Vapor Pressure Osmometry and Its Applications in the Osmotic Coefficients Determination of the Aqueous Monomer Glycol and Polymer Polyethylene Glycol Solutions at Various Temperature

Based on the principle and calibration of vapor pressure osmometer and its application in the thermodynamics of the aqueous solutions, the results on aqueous solution of monomer glycol,PEG200,PEG400,PEG1500 and PEG2000 over the different concentration range at various temperatures were reported.Using a linear least-square fitting routing,the osmotic coefficients were fitted by a simple polynomial equation.It was found that the relationship between the molar osmotic coefficients (Φ） and the molar concentration(c) of the solutions are in a quite good agreement with the fitted polynomial equation at various temperatures over the different concentration range.The experimental results also show that over the studied concentration range and at various temperatures,the concentration dependence of the molar osmotic coefficients of the aqueous solution systems with the solutes of PEG200,PEG400,PEG1500 and PEG2000 are totally presented in a rising tend,and their temperature dependence of the osmotic coefficients of the aqueous solution systems of the molar concentration exhibits their own regularities,respectively.The aqueous glycol solution system exhibits the properties of the dilute solution.     

Study of the aggregation of nonylammonium chloride in aqueous solutions of sodium chloride by vapor pressure osmometry

We determined osmotic coefficients from vapor pressure osmometry (VPO) measurements on aqueous solutions of nonylammonium chloride in the presence of NaCl at 30°C. VPO data were subsequently used to determine the critical micelle concentration (CMC) of the solutions of this surfactant. The values of this parameter obtained from VPO are well correlated with those obtained from light scattering. No premicellar aggregation was observed at surfactant concentrations below the CMC. The osmotic coefficients below the CMC may be evaluated from the extended form of the Debye–Hückel equation. Above the CMC, the dependence of the osmotic coefficient on the surfactant concentration was indicative of the occurrence of aggregation rather than the interactions in the system. Some comments are made on the uncertainty in the value of some parameters in micellar solutions and possible source of error using the VPO technique in these solutions.     

Enthalpic Interaction Coefficients of Formamide in Aqueous Methanol and Ethanol Solutions at 298.15 K

The dilution enthalpies of formamide in aqueous methanol and ethanol solutions have been determined using a CSC-4400 isothermal calorimeter at 298.15 K. The homogeneous solution enthalpic interaction coefficients have been calculated over a range of alcohol concentrations according to the excess enthalpy concept. The results show that the enthalpic pair interaction coefficients h ₂ of formamide are negative in aqueous alcohol solutions and pass through a minimum in mixed solvents, whereas the h ₂ coefficients of formamide in aqueous ethanol solutions are more negative than those in aqueous methanol solutions. The results are discussed in terms of solute-solute and solute-solvent interactions.     

Liquid-vapor equilibrium of dilute aqueous solutions of methanol

Numerous sets of vapor pressure-composition data for methanol in dilute aqueous solutions at 25°C and 35°C have been obtained with an automated vapor pressure apparatus developed in this laboratory. Activity coefficients of both components and values of the pairwise free energy of interaction of methanol molecules have been inferred from the results. The osmotic second virial coefficient of methanol has also been calculated and compared with literature values of this quantity.     

Activity coefficients of DL-valine in aqueous solutions of KCl at 25°C. Measurement with ion selective electrodes and modelling

Electrochemical cells with two ion selective electrodes, a cation and an anion ion selective electrode, versus a double junction reference electrode were used to measure the activity coefficients of DL-valine at 298.15 K, up to 0.5 molality, in aqueous solutions of KCl up to 1.0 molality. The results obtained in this work are compared with those reported before for the activity coefficients of DL-valine in aqueous solutions of NaCl. The experimental data were correlated using the model proposed previously by Khoshkbarchi and Vera for the activity coefficients of amino acids in aqueous electrolytes solutions.     

Osmotic and activity coefficients of ammonium thiocyanate in aqueous solution at 25°C

Osmotic and activity coefficients of ammonium thiocyanate in aqueous solution at 25°C have been determined by the isopiestic vapor pressure method. The activity coefficients do not agree with values reported previously but are consistent with trends shown by activity coefficients of ammonium chloride and bromide.     

A self-diffusion study of poly(ethylene-oxide) alkyl alcohols

The self-diffusion coefficients of HDO and some surfactants in aqueous mixtures at different concentrations, below the critical micelle concentration, have been determined by means of the NMR, spin-echo pulsed field gradient method. The surfactant solutes chosen were ethylene glycol-pentyl alcohol (diethylene glycolpentylalcohol, ethylene glycol-hexyalcohol, diethylene glycol-hexyl alcohol, triethylene glycol-hexyl alcohol, tetraethylene glycol-hexyl alcohol, pentaethylene glycol-hexyl alcohol). The interactions in solution are studied by analyzing the solute self-diffusion coefficients extrapolated to infinite dilution. These values are compared with those of 1-alkanols. The slope of the self diffusion coefficientsvs. the solute concentration are correlated with the microscopic friction coefficients. A model for interpreting the experimental data is suggested.     

Soret coefficients of mixed electrolytes

Practical equations are developed which relate the Soret coefficients of mixed electrolytes to the entropies and enthalpies of transport. The derived equations together with published binary thermal diffusion data can be used to estimate the Soret coefficients of mixed electrolytes. The procedure is illustrated for the systems NaCl+HCl+ water and NaCl+MgCl₂+ water. Aqueous NaCl, like most salts, diffuses to the cold plate in binary Soret experiments. In aqueous HCl solutions, however, NaCl can diffuse to the warm plate, and the magnitude of its Soret coefficient can take values twice as large as those for binary solutions. The thermal diffusion of trace amounts of a salt in a solution containing a large excess of another salt is discussed. Exceptionally large Soret effects are predicted for traces of strong acids in aqueous salt solutions.     

Osmotic and activity coefficients of aqueous NaTcO4 and NaReO4 solutions at 25°C

Isopiestic vapor-pressure comparison experiments were performed with aqueous binary sodium perchlorate, pertechnetate, and perrhenate solutions to concentrations of approximately 8.5 m. Osmotic coefficients for these solutions and mean molal ionic activity coefficients for NaTcO₄ and NaReO₄ were derived from the isotonic molalities. Pitzer's treatment was applied to describe the concentration dependence of the osmotic coefficients of NaClO₄, NaTcO₄, and NaReO₄, and the implications of the parameters derived from a leastsquares fit are discussed in terms of solvent structure and interionic forces.     

Activity coefficients and diffusion coefficients of dilute aqueous solutions of lithium,sodium, and potassium hydroxides

A simplified version of Harned's conductimetric technique has been used to measure binary diffusion coefficients of aqueous lithium, sodium, and potassium hydroxides at 25°C from 0.002 to 0.14 mol-dm^–3. Because of the large difference in mobility between OH^– and the cations, the electrophoretic effect tends to reduce the rate of diffusion of the alkali metal hydroxides; the largest effect is observed for LiOH solutions. The measured diffusion coefficients are in excellent agreement with predictions of the Onsager-Fuoss theory of ion transport. Precise activity coefficients determined from the diffusion measurements are compared with activity coefficients obtained previously by emf methods.     

Velocity correlations in aqueous electrolyte solutions from diffusion,conductance and transference data: Application to concentrated solutions of nickel chloride and magnesium chloride

Velocity cross-correlation coefficients have been calculated for aqueous solutions of NiCl ₂ and MgCl ₂ up to concentrations of 4M. Examination of the concentration-dependence of these coefficients show that it is very similar for the two salts. There is no evidence for any special structural characteristics in NiCl ₂ solutions. The velocity correlation technique is apparently not sensitive enough to detect the small amount of complexation that is thought to be present in NiCl ₂ solutions.     

Enthalpies of Dilution of Colchicine in Aqueous NaCl Solutions

The concentration effect on the dilution enthalpies (Δ_dil H _m) of colchicine (COL) in aqueous NaCl solutions has been investigated by isothermal titration microcalorimetry at 298.15 K. The corresponding homogeneous enthalpic interaction coefficients have been calculated according to the excess enthalpy concept. The results show that the dilution enthalpies of COL in aqueous NaCl solutions at different mass fractions are positive. The overall trend is that enthalpies of dilution become more positive with the increase of the salt mass fraction. The values of enthalpic pair-wise interaction coefficients, h ₂, have been obtained by fitting the data of the enthalpies of dilution with a viral expansion. The results can be interpreted from the view of solute-solute and solute-solvent interactions involved in the solvent effects.     

Enthalpic interaction between α-amino acids and pyridine and methylpyridine in aqueous solutions

Enthalpies of dilution of aqueous L-serine, pyridine and methylpyridine solutions and their enthalpies of mixing have been determined by a mixing-flow microcalorimeter at 298.15 K. The data have been analyzed in terms of McMillan-Mayer formalism to fit to virial polynomials from which the heterotactic enthalpic pairwise interaction coefficients, h _xy, betweenL-serine and pyridine and methylpyridine isomers have been evaluated. The results obtained in the present paper are compared with those reported in the earlier paper about glycine and L-alanine in the same organic solvent aqueous solutions, giving a global insight of the interaction mechanism between the a-amino acids and pyridine and methylpyridine from the point of view of solute-solute interactions and substituent effects of methyl groups introduced into the pyridine ring. This revised version was published online in July 2006 with corrections to the Cover Date.     

Isopiestic Study of Water + Mannitol(sat) + Sodium Chloride + Ammonium Chloride + Barium Chloride at <Emphasis Type="Italic">T</Emphasis> = 298.15 K and Comparison with the Ideal-Like Solution Model

Isopiestic measurements have been carried out at the temperature 298.15 K for the quinary system (water + mannitol(sat) + sodium chloride + ammonium chloride + barium chloride) saturated with mannitol and its ternary sub-systems (water + mannitol(sat) + sodium chloride), (water + mannitol(sat) + ammonium chloride) and (water + mannitol(sat) + barium chloride). Taking aqueous sodium chloride as reference solutions, osmotic coefficients of the other aqueous solutions were determined. The experimental results show that the isopiestic activities of the quinary system in relation to its ternary sub-systems are in excellent agreement with the ideal-like solution 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.     

Corrected values of osmotic and activity coefficients of aqueous NaTcO4 and HTcO4 at 25°C

Published isopiestic molalities for aqueous NaTcO₄ and HTcO₄ solutions at 25°C have been reexamined. Our calculations indicate that published smoothed values of the osmotic coefficients and mean molal activity coefficients _± of NaTcO₄ are substantially in error, by up to 100% for and 300% for _±. Published smoothed values of and _± for HTcO₄ solutions are in somewhat better agreement with the input data, but the reported are sometimes higher and sometimes lower than experimental values, by up to 6%. Consequently, we have reanalyzed isopiestic data for these two systems, and find that errors arose in representing the data mathematically. We report parameters for an extended form of the specific ion interaction equations and for Pitzer's equations, and corrected values of and _± are tabulated for aqueous NaTcO₄ and HTcO₄.     

Enthalpies of solution of glycine in aqueous solutions of 1,2-diols and glycerol at 25°C

Dissolution enthalpies of glycine in mixtures of water with 1,2-ethanediol, 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,3-propanediol and glycerol have been measured at 25°C. The enthalpic pair interaction coefficients of the glycine zwitterion with the polyalcohol molecule have been determined by using the standard solution enthalpies of glycine in water and in aqueous solutions of the polyalcohols. The values of the resultant enthalpic interaction coefficients are interpreted assuming a criterion in the form of the effect of hydrophobic alkyl radicals on the interactions between the hydroxyl groups of polyalcohols and the zwitterion of glycine.     

A pitzer mixed electrolyte solution theory approach to assignment of pH to standard buffer solutions

The IUPAC recommendations for the pH scale for aqueous solutions are based on the Bates-Guggenheim (B-G) convention (1961) for the single ion activity coefficient of the chloride ion in the standard buffer(s). This convention was adopted as a reasonable estimate based on the Debye-Huckel theory and is limited in its application to ionic strengths less than 0.1 mol-kg^–1. This approach ignores the results of many workers over the years on the properties of mixed electrolyte solutions and their prediction on the basis of the theories of Harned, Scatchard, Guggenheim and more recently of Pitzer. The literature data of EMF measurements on appropriate weak acid systems have been reexamined to determine both the pK_a values and values of appropriate Pitzer interaction coefficients. The latter are used to calculate single chloride ion activity coefficients for the chosen compositions of pH standard buffers, and compared with the B-G convention values. Calculations were made to check the consistency of the pH values with determined pK_a values using the Pitzer treatment for all the required single ion activity coefficients. The overall aim was to remove the ionic strength restriction of the B-G convention and rationalize the approach to pH standardization for such diverse aqueous media as sea water, blood and acid-rain water.An account of this work was presented at the 12^th International Conference on Chemical Thermodynamics, Snowbird, Utah, August 1992.     

Mutual diffusion coefficients of aqueous MnCl2 and CdCl2, and osmotic coefficients of aqueous CdCl2 at 25°C

Volume-fixed mutual diffusion coefficients have been measured for aqueous MnCl₂ and CdCl₂ solutions from 0.004 to 4.93–5.00 mol-dm^–3 (M) at 25°C. Diffusion coefficients for MnCl₂ decrease to a minimum, rise to a maximum, and then decrease rapidly; such behavior is typical for strong electrolytes. In contrast CdCl₂ diffusion coefficients decrease continuously with concentration; similar behavior is known for certain other associated electrolytes. Since thermodynamic diffusion coefficients for both salts are qualitatively similar, diffusion differences may be primarily due to thermodynamic rather than mobility factors. Isopiestic data were measured for CdCl₂ from 1.79 to 7.29 mol- (kg H₂O)^–1, and critically compared to other isopiestic and emf data for CdCl₂. Higher quality emf data are completely consistent with isopiestic data. Recommended smoothed values of activity coefficients, osmotic coefficients, water activities, and activity derivatives are given for CdCl₂ at 25°C.Work performed under the auspices of the Office of Basic Energy Sciences (Geosciences) of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract number W-7405-ENG-48.     

Interactions of DL-serine and L-serine with NaCl and KCl in aqueous solutions

The activity coefficients at 25‡C of DL-serine and L-serine in aqueous solutions of NaCl and KC1 were measured. This study examines the effect of the nature of the cation of the electrolyte on the activity coefficients of the optical-isomers of serine in aqueous solutions for molality of serine up to 0.4 and molality of electrolyte up to 1. An electrochemical cell with two ion-selective electrodes, a cation, and an anion ion selective electrode,vs. a double-junction reference electrode was used to measure the activity coefficients of the electrolyte and the results were converted to the activity coefficients of serine in the aqueous electrolyte solution. The comparison of the results obtained for DL- and L-serine indicates that the two optical isomers have identical interactions with electrolytes in aqueous solutions and that for this amino acid the effect of the cation of the electrolyte is not significant. Comparison of these results with previous measurements for DL-alanine in aqueous solutions of the same electrolytes show the notable effect of the backbone of the amino acid.