Densities and Apparent Molar Volumes of Aqueous Solutions of Metal Nitrates to Elevated Temperatures: 2. Nickel Nitrate, including Some Ternary Mixtures with Nitric Acid

Densities of binary aqueous solutions of nickel nitrate, Ni(NO3)2(aq), have been measured using two vibrating-tube densimeters, collectively covering the temperature range 293.15 ≤ T/K ≤ 473.15, at molalities 0.01 ≲ m/mol·kg–1 ≲ 5.0 and pressures p = 0.1 or 2.0 MPa. These data were used to calculate the corresponding apparent molar volumes, Vϕ, which were then fitted with semiempirical equations to obtain the standard values, Vϕo. At 298.15 K and 0.1 MPa, the present results agreed well with most literature data, with differences in Vϕ mostly <0.5 cm3·mol–1. Comparisons under other conditions were restricted by the limited literature data but agreed reasonably well up to 473.15 K. Densities were also measured for two series of ternary (Ni(NO3)2 + HNO3 + H2O) solutions: one with varying composition at constant ionic strength, I, and the other with varying I at a constant Ni2+/H+ mole ratio. These measurements showed that the volumetric properties of such mixtures could be predicted by Young’s (ideal mixing) rule using only the properties of the component binary solutions. An alternative model based on charge fractions was found to be equally useful. The present measurements considerably expand the volumetric database for Ni(NO3)2(aq).