Electrodes amalgam

Electrodes and Galvanic Cells. The Silver-Silver Chloride Electrode. The Hydrogen Electrode. Half-cells Containing an Amalgam, Electrode. Two Cells Placed Back to Back. Cells Containing Equimolal Solutions. The Alkali Chlorides as Solutes. HC1 in Methanol or Ethanol Containing a Trace of Water. The Alkali Chlorides in Methanol-Water Mixtures. The Heal of Solution of HC1. Proton Transfer Equilibrium from Measurements of E.M.F. 

In the experiments to be described, in each case the half-cell was coupled to a Ag/AgOl half-cell, which in each case formed the positive electrode of the cell that is to say, on closing the external circuit, electrons flowed in the external circuit from the amalgam electrode to the silver electrode. This was the situation whether the solvent was water, or methanol, or a mixture of methanol and water. 

The Alkali Chlorides as Solutes. In order to make a similar study of the transference of KC1, NaCl, and LiCl between water and methanol-water mixtures, the hydrogen electrode was replaced by an amalgam electrode, as described in Sec. 111. The arrangement when two cells having potassium amalgam electrodes are placed back to back may be written... 

In an Evans diagram 89> the mixed potential can easily be found and also be verified by measuring the open circuit potential of a zinc-amalgam electrode in a Cu2+-ion solution. Even the complication by the simultaneous presence of another reducible species, e.g., Pbz+ can be graphically demonstrated for different limiting conditions... 

This figure demonstrates that also under potentiometric conditions (- no external current flow) electrochemical net reactions occur. The EMF of the zinc-amalgam in a given Zn2 -ion solution depends on the current-voltage characteristic of other ions (in this example, Cu2 and Pb2 are interfering ions with respect to the Zn2 equilibrium potential) at the amalgam electrode. EMF drifts are thus explainable. 

Amalgam electrodes, and liquid and glass membrane electrodes... 

As has been shown 82 85 88), the behavior of amalgam electrodes under conditions of cementation is very similar to that of liquid and glass membrane electrodes under stationary state conditions. Here, Eq. (2) should be written in the following way ... 

P9.3 The potentials (emfs) of lithium amalgam electrodes in the cell... 

Totland KM, Harrington DA (1989) Anodic phase formation on lead amalgam electrodes in sodium sulfide solution. J Electroanal Chem 274 61-80... 

Thiols are easily oxidized to disulfides in solution, but this reaction occurs only very slowly at most electrode surfaces. However, use can be made of the unique reaction between thiols and mercury to detect these compounds at very favorable potentials. The thiol and mercury form a stable complex which is easily oxidized, in a formal sense it is mercury and not the thiol which is actually oxidized in these reactions. For the LCEC determination of thiols a Au/Hg amalgam electrode is used Using a series dual-electrode both thiols and disulfides can be determined in a single chromatographic experiment... 

For a metal amalgam electrode one cannot simplify the equation so that... 

Dieker et al.67 used a similar method but applied a dropping amalgam electrode (DAE) and followed amperometrically by means of pulse polarography the anodic dissolution wave of mercury in the presence of an excess of ligand by appropriate choices of pH and titrant they achieved selective determinations of metal ions at low concentrations. 

When eliminating the liquid junction potential by one of the methods described in Section 2.5.3, we obtain a concentration cell without transport. The value of its EMF is given simply by the difference between the two electrode potentials. More exactly than by the described elimination of the liquid junction potential, a concentration cell without transport can be obtained by using amalgam electrodes or electrodes of the second kind. 

In amalgam electrodes, the metal is dissolved in mercury, so that not only the concentration of metal cations in the solution but also the concentration of metal in the amalgam is variable. The potential of an amalgam electrode... 

If al>a2y then short circuiting of this cell results in potassium dissolution at the left-hand electrode and incorporation into the amalgam at the right-hand electrode. Amalgam electrodes can be used as reversible electrodes, even for metals as reactive as the alkali metals, especially in some non-aqueous solvents. 

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

Radioactive tracer techniques. In electrochemistry, the procedure is essentially the same as in studies of chemical reactions the electroactive substance or medium (solvent, electrolyte) is labelled, the product of the electrode reaction is isolated and its activity is determined, indicating which part of the electroactive substance was incorporated into a given product or which other component of the electrolysed system participated in product formation. Measurement of the exchange current at an amalgam electrode by means of a labelled metal in the amalgam (see page 262) is based on a similar principle. 

Rabenstein and Yamashita [52] determined penicillamine and its symmetrical and mixed disulfides by HPLC in biological fluids. Plasma and urine were deproteinized with trichloroacetic acid, and HPLC was performed on a column (25 cm x 4.6 mm) or Biophase ODS (5 pm) with a mobile phase comprising 0.1 M phosphate buffer (pH 3) and 0.34 mM Na octylsulfate at 1 mL/min. Detection was with a dual Hg-Au amalgam electrode versus a Ag-AgCl reference electrode. (z>)-penicillamine and homocysteine were determined at the downstream electrode at +0.15 V, and homocystine, penicillamine-homocysteine, and penicillamine disulfides were first reduced... 

Potentiometric EDTA titrations are best carried out with a mercury pool electrode (Figure 5.6) or a gold amalgam electrode. When this electrode dips into a solution containing the analyte together with a small amount of added Hg-EDTA complex, three interdependent reactions occur. For example, at pH = 8 the half cell reaction (a) which determines the electrode potential is related to the solution equilibrium by (b) and (c). 

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 final class of electrodes we encounter are amalgam electrodes, formed by dissolving a metal in elemental (liquid) mercury, generally to yield a solid. We denote an amalgam with brackets, so the amalgam of sodium in mercury is written as Na(Hg). The properties of such amalgams can be surprisingly different from their... 

Buffle, J., Bernhard, J. P. and Tercier, M. L. (1987). Extension of the sensitivity limit of amalgam electrodes in dilute aquatic media, based on the study of their oxidation process, J. Electroanal. Chem., 236, 67-86. 

Sodium amide has been prepared by the action of gaseous 2 or liquid3 ammonia on sodium, by the action of ammonia on alloys of sodium,4 and by the electrolysis of a solution of sodium cyanide 5 in liquid ammonia with a sodium amalgam electrode. A summary of the chemistry of alkali amides is given by Bergstrom and Fernelius.1... 

If two lead amalgam electrodes of different compositions (X2 and X are prepared and immersed in a suitable electrolyte, an electrical cell is obtained in which the following transfer process occurs when the cell is discharged ... 

Dropping indium and thallium amalgam electrodes [41] were used to determine kinetic parameters of Zn(II) reduction as a function of the amalgam composition. The formal potentials were shifted to more negative values with increasing thallium and indium amalgam concentrations. 

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