Mercury-mercurous sulfate electrode potential measurement

MetaUInsoluble Salt/Ion Electrodes. Electrode potentials are usually reported relative to normal hydrogen electrode (NHE a(H+) = 1, p(H2) = 1), but they are actually measured with respect to a secondary reference electrode. Frequently used secondary reference electrodes are calomel, silver-silver chloride, and mercury-mercurous sulfate electrodes. These secondary reference electrodes consist of a metal M covered by a layer of its sparingly soluble salt MA immersed in a solution having the same anion Az as the sparingly soluble MA. The generalized reference electrode of this type may be represented as M MA AZ and may be considered to be composed of two interfaces one between the metal electrode M and the metal ions Mz+ in the salt MA... 

Similar designs are used for other REs on the basis of poorly soluble mercury compounds (1) the mercury-mercurous sulfate RE with H2SO4 or K2SO4 solutions saturated with Hg2S04, for which = 0.6151V and (2) the mercury-mercuric oxide RE, for measuring electrode potentials in alkaline solutions, with KOH solution saturated with HgO, for which = 0.098 V and E = 0.920 V. 

The potentials of the two electrodes of the lead—acid cell are measured vs. a reference electrode. Thus, the lead—acid cell turns into a three-electrode cell. During measuring the potential of the two electrodes of the LA cell, the reference electrode should not be polarized, i.e. its potential should remain constant. The most common reference electrodes are hydrogen, cadmium, mercury-mercurous sulfate and silver-silver sulfate electrodes. Cadmium sticks are widely used in industrial quality control laboratories to measure the electrode potentials of the manufactured batteries. Cadmium does not form poorly soluble cadmium sulfate, which is the reason why during the measurement the electrolyte in the cell absorbs a few Cd ion impurities that do not affect the performance of the battery, however. 

The mercurous sulfate [7783-36-OJ, Hg2S04, mercury reference electrode, (Pt)H2 H2S04(y ) Hg2S04(Hg), is used to accurately measure the half-ceU potentials of the lead—acid battery. The standard potential of the mercury reference electrode is 0.6125 V (14). The potentials of the lead dioxide, lead sulfate, and mercurous sulfate, mercury electrodes versus a hydrogen electrode have been measured (24,25). These data may be used to calculate accurate half-ceU potentials for the lead dioxide, lead sulfate positive electrode from temperatures of 0 to 55°C and acid concentrations of from 0.1 to Sm. 

Hg UPD on Au(lll) electrodes in the presence of bisulfate anions has been studied by Abruna et al. [27] in order to illustrate the effects of the partial charge, retained by the metal, on the interactions between the adsorbed metal and the anion. In order to obtain structural information on the adsorbed species, the authors have carried out grazing incident X-ray diffraction measurements at several potentials. Three ordered structures were observed depending on the applied potentials, which were adjusted from cyclic voltammograms. At the early stages of Hg UPD, when mercury was still partially charged, an ordered mercurous-sulfate bilayer structure was formed at the electrode... 

The reference electrode most commonly used is a saturated calomel, a mercurous sulfate, or silver/silver-chloride electrode. When accurate measurement of the potential is not required, a mercury pool or a platinum wire, foil, or gauze can be used. In nonaqueous solutions, various other reference electrodes may be more suitable. 

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