title: Simultaneous determination of the acid and basic ionization constants of imidazole.
abstract: The acid and base ionization constants of imidazole (LH) have been determined simultaneously by potentiometry. Concentration constants were obtained at 10.0, 15.0, 25.0 and 40.0 degrees with I = 0.1M (KNO(3)), the values (and standard deviations) at 25.0 degrees being pK(a1)(LH(2)(+)) = 7.002 +/- 0.006 and pK(a2)(LH(2)(+)) = 12.588 +/- 0.004. The following values were obtained for the corresponding thermodynamic parameters: DeltaH(1) =38 and DeltaH(2) = 38 kJ mole ; DeltaS(1) = -8 and DeltaS(2)= -112 J.mole(-1).K(-1).
authors.affiliation: Chemistry Department, Faculty of Science, 4000 Oporto, Portugal.
authors.forename: M T
authors.initials: MT
authors.lastname: Vasconcelos
authors.forename: A A
authors.initials: AA
authors.lastname: Machado