Counter dropping mercury

Fig. 5.8 Schematic diagram of polarographic (or voltammetric) circuits for two-electrode (a) and three-electrode (b) systems. WE(DME) indicator or working electrode (dropping mercury electrode in the case of polarography) RE reference electrode CE counter electrode DC voltage (V) DC voltage source Current (/) current measuring device.

Fig. 10. Typical dropping mercury electrode assembly. A, Mercury reservoir B, Tygon tubing C, Pt wire connection to mercury D, capillary E, reference electrode F, counter electrode.

Fundamental knowledge about the behavior of charged surfaces comes from experiments with mercury. How can an electrocapillarity curve of mercury be measured A usual arrangement, the so-called dropping mercury electrode, is shown in Fig. 5.2 [70], A capillary filled with mercury and a counter electrode are placed into an electrolyte solution. A voltage is applied between both. The surface tension of mercury is determined by the maximum bubble pressure method. Mercury is thereby pressed into the electrolyte solution under constant pressure P. The number of drops per unit time is measured as a function of the applied voltage. 

Figure 6.2 Potential difference between a reference electrode in a movable Luggin capillary probe (P) and an identical fixed-reference electrode (R) placed opposite to the counter electrode (A). The dropping-mercury electrode (D) is placed between the fixed-reference electrode and the counter electrode the probe electrode is on side of DME opposite the fixed-reference electrode.

Bockris, Devanathan and Muller counter electrode dropping mercury electrode electrochemical impedance spectroscopy eleclric-lo-clectric (efficiency) faradaic efficiency... 

For the tetraazacopper(II) complexes, the reduction potentials of complexes A, C, and D are given in Tablel. These values were obtained in DMF at 25 C by the polarographic method with a dropping mercury electrode and a mercury pool as the working and counter... 

Color plate 1 3 Cell for polarographic measurements with the dropping mercury electrode, (a) Arrangement of the cell with the reference electrode on the left, the capillary working electrode at the top center, and the counter electrode of the right. The... 

Voltammetric measurements were performed with an AIS model DLK-100 voltammetric analyzer and a standard three electrode system consisting of a SCE reference electrode with salt bridge, a Pt counter electrode and a working electrode. In some experiments a solid state Au/Hg microelectrode was used as the working electrode and in others an EG G model 303A static dropping mercury electrode was interfaced to the analyzer. Both the Mn(III) to Mn(II) reduction and the Mn(II) to Mn(0) reduction onto the Hg electrode could be monitored simultaneously. 

From the experimental point of view, for reductions, DC-polarography at the dropping mercury electrode (DME) or cyclic voltammetry (CV) at the hanging mercury drop electrode (HMDE) were used and for controlled-potential electrolyses at negative potentials, a mercury pool electrode was employed. For both oxidative and reductive experiments, voltammetry at the platinum rotating disk electrode (RDE) and CV at the stationary platinum electrode were applied. All experiments were performed in a three-electrode system with a platinum counter electrode. For measurements in analytical scale (a standard aminocarbene concentration was 3x 10-" mol/1), an undivided cell for 5-10 ml was used and for preparative electrolyses a two-compartment cell of the H-type was employed [14]. The potentials were referred to the saturated calomel electrode (SCE), which was separated from the investigated solution by a double-frit bridge. 

Conventional 3-electrode cells, commercial potentiostats with external feedback IR compensation, and procedures similar to those described previously were used for electrochemical experiments. Working electrodes were a PARC Model 9323 hanging-drop-mercury electrode (HDME, A = 0.019 cm ) or a highly polished glassy carbon disk electrode (GCE, A = 0.071 cm ). A Pt wire served as the counter electrode and the reference was a saturated calomel electrode (SCE). For the HDME, a fresh Hg drop was used for each experiment. A polishing method described previously was used for GCE " and was repeated prior to each voltammetric scan. Area of the GCE was estimated electrochemicaly by using the Randles-Sevcik equation and CV peak for the oxidation of ferrocene in acetonitrile (D = 2.4 X 10 cm s i). Experiments in all CTAB solutions were thermo-statted at 30.0 0.1 C for SDS the temperature was usually 25.0 0.1 C. 

Experimental measurements1,2 of the uncompensated solution resistance indicate that it changes rapidly with distance in the immediate vicinity of the mercury drop, and attains an approximately constant limiting value at a distance greater than about 0.5 cm. The latter corresponds to a distance roughly 10 times the maximum radius of the mercury drop. This is illustrated in Figure 6.2, where the potential of a reference electrode in a movable Luggin capillary probe at different distances from the mercury drop has been measured with respect to an identical reference electrode located several centimeters away from the drop on the side opposite the counter electrode. An important feature... 

The schematic of the process cycle controller is shown in Figure 4. The solenoids are in the deactivated mode while the manometer is open to the reaction vessel. When the mercury level drops below electrode E2, the solenoids are activated and the manometer is shut off to the reaction vessel and opened to a source of fresh reactant gas. The rate of the refill, about seconds, can be controlled by the metering valve, C, shown in Figure 1. When the mercury level reaches El, the solenoids are deactivated, the counter is reset, and the manometer is opened to the reaction vessel once again.3... 

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