Mercury electrodes potential range

Mercury cyanide, 5, 1062 Mercury electrodes potential range aqueous solution, 1, 480 Mercury fluoride, 5. 1059 Mercury fulminate, 2, 7, 12 5, 1063 Mercury halides, 5, 1049 Mercury iodate, 5,1068 Mercury iodide, 5. 1059 Mercury ions Hgf... 

Mercury, tris(l,10-phenanthroline)-structure, 64 Mercury(II) complexes masking agent, 536 Mercury electrodes potential range aqueous solution, 480 Metal carbonyls structure, 16 Metallocenes nomenclature, 126,127 Metallochromic indicators, 554 Metallofluorescent indicators, 558 Metallothionein proteins, 142 Mettd-metal bonding, 137,169 gravimetry, 525 history, 21,23 nomenclature, 122, 123 Metal nitrosyls structure, 16 Metal-phthalein metallochromic indicator, 557 Metal template reactions, 416,433 equilibrium kinetic, 434 thermodynamic, 434 Methane, dichloro-... 

As the field intensity in the inner Helmholtz layer becomes extremely high, the field intensity E in the outer Helmholtz layer is reversed as shown in Fig. 5-29. Figure 5-30 illustrates the potential profile across the interfacial double layer of a mercury electrode in an aqueous chloride solution this result was obtained by calculations at various electrode potentials ranging fi om negative (cathodic) to positive (anodic) potentials. 

Electrically, the electrical double layer may be viewed as a capacitor with the charges separated by a distance of the order of molecular dimensions. The measured capacitance ranges from about two to several hundred microfarads per square centimeter depending on the stmcture of the double layer, the potential, and the composition of the electrode materials. Figure 4 illustrates the behavior of the capacitance and potential for a mercury electrode where the double layer capacitance is about 16 p.F/cm when cations occupy the OHP and about 38 p.F/cm when anions occupy the IHP. The behavior of other electrode materials is judged to be similar. 

The limited anodic potential range of mercury electrodes has precluded their utility for monitoring oxidizable compounds. Accordingly, solid electrodes with extended anodic potential windows have attracted considerable analytical interest. Of the many different solid materials that can be used as working electrodes, the most often used are carbon, platinum, and gold. Silver, nickel, and copper can also be used for specific applications. A monograph by Adams (17) is highly recommended for a detailed description of solid-electrode electrochemistry. 

In oxidative polarography there is still the difficulty of a considerably limited potential range owing to dissolution of the mercury itself with a direct dependence on the electrolyte composition this is well illustrated in Fig. 3.26 for the following electrode reactions of Hg ... 

The low-potential responses are detected on Hg. Solid electrodes like glassy carbon, gold or platinum show no response in this range. This implies that oxidation of the mercury electrode takes place as well. Indeed, the second DPP waves observed at +0.68 up to +0.72 V correspond to oxidation of mercury compounds such as Ph2Hg. The... 

The accessible potential ranges for platinum and mercury electrodes, in the commonest organic solvents are reported in Table 1. It is noted that gold exhibits characteristics very similar to platinum. 

A similar conclusion arises from the capacitance data for the mercury electrode at far negative potentials (q 0), where anions are desorbed. In this potential range, the double-layer capacitance in various electrolytes is generally equal to ca. 0.17 F Assuming that the molecular diameter of water is 0.31 nm, the electric permittivity can be calculated as j = Cd/e0 = 5.95. The data on thiourea adsorption on different metals and in different solvents have been used to find the apparent electric permittivity of the inner layer. According to the concept proposed by Parsons, thiourea can be treated as a probe dipole. It has been cdculated for the Hg electrode that at (7 / = O.fij is equal to 11.4, 5.8, 5.1, and 10.6 in water, methanol, ethanol, and acetone, respectively. 

Recently, Fuchs etal. [15], using the streaming mercury electrode and applying the Henderson equation, have determined the pzc value in the solutions of tetraethy-lammonium perchlorate in DMSO as —0.515 0.001 V (versus Ag/0.01 M Ag+ (DMSO) reference electrode). This value was corrected for the liquid junction potential and was independent of tetraethyl ammonium perchlorate (TEAR) concentration within the range 0.02 to 0.75 M. Using the same methodology, KiSova et al. 

As a result of that reductive process, a deposit of copper metal (denoted in Eq. 2.2 by s for solid ) is formed on the carbon electrode surface. The prominent anodic peak recorded in the reverse scan corresponds to the oxidative dissolution of the deposit of copper metal previously formed. The reason for the very intense anodic peak current is that the copper deposit is dissolved in a very small time range (i.e., potential range) because, in the dissolution of the thin copper layer, practically no diffusion limitations are involved, whereas in the deposition process (i.e., the cathodic peak), the copper ions have to diffuse through the expanding diffusion layer from the solution to the electrode surface. These processes, labeled as stripping processes, are typical of electrochemically deposited metals such as cadmium, copper, lead, mercury, zinc, etc., and are used for trace analysis in solution [84]. Remarkably, the peak profile is rather symmetrical because no solution-like diffusive behavior is observed. 

Fig. 7.193. The potential range marked on the electrocapillary curve. The potential of the mercury electrode oscillates between the points A1 and A2 in the Fe-triggered oscillation. (Reprinted from C. W. Kim, l-H. Yeo, and W.-K. Paik, Electrochim. Acta 41 2833, copyright 1996, with permission from Elsevier Science.)...

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