Chemical speciation effects on the volumetric properties of aqueous sulfuric acid solutions

Densities of fifteen aqueous solutions of sulfuric acid (H2SO4) have been measured by vibrating-tube densimetry at solute molalities (m) from (0.01 to 3.0) mol·kg−1 over the temperature range 293.15 ≤ T/K ≤ 343.15. These data have been used to calculate the corresponding apparent molar volumes Vϕ(H2SO4,aq), which represent a significant expansion of the volumetric database for this industrially-important acid. At 298.15 K the present results agree well with literature data, notably with the century-old values given in the 1926 International Critical Tables. At other temperatures, where comparisons are possible agreement with the present Vϕ values is also very satisfactory. Consistent with earlier studies, Vϕ(H2SO4,aq) was found to exhibit an abnormally-large decrease at low concentrations (m ≤ 0.1 mol·kg−1). This effect is consistent with a change in the chemical speciation of H2SO4(aq), from an essentially 1:1 electrolyte (H+(aq) + HSO4− (aq)) at higher concentrations to a predominantly 1:2 electrolyte (2H+(aq) + SO42− (aq)) in dilute solutions. The Vϕ values were modelled using variants of Young’s rule and the Pitzer formalism. Combination of these results with literature values for the standard volume V°(SO42−,aq) enabled estimation of V°(HSO4−,aq) and the standard volume change, ΔrV°, for the first protonation of the sulfate ion (H+(aq) + SO42−(aq) → HSO4−(aq)) as functions of temperature. It is shown that V°(HSO4−,aq) is sensitive to the value of the first protonation constant and probably cannot be determined to better than ± 0.3 cm3·mol−1 at present

Chemical speciation effects on the volumetric properties of aqueous sulfuric acid solutions

Densities of fifteen aqueous solutions of sulfuric acid (H2SO4) have been measured by vibrating-tube densimetry at solute molalities (m) from (0.01 to 3.0) mol·kg−1 over the temperature range 293.15 ≤ T/K ≤ 343.15. These data have been used to calculate the corresponding apparent molar volumes Vϕ(H2SO4,aq), which represent a significant expansion of the volumetric database for this industrially-important acid. At 298.15 K the present results agree well with literature data, notably with the century-old values given in the 1926 International Critical Tables. At other temperatures, where comparisons are possible agreement with the present Vϕ values is also very satisfactory. Consistent with earlier studies, Vϕ(H2SO4,aq) was found to exhibit an abnormally-large decrease at low concentrations (m ≤ 0.1 mol·kg−1). This effect is consistent with a change in the chemical speciation of H2SO4(aq), from an essentially 1:1 electrolyte (H+(aq) + HSO4− (aq)) at higher concentrations to a predominantly 1:2 electrolyte (2H+(aq) + SO42− (aq)) in dilute solutions. The Vϕ values were modelled using variants of Young’s rule and the Pitzer formalism. Combination of these results with literature values for the standard volume V°(SO42−,aq) enabled estimation of V°(HSO4−,aq) and the standard volume change, ΔrV°, for the first protonation of the sulfate ion (H+(aq) + SO42−(aq) → HSO4−(aq)) as functions of temperature. It is shown that V°(HSO4−,aq) is sensitive to the value of the first protonation constant and probably cannot be determined to better than ± 0.3 cm3·mol−1 at present

Partial molar volumes of organic solutes in water. XXIII. Cyclic ketones at T = (298 to 573) K and pressures up to 30 MPa

Density data for dilute aqueous solutions of four cyclic ketones (cyclopentanone, cyclohexanone, cycloheptanone, and cyclohexane-1,4-dione) are presented together with standard molar volumes (partial molar volumes at infinite dilution) calculated from the experimental data. The measurements were performed at temperatures from T = 298 K up to T = 573 K. Experimental pressures were close to the saturated vapor pressure of water, and (15 and 30) MPa. The data were obtained using a high-temperature high-pressure flow vibrating-tube densimeter. Experimental standard molar volumes were correlated as a function of temperature and pressure using an empirical polynomial function. Contributions of the molecular structural segments (methylene and carbonyl groups) to the standard molar volume were also evaluated and analyzed. © 2011 Elsevier Ltd. All rights reserved

Partial molar volumes of organic solutes in water. XXIV. Selected alkane-α,ω-diols at temperatures T=298K to 573K and pressures up to 30MPa

Density data for dilute aqueous solutions of three alkane-α,ω- diols (pentane-1,5-diol, octane-1,8-diol, nonane-1,9-diol) are presented together with standard molar volumes (partial molar volumes at infinite dilution) calculated from the experimental data. The measurements were performed at temperatures from T = 298 K up to T = 573 K. Experimental pressures were slightly above the saturation vapour pressure of water, and (15 and 30) MPa. The data were obtained using a high-temperature high-pressure flow vibrating-tube densimeter. Measured standard molar volumes were combined with data previously published for other members of the homologous series and discussed. Experimental standard molar volumes were correlated as a function of temperature and pressure using an empirical polynomial function. Dependences of standard molar volumes on temperature and pressure were analysed. Contributions of the methylene group to the standard molar volume were also evaluated and discussed

Volumes of aqueous solutions of CH4, CO2, H2S and NH3at temperatures from 298.15 K to 705 K and pressures to 35 MPa

Densities of dilute aqueous solutions of CH4, CO2, H2S and NH3were determined experimentally at temperatures ranging from 298.15 K to 705 K and pressures to 35 MPa by means of a vibrating tube densitometer. Appropriate techniques were developed for preparation, storing, and handling of solutions as well as their concentration determination. The apparent molar volumes were calculated and compared with available literature data. The temperature, pressure, and concentration variation of apparent molar volumes in the sub- and supercritical regions is discussed qualitatively

Volumes and heat capacities of H3BO3(aq) at temperatures from 298.15 K to 705 K and at pressures to 35 MPa

The densities and heat capacities of aqueous solutions of boric acid have been measured at temperatures from 298.15 K to 705 K and at pressures up to 35 MPa. The results are in reasonable agreement with the previous measurements at temperatures of 600 K and below. At temperatures and pressures in the neighborhood of the critical point of water, the results show the expected dependence of partial molar volume and partial molar heat capacity of H3BO3(aq) on temperature and density. The boric acid molecules have strong enough attractive interactions with water that the apparent molar volume and the apparent molar heat capacity of H3BO3(aq) show behavior with the same sign as of aqueous NaCl, although the magnitude is much less

Apparent molar volumes of aqueous solutions of sodium acetate and sodium benzoate at temperatures from 323K to 573K and pressure 10MPa

Densities of aqueous solutions of sodium acetate and sodium benzoate have been measured at 50 K intervals in the temperature range 323.15–573.15 K at constant pressure p = 10.0 MPa by vibrating tube densimetry. The solute molalities ranged from 0.05 to 4.0 mol·kg−1 (for sodium acetate) or 1.0 mol·kg−1 (for sodium benzoate). The observed densities were used to calculate apparent molar volumes, which were fitted with an extended Redlich-Rosenfeld-Meyer-type equation to yield standard partial molar volumes of the solutes at infinite dilution. No direct comparisons with literature data were possible but the present results are broadly consistent with previous studies. This work greatly expands the database for the volumetric behaviour of both solutes at high temperatures. Despite the probable presence of anion hydrolysis the volumes of both salts show the steep decrease at high temperatures typical of simple 1:1 electrolytes. As expected, the acetate ion has a smaller volume than benzoate, with the difference increasing markedly with temperature, possibly reflecting the greater hydrophobicity of the benzoate ion. Combination of the present results with appropriate literature data enabled calculation of the volume change for the neutralization reaction: HX(aq) + NaOH(aq) → NaX(aq) + H2O. The values were similar for the two solutes and show a complex dependence on temperature

Electrical conductances of aqueous electrolytes at high temperatures: Limiting mobilities of several ions including the proton and HCl dissociation constant

The empirical equation of R.H. Wood for limiting equivalent NaCl conductance and a set of equations for a proton and other ions in the aqueous solutions HCl, LiCl, NaCl, KCl, Li2SO4, K2SO4 and mixtures H2SO4–Na2SO4–H2O are revisited and compared with equations of other authors. The Wood equation is unique in an accurate description of the region close to the critical point of water. In this region the decrease in limiting ion mobilities correlate with the increase in water compressibility. In a remarkable way this effect corresponds to the decisive drop in the limiting proton mobility making it similar to the other univalent ions mobilities. Probably, in this water region the critical decrease in the number of hydrogen bonds per water molecule takes place and finally impeding the jump mechanism of proton mobility. The new high temperature data on electrical conductance of aqueous HCl are represented for molalities 10− 5–10− 3 mol kg− 1 at temperatures 298–673 K and pressures up to 28 MPa. The HCl conductivities have been fitted to the Turq, Blum, Bernard and Kunz equation using Wood mixing rule and mean spherical approximation activity coefficients. At 573–663 K the adjustable parameters are the proton limiting equivalent conductance and the HCl dissociation constant. At the measured state point of lowest water density (228.8 kg m− 3; 673 K) the additional account of ion triplets gives good fit to the data

On a temperature dependence of the van der Waals volume parameter in cubic equations of state

A dependence of the van der Waals volume parameter on temperature in cubic equations of state is analysed from the point of view of a consistency in the description of the compressed liquid region. The analysis shows that there may be a region in a PϱT space where the thermal pressure coefficient and the isobaric thermal expansion coefficient are negative if the van der Waals volume parameter decreases with increasing temperature. The results of the analysis are illustrated with a volume-translation method, which is the special case of the temperature dependence of the van der Waals volume parameter

Thermodynamics of aqueous acetic and propionic acids and their anions over a wide range of temperatures and pressures

The apparent molar volumes of aqueous acetic acid were determined [italic v (to differentiate from Times ital nu)]ia density measurements at 298 K<T<573 K and 10 MPa<p<38 MPa. The results were corrected for acid ionization and extrapolated to the standard state of infinite dilution. The new data have been combined with literature values of the standard molar volumes and standard molar heat capacities of acetic and propionic acids, and of acetate and propionate ions. Three correlation models were tested in the description of the standard thermodynamic properties at superambient conditions for the two acids and their anions. The most dependable model, inspired by the fluctuation solution theory, has been selected for generation of the recommended data. Adjustable parameters of the model were obtained by simultaneous correlation of the volumes and heat capacities together with experimental dissociation constants of the acid. It is shown that this model can be used for precise and consistent calculations of standard thermodynamic properties of the two acids and their conjugate ions over a wide range of temperatures and pressures