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 (CF 3 SO 3 − ), 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 (V ϕ ) 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, V o , for NaTf(aq) and KTf(aq) derived from various models were combined with the relevant literature data to provide the estimates of V o (Tf − , aq) as a function of temperature, using an appropriate extrathermodynamic assumption.

Densities and Apparent Molar Volumes of Aqueous Solutions of NaClO4, KClO4, and KCl at Temperatures from 293 to 343 K

“…As might be expected, V o (NaClO 4 ,aq) and V o (KClO 4 ,aq) are closely parallel over the studied temperature range. Interestingly, the present volumes for the two perchlorate salts almost parallel those recently determined for the corresponding “triflate” (CF 3 SO 3 – ) salt solutions, NaTf­(aq) and KTf­(aq), suggesting that all four electrolytes are indeed fully dissociated in aqueous solution.…”

“…The overall quality of the present results and their consistency with existing literature data 35,36 is illustrated in Figure 10, which plots differences in the standard partial molar volumes for three sets of sodium and potassium salts having a common anion. As ionic volumes (see below) are strictly additive at infinite dilution, such differences should be identical at all temperatures.…”

“…32 Required data were taken from the present work (Table 8) and the literature. 35 obtained via least-squares fitting of the standard volumes reported in this work and for NaCl, 36 NaTf 35 and KTf, 35 assuming strict ionic additivity at infinite dilution, e.g., V o (MX,aq) = V o (M + ,aq) + V o (X − ,aq). The values so obtained for various ions are listed in Table 9 as functions of temperature.…”

“…Differences between the standard partial molar volumes of potassium and sodium salts, V o (KX) – V o (NaX), as functions of temperature T , with X – : black circles, Cl – ; red diamonds, ClO 4 – ; green crosses, Tf – ; blue dashed line, Cl – ; ,, orange dash-dot line, Cl – . Required data were taken from the present work (Table ) and the literature. , …”

“…Values of V o (Na + ,aq) – V o (H + ,aq) listed in column 3 of Table were obtained from data reported by Marcus and from the standard volumes of HCl, NaCl, H 2 SO 4 , Na 2 SO 4 , HNO 3 , and NaNO 3 reported by Clegg et al Values of V o (Na + ,aq) in column 4 of Table were then derived as the sum of columns 2 and 3. Standard molar volumes of the remaining ions (K + , Cl – , ClO 4 – and Tf – ) were obtained via least-squares fitting of the standard volumes reported in this work and for NaCl, NaTf and KTf, assuming strict ionic additivity at infinite dilution, e.g., V o (MX,aq) = V o (M + ,aq) + V o (X – ,aq). The values so obtained for various ions are listed in Table as functions of temperature.…”