Mercury, Hg At

Mercury (Hg, at. mass 200.59) occurs in its compounds in the I and II oxidation states. Mercury(II) is similar in its chemical properties to copper(II) and lead (II), whereas mercury(I) resembles silver and gold(I). Mercury(II) forms stable, mostly water-soluble, halide complexes. 

These elements formed Group IIB of Mendeleef s original periodic table. As we have seen in Chapter 13, zinc does not show very marked transition-metaf characteristics. The other two elements in this group, cadmium and mercury, lie at the ends of the second and third transition series (Y-Cd, La-Hg) and, although they resemble zinc in some respects in showing a predominantly - - 2 oxidation state, they also show rather more transition-metal characteristics. Additionally, mercury has characteristics, some of which relate it quite closely to its immediate predecessors in the third transition series, platinum and gold, and some of which are decidedly peculiar to mercury. 

Mercuric Chloride. Mercuric c Aon.d.e.[7487-94-7] HgCl2, is also known as corrosive sublimate of mercury or mercury bichloride. It is extremely poisonous, and is particularly dangerous because of high (7 g/L at 25°C) water solubiUty and high vapor pressure. It sublimes without decomposition at 300°C, and has a vapor pressure of 13 Pa (0.1 mm Hg) at 100°C, and 400 Pa (3 mm Hg) at 150°C. The vapor density is high (9.8 g/cm ), and therefore mercuric chloride vapor dissipates slowly (5). 

Mercury is an extremely toxic substance. Inhalation of the vapor is just as dangerous as swallowing the liquid. How many milliliters of mercury will saturate a room that is 15 X 12 X 8.0 ft with mercury vapor at 25°C The vapor pressure of Hg at 25°C is 0.00163 mm Hg and its density is 13 g/mL. 

Mercury (Quicksilver, Hydrargyrum), Hg, at wt 200.61, silvery liq, mp —38.87°, bp 356.9°, d 13.546g/cc at 20°. Insol in w, HC1, ale and eth sol In nitric acid. Sometimes found native poisonous. Can be prepd by heating the ore cinnabar (HgS) either in air or with lime. Forms numerous salts, some of which are very expl, eg, Hg fulminate, Hg azide, etc. The presence of Hg in expls, even in minute quants, is unde-sireable because it affects the result of thermal stability tests. Marshall (Ref 1) describes various tests used in Engl and Ger for its detection in different expls and propints Refs 1) Marshall 2, 708-12(1917) 2) Mellor... 

NOTE The standard atmospheric pressure of mercury (Hg) is 760 mm Hg (29.92 in) at 0 °C. Thus, ignoring barometric or temperature differences, it can be seen that the condenser back-pressure is usually in the range of 29 to 29.92 inches down to 26 inches, which equals 1 to 4 in mercury absolute (3.4-13.6 kPa). 

Since different metals strip from mercury electrodes at characteristic peak potentials, several metal ions can be determined simultaneously. Metal ions which have been determined by ASV at a mercury electrode are BP, Cd, Cu, Ga, Ge, In, NP, Pb, Sb, Sn, Tl, and Zn. Solid electrodes such as graphite enable Hg, Au, Ag, and PP to be determined by ASV. In this case, the metal is preconcentrated on the surface of the electrode as a metallic film, which is then stripped off by the positive potential scan. 

Upon disabling the Hg flux, the surface compounds of mercury decompose at elevated temperatures ... 

The above considerations also apply to the ion of an amalgamating metal with the reversible equilibrium M"+ + ne M(Hg) at a stationary mercury electrode such as an HMDE (hanging mercury drop) or an MTFE (mercury thin-film) with the restriction, however, that the solution can contain only ox, so that merely the cathodic wave (cf., eqn. 3.15) represents a direct dependence of the analyte concentration, whilst the reverse anodic wave concerns only the clean-back of amalgam formed by the previous cathodic amplitude. When one or both of the electrodic reactions is or becomes (in the case of a rapid potential sweep) irreversible, the cathodic wave shifts to a more negative potential and the anodic wave to a more positive potential (cf., Fig. 3.10) this may even result in a complete separation of the cathodic and anodic waves (cf., Fig. 3.11). 

Eight trace elements of greatest environmental concern are chosen, which are arsenic (As), mercury (Hg), lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni), copper (Cu) and zinc (Zn). These eight trace elements will be discussed in this chapter in the order of their production and level of environmental concern, as presented above. Of these, copper and lead are known to be the earliest metals utilized by humans. Lead was used by humankind at least 5000 years ago (Settle and Patterson, 1980 Adriano, 1986). The production of these eight elements has increased considerably since the dawn of the industrial age in the 1850s (Table 9.1). 

The porosity of the materials were characterized by nitrogen (N2) adsorption-desorption at 77K, mercury (Hg) intrusion and electron microscopy (TEM) (table 1). 

The following analytical techniques seem to be adequate for the concentrations under consideration copper and nickel by Freon extraction and FAA cold vapour atomic absorption spectrometry, cobalt by Chelex extraction and differential pulse polarography, mercury by cold vapour atomic absorption absorptiometry, lead by isotope dilution plus clean room manipulation and mass spectrometry. These techniques may be used to detect changes in the above elements for storage tests Cu at 8 nmol/kg, Ni at 5 nmol/kg, Co at 0.5 nmol/kg, Hg at 0.1 nmol/kg, and Pb at 0.7 nmol/kg. 

A similar conclusion arises from the capacitance data for the mercury electrode at far negative potentials (q 0), where anions are desorbed. In this potential range, the double-layer capacitance in various electrolytes is generally equal to ca. 0.17 F Assuming that the molecular diameter of water is 0.31 nm, the electric permittivity can be calculated as j = Cd/e0 = 5.95. The data on thiourea adsorption on different metals and in different solvents have been used to find the apparent electric permittivity of the inner layer. According to the concept proposed by Parsons, thiourea can be treated as a probe dipole. It has been cdculated for the Hg electrode that at (7 / = O.fij is equal to 11.4, 5.8, 5.1, and 10.6 in water, methanol, ethanol, and acetone, respectively. 

Fig. 1. (A) 0(ls) spectra for gold exposed to carbon dioxide at 85 K (a) clean Au (b), (c), and (d) after exposure to CO2. (B) Au(4f) and Hg(4f) spectra after exposure of gold foil to mercury vapor at 290 K. The mercury and gold peaks are well separated and in contrast to Auger spectra which overlap.

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