The equilibrium NO3•+Cl-⇌NO3-+Cl•: A laser flash photolysis and pulse radiolysis study of the reactivity of NO3• with chloride ion in aqueous solution

Abstract

The equilibrium constant for the reaction NO₃+Cl^-NO₃^-+Cl^Nsbd, K₁, has been determined by measuring the rate constants for the forward, k₁, and reverse, k_-1, rate constants at 20±2°C . k_-1 was measured in the absence of Cl^- by generating Cl^Nsbd by laser flash photolysis of chloroacetone with 248 nm light. This yielded k_-1=(1.02±0.04)×10⁸ d mol^-1 s^-1. k₁ was determined by measuring the simultaneous rate of approach to equilibria (1) and (2), Cl^Nsbd+Cl^-Cl₂^-, following pulse radiolysis of concentrated solutions of NaNO₃ (1-4 mol dm^-3) with [Cl^-] in the range 2-20 mmol dm^-3. The treatment of the data indicated that k₁, k_-1 and k₂ depended on ionic strength according to the relationship log k_i=log k_i^o+ CI, with C=0.24±0.01 d mol^-1 and k₁^o=(3.40±0.11)×10⁸ d mol^-1 s^-1, where k_i^o are the rate constants for I→0. From k₁^o and k_-1^o we obtain K₁=(3.33±0.24). The value of C was shown to depend on the nature of the ions contributing to I. Reasons for the discrepancies between the value of k₁ found in this work and some previous determinations are discussed.