Aqueous solutions of copper(II) sulfate have been studied by dielectric relaxation spectroscopy (DRS) over a wide range of frequencies (0.2 less, similar nu/GHz < or = 89), concentrations (0.02 < or = m/mol kg(-1) less, similar 1.4), and temperatures (5 < or = t/ degrees C < or = 65). The spectra show clear evidence for the simultaneous existence of double-solvent-separated, solvent-shared, and contact ion pairs at all temperatures, with increasing formation especially of contact ion pairs with increasing temperature. The overall ion association constant corresponding to the equilibrium: Cu2+(aq) + SO4(2-)(aq) right harpoon over left harpoon CuSO4(0)(aq) was found to be in excellent agreement with literature data over the investigated temperature range. However, the precision of the spectra and other difficulties did not allow a thermodynamic analysis of the formation of the individual ion-pair types. Effective hydration numbers derived from the DRS spectra were high but consistent with simulation and diffraction data from the literature. They indicate that both ions influence solvent water molecules beyond the first hydration sphere. The implications of the present findings for previous observations on copper sulfate solutions are briefly discussed.

A detailed investigation of aqueous solutions of magnesium sulfate has been made by dielectric relaxation spectroscopy (DRS) over a wide range of frequencies (0.2 MgSO(4) (0)(aq) is in good agreement with literature data at lower temperatures but is overestimated at higher temperatures due to processing difficulties. Despite the limited precision of the spectra, analysis of the individual steps in the ion-association process is possible for the first time. The 2SIPs are formed with little disturbance to their hydration shells, the (partial) destruction of which appears to occur mostly during the formation of SIPs. Effective hydration numbers derived from the DRS spectra indicate that both Mg(2+) and SO(4) (2-) influence solvent water molecules beyond their first hydration spheres but that MgSO(4)(aq) is less strongly hydrated than the previously studied CuSO(4)(aq).

The complexation of copper(I) by cyanide ions (CN − ) in aqueous solution has been studied by glass electrode potentiometry at 25°C and ionic strengths (I) of 1, 3 and 5 M in NaCl media. Overall formation constants, β n , for the equilibria: Cu + (aq) + nCN − (aq) ⇌ Cu(CN) n (n−1)− (aq) with n = 2, 3 and 4, were quantified, along with the ionization constant (K w ) of water and the acid dissociation constant (K a ) of HCN(aq). The solubility constants *K sn for the equilibria: CuCN(s) + (n − 1)HCN 0 (aq) ⇌ Cu(CN) n (n −1)− (aq) + (n − 1)H + (aq) were also determined from a re-analysis of published solubility data for CuCN(s) in acidic cyanide solutions at I = 1 M(NaCl) and 25°C. Because of the instability of uncomplexed Cu + (aq) and parameter correlations in the data, neither β 1 nor the solubility product K s0 (CuCN(s) ⇌ Cu + (aq) + CN − (aq)) could be reliably determined from the present data although estimates are presented.

Isobaric volumetric heat capacities of aqueous solutions of K4Fe­(CN)6, K3Fe­(CN)6, K3Co­(CN)6, K2Ni­(CN)4, and KAg­(CN)2 have been measured at 298.15 K over the approximate concentration range 0.02 to 0.4 mol·kg–1 using a Picker flow calorimeter. These data were combined with measured densities to calculate the corresponding apparent molar isobaric heat capacities, C pϕ. The values so obtained were fitted as a function of concentration using an extended Redlich–Rosenfeld–Meyer-type equation to provide the standard state (infinite dilution) quantities, C pϕ o, for each salt. The C pϕ values for all the salts studied showed similar dependences on concentration, with a slight upward curvature at higher molalities, possibly due to anion aggregation. Values of C pϕ o for the aquated cyanometallate anions were estimated using the tetraphenylphosphonium tetraphenylborate extrathermodynamic assumption and were little affected by ion size but were strongly dependent on ionic charge, ranging from −191 J·K–1·mol–1 for [Fe­(CN)6]4–(aq) to +178 J·K–1·mol–1 for [Ag­(CN)2]−(aq). This indicates that the differences between the anions are mostly due to their effect on the surrounding water molecules.

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.