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

The equilibrium constant for the reaction NO3+Cl-NO3-+Cl-., K-1, has been determined by measuring the rate constants for the forward, k(1), and reverse, k(-1), rate constants at 20 +/- 2 degrees C . k(-1) was measured in the absence of Cl- by generating Cl-. by laser flash photolysis of chloroacetone with 248 nm light. This yielded k(-1)=(1.02 +/- 0.04)x10(8) d mol(-1) s(-1). k(1) was determined by measuring the simultaneous rate of approach to equilibria (1) and (2), Cl-.+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 k(1), k(-1) and k(2) 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 k(1)(o)=(3.40 +/- 0.11)x10(8) d mol(-1) s(-1), where k(i)(o) are the rate constants for I --> 0. From k(1)(o) and k(-1)(o) we obtain K-1=(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 k(1) found in this work and some previous determinations are discussed.