Interactions of Na-Salts and 1-Propanol in 1-Propanol−Na-Salt−H2O Systems: Toward an Understanding the Hofmeister Series (IV)

Structure of Sulfuric Acid Solutions Using Pair Distribution Function Analysis

Solvation and mesoscale ordering of sulfuric acid and other strong acid solutions leads to suppressed freezing points and strong rheological changes with varying concentration. While the solid-state structures are well-understood, studies focused on the evolving solvation structure in the solution phase have probed a limited concentration range (∼1-6 M). This study applies a total scattering approach in both the wide-angle X-ray scattering (WAXS) and pair distribution function (PDF) regimes to elucidate the evolving solvation structure over its full range of acid concentration (0-18 M). The emergence of a prepeak in the WAXS regime at intermediate concentrations indicates a transition from noninteracting sulfate molecules in the dilute limit to sterically limited sulfates at concentrations near its deep eutectic point. Fits to the PDF data quantify this trend, showing a transition from octahedrally hydrated sulfates up to 6-7 M concentrations, followed by gradual dehydration, and eventually reaching a solution structure similar to that of water-in-salt electrolyte systems at high acid concentrations.

Effects of the Hofmeister series of sodium salts on the solvent properties of water

The solvent features of water (solvent dipolarity/polarizability, π*, hydrogen bond donor acidity, α, and hydrogen bond acceptor basicity, β) were examined in aqueous solutions of Na₂SO₄, NaF, CH₃COONa, NaCl, NaBr, NaI, and NaClO₄ at concentrations of each salt from 0 to 1.0 M (up to 2.0 M for NaClO₄). The solvent features of water in solutions of different concentrations for each salt were found to be linearly related as π* = z + aα + bβ. The coefficients of this relationship were suggested to represent the signature of the salt effect on the solvent features of water. The normalized distances for each salt were calculated using glucose as a reference compound. These distances may be used as the relative measures of the salt-water interactions. It is demonstrated that the distances for all salts examined are interrelated with structural water entropies and static polarizabilities of anions. It is shown that the distance may be used as a measure of the relative effects of salts on precipitation of ferric oxide, excessive chemical potential of propanol in salt solutions, surface tension, and viscosity. The distance represents the relative measure of the salt effect on the solvent features of water in a salt solution. The examples presented confirm that the approach used does enable us to characterize the differences between the effects of salts in the Hofmeister series on the properties of water.