Densities and Apparent Molar Volumes of Aqueous Solutions of Metal Nitrates to Elevated Temperatures: 1. Zinc Nitrate, Including Some Ternary Mixtures with Nitric Acid

Densities of aqueous solutions of zinc nitrate, Zn(NO₃)₂, and some of its ternary mixtures with nitric acid have been determined by vibrating tube densimetry at temperatures 293.15 K ≤ T/K ≤ 473.15, molalities 0.02 ≲ m/mol kg^–1 ≲ 5, and pressures p = 0.102 or 2.00 MPa. Values of the apparent molar volumes (V_ϕ) of Zn(NO₃)₂(aq) derived from these data easily fitted within the estimated experimental uncertainties. At 298.15 K, the present results agreed well with literature values at m > 1 mol kg^–1. However, at lower molalities, the literature results were found to be scattered, with V_ϕ sometimes increasing anomalously with decreasing m, probably due to hydrolysis of Zn²⁺(aq). No meaningful comparisons were possible at other temperatures, but plots of the standard molar volumes, V°(Zn(NO₃)₂(aq)), against temperature, closely paralleled those of related nitrate salts. Volumes of some ternary mixtures (Zn(NO₃)₂ + HNO₃ + H₂O) were well-described by Young’s rule at low to moderate ionic strengths. The present results greatly expand the available volumetric database for both binary and ternary aqueous solutions of this industrially important electrolyte.