Temperature-Dependent Physicochemical Properties of Triammonium Citrate and Dipotassium <scp>l</scp> -Tartrate in Aqueous 1-Ethyl-3-methylimidazolium Methyl Sulfate Solutions

The purpose of this study is to investigate the temperature-dependent solute–solvent interactions of Triammonium citrate and Dipotassium l-tartrate in water and aqueous 1-ethyl-3-methylimidazolium methyl sulfate [Emim][MeSO4] solutions of varying molalities (0.05, 0.10, and 0.15 mol kg–1) over the temperature range of 293.15–313.15 K at a constant pressure of 101.3 kPa. Experimentally measured density, ultrasonic velocity, and viscosity data were used to evaluate volumetric, acoustic, and viscometric parameters, such as the apparent molar volume (Vϕ), partial molar volume at infinite dilution (Vϕo), limiting apparent molar expansibility (Eϕo), apparent molar isentropic compressibility (Kϕ,so), transfer parameters, hydration number (nH), and viscosity B-coefficient. The positive values of Vϕ and Vϕo, along with their increase with temperature, indicate the dominance of solute–solvent interactions over solute–solute interactions. Enhanced transfer parameters, along with a systematic decrease in hydration number in the presence of [Emim][MeSO4], indicate partial dehydration and reorganization of the solvation shell due to competitive solvation effects. The viscosity B-coefficients further support the presence of strong ion–dipole and hydrogen-bonding interactions involving the solutes, water molecules, and ionic-liquid components. Overall, the results demonstrate that [Emim][MeSO4] significantly modifies the solvation behavior and water structure around the studied salts, providing new insight into ammonium- and potassium-based organic salt interactions in aqueous ionic-liquid media.