Molar heat capacity of four aqueous ionic liquid mixtures

As a continuation of our systematic study on physicochemical characterization of aqueous solution of ionic liquids, new measurements of molar heat capacity for aqueous solutions of four ionic liquids were reported. The investigated ionic liquids were 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, and 1-butyl-2,3-dimethylimidazolium hexafluorophosphate. The molar heat capacities were measured at standard pressure and over the temperature range (303.2–353.2) K using a differential scanning calorimeter (DSC) having an estimated experimental uncertainty of about ±2% with liquid water as reference. The measured molar heat capacities were reported as function of temperature and composition and the excess molar heat capacities were calculated using a Redlich–Kister type equation. For the studied ionic liquids, results showed variations in the dependence of the excess molar heat capacities on temperature and composition. The applied correlation satisfactorily represented the molar heat capacity measurements as shown by an acceptable overall average deviation of 0.09%.