Diffusion coefficients of nickel chloride in aqueous solutions of lactose at T = 298.15 K and T = 310.15 K

Binary mutual diffusion coefficients (interdiffusion coefficients) of nickel chloride in water at T = 298.15 K and T = 310.15 K, and at concentrations between (0.000 and 0.100) mol · dm^?3, using a Taylor dispersion method have been measured. These data are discussed on the basis of the Onsager–Fuoss and Pikal models. The equivalent conductance at infinitesimal concentration of the nickel ion in these solutions at T = 310.15 K has been estimated using these results. Through the same technique, ternary mutual diffusion coefficients (D₁₁, D₂₂, D₁₂, and D₂₁) for aqueous solutions containing NiCl₂ and lactose, at T = 298.15 K and T = 310.15 K, and at different carrier concentrations were also measured. These data permit us to have a better understanding of the structure of these systems and the thermodynamic behaviour of NiCl₂ in different media.     

Heat of solution of polyhalite and its analogues at T = 298.15 K

Calorimetric measurements have been performed to determine the heat of dissolution of polyhalite K₂SO₄ · MgSO₄ · 2CaSO₄ · 2H₂O and its analogues K₂SO₄ · MSO₄ · 2CaSO₄ · 2H₂O (M = Mn, Co, Ni, Cu, and Zn) at T = 298.15 K. The dissolution experiments were carried out in NaClO₄ solution with varying concentrations (0.5 to 2.0) mol kg^?1. All polyhalites dissolve exothermically. Exothermicity increases with concentration of NaClO₄. An extrapolation to infinite dilution was done using the SIT model.Within the limits of experimental uncertainty, the enthalpies of dissolution for the triple salts K₂MgCa₂(SO₄)₄ · 2H₂O with M = Mg, Mn, Ni, and Zn coincide. The value for the cobalt salt is noticeably less exothermic. Dissolution enthalpy of leightonite K₂CuCa₂(SO₄)₄ · 2H₂O, which does not crystallize in the polyhalite structure, deviates considerably within the series.     

Density and activity of pertechnetic acid aqueous solutions at T = 298.15 K

The previous isopiestic investigations of HTcO₄ aqueous solutions at T = 298.15 K are believed to be unreliable, because of the formation of a ternary mixture at high molality. Consequently, published isopiestic molalities for aqueous HTcO₄ solutions at T = 298.15 K were completed and corrected. Binary data (variation of the osmotic coefficient and activity coefficient of the electrolyte in solution in the water) at T = 298.15 K for pertechnetic acid HTcO₄ were determined by direct water activity measurements. These measurements extend from molality m = 1.4 mol · kg⁻¹ to m = 8.32 mol · kg⁻¹. The variation of the osmotic coefficient of this acid in water is represented mathematically. Density variations at T = 298.15 K are also established and used to express the activity coefficient values on both the molar and molal concentration scale. The density law leads to the partial molar volume variations for aqueous HTcO₄ solutions at T = 298.15 K, which are compared with published data.     

Effect of potassium chloride on diffusion of theophylline at T = 298.15 K

Ternary mutual diffusion coefficients measured by Taylor dispersion method (D₁₁, D₂₂, D₁₂, and D₂₁) are reported for aqueous solutions of KCl + theophylline (THP) at T = 298.15 K at carrier concentrations from (0.000 to 0.010) mol · dm^?3, for each solute. These diffusion coefficients have been measured having in mind a better understanding of the structure of these systems and the thermodynamic behavior of potassium chloride and theophylline in solution. For example, from these data it will be possible to make conclusions about the influence of this electrolyte in diffusion of THP and to estimate some parameters, such as the diffusion coefficient of the aggregate between KCl and THP.     

Diffusion of sodium alginate in aqueous solutions at T = 298.15 K

Taylor dispersion technique was used for measuring mutual diffusion coefficients of sodium alginate aqueous solutions at T = 298.15 K, by using as carrier stream solution both pure water and solutions of this polyelectrolyte at a slightly different concentration. The limiting values found at infinitesimal ionic strength, D⁰, were determined by extrapolating to c → 0. These studies were complemented by molecular mechanics calculations. From the experimental data, it was possible to estimate both the limiting conductivity and the tracer diffusion coefficient values for the alginate anion, and the hydrodynamic radius of the sodium alginate (NaC₆H₇O₆), as well as to discuss the influence of the kinetic, thermodynamic and viscosity factors on the diffusion of sodium alginate in aqueous solutions at finite concentrations. Thus, the aim of our innovative research is to contribute to a better understanding of the structure and the thermodynamic behavior of these polymeric systems in solution and supplying the scientific and technological communities with data on these important parameters in solution transport processes.     

Thermodynamic properties of chiral fenchones in some solutions at T = 298.15 K

Excess enthalpies for binary mixtures (S-fenchone + ethanol/benzene/cyclohexane/carbon tetrachloride) were measured over the whole concentration at T = 298.15 K. The experimental results were compared with the values obtained from the UNIFAC, COSMO-RS and regular solution theory. Excess enthalpies of binary mixtures of R-fenchone and S-fenchone in ethanol, benzene, and cyclohexane solution at different specified mole fractions of fenchone have been measured under the same conditions. With the decreasing of the specified mole fraction of fenchone in different solutions, the excess enthalpies of mixing of chiral orientated solutions increased and became close to zero. Results were compared with those of chiral limonene in ethanol solution. Pair interaction energies were also investigated.     

Effect of hydrolysis on the diffusion of ferric sulphate in aqueous solutions at T = 298.15 K

Diffusion coefficients of the Fe₂(SO₄)₃)/water system at T = 298.15 K and at concentrations between 0.050 mol · dm⁻³ and 0.200 mol · dm⁻³ have been measured, using a conductimetric cell and an automatic apparatus to follow diffusion. The cell uses an open-ended capillary method. A conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries at recorded times. These data are discussed on the basis of the Onsager–Fuoss model. The diffusion of Fe₂(SO₄)₃ is clearly affected by the Fe (III) hydrolysis. These data permit us to have a better understanding of the structure of such systems and the thermodynamic behaviour of ferric sulphate in different media.     

Activity coefficients of CaCl2 in (serine or proline + water) mixtures at T = 298.15 K

Activity coefficients for the (CaCl₂ + amino acid + water) system were determined at a temperature of 298.15 K using ion-selective electrodes. The range of molalities of CaCl₂ is (0.01 to 0.20) mol · kg^?1, and that of amino acids is (0.10 to 0.40) mol · kg^?1. The activity coefficients obtained from the Debye–Hückel extended equation and the Pitzer equation are in good agreement with each other. Results show that the interactions between CaCl₂ and amino acid are controlled mainly by the electrostatic interactions (attraction). Gibbs free energy interaction parameters (g_EA) and salting constants (k_S) are positive, indicating that these amino acids are salted out by CaCl₂. These results are discussed based on group additivity model.     

Thermodynamics of solvation of some small peptides in water at T = 298.15 K

The enthalpies of solution in water, Δ_solH_m, of some small peptides, namely the amides of five N-acetyl substituted amino acids of glycine, l-alanine, l-proline, l-valine, l-leucine and two cyclic anhydrides of glycine and l-sarcosine (diketopiperazines), were measured by isothermal calorimetry at T = (296.84, 306.89, and 316.95) K. The enthalpies of solution at infinite dilution at T = 298.15 K were derived and added to the enthalpies of sublimation, ${\mathrm{\Delta }}_{\mathrm{sub}}{H}_{\mathrm{m}}^{\circ }$, at the same temperature, to obtain the corresponding solvation enthalpies at infinite dilution, ${\mathrm{\Delta }}_{\mathrm{solv}}{H}_{\mathrm{m}}^{\infty }$. Moreover, the partial molar heat capacities at infinite dilution at T = 298.15 K, $C_{p\text{,}2}^{\infty }$, were calculated by adding molar heat capacities of solid small peptides, C_p,m(cr), to the ${\mathrm{\Delta }}_{\mathrm{sol}}{C}_{p\text{,}\mathrm{m}}^{\infty }$ values obtained from our experimental data. CH₂ group contributions, in terms of solvation enthalpy and partial molar heat capacity, were −3.2 kJ · mol⁻¹ and 89.3 J · K⁻¹ · mol⁻¹, respectively, in good agreement with the literature data. Simple additive methods were used to estimate the average molar enthalpy of solvation and partial molar heat capacity at infinite dilution for the 1/2CONH⋯CONH functional group in the small peptides. Values obtained were −46.7 kJ · mol⁻¹ for solvation enthalpy and −42.4 J · K⁻¹ · mol⁻¹ for partial molar heat capacity, significantly lower than values obtained for the CONH functional group in monofunctional model compounds.     

Hygrometric determination of water activities,osmotic and activity coefficients of (NaCl + KCl)(aq) at T = 298.15 K

The purpose of this study is to present a model for the prediction of water activity in multicomponent aqueous solutions containing a common ion from available binary data. The hygrometric method has been used to measure relative humidities for the aqueous electrolyte mixture (NaCl  +  KCl)(aq) at total molalities ranging from 0.2 mol · kg ^− 1to saturation for different molal ratiosr of NaCl(aq) to KCl(aq) with r =  (0.2, 0.5, 1, 2, 3, and 4) at T =  298.15 K. The data obtained have been used to determine water activities and osmotic coefficients. The results show that the values of water activities and osmotic coefficients calculated with the proposed model are close to the experimental ones. This model is also compared with four other models (RS, Pitzer, RWR, and LS II) over the range of the studied total molalities. From the measurements, the activity coefficients of NaCl(aq) and KCl(aq) in the mixture have also been determined.     

Excess properties of the binary mixtures of methylcyclohexane + alkanes (C6 to C12) at T = 298.15 K to T = 308.15 K

Experimental values of density, viscosity, and refractive index at T = (298.15, 303.15, and 308.15) K while the speed of sound at T = 298.15 K in the binary mixtures of methylcyclohexane with n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-dodecane, and iso-octane are presented over the entire mole fraction range of the binary mixtures. Using these data, excess molar volume, deviations in viscosity, molar refraction, speed of sound, and isentropic compressibility are calculated. All the computed quantities are fitted to Redlich and Kister equation to derive the coefficients and estimate the standard error values. Such a study on model calculations in addition to presentation of experimental data on binary mixtures are useful to understand the mixing behaviour of liquids in terms of molecular interactions and orientational order–disorder effects.     

The dilution enthalpies of l-prolinol in N,N-dimethylformamide aqueous solutions at T = 298.15 K

Values of the enthalpy of dilution were measured for l-prolinol in pure water and N,N-dimethylformamide (DMF) aqueous solutions with various mass fractions of DMF at T = 298.15 K using a flow-mixing microcalorimeter. A pseudo phase equilibrium model was proposed to simplify the complex aggregation equilibrium and interpret the abnormality in the dilution enthalpy, which together with the McMillan–Mayer approach was used to fit the experimental data to obtain the enthalpic pairwise interaction coefficients and the molar aggregation enthalpies of l-prolinol in DMF aqueous solutions. The results are discussed in terms of the hydrophobic interaction and the interactions between the solvated solutes.     

Activity coefficients of electrolyte and amino acid in the systems (water + potassium chloride + dl -valine) at T = 298.15 K and (water + sodium chloride + l -valine) at T = 308.15 K

The activity coefficient data were reported for (water  +  potassium chloride  + dl -valine) at T =  298.15 K and (water  +  sodium chloride  + l -valine) at T =  308.15 K. The measurements were performed in an electrochemical cell using ion-selective electrodes. The maximum concentrations of the electrolytes and the amino acids studied were 1.0 molality and 0.4 molality, respectively. The results of the activity coefficients of dl -valine are compared with the activity coefficients of dl -valine in (water  +  sodium chloride  + dl -valine) system obtained from the previous study. The results show that the presence of an electrolyte and the nature of its cation have a significant effect on the activity coefficient of dl -valine in aqueous electrolyte solutions.