Electrical Conductance and Volumetric Studies in Aqueous Solutions of Nicotinic Acid

Conductivity measurements of nicotinic acid and sodium nicotinate in dilute aqueous solutions were performed in the (288.15 to 323.15) K temperature range. The limiting equivalent conductances of the nicotinate anion, λ⁰(Nic⁻, T), and the dissociation constants of nicotinic acid, K(T), were derived by the use of the Onsager and the Quint and Viallard conductivity equations. Densities of aqueous solutions with molalities lower than 0.2 mol-kg⁻¹ were determined at 5 K temperature intervals, from T = (288.15 to 333.15) K. The measured densities were used to evaluate the apparent molar volumes, V_{2, φ}(m, T), the cubic expansion coefficients, α(m, T), and the changes of isobaric heat capacities with respect to pressure, (∂C_P/∂p)_{T, m}. They were qualitatively correlated with the changes in the structure of water when nicotinic acid is dissolved in it.     

Volumetric Properties of Aqueous Solutions of L-Glutamic Acid and Magnesium-L-Glutamate

Densities of aqueous solutions of L-glutamic acid and magnesium-L-glutamate were determined from T=288.15 to 333.15 K at 5 K temperature intervals. The measured densities were used to evaluate the apparent molar volumes, V _2,φ (m,T), the cubic expansion coefficients, α(m,T), and the changes of isobaric heat capacities with respect to pressure, (∂ C _p /∂ p) _T,m . They were qualitatively correlated with changes in the structure of water that occur when L-glutamic acid or magnesium-L-glutamate are present.     

Electrical Conductance Studies in Aqueous Solutions with Aspartic Ions

Conductivity measurements of dilute aqueous solutions of DL-aspartic acid, potassium-DL-aspartate and magnesium-DL-aspartate were performed in the 288.15 to 323.15 K temperature range. The limiting molar conductances of aspartate anions, λ ⁰(HAsp⁻,T) and the dissociation constants of aspartic acid, K ₂(T) were derived by use of the Debye-Hückel equation for the activity coefficients and the Onsager, and Quint and Viallard conductivity equations.     

Electrical Conductance Studies in Aqueous Solutions with Glutamic Ions

Conductivity measurements in dilute aqueous solutions of L-glutamic acid, DL-glutamic acid, sodium-L-glutamate and magnesium-L-glutamate, were performed in the 288.15 to 323.15 K temperature range. The limiting molar conductivities of glutamic anions, λ ^o(HGlu⁻,T) and the dissociation constants of glutamic acid, K ₂(T) were derived by the use of the Debye–Hückel equation for the activity coefficients and the Onsager, and Quint and Viallard conductivity equations.     

Electrical Conductance Studies in Aqueous Solutions of Glutaric Acid,Disodium Glutarate and Sodium Hydrogen Glutarate

Conductivity measurements of glutaric acid and disodium glutarate in dilute aqueous solutions were performed in the 288.15 to 323.15 K temperature range. The limiting equivalent conductances of glutarate anions, λ ^o(HGlut⁻,T) and λ ^o(1/2Glut²⁻,T), and the dissociation constants of glutaric acid, K ₁(T) and K ₂(T), were derived by the use of the Onsager and the Quint and Viallard conductivity equations. The applied molecular model was successfully confirmed by analyzing the conductivities of sodium hydrogen glutarate at 298.15 K.     

Volumetric properties of aqueous solutions of glutaric acid

Densities of aqueous solutions with molalities up to 6 mol · kg⁻¹ were determined at 5 K temperature intervals, from T = 288.15 K to T = 333.15 K. Densities served to evaluate the apparent molar volumes, V_2,ϕ(m, T), the cubic expansion coefficients, α(m, T), and the changes of isobaric heat capacities with respect to pressure, (∂C_P/∂P)_T,m. They were qualitatively correlated with the changes in the structure of water when glutaric acid is dissolved in it.     

Electrical Conductance Studies in Aqueous Solutions with Ascorbate Ions

Conductivity measurements in dilute aqueous solutions of L-ascorbic acid, sodium-L-ascorbate, magnesium-L-ascorbate, calcium-L-ascorbate and ferrous-L-ascorbate were performed in the (288.15 to 323.15) K temperature range. The limiting molar conductances of the ascorbic anion, λ^∘(HAsc⁻, T), and the dissociation constants of ascorbic acid, K(T), were derived by the use of the Debye-Hückel equation for the activity coefficients and the Onsager and Quint and Viallard conductivity equations.     

Volumetric properties of glucose in aqueous HCl solutions at temperatures from 278.15 to 318.15 K

Densities have been measured for Glucose + HCl +Water at 10-degree intervals from 278.15 to 318.15 K. The apparent molar volumes (V _Φ,G) and standard partial molar volumes (V _Φ,G ⁰ ) for Glucose in aqueous solution of 0.2, 0.4, 0.7, 1.1, 1.6, 2.1 mol·kg⁻¹ HCl have been calculated as well as volumetric interaction parameters (V _EG) for Glucose — HCl in water and standard partial molar expansion coefficients (∂V _Φ,G ⁰ / ∂T)_p. Results show that (1) the apparent molar volume for Glucose in aqueous HCl solutions increases lineally with increasing molality of Glucose and HCl; (2) V _Φ,G/0 for Glucose in aqueous HCl solutions increases lineally with increasing molality of HCl; (3) the volumetric interaction parameters for Glucose — HCl pair in water are small positive and vary slightly with temperature; (4) the relation between V _Φ,G ⁰ and temperature exists as V _Φ,G ⁰ = a ₀ + a ₁(T − 273.15 K)^2/3; (5) values of (∂V _Φ,G ⁰ / ∂T)_p are positive and increase as temperatures rise, and at given temperatures decrease slightly with increasing molalities of HCl, indicating that the hydration of glucose decreases with increasing temperature and molality of HCl. These phenomena are interpreted successfully by the structure interaction model. Translated from Acta Chimica Sinica, 2006, 64(16): 1635–1641 (in Chinese)     

Apparent Molar Heat Capacities and Apparent Molar Volumes of Aqueous Nicotinamide at Different Temperatures

Specific heat capacities and apparent molar heat capacities of aqueous nicotinamide have been determined from 25.0 to 55.0°C using microdifferential scanning calorimetry in the molality range of 0.07433 to 1.50124 mol-kg^–1. Densities and apparent molar volumes have also been determined for aqueous nicotinamide from 10.30 to 34.98°C using a digital densimeter in the molality range 0.07804–2.02435 mol-kg^–1. The results of these measurements have been used to calculate the following partial molar quantities and temperature derivatives for aqueous nicotinamide as a function of temperature: C _p,2,m ^o, (C _p,2,m ^o/T)_p, (²C_p,2,m ^o/T ²)_p, V _2,m ^o, ( V _2,m ^o/T)_p, and (² V _2,m ²/T ²)_p. The results are discussed in terms of the changes in the packing of nicotinamide molecules in the crystal, interactions in the aqueous form, and its structure-promoting ability with rise in temperature.     

The standard partial molar entropy of the aqueous tetra-n-butylammonium cation

The standard partial molar entropy of the aqueous tetrabutylammonium cation, not known previously, has now been obtained, based on the molar entropy of two of its crystalline salts, the iodide and the tetraphenylborate, recently determined experimentally for this purpose. The calculation required also published molar enthalpies of solution and solubilities of these two salts as well as of the perchlorate. The choice of the anions depended mainly on the limited solubilities of the examined salts in water, facilitating the estimation of the relevant activity coefficients. The result is S^∞(Bu₄N⁺, aq) = (380 ± 20) J · K⁻¹ · mol⁻¹ at T = 298.15 K, on the mol · dm⁻³ scale and based on S^∞(H⁺, aq) = (−22.2 ± 1.2) J · K⁻¹ · mol⁻¹ (yielding the ‘absolute’ value). The molar entropy of this cation in the ideal gas standard state, S(Bu₄N⁺, g) = (798 ± 8) J · K⁻¹ · mol⁻¹ then yielded the molar entropy of hydration Δ_hydS^∞ (Bu₄N⁺) = (−418 ± 23) J · K⁻¹ · mol⁻¹.     

Thermodynamics of binary liquid mixtures of cyclopentane with 2-propanol, 1-butanol and 2-butanol at different temperatures

Densities and speeds of sound of the cyclopentane with 2-propanol, 1-butanol and 2-butanol are measured over the whole composition range at different temperatures in the range 288.15–308.15 K and atmospheric pressure using Anton Paar DSA 5000 densimeter. The experimental densities and speeds of sound have been used to calculate excess molar volumes, excess molar isentropic compressibilities and excess intermolecular free length. The partial molar volumes and apparent molar volumes at infinite dilution have also been calculated. The mixing quantities like (∂V _m^E/∂T)_P and (∂H _m^E/∂P)_T have been calculated at T = 298.15 K and these values are compared with the values calculated from Flory’s theory at equimolar composition.     

D<Subscript>2</Subscript>O — H<Subscript>2</Subscript>O Solvent Isotope Effects on the Apparent Molar Volumes of Tetramethyl-<Emphasis Type="Italic">bis</Emphasis>-urea (Mebicarum) Solutions

Densities of solutions of tetramethyl-bis-urea (TMbU) or “Mebicarum” in H₂O and D₂O, with solute mole fraction concentrations (x ₂) ranging up to 3.2 × 10⁻³, have been measured at 288.15, 298.15, 308.15 and 318.15 K using a precision vibrating-tube densimeter. The limiting apparent molar volumes, V _φ,2 ^∞, and expansibilities, E _{p, φ, 2} ^∞, of the solute have been calculated. The isotope effect δ V _φ,2 ^∞(H₂O → D₂O;T) is negative, monotonously decreases in magnitude with temperature and reverses sign at T ≈ 318 K. Water (H₂O, D₂O) and TMbU molecules in infinitely- and highly-dilute aqueous solutions form H(D)-bonded hydration complexes with a high packing density. The hydration of TMbU should be treated as a superposition of two mechanisms, hydrophobic and hydrophilic, with the latter one predominating.     

Densities and Apparent Molar Volumes of Aqueous H<Subscript><Emphasis Type="Bold">3</Emphasis></Subscript>BO<Subscript><Emphasis Type="Bold">3</Emphasis></Subscript> Solutions at Temperatures from 296 to 573 K and at Pressures up to 48 MPa

Densities of four aqueous H₃BO₃ solutions (0.062, 0.155, 0.315, and 0.529 mol-kg^–1) have been measured in the liquid phase with a constant volume piezometer immersed in a precisely controlled liquid thermostat. Measurements were made at temperatures between 296 and 573 K and pressures from 0.82 to 48 MPa. The total uncertainties of the density, pressure, temperature, and molality measurements were estimated to be less than 0.06%, 0.05%, 10 mK, and 0.0005 mol-kg^–1, respectively. The accuracy of the method was confirmed by PVT measurements on pure water for two isobars (30 and 39 MPa) at temperatures from 313 to 573 K. The experimental and calculated (IAPWS formulation) densities for pure water show excellent agreement which is within their experimental uncertainties (average absolute deviation, AAD=0.012%;). Apparent and partial molar volumes were derived using the measured densities for solutions and pure water, and these results were extrapolated to zero concentration to yield the partial molar volumes of the electrolyte (H₃BO₃) at infinite dilution. The temperature, pressure, and concentration dependencies of the apparent and partial molar volumes were studied. Small pressure and concentration effects on the apparent molar volumes were found at temperatures up to 500 K. The parameters of a polynomial type of equation of state for the specific volume V_sol(P, T, m) as a function of pressure, temperature, and molality were obtained with a least-squares method using the experimental data. The root-mean-square deviation between measured and calculated values from this polynomial equation of state is ±0.2 kg-m^–3 for density. Measured values of the solution densities and the apparent and partial molar volumes are compared with data reported in the literature.     

Effect of Temperature on the Volumetric Properties of [Difurylmethane+(C<Subscript>2</Subscript>–C<Subscript>6</Subscript>) Alkan-1-ol] Binary Systems: Analyses of New and Literature Density Data in the Temperature Range 288.15–308.15 K

Densities, ρ, of the binary systems {difurylmethane + (ethanol or propan-1-ol or butan-1-ol or pentan-1-ol or hexan-1-ol)} have been measured with an Anton Paar DMA 4500 vibrating-tube densimeter over the entire composition range at 288.15 and 308.15 K and atmospheric pressure. The measured and literature densities of [difurylmethane + n-alkanol] binary systems have been used to check the validity of the relationship describing the dependence of density on composition. This relation is useful for obtaining interpolated ρ values corresponding to the experimental data. Excess molar volumes (V _m^E) of each mixture, limiting (V _m,i ^E,∞) and excess partial (V _m,i ^E) molar volumes and the limiting partial molar expansion (E _p,i ^∞) of both components of each binary system have been examined to provide insight into the temperature variations of the intermolecular interactions and molecular packing efficiencies. The results have been discussed in terms of specific intermolecular interactions and structural effects.     

Specific thermal and thermodynamic properties of the tellurites Fe2(TeO3)3, Fe2TeO5 and Fe2Te4O11

The temperature dependence of the molar heat capacities of the tellurites Fe₂(TeO₃)₃, Fe₂TeO₅ and Fe₂Te₄O₁₁ were determined. By statistical manipulation of the values obtained, the parameters in the equations for the corresponding compounds showing this dependence were determined using the least-squares method. These equations together with the standard molar entropies were used to determine the thermodynamic functions Δ₀^T S _m⁰, Δ_T^T,H _m⁰ and (Φ_m⁰ + Δ₀^T’ H _m⁰ / T) for T’=298.15 K.     

Interactions of glycine,L-alanine and L-valine with aqueous solutions of trisodium citrate at different temperatures: A volumetric and acoustic approach

Densities, ρ, and speed of sound, u for glycine, L-alanine and L-valine in (0.2, 0.4, 0.6, and 0.8) mol · kg⁻¹ aqueous solutions of trisodium citrate at T = (288.15, 298.15, 308.15 and 318.15) K have been measured. The different parameters such as apparent molar volume, limiting apparent molar volume, transfer volume, have been derived from density data. Experimental values of the speed of sound were used to estimate apparent molar apparent molar isentropic compression, limiting apparent molar isentropic compression, and transfer parameter. The pair and triplet interaction coefficient have been calculated from transfer parameters.     

Volumetric Properties of Some Aliphatic Mono- and Dicarboxylic Acids in Water at 298.15 K

The apparent molar volumes, V _φ , of two series of homologous aliphatic carboxylic acids, H(CH₂) _n COOH [n=0–5] and (CH₂) _n (COOH)₂ [n=0–5], were determined in dilute aqueous solutions by density measurements at T=298.15 K. Densities were measured using a vibrating-tube densimeter (DMA 5000, Anton Paar, Austria) at T=298.15 K. These results were used to calculate the apparent molar volumes of each solute over the concentration range 0.0050≤m/(mol⋅kg⁻¹)≤0.3000. Values of the apparent molar volumes of undissociated acids V_f(u)⁰V_{\phi (u)}^{0} were also calculated. The variation of V_f(u)⁰V_{\phi (u)}^{0} was determined as a function of the aliphatic chain length of the studied carboxylic acids.     

Apparent molar volumes and apparent molar heat capacities of aqueous N-acetyl-d-glucosamine at temperatures from 278.15 K to 368.15 K and of aqueous N-methylacetamide at temperatures from 278.15 K to 393.15 K at the pressure 0.35 MPa

We determined apparent molar volumes V_? from densities measured with a vibrating-tube densimeter at 278.15 ? (T/K) ? 368.15 and apparent molar heat capacities C_p,? with a twin fixed-cell, differential, temperature-scanning calorimeter at 278.15 ? (T/K) ? 363.15 for aqueous solutions of N-acetyl-d-glucosamine at m from (0.01 to 1.0) mol · kg⁻¹ and at p = 0.35 MPa. We also determined V_? at 278.15 ? (T/K) ? 368.15 and C_p,? at 278.15 ? (T/K) ? 393.15 for aqueous solutions of N-methylacetamide at m from (0.015 to 1.0) mol · kg⁻¹ and at p = 0.35 MPa. Empirical functions of m and T for each compound were fitted to our results, which are then compared to those for N,N-dimethylacetamide. Estimated values of Δ_rV_m(m, T) and Δ_rC_p,m(m, T) for formation of aqueous N-acetyl-d-glucosamine from aqueous d-glucose and aqueous acetamide are calculated and discussed.     

Molar heat capacities and standard molar enthalpy of formation of 2-amino-5-methylpyridine

The heat capacities (C _p,m) of 2-amino-5-methylpyridine (AMP) were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 398 K. A solid-liquid phase transition was found in the range from 336 to 351 K with the peak heat capacity at 350.426 K. The melting temperature (T _m), the molar enthalpy (Δ_fus H _m⁰), and the molar entropy (Δ_fus S _m⁰) of fusion were determined to be 350.431±0.018 K, 18.108 kJ mol⁻¹ and 51.676 J K⁻¹ mol⁻¹, respectively. The mole fraction purity of the sample used was determined to be 0.99734 through the Van’t Hoff equation. The thermodynamic functions (H _T-H _298.15 and S _T-S _298.15) were calculated. The molar energy of combustion and the standard molar enthalpy of combustion were determined, ΔU _c(C₆H₈N₂,cr)= −3500.15±1.51 kJ mol⁻¹ and Δ_c H _m⁰ (C₆H₈N₂,cr)= −3502.64±1.51 kJ mol⁻¹, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. The standard molar enthalpy of formation of the crystalline compound was derived, Δ_r H _m⁰ (C₆H₈N₂,cr)= −1.74±0.57 kJ mol⁻¹.     

Densities,Apparent Molar Volumes and Viscosities of Concentrated Aqueous NaNO<Subscript>3</Subscript> Solutions at Temperatures from 298 to 607 K and at Pressures up to 30 MPa

Densities of four (2.124, 2.953, 5.015 and 6.271 mol-kg⁻¹) and viscosities of eight (0.265, 0.503, 0.665, 1.412, 2.106, 2.977, 5.015 and 6.271 mol-kg⁻¹) NaNO₃(aq) solutions have been measured with a constant-volume piezometer immersed in a precision liquid thermostat and using capillary flow techniques, respectively. Measurements were made at pressures up to 30 MPa. The temperature range was 298–607 K for the density measurements and 298–576 K for the viscosity measurements. The total uncertainty of density, viscosity, pressure, temperature and composition measurements were estimated to be less than 0.06%, 1.6%, 0.05%, 15 mK and 0.02%, respectively. The temperature, pressure and concentration dependence of density and viscosity of NaNO₃(aq) solutions were studied. The measured values of density and viscosity of NaNO₃(aq) were compared with data and correlations reported in the literature. Apparent molar volumes were derived using the measured density values. The viscosity data have been interpreted in terms of the extended Jones–Dole equation for strong electrolytes. The values of the viscosity A-, B-, D- and F-coefficients of the extended Jones–Dole equation for the relative viscosity (η/η₀) of NaNO₃(aq) solutions were evaluated as a function of temperature. The derived values of the viscosity A- and B-coefficients were compared with the results predicted by Falkenhagen–Dole theory of electrolyte solutions and calculated with the ionic B-coefficient data.