| Summary: | General relations among thermodynamic parameters characterizing chemical equilibria including species H2A+, HA, H+ and A- in both phases of a two-phase water-nitrobenzene extraction system have been derived. From the extraction measurements, the equilibrium distribution constant of electroneutral 1-(2-thiazolylazo)-2-naphthol (TAN, HA) between the nitrobenzene and aqueous phases has been determined: log KD(HA) = 3.90±0.02. By using this value and further known constants and applying the mentioned relations, the following values of dissociation constants of TAN in nitrobenzene saturated with water have been calculated for a temperature of 25°C: pKdnb(H2A+) = -log Kdnb(H2A+) = 4.9 and pKdnb(HA) = -log Kdnb(HA) = 16.5.
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