Densities and Apparent Molar Volumes of Aqueous Solutions of Li₂SO₄ and LiCF₃SO₃ at Temperatures from 293 to 343 K

Abstract

Densities of aqueous solutions of lithium sulfate (Li 2 SO 4 ) and lithium trifluoromethanesulfonate (LiCF 3 SO 3 ) at solute molalities ranging from 0.05 to 2.7 or 9.6 mol•kg −1 , respectively, have been measured by vibrating-tube densimetry over the temperature range 293.15 ≤ T/K ≤ 343.15 at 0.1 MPa pressure. The apparent molar volumes (V ϕ ) of Li 2 SO 4 (aq) and LiCF 3 SO 3 (aq) derived from these data were fitted using an extended Redlich−Rosenfeld−Meyer equation. The V ϕ values for the two systems exhibit quite different dependences on concentration and temperature, as do the isobaric expansibilities. A combination of the present and literature data reveals that the densities for Li 2 SO 4 (aq) given in standard compilations are unreliable at low concentrations. Comparison of the present results with literature data for related salts shows that V ϕ (Li n X) and V ϕ (Na n X) exhibit a crossover at ≈0.5 mol•kg −1 for both systems, similar to those observed previously for other lithium and sodium salts. Consideration of an appropriate series of lithium salts suggests that anion size influences departures from the Debye−Huckel limiting law for volumes, whereas for a series of sulfate salts cation size does not appear to be a major factor.

Densities and Molar Volumes of Aqueous Solutions of Li2SO4 at Temperatures from 343 to 573 K

“…that of Na + (aq) and K + (aq). Similar effects have been noted for the volumes 8 and heat capacities 15 of a number of other lithium salts in aqueous solution under near-ambient conditions.…”

“…It can be noted that, consistent with its diminution of the expansibility of the solutions cf. pure water (Figure 11), dissolved Li 2 SO 4 continues to act, as at near-ambient temperatures, 8 as a solvent structure maker under all of the investigated conditions. The same appears to be true for Na 2 SO 4 and K 2 SO 4 , suggesting that, at least for these salts, the effect of the anion on solvent structure far outweighs those of the cations.…”

“…Data Fitting. The temperature and molality dependences of V ϕ were described using an extended Redlich−Rosenfeld− Meyer (RRM) equation: 8,23…”

“…7 The volumetric properties of Li 2 SO 4 (aq) at temperatures up to 343 K and concentrations up to near-saturation have been reviewed and quantified in an earlier paper from this laboratory. 8 For convenience the available literature sources for the densities of Li 2 SO 4 (aq) at elevated temperatures 9−13 are listed in Table 1. Of the various experimental investigations at T > 343 K, the approximate pycnometric data of Maksimova et al 10 at T ≤ 363 K are of historic interest only.…”

Comparative Study of Solvation Behaviour of Oxidising Agents Like Kclo3, Kbro3 and KIO3 in Aqueous Solvent Systems at Different Temperatures

“…The measured density data is used to evaluate the apparent molar volumes ∅ V , using the following equation [10][11][12][13] .…”