Adiabatic compressibility and structural features of non-electrolyte aqueous solutions

Structural characteristics of the hydration complexes of non-electrolytes such as the hydration numbers h, molar adiabatic compressibility of hydration complexes β _h V _h , the molar volume of water in the hydration sphere V _1h , the solute molar volume without hydration environments V _2h and others are determined using the data on the ultrasonic velocity, the density and heat capacity of aqueous solutions of urea, urotropine, acetonitrile, and a number of amides of N-acetyl amino acids. A theoretical model of solvation is also applied. A comparison of the environments of hydrated urotropine molecules with those of urea and acetonitrile molecules in an aqueous medium shows a considerable hydrophobic interaction of urotropine with a solvent.     

Verification of Solvation Theory of Dilute to Concentrated Solutions of Some Strong 1–1 Electrolytes

Density, ultrasonic velocity and isobaric heat capacity data have been used to study solvation parameters of aqueous solutions of NaCl, NaNO₃, and KI. Using correct thermodynamic relations, quantitative solvation parameters have been determined at temperatures from 278.15 to 323.15 K: the hydration numbers h, the molar isentropic compressibilities of the solvation complexes $ \beta_{S,h} V_{h} , $ the volume V _1h , the coefficient of isentropic compressibility β _1h of water in the solvation shells of ions, and others. It has been shown that h is independent of the temperature in the range of the investigated conditions, $ \beta_{S,h} V_{h} $ is dependent both on the temperature and concentration, whereas the electrostriction compression in the vicinity of ions has a greater effect on its structure than that due to the mere change of pressure.     

Solvation of the Electrolytic Components of Seawater

A new modification of the adiabatic compressibility method of investigating solvation in solutions is presented and applied to the analysis of the following structurally-related characteristics of hydrated complexes of seawater electrolytes (NaCl, KCl, MgCl₂, CaCl₂, Na₂SO₄, MgSO₄) at different concentrations (0.1 to 5.0 mol⋅kg⁻¹) and temperatures (278.15 to 308.15 K): solvation numbers (h) and their dependences on concentration, volumes of stoichiometric mixtures of ions without their hydration shells (V _2h ), compressibilities (β _1h ) and molar volumes of water in their solvation shells (V _1h ), their dependences on concentration and temperature, etc.     

Acoustic Study of Solvent Coordination in the Hydration Shells of Potassium Iodide

The isentropic compressibilities of aqueous solutions of potassium iodide, from dilute to almost saturated, were determined at 288 to 308 K based on precise measurements of the speed of ultrasound. Using proper correlations, the hydration numbers (h) were calculated as well as the molar volume and compressibility parameters of the hydrated complexes (V _h , β _h V _h ) of water in the hydration shell (V _1h , β_1h V _1h), and of the cavity containing stochiometric mixtures of K⁺ and I⁻ ions (V _2h, β_2h V _2h). It is revealed that under the studied conditions, the obtained values of h and β _h V _h are independent of temperature whereas the molar compressibility of the hydration shell β _h V _h) is independent of concentration. The electrostatic field of the ions is shown to influence the temperature dependence of the molar volume of water in the hydration shell more substantially than a change of pressure alone influences the temperature dependence of the molar volume of pure water.     

Evidence of solvation of aqueous electrolytes in a range from diluted to concentrated solutions

Parameters of solvation of strong electrolytes in aqueous solutions have been investigated based on literature data on their densities, thermal capacities, and rates of ultrasound propagation. By using appropriate thermodynamic equations, such quantitative parameters of solvation as hydration number (h), molar adiabatic compressibility of the hydrated forms (β _h V _h ), volume (V _1h ), and compressibility (β_1h ) of water in the hydrated shells of ions have been determined in the temperature interval from 278.15 to 323.15 K. It has been demonstrated that the h and β _h V _h values are temperature-independent within the studied interval and that electrostrictive compression near ions has a stronger effect on their structure than a simple change in pressure.     

Quantitative estimation of the discontinuous function of the solvent in aqueous electrolyte solutions

The adiabatic compression method is used to determine quantitative solvation parameters such as hydration numbers h, the molar adiabatic compressibility of hydrated complexes β _h V _h , the volume V _1h and compressibility β_1h of water in ion hydration shells, and several other properties in the temperature range 278.15–323.15 K. Hydration numbers are used to determine the verified activity coefficient of the solvent, γ _R . The concentration dependence of the coefficient is shown to be a discontinuous function, with the discontinuity point corresponding to the complete solvation boundary.     

Quantitative characteristics of hydration in solutions of sodium sulfate and sodium chloride at 278.15–323.15 K

The solvation parameters of aqueous solutions of sodium chloride and sodium sulfate were studied on the basis of published density and ultrasound velocity data. Correct thermodynamic relations for temperature variation from 278.15 to 323.15 were used to determine quantitative parameters of solvation, in particular, the hydration numbers h, the molar adiabatic compressibility of hydrate structures β _h V _h , the volume V _1h and compressibility β _1h of water in the hydration shells of ions, and others. h and β _h V _h do not depend on temperature in the range of parameters studied, and electrostriction compression about the ions has a more pronounced effect on the structure than mere pressure change.     

Structural state of solvent in electrolyte solutions

Isoentropic compressibilities were determined for aqueous solutions of five electrolytes ranging from dilute to almost saturated solutions at 278.15–308.15 K based on precision measurements of ultrasound velocity. Using correct relations we have found hydration numbers (h) and molar parameters of volume and compressibility of hydrated complexes (V _h , β_h V _h ), water in the hydration shell (V _1h , β 1_h V _1h ), and void containing a stoichiometric mixture of ions (V _2h , β _2h V _2h ). In the temperature range under study, the hydration numbers h and the parameters β_h V _h are independent of temperature; molar compressibilities of hydration sphere (β _1h V1_h) are independent of concentration. Since β_h V _h is independent of temperature at a constant concentration of electrolyte, Y _K,S ^e also becomes independent of temperature. It is shown that the chemical potentials of bound and unbound water are equal and that γ_R = F(h) is an example of a discontinuous function that defines the abrupt change in the solvent at the complete solvation limit in solution.     

Apparent molar volumes and compressibilities of electrolytes and ions in γ-butyrolactone

The densities of tetraphenylphosphonium bromide, sodium tetraphenylborate, lithium perchlorate, sodium perchlorate and lithium bromide in γ-butyrolactone at (288.15, 293.15, 298.15, 303.15, 308.15 and 313.15) K and speed of sound at 298.15 K have been measured. From these data apparent molar volumes V_Φ at (288.15, 293.15, 298.15, 303.15, 308.15 and 313.15) K and the apparent molar isentropic compressibility K_S,Φ, at T = 298.15 K of the salts have been determined. The apparent molar volumes and the apparent molar isentropic compressibilities were fitted to the Redlich, Rosenfeld and Mayer equation as well as to the Pitzer and Masson equations yielding infinite dilution data. The obtained limiting values have been used to estimate the ionic data of the standard partial molar volume and the standard partial isentropic compressibility in γ-butyrolactone solutions.     

Partial molar volumes and partial molar adiabatic compressibilities of a short chain perfluorosurfactant: Sodium heptafluorobutyrate in aqueous solutions at different temperatures

Density and ultrasound measurements of sodium heptafluorobutyrate in aqueous solutions at T = (283.15, 288.15, 293.15, 298.15, 303.15, 308.15, 313.15, 318.15, and 323.15) K have been obtained. From these results partial molar volumes and isentropic partial molar adiabatic compressibilities were calculated. Deviations from the Debye-Hückel limiting law provide evidence for limited association at lower concentrations. The change of the partial molar volume and isentropic partial molar adiabatic compressibility upon aggregation was calculated. Variations of the change of partial molar volumes and isentropic partial molar adiabatic compressibility upon aggregation are discussed in terms of temperature.     

Solvation of magnesium chloride and sulfate in aqueous solutions at 278.15–323.15 K

Isoentropy compressibilities of aqueous magnesium chloride and sulfate were determined based on precision measurements of ultrasound velocity, density, and isobaric heat capacity at low to high concentrations at 278.15–323.15 K. The hydration numbers h and the molar parameters of volume and compressibility were calculated based on thermodynamically correct equations for hydration complexes (V _h , β _h V _h ), water in the hydration shell (V _1h , β_1h V _1h ), and the void containing a stoichiometric mixture of ions (V _2h , β_2h V _2h ). The h and β _h V _h values were found to be independent of temperature; the molar compressibility of the hydration sphere (β_1h V _1h ) and the stoichiometric mixture of ions without a hydration shell (β_2h V _2h ) were independent of the concentration under the stated conditions. The effect of the electrostatic field of ions on the temperature dependence of the molar volume of water in the hydration sphere was more significant than the effect of pressure on the temperature dependence of the molar volume of bulk water. This is attributed to changes in the dielectric constant of water in the vicinity of the electrolyte ions.     

Effect of free solvent on the solvation of electrolytes and nonelectrolytes

An approach is developed for analyzing hydration of sodium and magnesium sulfate electrolytes over a wide range of concentrations up to 1.8 mol/L at temperatures from 278.15 to 318.15 K. The model of free water (water that does not enter hydrate complexes) is used to analyze the hydration numbers, mean compressibility of water in the hydration sphere, its temperature dependence, and several other solvation parameters that are determined with difficulty. A comparative analysis of the behavior of the β_h V _h = f(h) function is carried out for zwitterions and electrolytes. This function has an identical slope for amino acids, halides, and nitrates; that is, the adiabatic compressibility of water in the hydrate complex of an electrolyte or nonelectrolyte (β_1h V1h) is independent of the solution concentration over a wide range of compositions. This suggests that the clathrate solvation mechanism operates both for a stoichiometric ion mixture and for zwitterions. Aqueous solutions of sodium sulfate and magnesium sulfate behave quite differently: they appreciably deviate from the solutions of the specified systems.     

Densities,viscosities, speed of sound,and IR spectroscopic studies of binary mixtures of tert-butyl acetate with benzene,methylbenzene, and ethylbenzene at T = (298.15 and 308.15) K

Densities, viscosities, speed of sound, and IR spectroscopy of binary mixtures of tert-butyl acetate (TBA) with benzene, methylbenzene, and ethylbenzene have been measured over the entire range of composition, at (298.15 and 308.15) K and at atmospheric pressure. From the experimental values of density, viscosity, speed of sound, and IR spectroscopy; excess molar volumes V^E, deviations in viscosity Δη, deviations in isentropic compressibility Δκ_s and stretching frequency ν have been calculated. The excess molar volumes and deviations in isentropic compressibility are positive for the binaries studied over the whole composition, while deviations in viscosities are negative for the binary mixtures. The excess molar volumes, deviations in viscosity, and deviations in isentropic compressibility have been fitted to the Redlich–Kister polynomial equation. The Jouyban–Acree model is used to correlate the experimental values of density, viscosity, and speed of sound.     

Densities, Viscosities, Speeds of Sound, FT-IR and 1H-NMR Studies of Binary Mixtures of n-Butyl Acetate with Ethanol, Propan-1-ol, Butan-1-ol and Pentan-1-ol at?298.15, 303.15, 308.15 and 313.15?K

Densities, viscosities and speeds of sound of binary mixtures of ethanol, propan-1-ol, butan-1-ol and pentane-1-ol with n-butyl acetate have been measured over the entire range of composition at temperatures of 298.15, 303.15, 308.15 and 313.15 K and atmospheric pressure. From the experimental densities, viscosities and speeds of sound, the excess molar volumes V ^E, deviations in viscosity ????, and deviations in isentropic compressibility ???? _S have been calculated. The excess molar volumes and deviations in isentropic compressibility are positive for all the binary systems studied over the whole composition, while deviations in viscosities are negative for all of the binary mixtures. The excess molar volumes, deviations in viscosity, and deviations in isentropic compressibility have been fitted to a Redlich?CKister type polynomial equation. FTIR and ¹H-NMR studies of these mixtures are also reported.     

Thermodynamic Properties of Peptide Solutions. Part 18. Partial Molar Isentropic Compressibilities of Gly-X-Gly Tripeptides (X = Tyr,Pro, Gln,Asp and Glu), and the Peptide Salts K[GlyAspGly], Na[GlyGluGly] and GlyLysGly Acetate in Aqueous Solution at 25 <Superscript>∘</Superscript>C

The partial molar isentropic compressibilities at infinite dilution, K∘_S,2, have been determined for several tripeptides of the sequence glycyl-X-glycine, where X is one of the amino acids tyrosine, proline, glutamine, aspartic acid, glutamic acid and lysine in aqueous solution at 25 ^∘C. These results, along with those for triglycine, were used to estimate the contributions of the amino acid side-chains to the partial molar isentropic compressibilities of polypeptides. Values for K∘_S,2 have also been determined for aqueous solutions of the two peptide salts K[glyaspgly] and Na[glyglugly]. The K∘_S,2 results for the peptides and their salts have been combined with literature data for electrolytes to calculate the changes in isentropic compressibility upon ionization of the acidic side-chains. The results are compared with those for other carboxylic acid systems.     

Effect of ultrasound on transport properties of nonaqueous solutions of lithium hexafluoroarsenate

The speed of ultrasound in solutions of LiAsF₆ in propylenecarbonate and γ-butyrolactone was measured with an ultrasonic laser interferometer over a concentration range from 0.076 to 1.2 mol/kg at 273, 288, 298, 308, and 313 K. The solvation number h and molar adiabatic compressibility of the solvation complexes (β_S,h V _h) of LiAsF₆ in propylenecarbonate and γ-butyrolactone were determined at concentrations typical of lithium batteries. Linear correlations between the molar physicochemical parameters of liquid-phase systems (time of propagation of ultrasound, fluidity, and electric conductivity) were established.     

Thermodynamics of the Interaction of a Homologous Series of Amino Acids with Sorbitol

The apparent molar volumes V _2,φ , apparent molar isentropic compressibilities K _S,2,φ , and enthalpies of dilution of aqueous glycine, alanine, α-amino butyric acid, valine, and leucine have been determined in aqueous 1.0 and 2.0 mol⋅dm⁻³ sorbitol solutions at 298.15 K. These data have been used to calculate the infinite dilution standard partial molar volumes V_2,m⁰V_{2,m}^{0}, partial molar isentropic compressibilities K_S,2,m⁰K_{S,2,m}^{0}, and enthalpies of dilution Δ_dil H ⁰ of the amino acids in aqueous sorbitol, along with the standard partial molar quantities of transfer of the amino acids from water to aqueous sorbitol. The linear correlation of V_2,m⁰V_{2,m}^{0} for this homologous series of amino acids has been utilized to calculate the contribution to V₂⁰V_{2}^{0} of the charged end groups (NH₃⁺\mathrm{NH}_{3}^{+}, COO⁻), the CH₂ group, and other alkyl chains of the amino acids. The results for the standard partial molar volumes of transfer, compressibilites and enthalpies of dilution from water to aqueous sorbitol solutions have been correlated and interpreted in terms of ion–polar, ion–hydrophobic, and hydrophobic–hydrophobic group interactions. A comparison of these thermodynamic properties of transfer suggest that an enhancement of the hydrophilic/polar group interactions is operating in ternary systems of amino acid, sorbitol, and water.     

Volumes and compressibilities of pentanol in aqueous dodecyltrimethylammonium bromide solutions at 15, 25 and 35°C

Ultrasonic velocities and densities of the water-dodecyltrimethylammonium bromide (DTAB)-pentanol (PentOH) ternary system were measured at 15, 25 and 35°C as a function of the surfactant and alcohol concentrations. The apparent molar volumes and isentropic compressibilities of PentOH were calculated. The standard partial molar volumes increase with surfactant concentration continuously whereas the standard partial molar isentropic compressibilities show sharp changes in slope at about 0.25 mol-kg^–1 DTAB, which can be ascribed to a micellar structural transition. The volume data for alcohol in micellar solutions were treated by a model reported for the distribution of polar additives between aqueous and micellar phases. In the application of the model to compressibility, the contributions due to the pressure effect on the shift of both the micellization equilibrium and the alcohol distribution constant cannot be neglected. This is in contrast to what is found in the case of heat capacity. The distribution constant and the partial molar volumes and compressibilities of PentOH in the micellar phase have been derived by linear regression. Also, the apparent molar volumes and isentropic compressibilities of DTAB in water-pentanol mixed solvents at fixed composition have been calculated. These properties as a function of the surfactant concentration show maxima depending on the temperature and the mixed solvent composition. The decrease beyond the maximum can be attributed to the extraction of PentOH from the aqueous into the micellar phase, where its concentration tends to zero with the progressive increase of the surfactant concentration. As a consequence, by increasing the surfactant concentration, the apparent molar properties of the surfactant in the mixed solvent shifts towards the value in water.     

Effect of temperature and ionic strength on volumetric and acoustic properties of solutions of urea alkyl derivatives in aqueous NaCl

The present work was undertaken to study volumetric and acoustic properties for diluted solutions of tetramethylurea in pure water and for urea, n-propylurea, n-butylurea and tetramethylurea in 0.5 or 1 mol · dm⁻³ aqueous solutions of sodium chloride. This paper presents measured values of densities and sound velocities at T = (288.15, 298.15 and 308.15) K. From these data the apparent molar volumes, V_Φ, adiabatic compressibilities, κ_S, and apparent molar adiabatic compressions, K_S,Φ, were obtained. The values of apparent molar volumes for infinite dilution and limited apparent adiabatic compressions were calculated from extrapolation of the concentration dependence. Further, the corresponding transfer data as well as hydration number of urea and its derivatives in the studied systems were estimated. The obtained parameters are discussed in terms of various solute-solvent and solute-cosolute interactions.     

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.