Ionic interactions of copper(ii) sulfate in water, aqueous maltose, and aqueous lactose at different temperatures: a volumetric and thermodynamic study

Abstract

Densities of pure water, aqueous maltose, and aqueous lactose solvents were measured at temperatures of 303.15, 308.15, 313.15, 318.15, and 323.15 K before and after the addition of different concentrations of copper(II) sulfate. The density of water, aqueous maltose, and aqueous lactose solvents increased with the addition of copper(II) sulfate, while an increase in temperature decreased the density. The apparent molar volume (V_ϕ) of copper(II) sulfate solutions was calculated from the density data by using a standard mathematical relationship. The V_ϕ decreased with the increase in the concentration of copper(II) sulfate and is also affected by the nature of the solvent and temperature. The limiting apparent molar volume (V⁰_ϕ) was evaluated by using Masson's and Redlich, Rosenfeld, & Meyer's equations. The structure-breaking or structure-making behavior of copper(II) sulfate was evaluated by calculating Hepler's constant (δ²V⁰_ϕ/δT²)_P. A negative value of Hepler's constant in water and aqueous maltose solvent confirmed the structure-breaking behavior of copper(II) sulfate, whereas a positive value of Hepler's constant in aqueous lactose solvent is indicative of the structuring of the solvent. The limiting apparent molar expansibility (E⁰_ϕ) and isobaric thermal expansion coefficient (α_p) were also evaluated from the V_ϕ to provide supporting evidence for the obtained conclusions.