Thermodynamic properties of aqueous solutions of two ammonium-based protic ionic liquids at 298.15 K

Densities ( ρ ), refractive indices ( n D ) and electrical conductivities ( κ ) of ethylammonium acetate (N2Ac) protic ionic liquid   +   water and propylammonium acetate (N3Ac) protic ionic liquid   +   water binary mixtures over the entire composition range were measured at 298.15   K under atmospheric pressure. The excess molar volumes ( V E ), apparent molar volumes ( V ϕi ), partial molar volumes ( V ¯ m , i ${\overline{V}}_{\text{m},i}$ ) and excess partial molar volumes ( V ¯ m , i E ${\overline{V}}_{\text{m},i}^{\text{E}}$ ) of the binary mixtures were calculated from the density data. The refractive index deviations (Δ n D ) of the binary mixtures were determined using the refractive index data. The excess molar volumes and refractive index deviations were correlated with the Redlich–Kister equation. The excess molar volumes of the above-mentioned systems are negative over the whole composition range, while the refractive index deviations are positive. The concentration dependence of electrical conductivity was fitted according to the empirical Casteel–Amis equation. The intermolecular interactions and structural effects were analyzed on the basis of the measured and the derived properties.