Heat Capacities of Aqueous Solutions of Lithium Sulfate, Lithium Perchlorate, and Lithium Trifluoromethanesulfonate at 298.15 K

Abstract

Isobaric heat capacities of aqueous solutions of Li 2 SO 4 , LiClO 4 , and LiCF 3 SO 3 have been measured at 298.15 K and 0.1 MPa up to high concentrations using a Picker flow calorimeter. Apparent molar isobaric heat capacities, C p,ϕ , derived from these data were fitted within the limits of experimental precision with an extended Redlich−Rosenfeld−Meyer type of equation, which was also used to estimate the standard state (infinite dilution) quantities, C p,ϕ o , for each salt. The latter values were combined with appropriate literature data to produce a robust estimate of C p,ϕ oWhere comparison was possible, C p,ϕ (Li n X) values were closely parallel to those of the corresponding acids over the whole concentration range, even when the shapes of the curves were highly unusual. In contrast, C p,ϕ (Na n X) values always exhibited a crossover with the lithium salt data at a concentration of about 1 mol•kg −1 , which appears to reflect differences in the hydration of the two cations.

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.…”

“…Briefly, a concentrated (near-saturated) stock solution of Li 2 SO 4 (aq) solution was prepared by neutralizing solid Li 2 CO 3 with H 2 SO 4 , heating to near boiling, sparging with nitrogen gas to remove CO 2 , and filtering (0.45 μm). Further details are given elsewhere . The main impurities in Li 2 CO 3 (s) as stated by the manufacturer were sulfate anions (≤0.3 mass %) and sodium cations (≤0.1 mass %).…”

“…Further details are given elsewhere. 15 The main impurities in Li 2 CO 3 (s) as stated by the manufacturer were sulfate anions (≤0.3 mass %) and sodium cations (≤0.1 mass %). The presence of moderate amounts of Na + has a negligible effect on the apparent molar volume of lithium salts.…”

“…The stock solution of Li 2 SO 4 (aq) was analyzed in triplicate by evaporative gravimetry, initially at 60 °C, then overnight at 190 °C under reduced pressure (p ≈ 5 Pa); the concentration of the solute was reproducible to ±0.01% (relative). Further checks on the accuracy of the concentrations of the solutions employed are described elsewhere, 15 but taking all factors into account the overall relative uncertainty is estimated to be ±0.05%. Working solutions were prepared by weight dilution using freshly degassed high-purity water (Ibis Technology, Australia); buoyancy corrections were applied throughout.…”

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

“…Common triflate salts are also mostly straightforward to recrystallize, typically from water or alcohols. 6 Despite the applications (both actual and potential) of triflate salts, the physicochemical properties of their aqueous solutions, even including those of the alkali metal salts, 7 are frequently rather poorly characterized. Of the many physicochemical properties of solutions, densities, and the molar volumes derived from them, are of particular interest as they are required for mass balance calculations for engineering purposes and for the interconversion of mass-and volumebased units.…”