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

Densities of aqueous solutions of the strong electrolytes sodium perchlorate, potassium perchlorate, and potassium chloride have been measured by vibrating-tube densimetry at 5 K intervals over the temperature range 293.15 ≤ T (K) ≤ 343.15 up to near-saturation concentrations (for NaClO4 and KClO4) or to about 2 mol·kg–1 (for KCl) at 0.1 MPa pressure. Particular attention was paid to solute purity and solution composition. The densities were used to calculate the corresponding apparent molar volumes, V ϕ, which considerably extend and improve the quality of the volumetric database for these salts, especially with respect to temperature. Where comparisons were possible, the present V ϕ results agreed well with most literature data, with the significant exception of NaClO4(aq) at higher temperatures. The V ϕ values were extrapolated to infinite dilution using an extended Redlich–Rosenfeld–Meyer equation to yield the standard state partial molar volumes (V 2 o). A combination of these values with relevant literature data and a well-established extra-thermodynamic assumption was used to estimate the standard molar volumes, V 2 o(ion), of several key monovalent ions as functions of temperature. These values appear to be more reliable than existing estimates based on older data, and will be useful for determining volumes of other ions in aqueous solution.