Densities of ethanol and 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate [Emim] + [CF3SO3] − aqueous solutions were estimated from refractive index data at different temperatures. The results are within the confidence interval established for densities reported in the literature for these systems and with calculated by using the Dale-Gladstone equation (GD). The estimated densities in this study were used to calculate the molar volumes and partial molar volumes at infinite dilution. The partial molar volume data correlated with the solute concentration and temperature to study qualitatively the interactions present in the treated aqueous solutions. The [Emim] + [CF3SO3] − + water system has a disruptor character on water molecules, whereas in the ethanol + water system the hydrophilic effect predominates over the hydrophobic.