Mercury dissolution

Reactions of solid metals with liquid metals (e.g. dissolution of aluminium in mercury) Dissolution of metal in their fused halides (e.g. lead in lead chloride). 

Fig. 8.11 The potentials at which the anodic mercury dissolution due to OIT starts to occur in H20-AN and H20-DMS0 mixtures. Solution 0.28 mM Et4NOH + 0.1 M Et4NCI04...

When the anion of the supporting electrolyte is CIO4, BF4, PFg or CF3SO3, the positive limit of the potential window is determined by the anodic dissolution of mercury (Hg->Hg2+ or Hg +). However, when it is a halide ion, the potential of the anodic mercury dissolution shifts to negative direction, because the halide ion forms a precipitate with Hg2+. The negative shift is more marked in aprotic solvents than in water (Section 8.2.3). Therefore, halides are not suitable as supporting electrolyte in aprotic solvents. 

Attempts to use polarography in the study of protolysis of phenyl-tropylium ions failed because the compounds react with metallic mercury and therefore give on polarographic curves a very positive wave, which arises from mercury dissolution and is unsuitable for quantitative treatment (57). 

If one decants the liquor one will have separated silver, and on the other side mercury dissolution in nitrous acid, if one adds a lead blade to this mercury dissolution, lead has... 

The cathodic versatility of mercury is not matched by its anodic behaviour, mercury dissolution setting in at about 0-4 V (v saturated calomel electrode). Usually, as far as metal ions are concerned, this is of little importance, since almost all metal ions reduce at potentials considerably more negative than this. 

In some cases, particularly with iaactive metals, electrolytic cells are the primary method of manufacture of the fluoroborate solution. The manufacture of Sn, Pb, Cu, and Ni fluoroborates by electrolytic dissolution (87,88) is patented. A typical cell for continous production consists of a polyethylene-lined tank with tin anodes at the bottom and a mercury pool (ia a porous basket) cathode near the top (88). Pluoroboric acid is added to the cell and electrolysis is begun. As tin fluoroborate is generated, differences ia specific gravity cause the product to layer at the bottom of the cell. When the desired concentration is reached ia this layer, the heavy solution is drawn from the bottom and fresh HBP is added to the top of the cell continuously. The direct reaction of tin with HBP is slow but can be accelerated by passiag air or oxygen through the solution (89). The stannic fluoroborate is reduced by reaction with mossy tin under an iaert atmosphere. In earlier procedures, HBP reacted with hydrated stannous oxide. 

Mercuric Nitrate. Mercuric nitrate [10045-94-0] Hg(N02)2, is a colorless dehquescent crystalline compound prepared by the exothermic dissolution of mercury in hot, concentrated nitric acid. The reaction is complete when a cloud of mercurous chloride is not formed when the solution is treated with sodium chloride solution. The product crystallizes upon cooling. Mercuric nitrate is used in organic synthesis as the starting material and for the formulation of a great many other mercuric products. 

Dissolution of Silver. Silver is dissolved by oxidising acids and alkaU metal cyanide solutions in the presence of oxygen. The latter method is the principal technique for dissolving silver from ore. Silver has extensive solubiUty in mercury (qv) and low melting metals such as sodium, potassium, and their mixtures. Cyanide solutions of silver are used for electroplating and electroforming. The silver is deposited at the cathode either as pure crystals or as layers on a mandrel. 

Contact with steel, though less harmful, may accelerate attack on aluminium, but in some natural waters and other special cases aluminium can be protected at the expense of ferrous materials. Stainless steels may increase attack on aluminium, notably in sea-water or marine atmospheres, but the high electrical resistance of the two surface oxide films minimises bimetallic effects in less aggressive environments. Titanium appears to behave in a similar manner to steel. Aluminium-zinc alloys are used as sacrificial anodes for steel structures, usually with trace additions of tin, indium or mercury to enhance dissolution characteristics and render the operating potential more electronegative. 

Fig. 3. Evans-diagram for the cementation of Cu2+ and Pb2 with zinc amalgam of different zinc content. If the zinc concentration in the mercury employed for this special extraction technique is low, the anodic zinc-dissolution current density may be diffusion controlled and below the limiting cathodic current density for the copper reduction. The resulting mixed potential will lie near the halfwave potential for the reaction Cu2+ + 2e j Cu°(Hg) and only Cu2 ions are cemented into the mercury.

Essentially, stripping analysis is a two-step technique. The first, or deposition, step involves die electrolytic deposition of a small portion of the metal ions hi solution into die mercury electrode to preconcentrate the metals. This is followed by die shipping step (the measurement step), which involves die dissolution (shipping) of die deposit. Different versions of stripping analysis can be employed, depending upon die nature of the deposition and measurement steps. 

MacDonald on the adsorption of chloride ions in passivation, 237 of CO on electrochemically facetted platinum, 135 of diols on mercury, 188 of neutral compounds on electrodes, 185 of perchlorate ions, copper and, 94 specific adsorption, anodic dissolution and, 256... 

Mercury provides an excellent example of the importance of metal speciation in understanding biogeochemical cycling and the impact of human activities on these cycles. Mercury exists in solid, aqueous, and gaseous phases, and is transported among reservoirs in all these forms. It undergoes precipitation-dissolution, volatilization, complexation, sorption, and biological reactions, all of which alter its mobility and its effect on exposed populations. The effect of all... 

MDHS 14 General method for the gravimetric determination of respirable and total dust MDHS 15 Carbon disulphide MDHS 16 Mercury vapour in air Laboratory method using hopcalite adsorbent tubes, and acid dissolution with cold vapour atomic absorption spectrometric analysis MDHS 17 Benzene in air Laboratory method using charcoal adsorbent tubes, solvent desorption and gas chromatography MDHS 18 Tetra alkyl lead compounds in air Continuous on-site monitoring method using PAC Check atomic absorption spirometry... 

Fig. 6.5 Schematic representation of a bioelectronic protocol for detection of DNA hybridization (A) binding of the target to magnetic beads (B) hybridization with CdS-labeled probe (C) dissolution of CdS tag (D) potentiometric stripping detection at a mercury-film electrode. (Reprinted from [136], Copyright 2009, with permission from Elsevier)...

The reduction wave of peroxydisulphate at dme starts at the potential of the anodic dissolution of mercury. The current-potential curve exhibits certain anomalous characteristics under various conditions. At potentials more negative than the electrocapillary maximum, a current minimum can be observed this is due to the electrostatic repulsion of the peroxydisulphate ion by the negatively charged electrode surface. The current minimum depends on the concentration and nature of the supporting electrolyte, and can be eliminated by the adsorption of capillary active cations of the type NR4. ... 

The addition of trichloro- ortetrachloroethylene to aluminium components in dry cleaning equipments is responsible for many accidents. The effect of the carbon tetrachloride/methanol mixture in the 1/9 proportion of aluminium, magnesium or zinc causes the dissolution of these metals, whose exothermicity makes the interaction dangerous. There is a period of induction with zinc, which is cancelled out when copper dichloride, mercury dichloride or chromium tribromide is present. 

In certain areas, particularly the rapidly developing area of organo-metalhc spedation, concern has been expressed that artifacts may lead to false results. One example are the doubts about the accuracy and suspicion of possible artifact formation of methyhner-cury (MeHg) duriri analytical procedures, mainly distillation and alkaline dissolution, which were expressed for the first time at the Conference Mercury as a Global Pollu-tanf in 1996 (Hintelmann and Evans 1997 Hintelmann et al.1997). 

Owing to the considerable mercury overpotential for hydrogen, reductive polarography even in acidic media is frequently used (potentials varying from 0 to 2.2 V), whereas oxidative polarography, owing to possible dissolution of Hg metal, remains limited (potentials varying from 0 to +0.6 V, cf., Fig. 3.26). 

In oxidative polarography there is still the difficulty of a considerably limited potential range owing to dissolution of the mercury itself with a direct dependence on the electrolyte composition this is well illustrated in Fig. 3.26 for the following electrode reactions of Hg ... 

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. 

Since mercury has a contact angle with most solids of about 140°, it follows that its cosine is negative (i.e., it takes applied pressure to introduce mercury into a pore). In a mercury porosimeter, a solids sample is evacuated in a cell, mercury is then intruded, and the volume, V, is noted (it actually reads out), and the pressure, P, is then increased stepwise. In this fashion it is possible to deduce the pore volume of a particular radius [corresponding to P by Eq. (21)]. A pore size distribution will give the total internal pore area as well, which can be of importance in dissolution. 

The high overpotential of hydrogen is an advantage of DME while this property can be exploited only with mercury-covered RDE and UME. On the other hand, the dissolution of mercury at rather low positive potentials is a disadvantage of DME which is not shared by RDE and UME made of nobler metals than mercury. 

Thus films can be divided into two groups according to their morphology. Discontinuous films are porous, have a low resistance and are formed at potentials close to the equilibrium potential of the corresponding electrode of the second kind. They often have substantial thickness (up to 1 mm). Films of this kind include halide films on copper, silver, lead and mercury, sulphate films on lead, iron and nickel oxide films on cadmium, zinc and magnesium, etc. Because of their low resistance and the reversible electrode reactions of their formation and dissolution, these films are often very important for electrode systems in storage batteries. 

In contrast to the equilibrium electrode potential, the mixed potential is given by a non-equilibrium state of two different electrode processes and is accompanied by a spontaneous change in the system. Besides an electrode reaction, the rate-controlling step of one of these processes can be a transport process. For example, in the dissolution of mercury in nitric acid, the cathodic process is the reduction of nitric acid to nitrous acid and the anodic process is the ionization of mercury. The anodic process is controlled by the transport of mercuric ions from the electrode this process is accelerated, for example, by stirring (see Fig. 5.54B), resulting in a shift of the mixed potential to a more negative value, E mix. 

---