Cadmium amalgam

Ideally a standard cell is constmcted simply and is characterized by a high constancy of emf, a low temperature coefficient of emf, and an emf close to one volt. The Weston cell, which uses a standard cadmium sulfate electrolyte and electrodes of cadmium amalgam and a paste of mercury and mercurous sulfate, essentially meets these conditions. The voltage of the cell is 1.0183 V at 20°C. The a-c Josephson effect, which relates the frequency of a superconducting oscillator to the potential difference between two superconducting components, is used by NIST to maintain the unit of emf. The definition of the volt, however, remains as the Q/A derivation described. 

The photochemical or thermal reaction between petfluoroalkyl iodides and mercury-cadmium amalgams has been used for the synthesis of perfluoro-alkylmercury compounds [150] Functionalized analogues have been prepared similarly via this route [151, 152] (equation 117), and the preparation of bis(tri-fluoromethyl)mercury has been described [153]... 

The mostly used Weston cell consists of mercurous sulphate and cadmium amalgam electrodes ... 

The main advantage of Weston s cell was its insensitivity to temperature, and the emf of almost 1 V to be precise, 1.0183 V at 20 °C. It is usually constructed in an Id-shaped glass vessel. One arm contains a cadmium amalgam electrode beneath a paste of hydrated cadmium sulphate (3CdS04 5H20) cadmium sulphate and mercury sulphate. The other arm contains elemental mercury. Its schematic is Cd(Hg) CdS04(aq), Hg2S04 Hg. 

The mechanism of Cd(II) discharge and cadmium amalgam dissolution in the absence and presence of adsorbed aliphatic alcohols and acids [51], and also the inhibiting influence of the adsorbed aliphatic alcohols and acids on the kinetics of the Cd(II)/Cd(Hg) system was studied [52,53]. 

Electrochemical oxidation of cadmium in a solution of ](4-methylphenyl)sulfonyl]-2-pyridylamine] (HL) in acetonitrile/di chloromethane mixtures resulted in CdL2 complex formation [149]. The electrochemical oxidation of cadmium amalgam in nonaqueous solvents CH2CI2, 1,2-C2H4CI2, and PC was also used for the preparation of cadmium complexes with 18-membered macromonocyclic ligands, 18-06, 18-S6, I8-N2O4, and 18-N6 [150]. The stoichiometry and stability of resulted complexes were determined. The same method was used to examine the complexation of Cd(II) cation with 12-crown-4 ether, azacrown ether 1,4,8,11-tetra-azacyclotetradecane, and thiaazacrown... 

The decomposition of cyanide ions at a cadmium amalgam electrode proceeds through a CEC mechanism... 

Figure 16.4 Cyclic voltammogram of 4.5 mM 2,3-dinitro-2,3-dimethylbutane in N,N-dimethylformamide/0.20 M Bu4NPF6 at a 25-pm-diameter mercury electrode. Curves experimental voltammograms after subtraction of background current. Points digital simulations. Potentials referred to cadmium reference electrode [cadmium amalgam/CdCl2 (sat d) in DMF]. [Reprinted with permission from W.J. Bowyer and D.H. Evans, J. Org. Chem. 53 5234 (1988). Copyright 1988 American Chemical Society.]...

The EC mechanism is that of Equation 23.21, the horizontal line in the scheme, encompassing the oxidation of Cd to Cd2+ (E) followed by complexation of Cd2+ by HY3- (C). The electrochemical reactant, Cd2+, was cleverly furnished by a cadmium amalgam working electrode, which upon oxidation gave Cd2+ at the electrode for reaction with HY3. Ca2+ added to the bulk solution served to compete with Cd2+ for available HY3. ... 

HgmCdn (c), HgTOCd (liq.). The values for the liquid and solid cadmium amalgams are from Richards and Garrod-Thomas,1 Biji,1 Richards and Forbes,1 Cohen,5 Carhart,1 Richards and Lewis,1,2 Richards, Frevert, and Teeter,1 Hulett,1 Tammann and Ohler,1 Richards and Wilson,1 Getman,1 and Hildebrand, Foster, and Beebe.1... 

Reduction of the neutral complex in nonaqueous media with cadmium amalgam produced (1,2-B9C2H,, )2Pd, an air-sensitive and water-sensitive compound. In contrast, the analogous Ni(III) species is water stable. 

Other reference electrodes for use in polar aptotic solvents. Emphasis has been given to the use of the silver-silver ion reference electrode because it is almost universally applicable, and because standardization on the use of one reference electrode system simplifies the comparison of data between different workers. However, a number of other reference electrodes have been used (see Table 5.4), particularly those that have resulted from the vast amount of batteiy research. These include the Li/Li(solv)+ and other alkali metal electrodes that function reversibly in Me2SO, propylene carbonate, and hexa-methylphosphoramide. The thallium-thallous halide electrodes of the second kind also function reversibly in Me2SO and propylene carbonate. The cadmium amalgam-cadmium chloride reference electrode also functions reversibly in dimethylformamide and may be a useful substitute for the silver-silver ion reference electrode, which may be unstable in dimethyformamide.54... 

An H shaped glass container has electrodes at the bottom of the lower arms connected to the external wires by sealed-in platinum wires. The negative electrode is of cadmium amalgam containing 12.5 % cadmium, while the positive electrode is formed by mercury with a layer of paste, which consists of mercurous sulphate, dispersed mercury and small crystals of cadmium sulphate. 

Weston normal element (cell) — Electrochemical -> standard cell showing a particularly stable and reproducible cell voltage. In the international Weston normal element a cadmium amalgam (cadmium content in the solid phase approx. 15 wt %, in the liquid phase approx. 5wt%, total average 12 to 12.5 wt%, the electrode potential depends only on the temperature, not on the mass ratio of liquid and solid phases) and a mercury electrode (half-cell) are combined according to... 

In the case of cadmium (63), the initial exchange with cadmium amalgam In the extraction step is followed by a back extraction or elution with thallous ion to selectively remove... 

Effective decontamination Is obtained from ell Isotopes except Cu° and Mnao. Mnse would not be a serious Interference In monitoring application In waste streams. Cu6 can be removed by pre-extraction Into cadmium amalgam (l gm Cd In 5 ml Hg). The cadmium amalgam will reduce and extract the Cu, and leave the radlozlnc in solution. 

The cell consists of a small beaker with a top that will accommodate two electrodes as shown in Fig. 1. The cadmium electrode is made by plating cadmium onto a platinum wire that is sealed through the bottom of a small glass tube. The amalgam electrode is made by placing a small quantity of the cadmium amalgam in the cup of a special J-shaped glass tube with a platinum wire sealed into it. Electrical contacts are made by copper wires spot-welded to the platinum lead wires. 

Provision for electroplating cadmium from 0.1 MCdS04 onto platinum electrode dilute (2 percent) cadmium amalgam (1 mL) eye dropper constant-temperature baths set at 15, 25, and 35°C ice bath approximately 0.1 A/CdS04 solution (150 mL) ice (1 kg). 

Perfluoroalkylmercury compounds have been prepared by reaction of perfluoroalkyl halides with cadmium amalgam or by reaction of fluoroalkenes with mercury(II) fluoride. Due to the high thermal stability of perfluoroalkylmercury compounds, they can be sublimed from concentrated sulfuric acid without decomposition and are of limited synthetic utility. These reagents have found use as difluorocarbene sources and do react with elemental sulfur at elevated temperatures to afford thioacid fluorides, di- and polysulfides, and thioketones. ... 

It is important to note that the mercury electrode of a commercial Weston cell is always marked positive while the cadmium amalgam electrode is marked negative,... 

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