Electrodes cadmium amalgam

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.]...

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

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. ... 

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... 

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). 

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,... 

The E.M.F. of a cell consisting of cadmium amalgam (N2 = 1.781 X 10" ) as one electrode and a saturated amalgam as the other is — 0.05294 volt at 25 C. What are the activity and activity coefficient of the cadmium in the dilute amalgam with reference to that in the saturated amalgam as the standard state ... 

A similar electrode is the cadmium amalgam electrode, Cd(Hg) Cd (aq) where ... 

Nitrates can also be determined after their reduction with zinc or cadmium amalgam to nitrites, employing photometry with sulphanilic acid and a-naphthylamine. In the case of polarographic determination nitrates are reduced on the mercury droping electrode in a weak acid medium under catalytic effects of uranyl ions. 

Weston cell (cadmium cell) A type of primary voltaic cell, which is used as a standard it produces a constant e.m.f. of 1.0186 volts at 20°C. The cell is usually made in an H-shaped glass vessel with a mercury anode covert with a paste of cadmium sulphate and mercury(l) sulphate in one leg and a cadmium amalgam cathode covered with cadmium sulphate in the other leg. The electrolyte, which connects the two electrodes by means of the bar of the H, is a saturated solution of cadmium sulphate. In some cells sulphuric acid is added to prevent the hydrolysis of mercury sulphate. It is named after Edward Weston (1850-1936). 

ASV can be used for trace measurements of more than 20 elements that can be readily reduced to the metallic state and reoxidized. Most successful are ASV measurements of amalgam-forming elements, such as lead, cadmium, copper, zinc, thallium, bismuth, tin, or antimony, at a mercury working electrode. The amalgam-forming preconcentration step is given by... 

Evaluate the concentration overpotential at a cadmium amalgam electrode, the diffusion flux of Cd ions, and the current per square centimeter for 298.15 K. Assume that d = 200 /xm, that the concentration at the electrode is 0.0100molL, and that the concentration in the bulk is 0.0200 mol L. The diffusion coefficient for Cd " " ions at this temperature equals 8.7 X 10 0m2s . ... 

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