Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

General relations among thermodynamic parameters characterizing dissociation equilibria with species H₂A, HA^- and A^2- (H₂A is a symbol for an electroneutral undissociated acid) in a two-phase extraction system have been derived. From the extraction measurements, the equilibrium distribution constant of electroneutral bromophenol blue between the nitrobenzene phase and the aqueous one has been determined: log K_D(H₂A) = 3.60 ± 0.01. By using this value and further known constants and applying the mentioned relations the following values of dissociation constants of bromophenol blue in nitrobenzene saturated with water have been calculated for a temperature of 25 °C: pK_a^org(H₂A) = -log K_a^org(H₂A) = 10.1 and pK_a^org(HA^-) = -log K_a^org(HA^-) = 14.5.