Structure-making/breaking property and thermodynamic parameters of MgSO4 in water, ethanol, and water–ethanol mixtures

Abstract

The densities of magnesium sulfate (MgSO₄) solutions in water, ethanol, and water–ethanol mixtures, and the respective solvents, were determined by RD bottle at temperatures of 303.15–323.15 K. The density of the solvents increased with the addition of MgSO₄, while a temperature rise had a decreasing effect. The densities of the solvents and solutions were utilized for evaluating the apparent molar volume (V_ϕ) of MgSO₄ solutions. The V_ϕ decreased with increasing concentration of MgSO₄, whereas it increased with a change in solvent from pure water to ethanol and with a temperature rise. Limiting apparent molar volume (V^o_ϕ) was evaluated by Masson's and Redlich, Rosenfeld, and Meyer's (RRM) equations. V^o_ϕ was split into its ionic components, to evaluate the ionic contributions. The structure-making/breaking nature of MgSO₄ was characterized by Hepler's constant (δ²V^o_ϕ/δT²)_P. Hepler's constant is negative, confirming the structure-breaking conduct of MgSO₄, which is very well supported by the positive values of limiting apparent molar volume of transfer (Δ_tV^o_ϕ) and trends of thermodynamic parameters.