Apparent Specific Volume and Apparent Specific Refraction of Some Poly(oxyethylene) Glycols in 1,4-Dioxane and Benzene Solutions at 298.15 K

Summary. The density and refractive index of 1,4-dioxane and benzene solutions of poly(oxyethylene) glycols of the type HO–(CH₂CH₂O)_n–H (n varying from 4 to 36) were measured at 298.15K. From the experimental data the apparent specific volume and the apparent specific refraction at infinite dilution were calculated. The limiting apparent specific volume and the limiting apparent specific refraction were found to be inversely proportional to the number average molecular weight of solute. From the limiting apparent specific values at the infinite degree of polymerization, the partial molar volume and partial molar refraction of the monomeric unit were calculated. The partial molar volume as well as the partial molar refraction of the investigated compounds at infinite dilution are additive and depend linearly on the number of oxyethylene groups. The volumetric data were analyzed in terms of the intrinsic volume of solute molecules and by a void partial molar volume. The packing density of the investigated compounds approaches a uniform value as the size of the molecules increases and in both solvents limiting values are reached.     

Partial molar volumes of cryptand-222 in organic solvents at 25°C

The partial molar volumes at infinite dilution of cryptand-222 (C-222) in water, methanol, acetonitrile, ethanol, dimethylsulfoxide, propanol, 2-propanol, chloroform, benzene, 1-butanol, cyclohexane, butyl-methylketone, hexane, tetrahydronaphthalene, heptane, octane, cyclohexylbenzene and decane were measured at concentrations ranging from 0.01 to 0.1 mol-L^–1 at 25°C. The partial molar volumes at infinite dilution showed remarkable dependency on the molar volume of the solvent. The partial molar volumes at infinite dilution for C-222 increase as the solvent molar volume increases.     

Partial Molar Volumes of Hexaamminecobalt(III) Nitrate in Proteated and Deuterated Water

The partial molar volumes (V ₂) for hexaamminecobalt(III) nitrate in proteated and deuterated water were determined at 0.00 (for H₂O only), 5.00, 10.00, 15.00, and 20.00?°C. The increase of the solute??s partial molar volume with increasing concentration and the negative second derivative of the solute??s partial molar volume at infinite dilution with respect to temperature were interpreted in terms of the solvent structure breaking property of the solute. In addition, the difference at each temperature between the solute??s partial molar volume at infinite dilution for proteated and deuterated water was used to estimate the solvent coordination number at each temperature.     

Volumetric Properties of Dilute Solutions of Water in Acetone between 288.15 and 318.15 K

Densities of dilute solutions of water in acetone, with solute mole fractions ranging up to 0.03, have been measured with an error of 8 ×10⁻⁶ g⋅cm⁻³, at 288.15, 298.15, 308.15 and 318.15 K, using a precision vibrating-tube densimeter. The partial molar volumes of the solute water (down to infinite dilution) and solvent acetone, as well as the excess molar volumes of the specified mixtures, have been calculated. The effects of the solute concentration and temperature on the volume packing changes, caused by solvation of water in acetone, have been considered.     

Partial molar volumes of 18-crown-6 ether in organic solvents at 25°C

The partial molar volumes at infinite dilution of 18-crown-6 ether (CE) in a variety of polar and polarizable solvents with molar volumes ranging from 18 to 170 cm³-mol^–1, were measured at concentrations ranging from 0.02 to 0.1 mol-L^–1 at 25°C. The partial molar volumes of the solute at infinite dilution showed remarkable dependancy on the molar volume of the solvent. The partial molar volumes at infinite dilution for the CE increases as the solvent molar volume increases.     

Partial Molar Volumes and Refractions of Aqueous Solutions of Poly[vinyl alcohol]

The partial molar volumes (V ₂) and refractions (R ₂) for poly[vinyl alcohol] (PVOH) in water were determined at 0.00, 5.00, 15.00, 20.00, and 25.00 °C. Each of the partial molar quantities exhibits a small but significant dependence upon concentration which is analyzed using a previously reported model of solvation. This study concludes that the water in the regions surrounding the solute molecules exhibits less hydrogen bonding and as a consequence is denser than the bulk water. In addition, the study finds that the partial molar volume of PVOH at infinite dilution is the simple sum of contributions from its monomer units (–CH₂–CHOH–).     

Volumes and heat capacities of water andN-methylformamide in mixtures of these solvents

The densities of mixtures ofN-methylformamide (NMF) and water (W) have been measured at 5, 15, 25, 35, and 45°C, and the heat capacities of the same system at 25°C, both over the whole mole-fraction range. From the experimental data the apparent molar volumes (_v) and heat capacities (_c) of NMF and of water are evaluated. The relatively small difference between the partial molar volumes or heat capacities at infinite dilution and the corresponding molar volumes or heat capacities of the pure liquids for both NMF and water suggests that with regard to these quantities replacement of a NMF molecule by a water molecule or vice versa produces no drastic changes. The partial molar volume of water at infinite dilution in NMF is smaller than the molar volume of pure water, but the corresponding partial molar heat capacity is unexpectedly high.     

Volumes of aqueous alcohols, ethers, and ketones to T = 523 K and p = 28 MPa.

Densities of dilute aqueous solutions of isopropanol, 1,5-pentanediol, cyclohexanol, benzyl alcohol, diethyl ether, 1,2-dimethoxyethane, acetone, and 2,5-hexanedione were measured by means of a vibrating-tube flow densimeter at temperatures near T = (302, 373, 423, 473, and 521) K at a pressure of p = 28 MPa. At the lowest and highest temperatures, measurements were also made close to the saturation vapour pressure of water to investigate the effect of pressure on the volumes of solutes. Apparent molar volumes were calculated for each solute and extrapolated to give partial molar volumes at infinite dilution. The variation of the volume with temperature, pressure, and structure of solute is discussed qualitatively, and group contributions are determined at the temperatures of measurements and p = 28 MPa. Several equations proposed in the literature for correlating the partial molar volumes at infinite dilution as a function of state parameters are tested. Parameters of one selected equation are tabulated allowing calculation of the partial molar volumes at infinite dilution at temperatures and pressures up to T = 573 K and p = 40 MPa. respectively.     

Use of partial molar volume for determining conformations of macromolecules in a solution

A formula was derived for determining the partial molar volume (PMO) of solute at various concentrations and on this basis a method was developed for determining the PMO at infinite dilution. The partial molar volumes of the homologous series of poly(ethylene glycol) with molecular masses 400, 1000, 1500, 2000, 4000, 20000 in aqueous solutions at infinite dilution were determined. Analysis of the calculated and experimental PMO showed that poly(ethylene glycol) molecules exist in dilute solutions in the conformations of elongated helices. In addition, the high-molecular polyethylene glycol molecules include the areas of statistical chaos, which leads to sites unavailable for the solvent molecules. Based on literature data were revealed the values of PMO for highly concentrated solutions of poly(ethylene glycol) PEG 400, PEG 4000, and PEG 6000. Effect of concentration on the structure of PEG solutions was demonstrated. We found that in the temperature range 25–40°C the conformational transitions were not observed.     

Thermodynamic properties of peptide solutions: 14. Partial molar expansibilities and isothermal compressibilities of some glycyl dipeptides in aqueous solution

The partial molar volumes at infinite dilution have been obtained for a series of glycyl dipeptides in aqueous solution at 15, 30, and 35°C. These results have been combined with data obtained at 25°C, that were reported earlier, to evaluate the partial molar expansibilities at infinite dilution for the dipeptides at 25°C. These quantities, along with the partial molar heat capacities and isentropic compressibilities at infinite dilution that were reported in previous studies, were used to derive the partial molar isothermal compressibilities at infinite dilution for the glycyl dipeptides at 25°C. The results obtained are rationalized in terms of the hydration of the constituent groups of the dipeptides.     

Volumetric properties of ascorbic acid (vitamin C) and thiamine hydrochloride (vitamin B1) in dilute HCl and in aqueous NaCl solutions at (283.15, 293.15, 298.15, 303.15, 308.15, and 313.15) K

Apparent molar volumes and apparent molar isentropic compressibilities of ascorbic acid (vitamin C) and thiamine hydrochloride (vitamin B₁) were determined from accurately measured density and sound velocity data in water and in aqueous NaCl solutions at (283.15, 293.15, 298.15, 303.15, 308.15, and 313.15) K. These volume and compressibility data were extrapolated to zero concentration using suitable empirical or theoretical equations to determine the corresponding infinite dilution values. Apparent molar expansibilities at infinite dilution were determined from slopes of apparent molar volume vs. temperature plots. Ionization of both ascorbic acid and thiamine hydrochloride were suppressed using sufficiently acidic solutions. Apparent molar volumes at infinite dilution for ascorbic acid and thiamine hydrochloride were found to increase with temperature in acidic solutions and in the presence of co-solute, NaCl. Apparent molar expansibility at infinite dilution were found to be constant over the temperature range studied and were all positive, indicating the hydrophilic character of the two vitamins studied in water and in the presence of co-solute, NaCl. Apparent molar isentropic compressibilities of ascorbic acid at infinite dilution were positive in water and in the presence of co-solute, NaCl, at low molalities. Those of thiamine hydrochloride at infinitive dilution were all negative, consistent with its ionic nature. Transfer apparent molar volumes of vitamins at infinite dilution from water solutions to NaCl solutions at various temperatures were determined. The results were interpreted in terms of complex vitamin-water-co-solute (NaCl) interactions.     

Partial molar volumes of l-alanine,dl-serine,dl-threonine,l-histidine,glycine, and glycylglycine in water,NaCl, and DMSO aqueous solutions at T = 298.15 K

The apparent molar volumes of l-alanine, dl-serine, dl-threonine, l-histidine, glycine, and glycylglycine in water and in the aqueous solutions of NaCl and DMSO with various concentrations at T = 298.15 K have been measured by the precise vibrating-tube digital densimeter. The calculated partial molar volumes at infinite dilution have been used to obtain corresponding transfer volumes from water to various solutions. The experimental results show that the standard partial molar volumes of the above amino acids and peptide at the dilute DMSO aqueous solutions are very close to those in water. However, the volumes show several types of variations with the increase of the concentrations of DMSO due to different types of side chain of amino acids, which should be discussed specifically. The NaCl changes considerably the infinite dilution standard partial molar volumes of the above amino acids and peptide in the aqueous solutions. The infinite dilution standard partial molar volumes of the each amino acids and peptide increase with the concentrations of NaCl. The experimental results have been rationalized by a cosphere overlap model.     

Electrostriction, ion solvation, and solvent release on ion pairing

The theoretical mean molar electrostriction volume of electrolytic solvents, DeltaVel(solvent), was calculated from their properties: the relative pressure derivatives of the density (the compressibility) and permittivity and their second pressure derivatives. The molar electrostriction caused by ions at infinite dilution was taken as the differences of their standard partial molar volumes in the solution and their intrinsic volumes: DeltaVel(ion) = Vinfinity(ion) - Vin(ion). The ratio ninfinity = DeltaVel(ion)/DeltaVel(solvent) then represents the solvation number of the ion in the solvent at infinite dilution. Similarly, from the molar volume change on ion pair formation, DeltaVip, the ratio Deltanip = DeltaVip/DeltaVel(solvent) represents the number of solvent molecules released thereby. These values were tabulated for those solvents, ions, and ion pairs for which the relevant information could be found, the extension to nonaqueous solvents not having been attempted previously.     

Volumetric properties of the water + ethylenediamine mixture at atmospheric pressure from 288.15 to 353.15 K

Densities of the water + ethylenediamine binary system were measured at atmospheric pressure over the whole range of compositions at temperatures from 288.15 to 353.15 K using an Anton Paar digital vibrating glass tube densimeter. Density increases with water content. The experimental excess molar volume data have been correlated with the Redlich-Kister equation, and partial molar volumes calculated at infinite dilution for each component.     

Application of the Bjerrum association model to volumes of electrolytes in water and acetonitrile

The Bjerrum association model has been extended to partial and apparent molar volumes. It was tested for electrolytes in water and in acetonitrile using literature or new (n-propylammonium bromide) data to cover systems having association constants between 0 and 10⁵. The association constants and apparent distances of closest approach were obtained from conductivities. The volumes at low concentration can be fitted quantitatively to obtain by extrapolation the standard infinite dilution partial molar volume. Deviations at higher concentrations can be accounted for with a second virial coefficient.     

Hydration of alcohol clusters in 1-propanol-water mixture studied by quasielastic neutron scattering and an interpretation of anomalous excess partial molar volume

Quasielastic neutron scattering measurements have been made for 1-propanol-water mixtures in a range of alcohol concentration from 0.0 to 0.167 in mole fraction at 25 degrees C. Fraction alpha of water molecules hydrated to fractal surface of alcohol clusters in 1-propanol-water mixture was obtained as a function of alcohol concentration. Average hydration number N(ws) of 1-propanol molecule is derived from the value of alpha as a function of alcohol concentration. By extrapolating N(ws) to infinite dilution, we obtain values of 12-13 as hydration number of isolated 1-propanol molecule. A simple interpretation of structural origin of anomalous excess partial molar volume of water is proposed and as a result a simple equation for the excess partial molar volume is deduced in terms of alpha. Calculated values of the excess partial molar volumes of water and 1-propanol and the excess molar volume of the mixture are in good agreement with experimental values.     

Excess molar volume and isentropic compressibility of monoethanolamine in aqueous system at temperatures from 298.15 to 318.15 K

Densities and sound velocities for aqueous monoethanolamine (MEA) system are reported over the entire composition range at different temperatures (298.15, 303.15, 313.15 and 318.15 K). These experimental data have been further used in calculating the excess molar volume, partial molar volumes, isobaric thermal expansion coefficients and the deviation in isentropic compressibility. The excess molar volumes data were fitted to the Redlich–Kister polynomial equation to obtain their coefficients and standard deviations. The partial molar volume at infinite dilution of both water in MEA and MEA in water and have been determined using two different methods. Knowledge of the above properties of these mixtures is a basis for understanding some of the molecular interactions in these systems. From the analysis of the results, the type of interactions between the MEA and water is discussed in terms of the number and size of the alkyl groups attached to the nitrogen atom of MEA.     

Determination of the Apparent Molar Refraction and Partial Molar Volume at Infinite Dilution of Thiophene-, Pyrrole- and Furan-2-Carboxaldehyde Phenylhydrazone Derivatives in Acetonitrile at 293.15 K

High-precision densitometry and high-accuracy refractometry measurements of extremely dilute solutions of the thiophene-2- (TCPH), pyrrole-2- (PCPH) and furan-2-carboxaldehyde-phenylhydrazone (FCPH) compounds in acetonitrile have been obtained at 293.15 K. The partial molar volumes V ₂^∞ of each compound at infinite dilution were determined. The apparent molar refraction of these solutes at infinite dilution at 293.15 K has been experimentally determined within the Kohner-Geffcken-Grunwald-Haley approximation. The volumetric and refractometric results were interpreted in terms of the Pauling electronegativity and intrinsic molar volume of the heteroatom, and the aromaticity of the heterocyclic rings. The experimental results indicate that solute-solute interactions are negligible within the concentration range studied. Theoretical calculations at the DFT-B3LYP/6−311++G(3d,3p) level of molecular volumes support the interpretation that the volumetric contribution from the solute-solvent interactions to the limiting partial molar volumes of solutes are very small and thus solute molecules are isolated in this medium.     

Limiting Partial Molar Volume of Sodium Chloride in 2-Methyl-2,4-pentandiol-Water Mixed Solvents at 25 °C

Herein we report density measurements for the binary system 2-methyl-2,4-pentanediol(MPD,1)-water(0), and for the ternary system MPD(1)-NaCl(2)-water(0), at several fixed MPD/water ratios and at varying NaCl concentrations. The partial molar volume of MPD in the binary system has been discussed according to the McMillan-Meyer theory. At low MPD concentrations, the non-bonding MPD-MPD interactions are related to the overlapping of the hydrophobic parts of the hydration cospheres, whereas at higher concentrations the hydrophilic moieties are also involved in the solute-solute interactions. The ternary density data allowed us to determine the salt partial molar volume at infinite dilution. The trend of this quantity as a function of the MPD content in the MPD-water “mixed solvent” has been interpreted on the basis of the water partial molar volume in the binary MPD-water system.     

Limiting Partial Molar Excess Heat Capacities and Volumes of Selected Organic Compounds in Water at 25°C

Well-known Picker flow microcalorimeters for the differential measurements of volumetric heat capacities have been employed in conjunction with vibrating tube densimeters to determine the molar heat capacity, volume, and the apparent properties in dilute aqueous solutions for 17 organic solutes of moderate hydrophobicity. The dependence on concentration of the apparent properties allowed the limiting partial molar quantities at infinite dilution to be extrapolated and the limiting partial molar excess quantities to be evaluated. Comparison with available literature data shows good agreement. The application of group contribution rules to the limiting partial properties has been tested using the original method and parameters proposed by Cabani et al. The predicted values of the partial molar volumes are in fair agreement with the present data except for some less common solutes. With partial molar heat capacities, the agreement is less satisfactory. To improve the performance of the method, missing parameters for some types of monofunctional and bifunctional molecules have been evaluated.