The locations of inflection points on titration curves for symmetrical redox reactions

Abstract

For titration curves of symmetrical ( n 1 = n 2 = p) redox reactions, it has been demonstrated that there are always two inflection points whenever pΔ E°' > 85.6 mV at 25°; the location of the point of maximum slope is always prior to the equivalence point, whereas the point of minimum slope is always located subsequent to the half way point. For practical titrations where pΔ E°' is customarily greater than 300 mV, the differences between the locations of these points and the half-way point and the equivalence point, respectively, are considerably less than the experimental error incurred in the determination of their location. When pΔ E°' = 85.6 mV. the titration curve has neither a minimum nor a maximum slope but there is a region, in the vicinity of 71% titrated, wherein the slope remains constant as the titration progresses whereas it pΔ E°' < 85.6 mV, no maximum nor minimum slope exits and throughout the titration the slope decreases continuously from its value at the start of the titration.