Raman Spectrophotometric Study of Ion Pairing in Aqueous Zinc Nitrate Systems

Abstract

Raman spectrophotometric measurements of concentrated aqueous zinc nitrate solutions at 50°C, 70°C, and 88°C are explained in terms of a model consisting of three nitrate ion species: contact ion paired nitrate, solvent separated nitrate, and ``free'' nitrate. Integrated intensity measurements are related to concentrations of each type of nitrate ion, and concentration quotients for the equilibrium reactions between species are calculated. For the free nitrate to solvent separated nitrate reaction, the apparent ΔG° is 0.89 kcal/mole at 50°C and 1.31 kcal/mole at 88°C. The apparent ΔS° is −14.5 e.u.. For the solvent separated nitrate to contact ion paired nitrate reaction the apparent ΔG° is −0.92 kcal/mole at 50°C and −2.4 kcal/mole at 88°C. The apparent ΔS° is +40 e.u..