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Theory of the oscillographic polarography with an alternating current

K. Micka

Polarographic Institute, Czechoslovak Academy of Sciences, Praha

 

Abstract: The theory of the oscillographic polarography begins from the general integral equation describing reversible processes at the mercury electrode during the polarization by a current of an arbitrary time course. This equation can be solved exactly, to show the functional relation between the electrode potential E and the time, E = f'(t) in 3 limiting cases: (1) sp. charge of the electrode is negligible, (2) the faradaic current is negligible, (3) the changes of the electrode potential are small. From these, an equation, contg. 2 not closely defined parameters, is derived to approx. describe the true state of the electrode during polarization with a.c. From this latter equation (exptl. proven) E = f(t), dE/dt = f'(t) and dE/dt = f1(E) is derived. The potential of the peak of the inflection at the curve dE/dt = f1(E) is equal to the half-wave potential of the depolarizer. The relative depth of the inflection (equal to the ratio between the depth of the inflection and the height of the curve without the depolarizer) is decreased slowly with increasing frequency of the a.c. With increasing temp. it is either slightly increased or remains unchanged. The capacity effects are defined like all changes of the shape of the curve dE/dt = f1(E), caused by the change of the differential capacity of mercury. According to the theory, these effects can be distinguished from the inflections caused by the depolarizer. The d.c. component is necessary for compensation of the losses of the redn. products at the electrode. In an ideal case when these losses do not occur, the mercury electrode can be polarized by a.c. without the d.c. component to obtain a correctly developed curve dE/dt = f1(E) on the screen of the polaroscope. The losses of the redn. products are caused by the instability of amalgams, by the vibration of the mercury electrode, and by the irreversibility of the electrode process and are manifested by the tendency of the electrode potential to shift towards more pos. values.

Full paper in Portable Document Format: 1411-12a829.pdf (in Czech)

 

Chemical Papers 14 (11-12) 829–833 (1960)

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