Nitrogen and Oxygen Exchange between Nitric Oxide and Aqueous Solutions of Nitric Acid1

Abstract

The simultaneous processes NO + H2O → O exchange and NO + NO3- → N exchange have been explored by isotopic analysis of 15NO brought into contact with aqueous solutions of HNO3 in H218SO. Exchange has been observed in the concentration range 0.05-0.94 M HNO3 but only after a characteristic induction time which at each concentration is longer for N exchange than for O exchange. The induction period is related to production of HNO2 by oxidation of NO by HNO3. Linear exchange plots are obtained for systems at chemical equilibrium, and O exchange is found to be much faster than N exchange under all conditions explored. Neither atom exchange occurs between NO and NO3- in neutral solution. Nitrogen exchange has been shown to be limited by NO3--HNO2 exchange, at an overall rate that appears to correspond to the reversible NO-HNO3 reaction under equilibrium conditions. This same process will produce oxygen exchange, but NO-H2O oxygen exchange has been found to occur at a much greater rate, in a process that is assumed to proceed via HNO2 without involvement of nitrate, probably by a mechanism similar to that pertaining in all-nitrite systems. © 1973, American Chemical Society. All rights reserved.