Lubomir Hnedkovsky

Electrical conductances of aqueous Na2SO4, H2SO4, and their mixtures : Limiting equivalent ion conductances, dissociation constants, and speciation to 673 K and 28 MPa

The electrical conductivities of aqueous solutions of Na(2)SO(4), H(2)SO(4), and their mixtures have been measured at 373-673 K at 12-28 MPa in dilute solutions for molalities up to 10(-2) mol kg(-1). These conductivities have been fit to the conductance equation of Turq et al.(1) with a consensus mixing rule and mean spherical approximation activity coefficients. Provided the concentration is not too high, all of the data can be fitted by a solution model that includes ion association to form NaSO(4)(-), Na(2)SO(4)(0), HSO(4)(-), H(2)SO(4)(0), and NaHSO(4)(0). The adjustable parameters of this model are the dissociation constants of the SO(4)(-) species and the H(+), SO(4)(-2), and HSO(4)(-) conductances (ion mobilities) at infinite dilution. For the 673 K and 230 kg m(-3) state point with the lowest dielectric constant, epsilon = 3.5, where the Coulomb interactions are the strongest, this model does not fit the experimental data above a solution molality of 0.016. Including the species H(9)(SO(4))(5)(-) gave satisfactory fits to the conductance data at the higher concentrations.

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 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.