Mercurous sulfate reference electrodes

An alternative method was described by Pinzauti et al (40) for determination of several antithyroid drugs potentimetrically with 0.01 M mercuric acetate with use of a mercuric sulfate reference electrode and an amalgamated gold or a silver indicator-electrode. The method is rapid and the results are reproducible the errors are all within + 0.38%. 

The peak around —0.38 V versus mercury/mercurous sulfate reference electrode (MSE), during the negative sweep, is associated to gold species whereas the one at —0.8 V versus MSE corresponds to platinum species. For pure catalysts, with an upper potential limit of +0.25 V versus MSE, the charge values of 493 and 543 pC cm-2 were obtained for platinum and gold, respectively (Figure 21.7).43,44 The atomic content of the Pt-Au nanoparticles can be deduced as follows ... 

When leakage of chloride ion through the reference electrode into the test solution is not permissible (as in titrations involving Ag+), a mercury/mercurous-sulfate reference electrode may be used instead of calomel or silver-chloride electrodes. This consists of a mercury electrode in contact with a sulfate electrolyte saturated with excess mercurous sulfate ... 

Table 15.5 Potentials of the mercury-mercurous sulfate reference electrode vs. H2 H electrode at different sulfuric acid concentrations and temperatures.

Figure 9.34 Plots of potential versus time for composite coatings containing corrosion inhibitor-microcapsules (solution 0.1 M sulfuric acid, mercurous sulfate reference electrode).

To simulate corrosion in lead-acid battery environments, Dacres et al. [118] and others [119,120] anoically polarized test materials at 1.226 V (versus mercury/mercurous sulfate reference electrode) in sulfuric acid solutions (of 1.285 specific gravity) at 50, 60, and/or 70°C. At 1.226 V, lead and water are oxidized to lead dioxide (Pb02) and molecular oxygen (O2), respectively [122,123]. About one third of the total anodic current is consumed in the oxidation of lead under these conditions [120]. 

MSE saturated mercurous sulfate reference electrode SCE satnrated calomel reference electrode. 

In battery practice, hydrogen reference electrodes are not used. They are not only difficult to handle, but include in addition the risk of contamination of the battery s electrodes by noble metals like platinum or palladium (4). Instead, a number of reference electrodes are used, e.g. the mercury/mercurous sulfate reference electrode (Hg/Hg2S04) in lead-acid batteries, and the mercury/mercuric oxide reference electrode (Hg/HgO) in alkaline solutions (e.g. Ref. 5). In lithium ion batteries with organic electrolyte the electrode potential is mostly referred to that of the lithium electrode (cf. Chapter 18). 

Fig. 6 Steady state bistability in the optical density (- - ) and the Pt-potential —x—) versus mercurous sulfate reference electrode as a function of flow rate. All other constraints kept cons-tant [MnO ] = IxIO M, [H,0Jq = 2x10- M, rS,0Mo = 0-075 M,...

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. 

Fig. 5.6 (Left) Comparison of band energy levels for different II-VI compounds. Note the high-energy levels of ZnSe. Representation is made here for electrodes in contact with 1 M HQO4. The reference is a saturated mercury-mercurous sulfate electrode, denoted as esm (0 V/esm = +0.65 V vs. SHE). (Right) Anodic and cathodic decomposition reactions for ZnSe at their respective potentials (fidp, Fdn) and water redox levels in the electrolytic medium of pH 0. (Adapted from [121])...

Next we discuss four types of reference electrodes hydrogen, calomel, silver-silver chloric, and mercury-mercurous sulfate electrodes. 

Mercury-Mercurous Sulfate Electrode. In this reference electrode the metal is mercury, the sparingly soluble compound is mercurous sulfate (Hg2S04), and the source of S04 anions is sulfuric acid or potassium sulfate. The electrode is made in the same way as a calomel electrode, and it is represented as... 

Nikolic et al. reported the preparation and coulometric determination of quaternary ammonium iodides of procaine and of other local anesthetics [63]. After extraction from 0.33 M NaOH, the quaternary iodide salts were prepared by precipitation with methyl iodide in ethyl ether. The quaternary iodides were then coulometrically determined with the use of a Radiometer titrator. The method used a silver cathode and anode (in electrolytes of 2 M and 0.4 M H2SO4, respectively), and a reference mercurous sulfate electrode. For drug determinations in the range of 0.12 to 0. 96 mg, the standard deviations were typically found to be 4 to 8 pg. 

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... 

The sample is titrated with standardized silver nitrate (0.0141 M) in a continuously mixed beaker with an Ag electrode, an Ag/ AgCl electrode, or a chloride—ISE. The reference can be a glass mercuric sulfate, calomel, or Ag/ AgCl electrode. 

Because special preparative procedures are not necessary (except for the preparation of mercurous sulfate electrolytically), this reference electrode is recommended for use in place of the silver chloride or calomel electrodes when chloride ion must be rigorously excluded. 

A mercury/mercurous sulfate (Hg/Hg2S04) reference electrode A voltmeter... 

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. 

There are several issues related to the reference and counterelectrodes. Reliable reference electrodes are commercially available. The saturated calomel electrode (SCE) is extremely robust and is commonly used for studies in chloride solutions. For studies in which chloride is to be avoided, the mercurous sulfate electrode (MSB) is suitable. The location of the reference electrode is critical in cells in which large ohmic potential drops exist. In these cases, a Luggin capillary should be used to bring the sensing location of the reference electrode close to the working electrode... 

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. 

Mercurylmercury(I) sulfate also mercurous sulfate), abbreviated as Mercury Sulfate Reference Electrode (MSRE), is the second (26) most used mercury RE after SCE. The construction of the MSRE is similar to that of the SCE, although it is less sensitive to the purity of the mercury. The reproducibility (31) of the MSRE is second only to the NHE, and given the absence of chloride ion in the construction of the MSRE, it has found use in systems with sensitivity to chloride content. The reference potential of the MSRE is calculated as follows ... 

SSE mercury/mercurous sulfate/ saturated potassium sulfate reference electrode (Esse = +0.65 V/NHE). 

Mercuric and mercurous salts — Salts of Hg(II) and Hg(I), respectively. Soluble mercuric and mercurous salts such as acetates and nitrates are used for the deposition of mercury films on conducting substrates (see -> anodic stripping voltammetry). Insoluble salts, e.g., chloride and sulfate of Hg(I) in chloride and sulfate medium, respectively, can be used to prepare reference electrodes (see -> calomel electrode). The formation of insoluble salts of mercury on - mercury electrodes determines, among others, the positive limit of their voltam-metric potential window. 

The book edited by Ives and Janz [1 ] and more recently that by Bard, Parsons, and Jordan [2] contain both theoretical and practical aspects related to reference electrodes. Preparation, application and limitations of various types of reference electrodes such as the hydrogen electrode, the calomel and other mercury-mercurous salt electrodes, the silver-silver halide electrodes, and sulfide and sulfate electrodes are covered and general reference to these excellent critical reviews is recommended. 

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