Sodium amalgam electrodes

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... 

The use of a sodium amalgam electrode [Na(Hg)/NaC104(s)] in DMF has been reported [205] and a similar lithium amalgam electrode has been employed in DMSO [207]. The potential of the cell, Li(Hg)/Li Cr (DMSO), has been measured for LiCl concentrations from 0.01 to 1.0 M and the Nernst relation was verified within 1 mV the Li(Hg) electrode obeys the Tafel equation with the transfer coefficient a = 0.5 over... 

The reversible potential of the sodium amalgam electrode, considering an amalgam concentration of 0.2 wt% sodium and the already mentioned sodium concentration, amounts to —1.78 V (the difference to the Na/Na+-standard potential —2.71 V is due to the fact that in the case of amalgam the discharged sodium ions must not be incorporated into a metallic structure). 

Figure 12. Polarization curves of sodium amalgam electrode in 50% NaOH.

Equation (53) represents the reversible potential of the sodium amalgam electrode at any concentration, with respect to the same electrode at a specific concentration or activity. For example, the potential of the 0.1 w/o Na amalgam at 80°C is ... 

Although Na(s) reacts violently with water to produce H2(g), at least for a short time, a sodium amalgam electrode does not react with water. This makes it possible to determine Eceii for the following voltaic cell. 

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

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... 

It is found that in alkaline solutions (Ph > H for soft glass) the glass no longer functions as a hydrogen electrode but is affected by an alteration in the sodium ion concentration of the solution. With sodium amalgams, in fact, glass may serve as a sodium electrode of constant thermodynamic potential. 

Numerous methods for the synthesis of salicyl alcohol exist. These involve the reduction of salicylaldehyde or of salicylic acid and its derivatives. The alcohol can be prepared in almost theoretical yield by the reduction of salicylaldehyde with sodium amalgam, sodium borohydride, or lithium aluminum hydride by catalytic hydrogenation over platinum black or Raney nickel or by hydrogenation over platinum and ferrous chloride in alcohol. The electrolytic reduction of salicylaldehyde in sodium bicarbonate solution at a mercury cathode with carbon dioxide passed into the mixture also yields saligenin. It is formed by the electrolytic reduction at lead electrodes of salicylic acids in aqueous alcoholic solution or sodium salicylate in the presence of boric acid and sodium sulfate. Salicylamide in aqueous alcohol solution acidified with acetic acid is reduced to salicyl alcohol by sodium amalgam in 63% yield. Salicyl alcohol forms along with -hydroxybenzyl alcohol by the action of formaldehyde on phenol in the presence of sodium hydroxide or calcium oxide. High yields of salicyl alcohol from phenol and formaldehyde in the presence of a molar equivalent of ether additives have been reported (60). Phenyl metaborate prepared from phenol and boric acid yields salicyl alcohol after treatment with formaldehyde and hydrolysis (61). 

In order to get the potential of the sodium electrode in aqueous 0.100M NaCl against a calomel electrode in the same solution, one measures the emfs of cells (1) and (2). Cell (1) is to measure the potential of the amalgam electrode (Na(Hg)) and cell (2) to measure the potential of the Na electrode against the Na(Hg) electrode. The sum of the emfs of the two cells (-3.113 V) corresponds to the emf of the hypothetical cell (3) and is equal to the potential of the Na electrode in the aqueous solution. 

By running a potentiometric precipitation titration, we can determine both the compositions of the precipitate and its solubility product. Various cation- and anion-selective electrodes as well as metal (or metal amalgam) electrodes work as indicator electrodes. For example, Coetzee and Martin [23] determined the solubility products of metal fluorides in AN, using a fluoride ion-selective LaF3 single-crystal membrane electrode. Nakamura et al. [2] also determined the solubility product of sodium fluoride in AN and PC, using a fluoride ion-sensitive polymer membrane electrode, which was prepared by chemically bonding the phthalocyanin cobalt complex to polyacrylamide (PAA). The polymer membrane electrode was durable and responded in Nernstian ways to F and CN in solvents like AN and PC. 

The theoretical decomposition voltage of sodium chloride may be calculated as the sum of the reversible oxidation potential of the chlorine electrode and the reversible reduction potential of the amalgam electrode. 

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. 

Figure 6.1 Schematic of a chlor-alkali cell in which an electric current is passed through a sodium chloride solution (hrine). Chlorine gas is produced at the anode (note the paddle-like electrodes with the positive charge at the top), and sodium dissolves in the cathode (note the negative charge at the bottom). In this case, the cathode is a pool of elemental mercury, and the sodium amalgam is later hydrolyzed to produce sodium hydroxide.

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