Second ionization constant of sulfuric acid in H2O and D2O from 150 to 300 °C at p = 11.5 MPa using flow AC conductivity

Abstract

A custom-built flow-through AC conductivity instrument was used to measure the deuterium isotope effect on the ionization quotient of bisulfate from 150 to 300 °C, at p = 11.5 MPa. Standardized solutions of KCl, HCl, KOH, KHSO₄, K₂SO₄, and H₂SO₄ were prepared in light and heavy waters and their conductivities were measured and fitted with the Quint–Viallard conductivity model to obtain single ion conductivities at infinite dilution for K⁺, Cl⁻, H⁺, OH⁻, HSO₄⁻, and SO₄²⁻. These are the first conductivities of DSO₄⁻ and SO₄²⁻ measured in heavy water at any temperature, and the first ionization constants for bisulfate reported in heavy water above 225 °C. The deuterium isotope effect on the chemical equilibrium constant, ΔpK_2a = pK_2a,D − pK_2a,H, was found to increase with temperature, in contrast to the behaviour seen for other simple oxyacids.