Liquid densities, heat capacities, refractive index and excess quantities for {protic ionic liquids + water} binary system

Densities, ρ, of aqueous solutions of the room temperature protic ionic liquid (PIL), pyrrolidinium nitrate are determined at the atmospheric pressure over the temperature range from (283.15 to 323.15) K and within the whole composition range. The molar isobaric heat capacities, Cp, and refractive index, nD, of {PIL + water} binary system are measured at 298.15 K. The excess molar volumes VE, excess molar isobaric heat capacities CpE, and deviation from ideality of refractive index Δϕn, of pyrrolidinium nitrate aqueous solutions were deduced from the experimental results as well as apparent molar volumes Vϕ  , partial molar volumes V¯m,i, and thermal expansion coefficients αp. The VE values were found to be positive over the entire composition range at all temperatures studied therein, whereas deviations from ideality were negative for refractive index Δϕn. The volumetric properties of binary mixtures containing water and four other protic ionic liquids, such as pyrrolidinium hydrogen sulfate, pyrrolidinium formate, collidinium formate, and diisopropyl-ethylammonium formate were also determined at 298.15 K. Results have been then discussed in terms of molecular interactions and molecular structures in these binary mixtures.