Investigating the phase diagram-ionic conductivity isotherm relationship in aqueous solutions of common acids: hydrochloric, nitric, sulfuric and phosphoric acid

Hilal Al-Salih; Yaser Abu-Lebdeh

doi:10.1038/s41598-024-56552-x

Investigating the phase diagram-ionic conductivity isotherm relationship in aqueous solutions of common acids: hydrochloric, nitric, sulfuric and phosphoric acid

Sci Rep. 2024 Apr 3;14(1):7894. doi: 10.1038/s41598-024-56552-x.

Authors

Hilal Al-Salih¹, Yaser Abu-Lebdeh²

Affiliations

¹ Energy, Mining, and Environment Research Centre, National Research Council of Canada, 1200 Montreal Road, Ottawa, ON, K1A 0R6, Canada.
² Energy, Mining, and Environment Research Centre, National Research Council of Canada, 1200 Montreal Road, Ottawa, ON, K1A 0R6, Canada. Yaser.Abu-Lebdeh@nrc-cnrc.gc.ca.

Abstract

The relationship between phase diagram features around the solid-liquid equilibrium region and ionic conductivity in aqueous solutions is not well understood over the whole concentration range as is the case for acidic aqueous solutions. In this work, we have studied the ionic conductivity (κ) as a function of molar fraction (x) and temperature (T) for four acid/water solutions namely, monoprotic hydrochloric acid (HCl) and nitric acid (HNO₃), diprotic sulfuric acid (H₂SO₄) and triprotic phosphoric acid (H₃PO₄) along with their binary phase diagrams. The connection between the main features of the phase diagrams and the trends in the ionic conductivity isotherms is established with a new insight on the two pertinent dominant conductivity mechanisms (hopping and vehicular). Ionic conductivity at different temperatures were collected from literature and fitted to reported isothermal (κ vs. x) and iso-compositional (κ vs. T) equations along with a novel semi-empirical equation (κ = f (x, T)) for diprotic and triprotic acids. This equation not only has the best fit for acids with different valency; but also contains four parameters, less than any other similar equation in literature. This work is one of few that advances the understanding of the intricate relationship between structure and ionic transport in various acidic aqueous solutions.

Keywords: Acids; Aqueous electrolyte; Hydrochloric acid; Ionic conductivity; Liquid solution structure; Nitric acid; Phase diagram; Phosphoric acid; Sulfuric acid.