Volumes and Heat Capacities of Cobalt(II), Nickel(II), and Copper(II) Sulfates in Aqueous Solution

Abstract

Densities and isobaric volumetric heat capacities of aqueous solutions of the sulfate salts of cobalt(II), nickel(II) and copper(II) have been measured at 298.15 K and 0.1 MPa using vibrating tube densimetry and Picker flow calorimetry, respectively, at concentrations in the range 0.01 ≲ m/mol•kg -1 ≲ 1.5. These data were used to derive the corresponding apparent molar volumes, V, and apparent molar isobaric heat capacities, Cp.Where comparisons were possible the present V results were in good agreement with literature data. No Cp data appear to have been reported previously for any of these salts. The variations of V and Cp with concentration were well correlated using the Pitzer formalism combined with values of V o and Cp o estimated from literature data. Both V and Cp for all three salts show remarkable similarities and can be shown to lie on a common line by applying fixed addends over almost the whole concentration range studied.

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

“…The temperature dependence of V o (Tf – , aq) over the range 293.15 ≤ T /K ≤ 343.15 K was well described by The values of V o (Tf – ) as a function of temperature will be particularly useful for characterizing the standard volumes, V o (M z + ), of higher charged ( z > 1) metal cations because of the minimal tendency of Tf – to associate (ion pair) with such cations. ,, This feature is important because most of the higher valent salts that have been used to date for such purposes contained anions (such as the halide ions or sulfate) that are known to bind metal ions, at least to some extent. , As is well understood, even relatively minor levels of self-association can have significant effects on the observed V ϕ ( m ) values and can introduce serious uncertainties into their extrapolation to infinite dilution …”

“…3,6,10 This feature is important because most of the higher valent salts that have been used to date for such purposes contained anions (such as the halide ions or sulfate) that are known to bind metal ions, at least to some extent. 29,30 As is well understood, even relatively minor levels of selfassociation can have significant effects on the observed V ϕ (m) values and can introduce serious uncertainties into their extrapolation to infinite dilution. 29 ■ CONCLUSIONS Apparent molar volumes, V ϕ , for sodium and potassium triflates in aqueous solutions, derived from density measurements, vary smoothly over the temperature range 293.15 ≤ T/ K ≤ 343.15 up to very high concentrations (of ∼7 and ∼16 mol•kg −1 , respectively).…”

Understanding specific ion effects and the Hofmeister series

“…Whilst DH theory is often considered capable of only accounting for phenomena in dilute aqueous environments (o10 À3 M), for long-range electrostatic interactions it is often adequate up to concentrations of B0.5 M. 114 The extended DH model of Stokes and Robinson, 115 which includes a description of the ionic radius, is accurate up to B0.1 M. Similarly, specific ion interaction theory was developed from DH theory to estimate single ion activity coefficients at even higher concentrations (B10 M) via interaction coefficients. 116,117 The Pitzer Method 118 has become an increasingly popular tool for determining the thermodynamic properties of electrolytes [119][120][121][122] and is considered the best model for predicting ion activity coefficients to date. 123,124 Nevertheless, it too is based on DH theory, although it also accounts for the hydrated size of individual ions and their short-range binary and ternary interactions via a virial expansion (thereby requiring additional empirical parameterisation).…”

Thermodynamic model for CoSO4(aq) and the related solid hydrates in the temperature range from 270 to 374 K and at atmospheric pressure

“…Brodale and Giauque [14] and Goldberg et al [17] have reported some heats of solution measurements for cobalt sulfate heptahydrate and hexahydrate at low concentrations and near ambient conditions. Solution heat capacities have been reported only by Akilan et al [18].…”

“…As such, experimental activity data is needed, which, unfortunately for these systems, does not appear to be available. It has been noted previously that the thermodynamic properties of the bivalent sulfates show striking similarities, as evidenced by their ion-pairing stability constants [36], osmotic coefficients [59], heat capacities and volumetric properties [18] and dielectric relaxation behaviour [37,38], to…”