Electrode mercury sulfate

Fig. 11.7 Parallel voltammetric screening of 64 Pt thin film catalysts for the electroreduction of oxygen in acidic solution. In the kinetically controlled region, the activity of all 64 catalysts shows good reproducibility. Conditions 0.5 M H2S04, oxygen saturated 20 mV s 1 anodic scan rate, 60°C, electrolyte stirring, potentials are plotted on the mercury/mercury sulfate electrode scale. Inset voltammogram of 64 Pt thin film catalysts in oxygen-free sulfuric acid, 20 mV s-1, prior to oxygen screening.

A mercury-sulfate electrode served as a reference electrode. All electrode potentials are referred to the potential of the reversible hydrogen electrode in the same electrolyte and at the same temperature as the test electrode. Adsorption measurements were performed in the 0.5 M H2SO4 solution prepared using special purity B-5 sulfuric acid and water doubly-distilled. To remove oxygen dissolved in the electrolyte, pure helium or argon was bubbled through acid solution. 

The function of the central electrode is to facilitate the exchange of sulfate ions between the two solutions. The equilibrium associated with a single mercury mercury sulfate electrode is... 

Reagent grade chemicals were utilized. Electrodeposition was carried out in a conventional three-electrode cell under potentiostatic control with a mercury sulfate electrode as reference (in the following, all potentials are quoted versus this reference) and a platinum wire as counter electrode. Solutions were stirred and deoxygenated by bubbling nitrogen. Backside ohmic contacts of Si samples were achieved with an InGa eutectic. The i-U characteristics of the solid state junctions were measured in air. 

Infrared absorption spectroscopy Isophthalic acid Low energy electron diffraction Lowest imoccupied molecular orbital Mechanically controlled break-junction Mercury-sulfate electrode Potential of zero charge q = 0 Quasireference electrode Real hydrogen electrode Reference electrode Alkanedithiols HS(CH2)nSH Self-assembled monolayer(s)... 

Under experimental conditions the SHE is rarely used. Reference electrodes of a second kind are used instead, which are simpler to handle and are commercially available. The Ag/AgCl electrode was already mentioned. Other examples are the calomel electrode based on Hg/Hg2Cl2/KCl (for instance, as saturated calomel electrode (SCE)), the mercury sulfate electrode Hg/Hg2S04/H2S04 (0.5 mol 1 ), and the mercury oxide electrode Hg/HgO/ NaOH (Imol 1 ). Potentials of some reference electrodes versus the SHE are shown in Table 3.2. 

A single ferrosilicon cathode was used in the form of a cast, 40 mm in diameter and 400 mm in length. This was attached to the structure by teflon insulation, which is simultaneously the electric cable tube. The mercury sulfate electrode was applied with a salt bridge filled with H2SO4 solution... 

The tank was filled to 2/3 rds of the volume (surface of approx. 60 m ) with sulfuric acid. Next, the tank was polarized with a 30 A current and 10 V voltage for 20 min, after which the current parameters were reduced. During operation, the potential of steel was maintained by a potentiostat at an average value of +1.2 V versus the mercury sulfate electrode at a current intensity of 1.5 -2 A. As a result of application of anodic protection, the contents of iron in the stored sulfuric acid decreased by ten times. 

Anodic stripping voltammetry at a mercury film electrode can be used to determine whether an individual has recently fired a gun by looking for traces of antimony in residue collected from the individual s hands, fn a typical analysis a sample is collected with a cotton-tipped swab that had been wetted with 5% v/v HNO3. When returned to the lab, the swab is placed in a vial containing 5.00 mb of 4 M HCl that is 0.02 M in hydrazine sulfate. After allowing the swab to soak overnight,... 

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. 

Electrochemical analytical techniques are a class of titration methods which in turn can be subdivided into potentiometric titrations using ion-selective electrodes and polarographic methods. Polarographic methods are based on the suppression of the overpotential associated with oxygen or other species in the polarographic cell caused by surfactants or on the effect of surfactants on the capacitance of the electrode. One example of this latter case is the method based on the interference of anionic surfactants with cationic surfactants, or vice versa, on the capacitance of a mercury drop electrode. This interference can be used in the one-phase titration of sulfates without indicator to determine the endpoint... 

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... 

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 mercury-mercurous sulfate electrode. Several commercial suppliers offer the mercury-mercurous sulfate electrode with a saturated potassium sulfate electrolyte. The potential (E° + E ) of this electrode system is 0.658 V on the hydrogen scale at 22°C.34 The electrode constitutes one-half of the Weston standard cell,35 an international secondary voltage standard, and is outstanding in reproducibility,36 in spite of the slight tendency of mercurous sulfate to hydrolyze and its rather high solubility. 

Marie-Davy cell — This was a -+ Bunsen cell with a carbon electrode in a paste of mercury sulfate, i.e., it was a zinc-mercury - battery. 

Sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca), concentrations were measured by atomic absorption spectrophotometry (Perkin Elmer 2380 equipped with deuterium background corrector). Cd, Zr, and Cu concentrations were obtained in a quartz cell, by differential pulse anodic stripping voltammetry (DPASV) with a assy carbon thin-film mercury covered electrode (Tacussel polarographic equipment fitted with a Tacussel EDI type electrode). Pure water was produced by a Milli. Q water purification system (Millipore). Chlorate, sulfate and carbonate were measured using classical methods. 

If chloride ions must be avoided, a mercury mercurous sulfate electrode [Hg/ Hg2S04(s), K2S04(s) E = 0.621 V versus NHE] may be employed. In alkaline solution a mercury mercuric oxide electrode (E = 0.098 versus NHE) may be useful. 

The Mercury-Mercurous Sulfate Electrode. A pool of mercury covered with a paste of mercurous sulfate and a solution containing sulfate. 

Weston cadmium cell A standard cell that produces a constant e.m.f. of 1.0186 volts at 20°C. It consists of an H-shaped glass vessel containing a negative cadmium-mercury amalgam electrode in one leg and a positive mercury electrode in the other. The electrolyte - saturated cadmium sulfate solution - fills the horizontal bar of the vessel to connect the two electrodes. The e.m.f. of the cell varies very little with temperature, being given by the equation = 1.0186 - 0.000 037 (T - 293), where T is the thermodynamic temperature. 

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. 

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. 

Mercury/mercurous sulfate electrode 0.6151(5) Ag/Ag2S04, Pb/Pb2S04 Aqueous, mixed... 

Mercury sulfate (ic) calomel electrodes Dimercury dichloride calomel mfg. 

Concentric cylindrical gauze electrodes ensure uniform potential and current distributions. When a reference electrode is employed - historically calomel or mercury/mercury sulfate, more recently (for occupational health reasons) using silver-based couples and occasionally a wire of the metal to be plated - placement of the tip of the salt bridge close to the working electrode minimizes the ohmic potential drop. 

These electrodes have nitrate-sensitive ion-exchange material incorporated into poly(vinyl chloride)-based membrane electrodes. Care is necessary to avoid contamination by the chloride from the saturated calomel reference electrode and a mercury/me-rcurous sulfate electrode is preferable as a reference electrode. Industrial monitors using nitrate ion-selective electrodes are commercially available. 

Most commonly used reference electrodes are based on mercury (calomel electrode) and silver, in equilibrium with the saturated solution of the corresponding chlorides. Their potential will be constant if the chloride ion concentration around the electrode is constant. The mercury-mercury(I) sulfate electrode is used instead of the calomel electrode when the presence of chloride is undesirable. 

Another commonly used electrode is the mercury-mercurous sulfate electrode, represented by Eq. (10) ... 

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