The Use of the Dropping Mercury Electrode as an Indicator Electrode in Poorly Poised Systems

Abstract

Müller and Baumberger1 and Müller2 have shown that the dropping mercury electrode can be used to measure the oxidation potential of the quinone-hydroquinone system. In their work the oxidation potential of the system was taken as that value of the potential of the dropping electrode at which the current flowing was zero. This procedure was found to give good results in the majority of practical cases where the solution used was reasonably well poised. However, when the same method was extended to very poorly poised (buffered) systems a fairly large error appeared to be made. Thus, in Müller's2 work, a 10_1 M phosphate buffer of pH 6.9 gave a zero current potential at the dropping electrode corresponding to a pH 7.7 when the buffer was diluted by a factor of 10,000. A more probable value of the pH of this buffer diluted under ordinary conditions would be of the order of 6.7. It is our purpose in the first part of the present paper to offer an explanation for the apparent deviation. 0.240 0.120 0 -0.120 -0.240 Potential of dropping electrode vs. S. C. E.

Voltammetry of Electroinactive Species Using Quinone/Hydroquinone Redox: A Known Redox System Viewed in a New Perspective

“…At constant temperatures and well-buffered solutions its potential is a linear function of pH with a slope of 59 mV [2]. Also poorly buffered solutions were studied with this electrode and the pH values thus found agreed well with results obtained in different ways [3].…”

Electrochemical Reduction of Quinones in Different Media: A Review

“…Media. There are few reports on the electrochemical behavior of quinones in unbuffered aqueous media [2,3,[139][140][141][142][143][144][145][146][147][148]. When the proton concentration nearly equals concentration of the quinone results are consistent with that observed in aqueous buffered media but sometimes explanations are different.…”

Development of Methods for the Determination of pKaValues

“…38 As early as 1941, voltammetric methods were deployed to determine local pH at the electrode surface. 39 However the use of voltammetry to specifically determine bulk pK a values came into use in the 1960s. 40 When the pK a of a substance is being determined voltammetrically, one could in principle measure the electrochemical response of the molecule itself.…”