The electric conductance of dilute sulfuric acid in water: a new theoretical interpretation

Abstract

The variation of the activity coefficient of aqueous sulfuric acid with acid concentration, solution's temperature, and solvent's (water) dielectric constant, clearly fits a typical strong 1–3 electrolyte behaviour [Fraenkel, J. Phys. Chem. B. 116, 11662 (2012)]. Therefore, the aqueous acid was proposed to have the molecular formula H4SO5, and to dissociate to 3H+ (3H3O+) and 1HSO5 3−. When the above study was reported, electric conductivity data of the aqueous acid could not be theoretically interpreted to prove or disprove the 1–3 electrolyte behaviour, due to the lack of an appropriate conductance theory. The improved Debye–Hückel–Onsager (DHO) theory, DHO–SiS, recently reported [Fraenkel, Phys. Chem. Chem. Phys. 20, 29896 (2018)], allows, unlike its parent theory, a quantitative analysis of strong 1–1, 1–2 and 1–3 electrolytes. A good-to-excellent theory–experiment agreement is achieved for dilute aqueous H2SO4 at 0–50°C, but only if the acid is considered, as before, as a strong 1–3 electrolyte; the new analysis thus corroborates the previous activity-based findings. In contrast, the conductance of dilute sulfuric acid in pure methanol follows the conventional H2SO4 dissociation pattern, exhibiting a ‘mixed 1–1/1–2’ electrolyte behaviour.