Diagrams of existence of chloramines and bromamines in aqueous solution

Abstract

Ultraviolet spectrophotometric analysis of haloamines produced by mixing aqueous helogen and ammonia solutions allowed distribution diagrams for the various species to be established as a function of pH and log R(R=[initial halogen]/[initial ammonia]). These diagrams are interpreted by using a model involving reversible reactions between the different compounds, whilst neglecting their decomposition. The reactions (equilibrium constants in parentheses) controlling concentrations of the species are as shown in equations (1)–(6). These equilibria and X₂+ H₂O ⇄ HXO + H⁺+ X^–(1), HXO ⇄ H⁺+ XO^–(2), NH₃+ H+⇄ NH₄⁺(3), NH₂X + H₂O ⇄ NH₄⁺+ XO^–(K_hm)(4), 2NH₂X + H⁺⇄ NHX₂+ NH₄⁺(K_md)(5), 3NHX₂+ H⁺⇄ 2NX₃+ NH₄⁺(K_dt)(6) the law of N and X⁺ mass conservation led to a non-linear system of eight equations with eight unknowns, solved by iteration. Experimental values of the constants, derived from isocontent curves between two species, are (at 25 °C): K_hm(Cl)= 4 × 10^–7 mol dm^–3, K_hm(Br)= 1 × 10^–7 mol dm^–3, K_md(Cl)= 5.2 × 10⁶ dm³ mol^–1, K_md(Br)= 8 × 10⁷ dm³ mol^–1, K_dt(Cl)= 1.7 × 10⁴ dm³ mol^–1, K_dt(Br)= 1.5 × 10⁵ dm³ mol^–1. Satisfactory agreement was found between calculated and measured values for the various species.