Stoichiometry and Kinetics of the Reaction of Nitrite with Free Chlorine in Aqueous Solutions

The reaction of nitrite with free chlorine in dilute aqueous solution (3.4 < pH < 11.5) was studied under continuous-flow mixing conditions. Chlorine, chloride, nitrite, and nitrate were all measured analytically. Stoichiometric balances demonstrated that nitrite was oxidized to nitrate, and chlorine was reduced to chloride, without the significant production of any other chemical species. The kinetic studies demonstrated that the reaction is very fast at neutral or acidic pH with the rate decreasing with increasing pH. The reaction was strictly bimolecular in the pH range of 9.5–11.6, whereas it was sufficiently slow to be followed with time. The reaction appears to proceed between nitrous and hypochlorous acid molecules, or HNO₂ + HOCl → 2H⁺ + NO₃ + Cl⁻.