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 Na2SO4, H2SO4, 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. 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 NaSO4 -, Na2SO4 0, HSO4 -, H2SO4 0, and NaHSO4 0. The adjustable parameters of this model are the dissociation constants of the SO4 - species and the H+, SO4 -2, and HSO4 - conductances (ion mobilities) at infinite dilution. For the 673 K and 230 kg m-3 state point with the lowest dielectric constant, ε = 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 H9(SO4)5 - gave satisfactory fits to the conductance data at the higher concentrations.