Buffer Solutions of Potassium Dihydrogen Phosphate and Sodium Succinate at 25 °C

A buffer mixture consisting of equal molalities (m) of potassium dihydrogen phosphate and sodium succinate is proposed as a useful reference point in the study of acid-base equilibria, bridging the present gap between pH 5.5 and pH 6.8. The p(a_H γ _Cl) at 25 °C has been determined by electromotive-force measurements for five buffer solutions in which m varied from 0.005 to 0.025. The conventional pa _H of each solution has been derived and found to be in good agreement with that calculated from existing data for the two equilibria concerned. The pa _H varies from 6.251 at m=0.005 to 6.109 at m= 0.025. The buffer mixture has been used successfully for the determination of the dissociation constants of 2-nitro-4-chlorophenol and 2,6-dichlorophenol.