Solutions of nitrous acid in dilute (0.1 M HCl) or more concentrated (~5 M HClO4) acid exhibit a contribution to the ultraviolet absorbance that is quadratic in [HNO2]. In dilute acid this excess absorbance is attributed to N2O3 formed through equilibrium 1, 2HNO2 = N2O3 + H2O. From the measured spectrum of εN2O3 vs. wavelength (245-260 nm) and by comparison with εN2O3 obtained in pulse radiolysis by Gratzel et al., K1 is determined as (3.03 ± 0.23) × 10-3 M-1, in agreement with the value calculated thermochemically. The coefficient of physical solubility of N2O3 in water is computed as 0.70 ± 0.05 M atm-1. The extinction quadratic in [HNO2] is independent of acid concentration in dilute acid but increases strongly in more concentrated acid, suggesting a possible second absorbing species of stoichiometry HN2O3+.
This page was last updated 2012-08-29.
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