.0017 mol-kg^–1 for Lu₂(SO₄)₃·8H₂O, a thermodynamic solubility product of 2.3×10^–10 was obtained. This value yields the Gibbs energy of formation G _f ^° (Lu₂(SO₄)₃·8H₂O, cr)=–5518.9±16.4 kJ-mol^–1.     

Partial molar volume and isentropic compressibility of symmetrical and asymmetrical quaternary ammonium bromides in aqueous solution

Values of apparent molar volume and isentropic compressibility of symmetric and asymmetric isomers of tetrabutylammonium bromide, namely tetra-n-butylammonium bromide, tetra-iso-butylammonium bromide, tetra-sec-butylammonium bromide, di-n-butyl-di-iso-butylammonium bromide and di-n-butyl-di-sec-butylammonium bromide, in aqueous solution were determined from density and speed of sound measurements. These properties were obtained as a function of molal concentration within the range of 0.01 < m/mol · kg⁻¹ < 0.1 covering temperatures from 278.15 ⩽ T/K ⩽ 293.15. The partial molar volumes and the apparent isentropic molar compressibility at infinite dilution were calculated and their dependence on temperature examined. The results show that cations with sec-butyl chains have larger structural volumes compared to those with iso-butyl chains. In addition, cations with sec-butyl chains induce smaller structural changes in their hydration shell than the others.     

Enthalpies of dilution of mono-, di- and poly-alcohols in dilute aqueous solutions at 298.15 K

The enthalpies of dilution of aqueous solutions of methanol, ethanol, l-propanol, 2-propanol, 1-butanol, l-pentanol, 1-hexanol, cyclohexanol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol and poly-alcohol(cyclohexaamylose) have been determined at high dilution as a function of the mole fraction of alcohol at 298.15 K, by a rocking twin-microcalorimeter of the heat-conduction type. A smoothing equation of the enthalpies of dilution against the mole fractions of alcohols are given. The graphical comparison of experimental results with their smoothed values or literature ones, taking into account the dependence of the mole fractions, are also presented. It has been found for the aqueous solutions of shorter n-alcohols than hexanol that at very high dilution, exothermic values of molar enthalpies of dilution from a definite mole fraction of alcohols to infinite dilution with the change of mole fraction is proportional to carbon number of n-alcohols. The molar enthalpies of infinite dilution of aqueous butanediol isomers and 1-hexanol were very large. Molar enthalpies of infinite dilution of aqueous poly-alcohol (cyclohexaamylose) were endothermic. This revised version was published online in August 2006 with corrections to the Cover Date.