Cell, amalgam reversible

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. 

It will be seen that the electromotive force E2 of the reversible galvanic cell which consists of an amalgam electrode (0.206 per cent Na) and of a hydrogen electrode in a solution of sodium hydroxide of unit mean activity equal 1.039 V. 

Amalgam Cells.—If the electrolyte in the concentration cell without transference is a salt of an alkali metal, e.g., potassium chloride, it is necessary to set up some form of reversible alkali metal electrode. This is achieved by dissolving the metal in mercury, thus forming a dilute alkali metal amalgam which is attacked much less vigorously by water than is the metal in the pure state." The amalgam nevertheless reactia with water to some extent, and also with traces of oxygen that may be... 

Concentration Cells with a Single Electrolyte Amalgam Concentration Cells.—In the concentration cells already described the e.m.p. is a result of the difference of activity or chemical potential, i.e., partial molal free energy, of the electrolyte in the two solutions it is possible, however, to obtain concentration cells with only one solution, but the activities of the element with respect to which the ions in the solution are reversible are different in the two electrodes. A simple method of realizing such a cell is to employ two amalgams of a base metal at different concentrations as electrodes and a solution of a salt of the metal as electrolyte thus... 

In seawater, Zn, Cd, Pb, and Cu amalgamate quasi-reversibly with Hg. Thus, these metals are routinely analyzed. Nonroutine methods for the analysis of many more transition metals in seawater by either cathodic or anodic stripping are being developed daily. Also, because of the low concentration of trace metals in oceanwater ( 1 jixg/L), the stripping process is routinely carried out in the differential pulse (DP) mode, a process that enhances the metal-related component of the current over the background. Calibration of the cell (and of the analysis) is carried out by adding known... 

The basic kinetics of the amalgam, the diaphragm, and the membrane cells are discussed according to Fig. 11, containing reversible electrode potentials and current-potential relationships. 

Amalgam Cell Starting with the chlorine electrode, the reversible standard potential is +1.37 V (all potentials are given versus NHE), due to the sodium concentration of 6 mol L-1 we have to note +1.33 V. The current-overpotential curve represents an unhindered process... 

Since metallic sodium is unstable in aqueous solutions, the measurement of the reversible potential for reaction (44) is difficult. This was, however, overcome by measuring the voltage of a cell with sodium metal and amalgam as the electrode in an aprotic electrolyte, to ensure stability of sodium, as ... 

Bale] and coworkers published a number of papers on the thermodynamics and the reversible potential of sodium amalgam in contact with Na" " [18-27]. They measured the reversible potential of electrochemical cells consisting of... 

The second class of metallic solutes is represented by the less electropositive metals. Here, the situation is the reverse of that discussed above. Sodium amalgam is widely used in industry and in the laboratory and is a good example of this class. Upon addition of mercury to liquid sodium, the reactivity of the sodium toward aqueous solutions is vastly reduced, and reaction with hydrogen is slower by an order of magnitude than that for pure sodium. This fact is important in the operation of the Solvay cell for the industrial production of sodium hydroxide by electrolysis of brine, in which sodium amalgam forms one of the electrodes. In such amalgams, valency electrons from the conduction band of liquid sodium, which would normally be responsible for its chemical reactivity, are partially localized on the mercury atoms, thus inhibiting the reactivity of sodium. 

Amalgam electrodes are of value because they allow active metals, e.g. Na and K, to be used as electrodes. Reproducible, reversible potentials can be obtained at very low concentrations of the metal it is best to use dropping electrodes, in which the amalgam drips slowly into the electrolyte, so that the surface is always fresh. The potential of the amalgam is compared with that of the pure metal by using both in a cell in which the electrolyte is dissolved in a solvent which does not attack the pure metal (e.g. ethylamine). Thus, to determine E (K, K), the sum of the standard e.m.f. values of the two cells ... 

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