Densities and Apparent Molar Volumes of Aqueous Solutions of Zinc Sulfate at Temperatures from 293 to 373 K and 0.1 MPa Pressure

Densities of up to 16 aqueous solutions of zinc sulfate have been measured at 5 K intervals over the temperature range of 293.15 ≤ T/K ≤ 353.15 at concentrations 0.004 ≤ m/mol·kg-1 ≤ 2.5 and 0.1 MPa pressure using a commercial glass vibrating tube densimeter (vtd). Particular attention was paid to establishing the concentrations and pH values of the solutions. Densities of the same solutions were also measured at 343.15 and 373.15 K at 0.3 MPa pressure in a purpose-built high-temperature Pt/Rh-vtd. The two sets of densities at 343.15 K were in excellent agreement, with an average difference of 0.01%. Apparent molar volumes, Vφ, calculated from the densities were fitted with an extended Redlich-Rosenfeld-Meyer equation. However, the standard (infinite dilution) molar volumes, Vo(ZnSO4, aq), derived via this equation differed significantly (by up to 2 cm3·mol-1) from the values obtained by ionic additivity using literature data. This difference is probably mostly due to ion-pairing effects.