Abstract

Densities of aqueous solutions of MnSO4, CoSO4, NiSO4 and CuSO4 have been measured by vibrating tube densimetry up to near-saturation concentrations over the temperature range 293.15 ≤T/K ≤ 343.15 at 5 K intervals and at 0.1 MPa pressure. Apparent molar volumes, Vϕ, calculated from the densities revealed close similarities among all four electrolytes, with their Vϕ values essentially differing by constant concentration-independent addends for each salt at each temperature. It was found that there is an almost linear relationship between Vϕ(MSO4,aq) and the M–O bond length of the hydrated cations obtained from structural studies. This relationship can be used to predict values of Vϕ(MSO4,aq) for other sulfate salts over wide ranges of concentration and temperature, providing that the requisite structural data are available. Measurements of selected ternary, quaternary and quinary mixtures of these electrolytes at constant total concentrations showed that their Vϕ values almost always exhibit linear mixing (Young’s rule) behavior at all temperatures investigated. This finding can be exploited to predict the volumetric properties of solutions containing complex mixtures of bivalent metal sulfates.