Densities and Apparent Molar Volumes of Aqueous Solutions of Sodium and Potassium Triflates up to High Concentrations at Temperatures 293.15–343.15 K

Abstract

Densities of aqueous solutions of sodium triflate (NaTf) and potassium triflate (KTf), where Tf– is the trifluoromethanesulfonate ion (CF3SO3–), have been measured by vibrating-tube densimetry at temperatures from 293.15 to 343.15 K at 5 K intervals. Concentrations ranged from 0.02 to 7.0 mol·kg–1 for NaTf and from 0.03 to 15.7 mol·kg–1 for KTf. The present results for NaTf are in good agreement with literature data where comparisons are possible but considerably extend the existing database. No volumetric data appear to have been published previously for KTf. Apparent molar volumes (Vϕ) calculated from the densities were used to test three semi-empirical fitting models based on extended Redlich–Rosenfeld–Meyer, Pitzer, and extended Debye–Huckel equations. All three equations gave satisfactory fits over the studied ranges of temperature and concentration, but the Pitzer model required fewer adjustable parameters to provide a similar quality of fit for both salt systems. The values of standard partial molar volumes, Vo, for NaTf(aq) and KTf(aq) derived from various models were combined with the relevant literature data to provide the estimates of Vo(Tf–, aq) as a function of temperature, using an appropriate extrathermodynamic assumption.