Density, speed of sound, refractive index, dynamic viscosity, and surface tension measurements of 1-butyl-3-methylimidazolium methyl sulfate have been made as a function of temperature. The synthesis of the ionic liquid is given. The low viscosity of the ionic liquid suggests its use as a solvent in the extraction process for the separation of azeotropic mixtures. The thermal expansion coefficient of the ionic liquid was calculated from the ...