Jump to main content
Jump to site search

Issue 10, 2003
Previous Article Next Article

Existence of two forms of nitrate ion in dilute aqueous solutions. Thermodynamic parameters of interconversion

Author affiliations

Abstract

Two well-defined isosbestic points (at 265 and 313 nm) were found in the UV absorption spectra of dilute (0.06 mol dm−3) aqueous solutions of NaNO3, KNO3 and (NMe4)NO3, measured at 13 temperatures in the (10–70) °C range. This finding, together with the apparent cation-independence of the spectra (confirmed by several statistical tests) indicates the existence of a chemical equilibrium between two species differing in the structure of solvation shells: α-NO3 ⇌ β-NO3. Assuming the constancy of standard conversion enthalpy, ΔrH°, in the experimental temperature range, a simple nonlinear programming algorithm, maximizing the linearity of the ln K° vs. 1/T relationship, was devised in order to compute optimized estimates of K° (T), ΔrH° and ΔrS°, as well as the individual spectra of α-NO3 and β-NO3 species. The following results were obtained: K° ranges from ≈0.08 (10 °C) to ≈0.25 (70 °C), ΔrH° = 15 kJ mol−1, ΔrS° = 31 J K−1 mol−1, λmax(α-NO3) = 301 nm, εmax(α-NO3) = 7.8 cm2 mmol−1, λmax(β-NO3) = 317 nm, εmax(β-NO3) = 5.7 cm2 mmol−1. Since the ΔrH° value falls inside the range of the energies of hydrogen-bond breaking and, in addition, ΔrS° > 0, it is hypothesized that the α → β conversion might include the rupture of one hydrogen bond (in the hydration shell) per one α-NO3 entity.

Back to tab navigation

Publication details

The article was received on 13 Feb 2003, accepted on 26 Mar 2003 and first published on 14 Apr 2003


Article type: Paper
DOI: 10.1039/B301730C
Phys. Chem. Chem. Phys., 2003,5, 2015-2019

  •   Request permissions

    Existence of two forms of nitrate ion in dilute aqueous solutions. Thermodynamic parameters of interconversion

    V. Simeon, V. Butorac, V. Tomišić and N. Kallay, Phys. Chem. Chem. Phys., 2003, 5, 2015
    DOI: 10.1039/B301730C

Search articles by author

Spotlight

Advertisements