CORRELATION OF PARTIAL MOLAR VOLUMES AT INFINITE DILUTION OF SALTS IN WATER

Salt partial molar volumes at infinite dilution show the unusual behavior of increasing with pressure while at higher temperatures becoming large and negative, reaching negative infinity at the critical point of water. A simplified method for estimating the infinite dilution partial molar volumes for fully ionized aqueous salts up to 350°C and all pressures has been developed using generalized expressions based on fluctuation solution theory. Tabulations of parameters are given for several salts made from 10 different cations and 9 different anions that can be used to predict V^∞ _s for many solutions of practical interest.     

Apparent and partial molar volumes of concentrated solutions of some uni-univalent electrolytes in formamide

The density of solutions of NH₄SCN, KSCN, NH₄NO₃, LiNO₃, NH₄ClO₄, NH₄Br in formamide at 25° has been measured in the concentration range going from ≈ 0.5 m up to the saturated solution. By the least-square method the coefficients of the straight lines relating density and concentration have been calculated. It follows that the apparent molar volumes of salts (amv in the investigated concentration range result independent of the concentration, and close to the molar volume of the pure salt. Calculated by the V° (the partial molar volume at infinite dilution) values of the tetraalkylammonium salts and following a Robinson and Stokes suggestion, ionic partial molar volumes (pmv) at infinite dilution agree for both methods. The ionic pmv at infinite dilution follow the Hepler's equation, the A and B coefficients for alkali metal cations and halide anions being independent of the sign of the ionic charge. The value of the A term has been found close to the intrinsic ionic volume plus the volume of the void space which is generated around an ion in a “random close packing distribution”.The low values of the coefficient B, which takes into account the electrostriction of the solvent, has been explained in terms of solvent structure energetically equivalent to the structure of the solution and with the small compressibility of this solvent.     

Thermal diffusion of alkali chlorides in H2O and D2O

Entropies of transport for very dilute aqueous alkaline chlorides solution at 25° have been determined by the potentiometric method. The limiting slopes were calculated and the molar entropies of transport at infinite dilution obtained by extrapolation.The standard transported entropy of Cl^? ion was also derived by extrapolating the steady state thermoelectric powers to infinite dilution. The ‘absolute’ ionic entropies of transport have been estimated from the standard transported entropy following Gurney's choice of the absolute standard partial molar entropy of H⁺ ion as ?5.5eu.Soret data obtained in H₂O are compared with that obtained in D₂O. Results are discussed in terms of the structure of the solvent and ionic hydration phenomena.     

The development of a response surface model for the determination of infinite dilution partial molar volumes and excess volumes from dilute multi-component data alone. Implications for the characterization of non-isolatable solutes in complex homogeneous reactive systems

A non-ideal system containing several solutes, e.g. methanol, acetone, and 2-butanol in n-hexane was studied. Traditionally defined excess molar volumes (based on pure component molar volumes) of the multi-component solutions were measured in the limit of infinite dilution in n-hexane using a vibrating-tube densitometer at and . An experimental design in the concentration range 0.0015<x_solute-i<0.023 was explored, optimizing the metric distance among the solutes to avoid clustering. The partial molar volumes of methanol, acetone, and 2-butanol at infinite dilution determined from the multi-component data were very consistent with the values obtained from separate binary experiments. Next a total molar volume response surface model was developed. Only experimental total volume and component moles are needed for analysis. The partial molar volumes of all the solutes were accurately predicted from the multi-component data alone. A new expression for excess molar volume is proposed to express component interactions. This approach is undoubtedly of considerable usefulness for determination of the partial molar properties of non-isolated but observable species in multi-component reactive solutions.     

Ionic association and mobility in propylene carbonate

Molar conductivities were measured at 298.15 K for symmetric quaternary ammonium picrates, R₄NPic, with R equal to C₁ to C₅ as well as for potassium picrate in propylene carbonate. The molar conductivities at infinite dilution, association constants of ion pairs, ionic conductivities at infinite dilution, and Stokes radii were calculated for the ions employed. The salts, Me₄NPic and Et₄NPic, were found to be dissociated, the others are associated. For the associated salts the data conform to the Fuoss model for the association process.     

Density measurements of poly(acrylic acid) sodium salts

Summary Density measurements of poly(acrylic acid) sodium salts (PANa) with different degrees of neutralization and water contents are presented. The apparent partial molar volumes of polymer, V ₂ ^* , and the partial molar volumes of water, V₁, were calculated from the densities. The values of V ₂ ^* decreased with increasing water content and eventually leveled off. The values of Vj, which at low water contents were much smaller than that of free water increased with increasing water content and reached that of free water, showing consequently the appearance of free water. Before reaching the final value of free water, the data indicated the formation of primary and secondary hydration shells. The structure of primary hydration was suggested to be of octet coordination in which carboxyl oxygen atoms participate.     

Thermodynamic interactions of solvents with styrene–butadiene–styrene triblock copolymers

Fundamental thermodynamic interaction data for various solvents with two styrene–butadiene–styrene triblock copolymers (Kraton D-1101 and Kraton D-1300X) have been collected by the use of inverse gas chromatography at infinite dilution. Experimental results are presented for nine D-1101/solvent systems and nine D-1300X/solvent systems at 308, 328. and 348 K. Weight-fraction activity coefficients and Flory–Huggins χ interaction parameters have been calculated from the retention volumes. The χ parameter is used as a measure of the strength of interaction and therefore as a guide in the prediction of polymer–solvent compatibility. In addition, partial molar heats of mixing, ΔH_m^∞, and heats of solution, ΔH_s, were determined. The Hildebrand–Scatchard solubility theory was combined with the Flory theory in order to estimate the solubility parameter of the thermoplastic rubbers at the three different temperatures.     

Determination of the infinite dilution diffusion and activity coefficients of alkanes in polypropylene by inverse gas chromatography

Infinite dilution diffusion and activity coefficients of n‐hexane, n‐heptane, and n‐decane in polypropylene were measured from 373.15 to 393.15 K by inverse gas chromatography. The influences of small molecule solvent and temperature on the infinite dilution diffusion and activity coefficients were investigated. The results showed that the infinite dilution diffusion coefficient decreased but the infinite dilution activity coefficient increased with an increasing number of CH₂ group in the aliphatic solvents. The temperature increase resulted in the increase in the infinite dilution diffusion coefficient and the decrease in the infinite dilution activity coefficient. The graphs plotted according to the results of the infinite dilution diffusion coefficient versus temperature were in agreement with the Arrhenius equation. Diffusion constant and activation energy were obtained from the Arrhenius equation. Also, the interdependence on the infinite dilute activity coefficient and temperature accorded with Gibbs‐Helmholtz equation. From the temperature dependence of the limiting activity coefficients partial molar excess enthalpy at infinite dilution H^E,∞ was obtained. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1925–1930, 2006     

Electrical conductance and apparent molar volumes of Al(ClO4)3, Be(ClO4)2, and Cu(ClO4)2 in N,N-dimethylacetamide solutions at 25°C

Equivalent conductances and apparent molar volumes of Al(ClO₄)₃, Be(ClO₄)₂, and Cu(ClO₄)₂ in N,N-dimethylacetamide at 25°C are reported. The limiting equivalent conductances, the first step association constants, and the apparent molar volumes at infinite dilution are derived and discussed in terms of influence of nature of cation on the properties of DMA-solvated cations.     

Prediction of the infinite-dilution partial molar volumes of organic solutes in supercritical carbon dioxide using the Kirkwood-Buff fluctuation integral with the hard sphere expansion (HSE) theory

Two thermodynamic models were used to predict the infinite dilution partial molar volumes (PMVs) of organic solutes in supercritical carbon dioxide: (1) the Kirkwood Buff fluctuation integral with the hard sphere expansion (HSE) theory incorporated (KB-HSE fluctuation integral method) and (2) the Peng-Robinson equation of state with the classical mixing rule. While an equation of state only for pure supercritical carbon dioxide is needed in the KB-HSE fluctuation integral model, and thus, there is no need to know the critical properties of solutes, two molecular parameters (one size parameter σ₁₂ and one dimensionless parameter α₁₂) in the KB-HSE fluctuation integral model are determined to fit the experimental data published on the infinite dilution PMVs of solutes. The KB-HSE fluctuation integral method produced better results on the infinite dilution PMVs of eight organic solutes tested in this work than the Peng-Robinson equation of state with the classical mixing rule.     

Mixed-surfactant system of dodecylbenzene sulfonate and alpha-olefin sulfonate: Micellar and volumetric studies

Critical micelle concentrations of sodium salts of dodecylbenzene sulfonate, alpha-olefin (C₁₆) sulfonate, and their mixtures have been evaluated by measuring the surface tensions of solutions at 298.15 K. Interaction parameters for mixed monolayer formation (β^σ) and mixed-micelle formation (β^M) have been calculated from the critical micelle concentration data. Densities of solutions of surfactants and their mixtures were measured with a vibrating-tube densimeter at 298.15 K. Apparent and partial molar volumes have been evaluated from solution density data. Results of the micellar properties have been eplained on the basis of a nonideal multicomponent mixed-micelle model. The mixed-surfactant system exhibits synergism in all aspects when the mole fraction of alpha-olefin sulfonate in the mixture is 0.2. Volumetric properties correlate well, as the partial molar volumes also show a minimum at the same composition of the mixture. Formation of a compact mixed micelle at this composition has been envisaged.     

Molar volumes of multicharged electrolytes in water and aqueous sulphuric acid

The apparent molar volumes, φ_v, of aluminium ammonium sulphate and potassium aluminium sulphate in water and aqueous sulphuric acid (0.01, 0.05, 0.10 and 0.15 N) at different concentrations and temperatures have been estimated from the densities of the solutions measured by hydrostatic balance. The φ_v values vary linearly with square root of concentrations. The limiting apparent molar volume, φ⁰_v, and the experimental slope S_v, have been interpreted in terms of solute-solvent and solute-solute interactions, respectively. The φ⁰_v values vary with temperature and can be represented in the power series of temperature. Structure making/breaking capacity of the electrolyte is inferred from the sign of [?φ⁰_v/?T²] values. Both the electrolytes behave as structure breakers in water but structure makers in aqueous sulphuric acid. The molar expansibility, at infinite dilution have been found to be the same for both electrolytes at 290.5 K.     

Partial molal volumes of halogens in aqueous electrolyte solutions

Reversible voltages between chlorine, bromine, and iodine electrodes at platinum and the silver—silver halogenide electrodes in electrolytes containing sodium or potassium salts of the respective halogenides were measured as a function of static pressure up to 2.1 kb at 298.15K. From the resulting reaction volumes and the known partial molal volumes of silver and the silver halogenides the partial molal volumes of the halogenes in aqueous solution were obtained.The partial molal volmes of the diatomic gases in aqueous solution are a smooth function of the intrinsic volumes calculated from bond lengths, analoguos to the much steeper function for monovalent ions.Iodine behaves anomalously. The experimental partial molal volumes are relatively small and the compressibilities are negative. Both paramenters strongly depend on the concentration of iodide in the electrolyte. It is proposed to explain these effects by a theory based on the formation of the complex J₃^?.     

Conductivities and ion association of 1:1 electrolytes in mixed aprotic solvents

Molar conductivities of the 1:1 electrolytes LiClO₄, LiAsF₆, n-Bu₄NClO₄ and n-Bu₄NBPh₄ were measured in mixtures of propylene carbonate and dimethoxymethane over the concentration range 0.01?1 × 10^?4 mol dm^?3. In all cases a maximum in molar conductivity (and hence in electrolytic conductivity) is observed in a solvent mixture having a composition of around 40 mass % propylene carbonate. Molar conductivities at infinite dilution (Λ^∞) and thermodynamic ion association constants (K^∞_a) were evaluated from these data. Single ion molar conductivities (λ^∞_i) were evaluated using the assumption that λ^∞(n-BuN⁺₄) = λ^∞(BPh^?₄). In order to account for the observed conductivity behavior it is necessary to assume that lithium salts from solvent separated ion pairs in ethereal solvents. All other salts from contact ion pairs.     

密度法研究防腐剂苯甲酸钠与生物模型化合物的相互作用

用ＡｎｔｏｎＰａａｒＤＭＡ５５型精密数字密度计测定了２９８．１５Ｋ时苯甲酸钠在ＤＭＦ－Ｈ２Ｏ二元混合溶剂中的密度，利用这些数据，得到了苯甲酸钠在无限稀释时的偏摩尔体积和溶剂效应对偏摩尔体积的贡献值。研究结果表明，苯甲酸钠由水向ＤＭＦ－Ｈ２Ｏ混合溶剂迁移的偏摩尔体积在ｘＤＭＦ≈０．０２６７处出现极小值，ｘＤＭＦ≈０．３６５处出现极大值。利用溶质－溶剂相互作用和混合溶剂的结构对结果进行了讨论     

Thermodynamic Models for Hydrogen-Containing Systems at Infinite Dilution

For a supercritical gas such as hydrogen, thermodynamic models for Henry's constant, partial molar volume, and partial molar enthalpy are sufficient in representing the thermodynamics of hydrogen-containing systems at infinite dilution. This work presents a generalized method and correlations for Henry's constant in binary systems containing hydrogen as a function of temperature. Experimental vapor–liquid equilibrium data were used to obtain this Henry's constant correlation with (i) three specific parameters, (ii) one specific parameter, and (iii) no specific parameter. These three Henry's constant correlations for hydrogen vary in the degrees of generalization and accuracy. A generalized corresponding states correlation for partial molar enthalpy of hydrogen in hydrocarbon systems at infinite dilution was derived from the newly developed Henry's constant correlation and from a correlation for infinite-dilution partial molar volumes of hydrogen available in the literature. Overall, this work provides the most extensive method for infinite-dilution thermodynamic properties of hydrogen-containing systems.     

A study of some equation‐of‐state parameters of poly(methylhydrosiloxane‐co‐dimethylsiloxane) with some solvents by gas chromatography

Trace amount of methyl acetate, ethyl acetate, tert‐butyl acetate, pentane, hexane, and heptane were passed through the chromatographic column loaded with poly(methylhydrosiloxane‐co‐dimethylsiloxane) coated on Chromosorb W. The retention diagrams of the solvents on the copolymer were plotted by means of specific retention volumes at temperatures between 40 and 80°C by inverse gas chromatography technique. In this study, some thermodynamic interaction parameters such as Flory–Huggins polymer–solvent interaction parameter, equation‐of‐state polymer–solvent interaction parameter, effective exchange energy parameter, and weight fraction activity coefficients at infinite dilution of the solvent were determined. Then, the exchange enthalpy parameter and entropy parameter were determined by using a relation for the enthalpy interaction parameter of the equation‐of‐state theory, which is arranged for the inverse gas chromatography conditions. Later, the partial molar heat of sorption and the partial molar heat of mixing were obtained. The solubility parameter of this copolymer was determined as 6.64 (cal/cm³)^1/2 at room temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1627–1631, 2007     

Physico-chemical properties of concentrated solutions of some tetraalkylammonium salts in formamide in the temperature range 25–80°

In this work density and viscosity measurements for concentrated solutions in formamide of Bu₄NJ, Bu₄NBr, Bu₄NCl, Pr₄NJ salts in the temperature range 25–80° are reported. The apparent molar volumes φν are square root linear functions of the salt concentration. The values of the partial molar volumes $\text{V}$₂ decrease when the concentration increases and more over are almost constant at the last concentration used. Viscosity data have been analysed using Vand—Einstein model on viscosity of rigid sphere suspensions. In the diluted solution range a different behaviour between tetraalkylammonium salt solutions and alkaline-earth metal ones is shown. This difference is interpreted by supposing that the size of alkaline, alkaline-earth metal solvated cation varies with concentration, while the size of tetraalkylammonium solvated cation is unchangeable.     

Inverse gas chromatographic observation of thermodynamic interaction between poly (vinylidene fluoride) and organic solvents

Summary Inverse gas chromatography (IGC) has been applied to observe the interaction between poly(vinylidene fluoride) (PVDF) and organic solvent systems under conditions approaching infinite dilution of the volatile component. The specific retention volumes (V_g ⁰) were calculated from the retention volumes of the PVDF/solvent systems. The retention diagrams (RDs) which were plotted as ln V_g ⁰ vs. reciprocal temperature, corresponded with the thermodynamic behavior of PVDF. PVDF dissolves well in carbonyl-containing solvents at high temperatures. In these systems, the solution is converted easily to a thermoreversible gel by standing at room temperature. The Flory-Huggins interaction parameter (χ₁₂) and molar heat of sorption of probe absorbed by the amorphous part of PVDF (Δ H₁ ^s) calculated from the retention values indicated that the characteristics of the interaction between PVDF and the solvent (probe) varied with temperature and probe properties. The results of IGC of PVDF/solvent systems were discussed in relation to the dissolution and gelation behavior of PVDF. Received: 29 September 1999/Revised version: 30 November 1999/Accepted: 9 December 1999     

Determination of physicochemical properties of some fatty acid methyl esters by gas liquid chromatography

Physicochemical data such as vapor pressures (p⁰), heats of vaporization (ΔH_v), activity coefficents at infinite dilution (γ^∞) and excess partial molar entropy (ΔS _e ⁰ ) are considered important for conducting unit processes and designing reactor equipment. Scanty information regarding such data is available in the literature for the higher fatty acid methyl esters. The objective of this research was to determine the physicochemical properties of higher fatty acid methyl esters (C₁₁–C₂₃) by a gas-liquid chromatographic technique with SE-30 and diethylene glycol adipate as stationary phases. Correlations between carbon numbers and various thermodynamic properties have indicated definite trends, which could be useful in predicting the properties of unknown fatty acid methyl esters. The data generated may be useful to chemical engineers in the construction of storage tanks, solvent extractors and distillation columns. IICT communication no. 2993.