Mercury (Hg) is a chemical element of group II of the periodic system of elements. Mendeleev University; Atomic number 80, relative atomic mass 200.59. Mercury under normal conditions is a shiny, silver-white heavy liquid metal. Its specific gravity at 20 ° C is 13.54616 g / cm3; The melting point is -38.89 ° C, boiling point 357.25 ° C. When it freezes (-38.89 ° C), it becomes hard and easily liable to forging.
Even under normal conditions, mercury has an increased saturated vapor pressure and evaporates at a fairly high rate, which increases with increasing temperature. This leads to the creation of a mercury atmosphere that is dangerous to living organisms. For example, at 24 ° C, atmospheric air saturated with mercury vapor may contain about 18 mg / m3; This level is 1800 times higher than the maximum allowable concentration (maximum permissible concentration) of mercury in the air of the working area and 60,000 times the MPC in the ambient air. Mercury can evaporate through layers of water and other liquids.
When exposed to mercury vapor voltaic arc, electric spark and X-rays, phenomena of luminescence, fluorescence and phosphorescence are observed. In a vacuum tube between mercury electrodes in electrical discharges, a luminescence is obtained, rich in ultraviolet rays, which is used in engineering when designing mercury lamps. Another remarkable property of mercury is due to the fact that when metals are dissolved in it, amalgams are formed-metal systems, one of which is mercury. They do not differ from conventional alloys, although with excess mercury they are semi-liquid mixtures. The compounds resulting from amalgamation readily decompose below their melting point with the release of excess mercury, which has found wide application in the extraction of gold and silver from ores. Metals wetted by mercury are subject to amalgamation. Steels alloyed with carbon, silicon, chromium, nickel, molybdenum and niobium are not amalgamated.
Mercury – is very aggressive with respect to various construction materials, which leads to corrosion and destruction of production facilities and vehicles. So, in the 1970s. The problem of the contamination of airplanes, in the design of which mercury got into, causing liquid metal embrittlement of aluminum alloys, was quite actual. The aircraft were sent for major repairs and even decommissioned.
In compounds, mercury exhibits an oxidation state of +2 and +1. In the special literature, Hg (ll) or Hg (l) is usually indicated in such cases. With high ionization potential, high positive oxidation potential, mercury is a relatively chemically stable element.
This determines its ability to recover to the metal from various compounds and explains the frequent occurrences of mercury in nature in the native state.
In air, mercury is not oxidized at room temperature. When heated to temperatures close to the boiling point (300-350 ° C), it combines with air oxygen to form a red oxide of divalent mercury HgO, which upon further heating (up to 400 ° C and higher) again decomposes into mercury and oxygen. Yellow mercury oxide HgO is obtained by adding alkalis to an aqueous solution of the salt Hg (ll). There is also mercury oxide of black color (Hg2O), unstable compound, in which the oxidation state is +1. In hydrochloric and dilute sulfuric acids and in alkalis, mercury does not dissolve. But it dissolves easily in nitric acid and in royal vodka, and when heated in concentrated sulfuric acid. Metal mercury can dissolve in organic solvents, as well as in water, especially in the absence of free oxygen. Its solubility in water also depends on the pH of the solution. Minimal solubility is observed at pH 8, with increasing acidity or alkalinity of water it increases. In the presence of oxygen, mercury in water is oxidized to the ionic form of Hg2 + (creating concentrations of up to 40 μg / l).
Mercury reacts with halogens (chlorine, iodine, fluorine, bromine), sulfur, selenium, phosphorus and other non-metals. Of practical importance are iodine mercury HgJ, mercury chloride (calomel) Hg2Cl2 and chlorine mercury (mercuric chloride) HgCl2. When mercury reacts with sulfur, mercury sulphide HgS is formed, the most common in nature is its compound, in the form of which almost all of the mercury is extracted. It is known in three modifications: red (identical to the mineral cinnabar), black (black mercury sulphide, or metacinnabarite) and – p-cinnabar (in natural conditions it is not found). Other mercury compounds include mercury mercury Hg (ONC) 2, nitrate Hg (NO3) 2, sulfate (HgSO4) and sulfite (HgSO3), mercury red and yellow iodide, etc.
There is a large number of mercury-containing organic compounds in which metal atoms are bound to carbon atoms. The chemical bond between carbon and mercury is very stable. It is not destroyed by water, weak acids, or bases. From the standpoint of danger to living organisms (that is, from toxicology – the science of poisons), the most toxic of organometallic compounds of mercury are short-chain alkyl mercury compounds, primarily methylmercury.
Mercury is widely used in the manufacture of scientific instruments (barometers, thermometers, manometers, vacuum pumps, normal elements, polarographs, capillary electrometers, etc.), mercury lamps, switches, rectifiers; As a liquid cathode in the production of caustic alkali and chlorine by electrolysis, as a catalyst in the synthesis of acetic acid, in metallurgy for amalgamation of gold and silver, in the manufacture of explosives; In medicine (calomel, mercuric organic compounds, etc.), as a pigment (cinnabar), in agriculture (organic compounds of mercury) as a seed dressing and herbicide, as well as as a component of the paint of sea-going ships (to combat fouling by their organisms ). Mercury and its compounds are toxic, so working with them requires taking the necessary precautions.
Mercury has always found wide application in various spheres of practical, scientific and cultural activities of man. By the early 1980’s. It was known for over a thousand different areas of its application. Here are the main ones, in which mercury and its compounds are used to some extent and now:
– chemical industry – production of chlorine and caustic, acetaldehyde, chlorovinyl, polyurethanes, organomercury pesticides, paints;
– Electrotechnical industry – manufacture of various lamps, relays, dry batteries, switches, rectifiers, ignitrons, etc .;
– radio engineering industry and instrument making – production of instrumentation (thermometers, barometers, manometers, polarographs, electrometers), radio and television equipment;
– medicine and pharmaceutical industry – manufacturing of eye and skin ointments, substances of bactericidal action, production of vitamin B, making dental fillings (amalgams of silver and copper);
– Agriculture (pesticides, antiseptics);
– mechanical engineering and vacuum technology – the production of vacuum pumps, etc .;
– military business – the production of detonators, guided missiles;
– metallurgy – production of ultrapure metals, precise casting, amalgamation of precious metals;
– mining (rattling mercury);
– laboratory practice and analytical chemistry.
In the energy sector, mercury was used as a working fluid in powerful industrial-type binary installations, where mercury steam turbines were used to generate electricity at the first stages, as well as in nuclear reactors for heat removal. Elemental mercury is used in the processes of separation of lithium isotopes. Mercury is sometimes alloyed with other metals. Its small additives increase the hardness of the lead alloy with alkaline earth metals. It was even used for soldering. Mercury cyanide was used in the production of antiseptic soap.