Amalgam, Formation

If the reductant is insoluble in water but soluble in the mercury phase (amalgam formation), equation (7) still holds. Substituting in equation (3), we have ... 

The electrode reaction, assuming amalgam formation, can be represented ... 

One way to view UPD is as formation of a surface compound. In other words, deposition of the first atomic layer of an element on a second element involves a larger deposition driving force than subsequent layers, as it benefits from the AG of compound formation. For deposits formed at underpotential, once the substrate is covered the deposition stops because the reaction is surface limited. No more of the substrate element is available to react, unless it can quickly diffuse to the surface through or around the initially deposited monolayer (an example would be amalgam formation at a mercury electrode surface). Subsequent deposition is then only observed when the bulk deposition potential has been exceeded. 

Terbium metal is obtained from its anhydrous trifluoride, TbFs, or trichloride, TbCls, by thermal reduction with calcium, carried out in a tantalum crucible. Terbium produced by such methods may contain traces of calcium and tantalum. High purity metal can be prepared by various methods such as vacuum remelting, distillation, amalgam formation, floating zone melting, and various chemical processes. 

Amalgam formation shifts the equilibrium potential of a metal (polarographic... 

The double-layer effect in the electrode kinetics of the amalgam formation reactions was discussed [67]. The dependences on the potential of two reduction (EE) mechanisms of divalent cations at mercury electrode, and ion transfer-adsorption (lA) were compared. It was suggested that a study of temperature dependence of the course of these reactions would be helpful to differentiate these two mechanisms. 

Caution. Amalgam formation is very exothermic. Do not continue adding sodium until each piece has reacted. 

We can get the formal potential for the amalgam formation by Eq. (5.18). Data on the diffusion coefficients of metals in mercury (DM(Hg)) are available in the IUPAC report [Galus, Z. Pure Appl. Chem. 1984, 56, 636],... 

Because alkali metals are stabilized by amalgam formation, the reductions of alkali metal ions occur at 0.5 to 1.0 V more positive potential than those of tLtbT ions. 

Anodic stripping voltammetry (ASV) is the most common version of stripping analysis. It involves the reduction of a metal ion to the metal (which usually dissolves in mercury, i.e., amalgam formation), as the preconcentration step ... 

The boundary value problem (bvp) by considering that the reduced species is initially present in the solution (solution soluble product) or in the electrode (amalgam formation), and that diffusion coefficients of both species are different, is... 

In Eq. (4.39), the upper sign refers to solution soluble product and the lower one to amalgam formation. When species R is amalgamated inside the electrode, the applicability of this analytical equation is limited by Koutecky approximation, which considers semi-infinite diffusion inside the electrode, neglecting its finite size and simplifying the calculations. Due to the limitations of this approximation, the analytical and numerical results coincide only for < 1 with a relative difference < 1.7% [20]. For higher values of c,. a numerical solution obtained with the condition (3cR/3r)r=0 = 0 should be used. 

An alternative which is attractive for large scale work is the electrochemical reduction of aldonolac-tones.42 43 Particular attention has been paid to the electroreductive synthesis of ribose from ribonolac-tone because of the importance of the former in the synthesis of riboflavin (vitamin 62). Processes generally involve a mercury cathode and maintenance of an acidic pH, often with the assistance of a phosphate or borate buffer. It has been reported that alkali metal ions are also necessary, suggesting that the reduction occurs via metal amalgam formation. However, other accounts make no mention of metal... 

Many lithium salts, such as lithium perchlorate and the halides, are soluble in nonaqueous solvents. The reduction potential of Li depends on the electrode and the solvent. At a mercury cathode amalgam formation takes place, whereas formation of lithium metal occurs at platinum in aprotic media. Lithium metal is less reactive than sodium, and in some solvents sodium attacks the solvent whereas lithium is unreactive. A small water content in an aprotic solvent may react with lithium (or Li may react with hydroxyl ions formed at the cathode) to form lithium hydroxide, which may cover the electrode with an insoluble, insulating layer. 

If a mercury cathode is expected to be necessary, the aprotic solvent-alkali-metal salt system appears to be inconvenient since many compounds are cathodically cleaved, reduced, or/and deprotected at potentials beyond that of alkali-metal amalgam formation. nevertheless, in certain cases the use of lithium salts as an electrolyte possessing strong electrophilic properties appears necessary in order to avoid the possibility of a Hofmann degradation of the tetraalkylammonium ion by electrogenerated bases. Under such experimental conditions, the cathodic synthesis of some aza and aza-oxa ligands [31] has been successfully achieved from the corresponding and readily obtained poly-... 

A study involving iron amalgams in acidic and alkaline media indicates a magnetic field effect on the Tafel slope, probably due to a complex interaction of the magnetic field with amalgam formation, diffusion, and hydrogen evolution. Experimental results obtained with cupric sulfate solutions show no magnetic field effect on the transfer coefficient... 

MERCURIC IODIDE or MERCURIC IODIDE, RED (7774-29-0) Hglj Aqueous solution is a weak reducing agent. Incompatible with acetylene, alkalis, ammonia, azides, chlorine dioxide, azides, bromides, calcium (amalgam formation), chlorides, cyanides, copper salts hydrogen... 

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