Apparent molar volumes and apparent molar heat capacities of aqueous solutions ofN,N- dimethylformamide andN,N- dimethylacetamide at temperatures from 278.15 to 393.15 K and at the pressure 0.35 MPa

Apparent molar heat capacities C_{p, φ}and apparent molar volumesV_φ were determined for aqueous solutions of N, N - dimethylformamide andN , N - dimethylacetamide at temperatures from 278.15 to 393.15 K and at the pressure 0.35 MPa. The molalities investigated ranged from 0.015 mol ·kg ^− 1to 1.0 mol · kg ^− 1. We used a vibrating-tube densimeter (DMA 512P, Anton PAAR, Austria) to determine the densities and volumetric properties. Heat capacities were obtained using a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter (NanoDSC 6100, Calorimetry Sciences Corporation, Spanish Fork, UT, U.S.A.). The results were fit by regression to equations that describe the surfaces (V_φ,T , m) and (C_{p, φ}, T, m). Infinite dilution partial molar volumes V₂^oand heat capacitiesC_p,2^o were obtained over the range of temperatures by extrapolation of these surfaces to m =  0.     

Apparent molar volumes and apparent molar heat capacities of aqueous solutions of isomeric butanols at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa

Apparent molar heat capacities C_{p, φ}and apparent molar volumesV_φ were determined for aqueous solutions of 1-butanol, 2-butanol (both R andS isomers), isobutanol (2-methyl-1-propanol), and t -butanol (2-methyl-2-propanol) at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa. The molalities investigated ranged from 0.02 mol · kg ^− 1to 0.5 mol · kg ^− 1. We used a vibrating-tube densimeter (DMA 512P, Anton Paar, Austria) to determine the densities and volumetric properties. Heat capacities were obtained using a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter (NanoDSC 6100, Calorimetry Sciences Corporation, Provo, UT, U.S.A.). The results were fit by regression to equations that describe the surfaces (V_φ, T, m) and (C_p,φ, T, m). Infinite dilution partial molar volumesV₂^o and heat capacities C_p,2^owere obtained over the range of temperatures by extrapolation of these surfaces to m =  0.     

Thermodynamics of proton dissociations from aqueous l-methionine at temperatures from (278.15 to 393.15) K,molalities from (0.0125 to 1.0) mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of l-methionine,methioninium chloride,and sodium methioninate

We have measured the densities of aqueous solutions of l-methionine, l-methionine plus equimolal HCl, and l-methionine plus equimolal NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, at molalities 0.0125 ⩽ m/mol · kg⁻¹ ⩽ 1.0 as solubilities allowed, and at p = 0.35 MPa using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a twin fixed-cell differential temperature-scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values from the literature for V_ϕ(T, m) and C_p,ϕ(T, m) for HCl(aq), NaOH(aq), and NaCl(aq) and the molar heat capacity change Δ_rC_p,m(T, m) for ionization of water to calculate parameters for Δ_rC_p,m(T, m) for the two proton dissociations from protonated aqueous cationic l-methionine. We integrated these results in an iterative algorithm using Young’s Rule to account for the effects of speciation and chemical relaxation on V_ϕ(T, m) and C_p,ϕ(T, m). This procedure yielded parameters for V_ϕ(T, m) and C_p,ϕ(T, m) for methioninium chloride {H₂Met⁺Cl⁻(aq)} and for sodium methioninate {Na⁺Met⁻(aq)} which successfully modeled our observed results. Values are given for Δ_rC_p,m, Δ_rH_m, pQ_a, Δ_rS_m, and Δ_rV_m for the first and second proton dissociations from protonated aqueous l-methionine as functions of T and m.     

Apparent molar volumes and apparent molar heat capacities of aqueous solutions ofα- andβ-cyclodextrins at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa

Apparent molar heat capacities C_{p, φ}and apparent molar volumesV_φ were determined for aqueous solutions of α - and β -cyclodextrins at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa. The molalities investigated ranged from 0.008 mol · kg ^− 1to 0.12 mol · kg ^− 1forα -cyclodextrin and from 0.004 mol · kg ^− 1to 0.014 mol · kg ^− 1for β -cyclodextrin. We used a vibrating-tube densimeter (DMA 512P, Anton PAAR, Austria) to determine the densities and volumetric properties. Heat capacities were obtained using a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter (NanoDSC 6100, Calorimetry Sciences Corporation, Spanish Fork, UT, USA). Equations were fit by regression to our experimental (V_φ, T, m) and (C_{p, φ},T , m) results. Infinite dilution partial molar volumes V₂^oand heat capacities C_p,2^owere obtained over the range of temperatures by extrapolation of these surfaces to m =  0.     

Thermodynamics of dibenzo-p-dioxin and 1,2,3,4-tetrachlorodibenzo-p-dioxin fromT = 5 K toT = 490 K

In adiabatic low-pressure and dynamic calorimeters the temperature dependence of the standard molar heat capacity C_{p, m}^oof dibenzo- p -dioxin and 1,2,3,4-tetrachlorodibenzo- p -dioxin have been determined at temperatures in the range T =  5 K to T =  490 K: from T =  5 K to T =  340 K with an accuracy of about 0.2 per cent and with an accuracy of 0.5 per cent to 1.5 per cent between T =  340 K and T =  490 K. The temperatures, enthalpies, and entropies of melting of the above compounds have been determined. The experimental data were used to calculate the thermodynamic functions C_{p, m}^o / R, Δ₀^TH_m^o / (R·K), Δ₀^TS_m^o / R, and Φ_m^o = Δ₀^TS_m^o − Δ₀^TH_m^o / T(where R is the universal gas constant) in the range T →  0 to T =  490 K. The isochoric heat capacity C_{V, m}of both dioxins has been estimated over the range T →  0 to T_fus. The effect of substitution of four hydrogen atoms by chlorine atoms on the lattice and atomic components of the isochoric heat capacity was considered.     

Apparent molar volumes and apparent molar heat capacities of aqueous tetrahydrofuran,dimethyl sulfoxide, 1,4-dioxane,and 1,2-dimethoxyethane at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa

We determined apparent molar volumes V_? at 278.15 ? (T/K) ? 368.15 and apparent molar heat capacities C_p,? at 278.15 ? (T/K) ? 393.15 at p = 0.35 MPa for aqueous solutions of tetrahydrofuran at m from (0.016 to 2.5) mol · kg^?1, dimethyl sulfoxide at m from (0.02 to 3.0) mol · kg^?1, 1,4-dioxane at m from (0.015 to 2.0) mol · kg^?1, and 1,2-dimethoxyethane at m from (0.01 to 2.0) mol · kg^?1. Values of V_? were determined from densities measured with a vibrating-tube densimeter, and values of C_p,? were determined with a twin fixed-cell, differential, temperature-scanning calorimeter. Empirical functions of m and T for each compound were fitted to our V_? and C_p,? results.     

Thermodynamics of proton dissociations from aqueous threonine and isoleucine at temperatures from (278.15 to 393.15) K,molalities from (0.01 to 1.0) mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of zwitterionic,protonated cationic,and deprotonated anionic forms

We have measured the densities of aqueous solutions of isoleucine, threonine, and equimolal solutions of these two amino acids with HCl and with NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, at molalities 0.01 ⩽ m/mol · kg⁻¹ ⩽ 1.0, and at the pressure 0.35 MPa using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a twin fixed-cell differential temperature-scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values from the literature for V_ϕ(T, m) and C_p,ϕ(T, m) for HCl(aq), NaOH(aq), and NaCl(aq) and the molar heat capacity change Δ_rC_p,m(T, m) for ionization of water to calculate parameters for Δ_rC_p,m(T, m) for the two proton dissociations from each of the protonated aqueous cationic amino acids. We used Young’s Rule and integrated these results iteratively to account for the effects of equilibrium speciation and chemical relaxation on V_ϕ(T, m) and C_p,ϕ(T, m). This procedure gave parameters for V_ϕ(T, m) and C_p,ϕ(T, m) for threoninium and isoleucinium chloride and for sodium threoninate and isoleucinate which modeled our observed results within experimental uncertainties. We report values for Δ_rC_p,m, Δ_rH_m, pQ_a, Δ_rS_m, and Δ_rV_m for the first and second proton dissociations from protonated aqueous threonine and isoleucine as functions of T and m.     

Thermodynamics of proton dissociations from aqueous serine at temperatures from (278.15 to 393.15) K,molalities from (0.01 up to 1.0) mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of serine,serinium chloride,and sodium serinate

We have measured the densities of aqueous solutions of serine, serine plus equimolal HCl, and serine plus equimolal NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, molalities 0.01 ⩽ m/mol · kg⁻¹ ⩽ 1.0, and at the pressure p = 0.35 MPa, using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a fixed-cell differential temperature-scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values from the literature for V_ϕ(T,m) and C_p,ϕ(T,m) for HCl(aq), NaOH(aq), and NaCl(aq) and the molar heat capacity change Δ_rC_p,m(T,m) for ionization of water to calculate Δ_rC_p,m(T,m) for proton dissociations from protonated aqueous cationic serine and from the zwitterionic form. We integrated these results in an iterative algorithm using Young’s rule to account for the effects of speciation and chemical relaxation on the observed V_ϕ(T,m) and C_p,ϕ(T,m) of the solutions. This procedure yielded parameters for V_ϕ(T,m) and C_p,ϕ(T,m) for serinium chloride {H₂Ser⁺Cl⁻(aq)} and for sodium serinate {Na⁺Gly⁻(aq)} which successfully modeled our observed results. We have then calculated Δ_rC_p,m, Δ_rH_m, Δ_rV_m and pQ_a for the first and second proton dissociations from protonated aqueous serine as functions of T and m.     

Thermodynamics of proton dissociations from aqueous glycine at temperatures from 278.15 to 393.15 K,molalities from 0 to 1.0 mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of glycine,glycinium chloride,and sodium glycinate

We have measured the densities of aqueous solutions of glycine, glycine plus equimolal HCl, and glycine plus equimolal NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, molalities 0.01 ⩽ m/mol · kg⁻¹ ⩽ 1.0, and at p = 0.35 MPa, using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a fixed-cell differential scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values of V_ϕ(T, m) and C_p,ϕ(T, m) for HCl(aq), NaOH(aq), NaCl(aq) from the literature to calculate parameters for Δ_rC_p,m(T, m) for the first and second proton dissociations from protonated aqueous cationic glycine. We then integrated this value of Δ_rC_p,m(T, m) in an iterative algorithm, using Young’s Rule to account for the effects of speciation and chemical relaxation on the observed V_ϕ and C_p,ϕ of the solutions. This procedure yielded parameters for V_ϕ(T, m) and C_p,ϕ(T, m) for glycinium chloride {H₂Gly⁺Cl⁻(aq)} and sodium glycinate {Na⁺Gly⁻(aq)} which successfully modeled our observed results. We have then calculated values of Δ_rC_p,m, Δ_rH_m, Δ_rV_m, and pQ_a for the first and second proton dissociations from protonated aqueous glycine as functions of T and m.     

Thermodynamics of proton dissociations from aqueous alanine at temperatures from (278.15 to 393.15) K,molalities from (0.0075 to 1.0) mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of alanine,alaninium chloride,and sodium alaninate

We have measured the densities of aqueous solutions of alanine, alanine plus equimolal HCl, and alanine plus equimolal NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, at molalities 0.0075 ⩽ m/mol · kg⁻¹ ⩽ 1.0, and at the pressure p = 0.35 MPa using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a twin fixed-cell differential temperature-scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values from the literature for V_ϕ(T, m) and C_p,ϕ(T, m) for HCl(aq), NaOH(aq), and NaCl(aq) and the molar heat capacity change Δ_rC_p,m(T, m) for ionization of water to calculate parameters for Δ_rC_p,m(T, m) for the two proton dissociations from protonated aqueous cationic alanine. We integrated these results in an iterative algorithm using Young’s Rule to account for the effects of speciation and chemical relaxation on V_ϕ(T, m) and C_p,ϕ(T, m). This procedure yielded parameters for V_ϕ(T, m) and C_p,ϕ(T, m) for alaninium chloride {H₂Ala⁺Cl⁻(aq)} and for sodium alaninate {Na⁺Ala⁻(aq)} which successfully modeled our observed results. Values are given for Δ_rC_p,m, Δ_rH_m, pQ_a, Δ_rS_m, and Δ_rV_m for the first and second proton dissociations from protonated aqueous alanine as functions of T and m.     

Apparent molar volumes and apparent molar heat capacities of aqueous KI,HIO3, NaIO3, and KIO3 at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa

We determined apparent molar volumes V_? at 298.15 ? (T/K) ? 368.15 and apparent molar heat capacities C_p,? at 298.15 ? (T/K) ? 393.15 for aqueous solutions of HIO₃ at molalities m from (0.015 to 1.0) mol · kg^?1, and of aqueous KIO₃ at molalities m from (0.01 to 0.2) mol · kg^?1 at p = 0.35 MPa. We also determined V_? at the same p and at 298.15 ? (T/K) ? 368.15 for aqueous solutions of KI at m from (0.015 to 7.5) mol · kg^?1. We determined C_p,? at the same p and at 298.15 ? (T/K) ? 393.15 for aqueous solutions of KI at m from (0.015 to 5.5) mol · kg^?1, and for aqueous solutions of NaIO₃ at m from (0.02 to 0.15) mol · kg^?1. Values of V_? were determined from densities measured with a vibrating-tube densimeter, and values of C_p,? were determined with a twin fixed-cell, differential temperature-scanning calorimeter. Empirical functions of m and T were fitted to our results for each compound. Values of K_a, Δ_rH_m, and Δ_rC_p,m for the proton ionization reaction of aqueous HIO₃ are calculated and discussed.     

Thermodynamic properties of tetraphenylphosphonium perchlorate and tetraphenylarsonium perchlorate fromT → 0 toT = 340 K

The temperature dependence of the standard molar heat capacity C_{p, m}^oof samples of crystalline tetraphenylphosphonium perchlorate and tetraphenylarsonium perchlorate was measured in an adiabatic low-pressure calorimeter between T =  4.8 K and T =  340 K and from T =  5.8 K to T =  340 K, respectively, mostly to within a precision of 0.2 per cent. For tetraphenylphosphonium perchlorate, an anomalous change of the heat capacity in the range T =  125 K to T =  185 K, probably arising from the excitation of hindered rotations of atomic groups, was found and its thermodynamic characteristics were determined. No such anomaly was observed for tetraphenylarsonium perchlorate. The data obtained were used to calculate the thermodynamic functions C_{p, m}^o(T) / R, Δ₀^TH_m^o / R·K, Δ₀^TS_m^o / R, and Φ_m^o = Δ₀^TS_m^o − Δ₀^TH_m^o / T(where R is the universal gas constant) of the compounds between T →  0 and T =  340 K.     

The estimation of the heat capacity of NpO2

The heat capacity C_{p, m}of NpO₂was estimated for temperatures between 300 K and 1400 K. The C_{p, m}was evaluated as a sum of three terms, phonon vibration C_{ph, m}, dilation C_{d, m}, and Schottky specific heat C_{s, m}. The C_{ph, m}and C_d,mwere calculated using the Debye temperature, Grüneisen constant and thermal expansion data obtained by high-temperature X-ray diffractometry. The coefficient of the linear thermal expansion (l.t.e.) for NpO₂was given as a polynomial function up to T =  1573 K. The estimated C_p,mwas compared with that of previous studies. The present result at T =  300 K was 66.87 J · K ^− 1· mol ^− 1, which agreed well with previous results, 66.22 J · K ^− 1· mol ^− 1, measured by using calorimetry. The thermodynamic functions were given as a function of temperature.     

Apparent molar volumes and apparent molar heat capacities of aqueous magnesium nitrate,strontium nitrate,and manganese nitrate at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa

Apparent molar volumes V_ϕ and apparent molar heat capacities C_p,ϕ were determined at the pressure 0.35 MPa for aqueous solutions of magnesium nitrate Mg(NO₃)₂ at molalities m = (0.02 to 1.0) mol · kg⁻¹, strontium nitrate Sr(NO₃)₂ at m = (0.05 to 3.0) mol · kg⁻¹, and manganese nitrate Mn(NO₃)₂ at m = (0.01 to 0.5) mol · kg⁻¹. Our V_ϕ values were calculated from solution densities obtained at T = (278.15 to 368.15) K using a vibrating-tube densimeter, and our C_p,ϕ values were calculated from solution heat capacities obtained at T = (278.15 to 393.15) K using a twin fixed-cell, differential, temperature-scanning calorimeter. Empirical functions of m and T were fitted to our results, and standard state partial molar volumes and heat capacities were obtained over the ranges of T investigated.     

Interactions of some amino acids and glycine peptides with aqueous sodium dodecyl sulfate and cetyltrimethylammonium bromide at T=298.15 K: a volumetric approach

The apparent molar volumes V_φ of glycine, alanine, valine, leucine, and lysine have been determined in aqueous solutions of 0.05, 0.5, 1.0 mol · kg⁻¹ sodium dodecyl sulfate (SDS) and 1.0 mol · kg⁻¹ cetyltrimethylammonium bromide (CTAB) by density measurements at T=298.15 K. The apparent molar volumes have also been determined for diglycine and triglycine in 1 mol · kg⁻¹ SDS and CTAB solutions. These data have been used to calculate the infinite dilution apparent molar volumes V₂⁰ for the amino acids and peptides in aqueous SDS and CTAB and the standard partial molar volumes of transfer (Δ_trV_2,m⁰) of the amino acids and peptides to these aqueous surfactant solutions. The linear correlation of V₂⁰ for a homologous series of amino acids has been utilized to calculate the contribution of the charged end groups (NH₃⁺, COO⁻), CH₂ group and other alkyl chains of the amino acids to V₂⁰. The results on the partial molar volumes of transfer from water to aqueous SDS and CTAB have been interpreted in terms of ion–ion, ion–polar and hydrophobic–hydrophobic group interactions. The volume of transfer data suggests that ion–ion or ion–hydrophilic group interactions of the amino acids and peptides are stronger with SDS compared to those with CTAB. Comparison of the hydration numbers of amino acids calculated in the present studies with those in other solvents from literature shows that these numbers are almost the same at 1 mol · kg⁻¹ level of the cosolvent/cosolute. Increasing molality of the cosolvent/cosolute beyond 1 mol · kg⁻¹ lowers the hydration number of the amino acids due to increased interactions with the solvent and reduced electrostriction.     

Rheological behaviour of some saccharides in aqueous potassium chloride solutions over temperature range (288.15 to 318.15) K

The viscosities, η of mono-, di-, tri-saccharides and methylglycosides, viz., d(+)-xylose (XYL), d(?)-arabinose (ARA), d(?)-ribose (RIB), d(?)-fructose (FRU), d(+)-galactose (GAL), d(+)-mannose (MAN), d(+)-glucose (GLU), d(+)-melibiose (MEL), d(+)-cellobiose (CEL), d(+)-lactose monohydrate (LAC), d(+)-maltose monohydrate (MAL), d(+)-trehalose dihydrate (TRE), sucrose (SUC), d(+)-raffinose pentahydrate (RAF), α-methyl-d(+)-glucoside (α-Me-GLU), methyl-α-d-xylopyranoside (Me-α-XYL), and methyl-β-d-xylopyranoside (Me-β-XYL) in water and in (0.5, 1.0, 2.0, and 3.0) mol · kg^?1 aqueous solutions of potassium chloride (KCl) have been determined at T = (288.15, 298.15, 308.15, and 318.15) K from efflux time measurements by using a capillary viscometer. Densities used to determine viscosities have been reported earlier. The viscosity data have been utilized to determine the viscosity B-coefficients employing the Jones–Dole equation at different temperatures. From these data, the viscosity B-coefficients of transfer, Δ_tB have been estimated for the transfer of various saccharides/methylglycosides from water to aqueous potassium chloride solutions. The Δ_tB values have been found to be positive, whose magnitude increases with the increase in concentration of potassium chloride in all cases. The dB/dT coefficients, pair, η_AB and triplet, η_ABB viscometric interaction coefficients have also been determined. Gibbs free energies of activation and related thermodynamic parameters of activation of viscous flow have been determined employing Feakin’s transition-state theory. The signs and magnitudes of various parameters have been discussed in terms of solute–solute and solute–solvent interactions occurring in these solutions. The effect of substitution of –OH by methoxy group, –OCH₃ has also been discussed.     

The standard molar enthalpy of sublimation ofη5-bis-pentamethylcyclopentadienyl iron measured with an electrically calibrated vacuum-drop sublimation microcalorimetric apparatus

A heat-flow Calvet microcalorimeter was adapted for the measurement of sublimation enthalpies by the vacuum-drop method, with samples of masses in the range 1 mg to 5 mg. The electrically calibrated apparatus was tested by determining the enthalpies of sublimation of benzoic acid and ferrocene, at T =  298.15 K. The obtained results, Δ_cr^gH_m^o(C₇H₆O₂)  =  (88.3  ±  0.5)kJ · mol ^− 1and Δ_cr^gH_m^o(C₁₀H₁₀Fe) =  (73.3  ±  0.1)kJ · mol ^− 1, are in excellent agreement with the corresponding values recommended in the literature. Subsequent application of the apparatus to the determination of the enthalpy of sublimation of η⁵-bis-pentamethylcyclopentadyenyl iron, at T =  298.15 K, led to Δ_cr^gH_m^o(C₂₀H₃₀Fe)  =  (96.8  ±  0.6)kJ · mol ^− 1.     

Apparent molar volumes and apparent molar heat capacities of aqueous potassium hydrogen phthalate (KHP) and potassium sodium phthalate (KNaP) at temperatures fromT = 278.15 K toT = 393.15 K at the pressure 0.35 MPa

A vibrating-tube densimeter (DMA 512P, Anton Paar, Austria) was used to investigate the densities and volumetric properties of aqueous potassium hydrogen phthalate (KHP) and potassium sodium phthalate (KNaP). Measurements were made at molalities m from (0.006 to 0.66)mol · kg ^− 1, at temperatures from 278.15 K to 368.15 K and at the pressure 0.35 MPa. The densimeter was calibrated through measurements on pure water and on 1.0 mol · kg ^− 1NaCl(aq). We also used a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter (NanoDSC 6100, Calorimetry Sciences Corporation, Spanish Fork, UT, U.S.A.) to measure solution heat capacities. This was accomplished by scanning temperature and comparing the heat capacities of the unknown solutions to the heat capacity of water. Apparent molar volumes V_φand apparent molar heat capacities C_{p, φ}of the solutions were calculated and fit by regression to equations that describe the surfaces (V_φ, T, m) and (C_{p, φ}, T, m). Standard state partial molar volumesV₂^o and heat capacities C_p,2^owere estimated by extrapolation to the m =  0 plane of the fitted surfaces. Previously determinedC_{p, φ} for HCl(aq) and NaCl(aq) were used to obtain (Δ_rC_{p, m}, T, m) for the proton dissociation reaction of aqueous hydrogen phthalate. This (Δ_rC_p,m, T, m) surface was created by subtracting C_p,φfor KHP(aq) and for NaCl(aq) from the sum of C_p,φfor KNaP(aq) and for HCl(aq). Surfaces representing (Δ_rH_m, T, m) and (pQ_a, T, m), where pQ_adenotes the molality equilibrium quotient, were created by integration of our (Δ_rC_p,m, T, m) surface using values for (Δ_rH_m, m) and (pK_a, m) at T =  308.15 K from the literature as integration constants.     

Studies on the interactions of diglycine and triglycine with polyethylene glycol 400 in aqueous solutions by density and ultrasound speed measurements

Density and ultrasound speed were measured accurately for diglycine + water, triglycine + water, diglycine + water-polyethylene glycol 400 (PEG400) and triglycine + water-PEG400 solutions at T = (293.15, 298.15, 303.15 and 308.15) K. The results were used in evaluating thermodynamic properties as apparent molar volumes (V_Ø) and apparent molar isentropic compressions (K_SΦ) of diglycine and triglycine in water and in PEG400 solutions. Infinite dilution values of these parameters, V^o_Ø, and K^o_SΦ, were obtained from their plots as a function of molality by extrapolation and have been utilized in obtaining transfer volumes and transfer compressions at infinite dilution. All transfer volumes and transfer compressions were found to increase with increasing molality of PEG400. Apparent molar isobaric expansions were derived from the temperature dependence of V_Ø values at infinite dilution and at finite concentrations. All the results were interpreted in terms of solute (diglycine or triglycine) and co-solute (PEG400) and solvent (H₂O) interactions.     

Volumetric study of (2-methoxyethanol + tetrahydrofuran + cyclohexane) at T=298.15 K

The excess molar volumes V_m^E at T=298.15 have been determined in the whole composition domain for (2-methoxyethanol + tetrahydrofuran + cyclohexane) and for the parent binary mixtures. Data on V_m^E are also reported for (2-ethoxyethanol + cyclohexane). All binaries showed positive V_m^E values, small for (methoxyethanol + tetrahydrofuran) and large for the other ones. The ternary V_m^E surface is always positive and exhibits a smooth trend with a maximum corresponding to the binary (2-methoxyethanol + cyclohexane). The capabilities of various models of either predicting or reproducing the ternary data have been compared. The behaviour of V_m^E and of the excess apparent molar volume of the components is discussed in both binary and ternary mixtures. The results suggest that hydrogen bonding decreases with alcohol dilution and increases with the tetrahydrofuran content in the ternary solutions.