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.