Arsenic(lat. arsenicum), as, chemical element v groups periodic system Mendeleev, atomic number 33, atomic mass 74.9216; steel gray crystals. The element consists of one stable isotope 75 as.

History reference. Natural compounds of M. with sulfur (orpiment as 2 s 3, realgar as 4 s 4) were known to the peoples ancient world who used these minerals as medicines and paints. The product of burning sulfides of M. was also known - the oxide of M. (iii) as 2 o 3 (“white M.”). The name arsenik o n is already found in Aristotle; it is derived from the Greek a rsen - strong, courageous and served to designate M. compounds (according to their strong effect on the body). The Russian name is believed to have come from "mouse" (according to the use of M.'s preparations for the extermination of mice and rats). Getting M. in a free state is attributed Albert the Great(about 1250). In 1789 A. Lavoisier included M. in the list of chemical elements.

distribution in nature. The average content of M. in the earth's crust (clarke) is 1.7 × 10 -4% (by mass), in such quantities it is present in most igneous rocks. Since M.'s compounds are volatile at high temperatures, the element does not accumulate during magmatic processes; it is concentrated by precipitating from hot deep waters (together with s, se, sb, fe, co, ni, cu, and other elements). During volcanic eruptions, M. in the form of its volatile compounds enters the atmosphere. Since M. is multivalent, its migration is greatly influenced by the redox environment. Under the oxidizing conditions of the earth's surface, arsenates (as 5+) and arsenites (as 3+) are formed. These are rare minerals found only in areas of mineral deposits. Native mineral and as 2+ minerals are even rarer. Of the numerous minerals of M. (about 180), only arsenopyrite feass is of major industrial importance.

Small amounts of M. are necessary for life. However, in the areas of the M. deposit and the activity of young volcanoes, soils in places contain up to 1% M., which is associated with livestock diseases and the death of vegetation. M.'s accumulation is especially characteristic of the landscapes of the steppes and deserts, in the soils of which M. is inactive. In a humid climate, M. is easily washed out of the soil.

In living matter, on average, 3 × 10 -5% M., in rivers 3 × 10 -7%. M., brought by rivers into the ocean, is relatively quickly precipitated. AT sea ​​water only 1 10 -7% M., but in clays and shales 6.6 10 -4%. Sedimentary iron ores, ferromanganese nodules are often enriched in M.

Physical and chemical properties. M. has several allotropic modifications. Under normal conditions, the most stable is the so-called metallic, or gray, M. (a -as) - a gray-steel brittle crystalline mass; in a fresh fracture it has a metallic luster, quickly tarnishes in air, because it is covered with a thin film of as 2 o 3. The crystal lattice of gray M. is rhombohedral ( a= 4.123 a , angle a = 54°10", X= 0.226), layered. Density 5.72 g/cm 3(at 20°c), electrical resistivity 35 10 -8 ohm? m, or 35 10 -6 ohm? cm, temperature coefficient of electrical resistance 3.9 10 -3 (0°-100 °c), Brinell hardness 1470 MN/m 2, or 147 kgf/mm 2(3-4 according to Mohs); M. is diamagnetic. Under atmospheric pressure, M. sublimates at 615 ° C without melting, since the triple point a -as lies at 816 ° C and a pressure of 36 at. Steam M. up to 800 ° C consists of molecules as 4, above 1700 ° C - only from as 2. During the condensation of vapor M. on a surface cooled by liquid air, yellow M. is formed - transparent, wax-soft crystals, with a density of 1.97 g/cm 3, similar in properties to white phosphorus. Under the action of light or upon slight heating, it turns into gray M. Glassy-amorphous modifications are also known: black M. and brown M., which, when heated above 270 ° C, turn into gray M.

The configuration of the outer electrons of the atom M. 3 d 10 4 s 2 4 p 3 . In compounds, M. has the oxidation states + 5, + 3, and - 3. Gray M. is much less chemically active than phosphorus. When heated in air above 400 ° C, M. burns, forming as 2 o 3. M. connects to halogens directly; under normal conditions asf 5 - gas; asf 3 , ascl 3 , asbr 3 - colorless, easily volatile liquids; asi 3 and as 2 l 4 are red crystals. When M. is heated with sulfur, sulfides are obtained: orange-red as 4 s 4 and lemon-yellow as 2 s 3 . Pale yellow sulfide as 2 s 5 precipitates when h 2 s is passed into an ice-cooled solution of arsenic acid (or its salts) in fuming hydrochloric acid: 2h 3 aso 4 + 5h 2 s \u003d as 2 s 5 + 8h 2 o; around 500°c it decomposes into as 2 s 3 and sulfur. All M.'s sulfides are insoluble in water and dilute acids. Strong oxidizing agents (mixtures of hno 3 + hcl, hcl + kclo 3) convert them into a mixture of h 3 aso 4 and h 2 so 4. Sulfide as 2 s 3 is easily soluble in sulfides and polysulfides of ammonium and alkali metals, forming salts of acids - thioarsenous h 3 ass 3 and thioarsenic h 3 ass 4 . With oxygen, M. gives oxides: oxide M. (iii) as 2 o 3 - arsenic anhydride and oxide M. (v) as 2 o 5 - arsenic anhydride. The first of these is formed by the action of oxygen on M. or its sulfides, for example, 2as 2 s 3 + 9o 2 \u003d 2as 2 o 3 + 6so 2. Vapors as 2 o 3 condense into a colorless glassy mass, which becomes opaque over time due to the formation of small cubic crystals, density 3.865 g/cm 3. The vapor density corresponds to the formula as 4 o 6: above 1800°c, the vapor consists of as 2 o 3 . At 100 G water dissolves 2.1 G as 2 o 3 (at 25°c). Oxide M. (iii) is an amphoteric compound, with a predominance of acidic properties. Salts (arsenites) are known that correspond to orthoarsenic h 3 aso 3 and metaarsenic haso 2 acids; the acids themselves have not been obtained. Only alkali metal and ammonium arsenites are soluble in water. as 2 o 3 and arsenites are usually reducing agents (for example, as 2 o 3 + 2i 2 + 5h 2 o \u003d 4hi + 2h 3 aso 4), but they can also be oxidizing agents (for example, as 2 o 3 + 3c \u003d 2as + 3co ).

Oxide M. (v) is obtained by heating arsenic acid h 3 aso 4 (about 200°c). It is colorless, about 500°c decomposes into as 2 o 3 and o 2 . Arsenic acid is obtained by the action of concentrated hno 3 on as or as 2 o 3 . Salts of arsenic acid (arsenates) are insoluble in water, with the exception of alkali metal and ammonium salts. Salts corresponding to acids orthoarsenic h 3 aso 4 , metaarsenic haso 3 , and pyroarsenic h 4 as 2 o 7 are known; the last two acids have not been obtained in the free state. When fused with metals, M. for the most part forms compounds ( arsenides).

Getting and using . M. is obtained in industry by heating arsenic pyrites:

feass = fes + as

or (more rarely) as 2 o 3 reduction with charcoal. Both processes are carried out in refractory clay retorts connected to a receiver for condensing M vapor. Arsenic anhydride is obtained by oxidative roasting of arsenic ores or as a by-product of roasting polymetallic ores, which almost always contain M. During oxidative roasting, as 2 o 3 vapors are formed, which condense into capture chambers. Crude as 2 o 3 is purified by sublimation at 500-600°c. Purified as 2 o 3 is used for the production of M. and its preparations.

Small additives of M. (0.2-1.0% by weight) are introduced into lead used for the production of shotgun shot (M. increases the surface tension of molten lead, due to which the shot acquires a shape close to spherical; M. slightly increases the hardness of lead ). As a partial substitute for antimony, M. is part of some babbits and printing alloys.

Pure M. is not poisonous, but all its compounds that are soluble in water or that can go into solution under the action of gastric juice are extremely poisonous; especially dangerous arsenic hydrogen. Of the compounds used in the production of M., arsenic anhydride is the most toxic. Almost all sulfide ores of non-ferrous metals, as well as iron (sulfur) pyrite, contain an admixture of M.. Therefore, during their oxidative roasting, along with sulfur dioxide so 2, as 2 o 3 is always formed; most of it condenses in the smoke channels, but in the absence or low efficiency of treatment facilities, the exhaust gases of ore kilns entrain significant amounts of as 2 o 3 . Pure M., although not poisonous, is always covered with a coating of poisonous as 2 o 3 when stored in air. In the absence of proper ventilation, it is extremely dangerous to pickle metals (iron, zinc) with technical sulfuric or hydrochloric acid containing an admixture of M., since arsenic hydrogen is formed in this case.

S. A. Pogodin.

M. in the body. As trace element M. is ubiquitous in wildlife. The average content of M. in soils is 4 10 -4%, in plant ash - 3 10 -5%. The content of M. in marine organisms is higher than in terrestrial ones (in fish 0.6-4.7 mg in 1 kg crude matter accumulates in the liver). The average content of M. in the human body is 0.08-0.2 mg/kg. In the blood, M. is concentrated in erythrocytes, where it binds to the hemoglobin molecule (moreover, the globin fraction contains twice as much of it as the heme). The largest amount of it (per 1 G tissue) is found in the kidneys and liver. A lot of M. is contained in the lungs and spleen, skin and hair; relatively little - in the cerebrospinal fluid, brain (mainly the pituitary gland), gonads, etc. In the tissues of M. is in the main protein fraction, much less - in the acid-soluble and only a small part of it is found in the lipid fraction. M. is involved in redox reactions: the oxidative breakdown of complex carbohydrates, fermentation, glycolysis, etc. M. compounds are used in biochemistry as specific inhibitors enzymes to study metabolic reactions.

M. in medicine. Organic compounds M. (aminarson, miarsenol, novarsenal, osarsol) are used mainly for the treatment of syphilis and protozoal diseases. Inorganic preparations M. - sodium arsenite (sodium arsenic acid), potassium arsenite (potassium arsenic acid), arsenic anhydride as 2 o 3, are prescribed as general tonic and tonic. When applied topically, inorganic preparations of M. can cause a necrotizing effect without previous irritation, which is why this process proceeds almost painlessly; this property, which is most pronounced in as 2 o 3 , is used in dentistry to destroy the dental pulp. M.'s inorganic preparations are also used to treat psoriasis.

Artificially obtained radioactive isotopes M. 74 as (t 1 / 2 = 17.5 day) and 76 as (t 1/2 = 26.8 h) are used for diagnostic and therapeutic purposes. With their help, the localization of brain tumors is clarified and the degree of radicalness of their removal is determined. Radioactive M. is sometimes used for blood diseases, etc.

According to the recommendations of the International Commission on Radiation Protection, the maximum allowable content of 76 as in the body is 11 microcurie. According to the sanitary standards adopted in the USSR, the maximum permissible concentrations of 76 as in water and open reservoirs are 1 10 -7 curie/l, in the air of working rooms 5 10 -11 curie/l. All M.'s preparations are very poisonous. In acute poisoning, they experience severe abdominal pain, diarrhea, kidney damage; possible collapse, convulsions. In chronic poisoning, the most common are gastrointestinal disorders, catarrhs ​​of the mucous membranes of the respiratory tract (pharyngitis, laryngitis, bronchitis), skin lesions (exanthema, melanosis, hyperkeratosis), sensitivity disorders; possible development of aplastic anemia. In the treatment of poisoning with drugs M. highest value give unithiol.

Measures to prevent industrial poisoning should be aimed primarily at mechanization, sealing and dust removal of the technological process, at creating effective ventilation and providing workers with personal protective equipment against dust exposure. Regular medical examinations of workers are required. Preliminary medical examinations are carried out upon employment, and for employees - once every six months.

Lit.: Remi G., Course of inorganic chemistry, trans. from German, vol. 1, M., 1963, p. 700-712; Pogodin S. A., Arsenic, in the book: Brief Chemical Encyclopedia, vol. 3, M., 1964; Harmful substances in industry, under the general. ed. N. V. Lazareva, 6th ed., part 2, L., 1971.

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ARSENIC- a chemical element of group V periodic table belongs to the nitrogen family. Relative atomic mass 74.9216. In nature, arsenic is represented by only one stable nuclide, 75 As. More than ten of its radioactive isotopes with a half-life from several minutes to several months have also been artificially obtained. Typical oxidation states in compounds are –3, +3, +5. The name of arsenic in Russian is associated with the use of its compounds for the extermination of mice and rats; The Latin name Arsenicum comes from the Greek "Arsen" - strong, powerful.

Historical information.

Arsenic belongs to the five "alchemical" elements discovered in the Middle Ages (surprisingly, four of them - As, Sb, Bi and P are in the same group of the periodic table - the fifth). At the same time, arsenic compounds have been known since ancient times, they were used for the production of paints and medicines. Of particular interest is the use of arsenic in metallurgy.

Several millennia ago, the Stone Age gave way to the Bronze Age. Bronze is an alloy of copper and tin. Historians believe that the first bronze was cast in the Tigris and Euphrates valley, sometime between the 30th and 25th centuries. BC. In some regions, bronze was smelted with especially valuable properties - it was better cast and easier to forge. As modern scientists have found out, it was a copper alloy containing from 1 to 7% arsenic and no more than 3% tin. Probably, at first, during its smelting, the rich copper ore malachite was confused with the weathering products of some also green sulfide copper-arsenic minerals. Having appreciated the remarkable properties of the alloy, the ancient craftsmen then specifically looked for arsenic minerals. For searches, they used the property of such minerals to give a specific garlic smell when heated. However, over time, the smelting of arsenic bronze ceased. Most likely this happened due to frequent poisoning during the firing of arsenic-containing minerals.

Of course, arsenic was known in the distant past only in the form of its minerals. So, in ancient China, the solid mineral realgar (sulfide composition As 4 S 4, realgar in Arabic means “mine dust”) was used for stone carving, however, when heated or exposed to light, it “spoiled”, as it turned into As 2 S 3 . In the 4th c. BC. Aristotle described this mineral under the name "sandarak". In the 1st century AD the Roman writer and scientist Pliny the Elder, and the Roman physician and botanist Dioscorides described the mineral orpiment (arsenic sulfide As 2 S 3). Translated from Latin, the name of the mineral means "golden paint": it was used as a yellow dye. In the 11th century alchemists distinguished three "varieties" of arsenic: the so-called white arsenic (oxide As 2 O 3), yellow arsenic (sulfide As 2 S 3) and red arsenic (sulfide As 4 S 4). White arsenic was obtained by sublimation of arsenic impurities during the roasting of copper ores containing this element. Condensing from the gas phase, arsenic oxide precipitated in the form of a white deposit. White arsenic has been used since ancient times to kill pests, as well as...

In the 13th century Albert von Bolstedt (Albert the Great) obtained a metal-like substance by heating yellow arsenic with soap; it may have been the first sample of arsenic in the form a simple substance obtained artificially. But this substance broke the mystical "connection" of the seven known metals with the seven planets; this is probably why the alchemists considered arsenic an "illegitimate metal". At the same time, they discovered its property to give copper a white color, which gave reason to call it "a means that whitens Venus (that is, copper)."

Arsenic was unequivocally identified as an individual substance in the middle of the 17th century, when the German pharmacist Johann Schroeder obtained it in a relatively pure form by reducing the oxide with charcoal. Later, the French chemist and physician Nicolas Lemery obtained arsenic by heating a mixture of its oxide with soap and potash. In the 18th century arsenic was already well known as an unusual "semi-metal". In 1775 the Swedish chemist K.V. Scheele obtained arsenic acid and gaseous arsenic hydrogen, and in 1789 A.L. Lavoisier finally recognized arsenic as an independent chemical element. In the 19th century were opened organic compounds containing arsenic.

Arsenic in nature.

There is little arsenic in the earth's crust - about 5 10 -4% (that is, 5 g per ton), about the same as germanium, tin, molybdenum, tungsten or bromine. Often arsenic in minerals occurs together with iron, copper, cobalt, nickel.

The composition of the minerals formed by arsenic (and there are about 200 of them) reflects the "semi-metallic" properties of this element, which can be in both positive and negative oxidation states and combine with many elements; in the first case, arsenic can play the role of a metal (for example, in sulfides), in the second - a non-metal (for example, in arsenides). The complex composition of a number of arsenic minerals reflects its ability, on the one hand, to partially replace sulfur and antimony atoms in the crystal lattice (the ionic radii S -2, Sb -3 and As -3 are close and amount to 0.182, 0.208 and 0.191 nm, respectively), on the other hand are metal atoms. In the first case, arsenic atoms have rather a negative oxidation state, in the second - a positive one.

The electronegativity of arsenic (2.0) is low, but higher than that of antimony (1.9) and most metals; therefore, the oxidation state –3 is observed for arsenic only in metal arsenides, as well as in SbAs stibarsen and intergrowths of this mineral with pure crystals. antimony or arsenic (the mineral allemontite). Many compounds of arsenic with metals, judging by their composition, are related to intermetallic compounds rather than arsenides; some of them are characterized by a variable content of arsenic. In arsenides, several metals can be present simultaneously, the atoms of which, at a close ion radius, replace each other in the crystal lattice in arbitrary ratios; in such cases, in the mineral formula, the symbols of the elements are listed separated by commas. All arsenides have a metallic luster, they are opaque, heavy minerals, their hardness is low.

An example of natural arsenides (about 25 of them are known) are the minerals löllingite FeAs 2 (an analogue of pyrite FeS 2), skutterudite CoAs 2–3 and nickelskutterudite NiAs 2–3, nickeline (red nickel pyrite) NiAs, rammelsbergite (white nickel pyrite) NiAs 2 , safflorite (speis cobalt) CoAs 2 and clinosafflorite (Co,Fe,Ni)As 2, langisite (Co,Ni)As, sperrylite PtAs 2, maucherite Ni 11 As 8, oregonite Ni 2 FeAs 2, algodonite Cu 6 As. Due to their high density (more than 7 g/cm3), geologists refer many of them to the group of "super-heavy" minerals.

The most common arsenic mineral is arsenopyrite (arsenic pyrite) FeAsS can be considered as a product of the replacement of sulfur in pyrite FeS 2 by arsenic atoms (ordinary pyrite also always contains a little arsenic). Such compounds are called sulfosalts. The minerals cobaltite (cobalt luster) CoAsS, glaucodot (Co,Fe)AsS, gersdorfite (nickel luster) NiAsS, enargite and lusonite of the same composition, but different structure Cu 3 AsS 4 , proustite Ag 3 AsS 3 - an important silver ore, were formed similarly. sometimes called "ruby silver" due to its bright red color, it is often found in upper layers silver veins, where magnificent large crystals of this mineral are found. Sulfosalts may also contain noble metals of the platinum group; these minerals are osarsite (Os,Ru)AsS, ruarsite RuAsS, irarsite (Ir,Ru,Rh,Pt)AsS, platarsite (Pt,Rh,Ru)AsS, hollingworthite (Rd,Pt,Pd)AsS. Sometimes the role of sulfur atoms in such double arsenides is played by antimony atoms, for example, in seinjayokite (Fe,Ni)(Sb,As) 2, arsenopalladinite Pd 8 (As,Sb) 3, arsenepolybasite (Ag,Cu) 16 (Ar,Sb) 2 S 11 .

The structure of minerals is interesting, in which arsenic is present simultaneously with sulfur, but rather plays the role of a metal, grouping together with other metals. These are the minerals arsenosulvanite Cu 3 (As,V)S 4 , arsenohauchecornite Ni 9 BiAsS 8 , freibergite (Ag,Cu,Fe) 12 (Sb,As) 4 S 13 , tennantite (Cu,Fe) 12 As 4 S 13 , argentotennantite (Ag,Cu) 10 (Zn,Fe) 2 (As,Sb) 4 S 13, goldfieldite Cu 12 (Te,Sb,As) 4 S 13, girodite (Cu,Zn,Ag) 12 (As,Sb) 4 (Se,S) 13 . One can imagine what a complex structure the crystal lattice of all these minerals has.

Arsenic has a clearly positive oxidation state in natural sulfides - yellow orpiment As 2 S 3, orange-yellow dimorphite As 4 S 3, orange-red realgar As 4 S 4, carmine-red getchellite AsSbS 3, and also in colorless oxide As 2 O 3, which occurs as minerals arsenolite and claudetite with different crystal structures (they are formed as a result of weathering of other arsenic minerals). These minerals usually occur as small inclusions. But in the 30s of the 20th century. in the southern part of the Verkhoyansk Range, huge crystals of orpiment up to 60 cm in size and weighing up to 30 kg were found.

In natural salts of arsenic acid H 3 AsO 4 - arsenates (about 90 of them are known), the oxidation state of arsenic is +5; examples are bright pink erythrin (cobalt color) Co 3 (AsO 4) 2 8H 2 O, green annabergite Ni 3 (AsO 4) 2 8H 2 O, scorodite Fe III AsO 4 2H 2 O and simplesite Fe II 3 (AsO 4) 2 8H 2 O, brown-red gasparite (Ce, La, Nd) ArO 4, colorless gernesite Mg 3 (AsO 4) 2 8H 2 O, rooseveltite BiAsO 4 and kettigite Zn 3 (AsO 4) 2 8H 2 O, as well as many basic salts, for example, olivenite Cu 2 AsO 4 (OH), arsenobismite Bi 2 (AsO 4) (OH) 3. But natural arsenites - derivatives of arsenous acid H 3 AsO 3 are very rare.

In central Sweden, there are the famous Langban iron-manganese quarries, in which more than 50 samples of minerals representing arsenates have been found and described. Some of them are not found anywhere else. They were once formed as a result of the reaction of arsenic acid H 3 AsO 4 with pyrocroite Mn (OH) 2 at not very high temperatures. Usually, arsenates are products of the oxidation of sulfide ores. They usually do not have industrial applications, but some of them are very beautiful and adorn mineralogical collections.

In the names of numerous arsenic minerals one can find toponyms (Lölling in Austria, Freiberg in Saxony, Seinäjoki in Finland, Skutterud in Norway, Allemon in France, the Canadian Langis mine and the Getchell mine in Nevada, Oregon in the USA, etc.), the names of geologists, chemists, politicians, etc. (German chemist Karl Rammelsberg, Munich mineral merchant William Maucher, mine owner Johann von Gersdorff, French chemist F. Claude, English chemists John Proust and Smithson Tennant, Canadian chemist F. L. Sperry, US President Roosevelt, etc.), plant names (so, the name of the mineral safflorite comes from saffron), initial letters the names of the elements - arsenic, osmium, ruthenium, iridium, palladium, platinum, Greek roots ("erythros" - red, "enargon" - visible, "lithos" - stone), etc. etc.

An interesting ancient name for the mineral nickeline (NiAs) is kupfernickel. Medieval German miners called Nickel the evil mountain spirit, and Kupfernickel (Kupfernickel, from German Kupfer - copper) - "damn copper", "fake copper". The copper-red crystals of this ore looked very much like copper ore; it was used in glass making to color glass green. But no one could get copper from it. This ore was studied by the Swedish mineralogist Axel Kronstedt in 1751 and isolated a new metal from it, calling it nickel.

Since arsenic is chemically quite inert, it is also found in its native state - in the form of fused needles or cubes. Such arsenic usually contains from 2 to 16% impurities - most often it is Sb, Bi, Ag, Fe, Ni, Co. It is easy to grind into powder. In Russia, native arsenic was found by geologists in Transbaikalia, in the Amur Region, and it is also found in other countries.

Arsenic is unique in that it is found everywhere - in minerals, rocks, soil, water, plants and animals, it is not for nothing that it is called "ubiquitous". The distribution of arsenic over different regions of the globe was largely determined in the processes of formation of the lithosphere by the volatility of its compounds at high temperatures, as well as by the processes of sorption and desorption in soils and sedimentary rocks. Arsenic migrates easily, which is facilitated by the rather high solubility of some of its compounds in water. In humid climates, arsenic is washed out of the soil and carried away by groundwater and then by rivers. The average content of arsenic in the rivers is 3 µg/l, in surface waters- about 10 µg/l, in the water of the seas and oceans - only about 1 µg/l. This is due to the relatively rapid precipitation of its compounds from water with accumulation in bottom sediments, for example, in ferromanganese nodules.

In soils, the arsenic content is usually between 0.1 and 40 mg/kg. But in the area of ​​occurrence of arsenic ores, as well as in volcanic regions, the soil can contain a lot of arsenic - up to 8 g / kg, as in some areas of Switzerland and New Zealand. In such places, vegetation dies, and animals get sick. This is typical for steppes and deserts, where arsenic is not washed out of the soil. Clay rocks are also enriched in comparison with the average content - they contain four times more arsenic than the average. In our country, the maximum allowable concentration of arsenic in the soil is 2 mg/kg.

Arsenic can be removed from the soil not only by water, but also by wind. But for this, it must first turn into volatile organoarsenic compounds. This transformation occurs as a result of the so-called biomethylation - the addition of a methyl group with the formation of a C–As bond; this enzymatic process (it is well known for mercury compounds) occurs with the participation of the coenzyme methylcobalamin, a methylated derivative of vitamin B 12 (it is also found in the human body). Biomethylation of arsenic occurs both in fresh and sea water and leads to the formation of organoarsenic compounds - methylarsonic acid CH 3 AsO (OH) 2, dimethylarsine (dimethylarsenic, or cacodylic) acid (CH 3) 2 As (O)OH, trimethylarsine ( CH 3) 3 As and its oxide (CH 3) 3 As = O, which are also found in nature. Using 14 C-labeled methylcobalamin and 74 As-labeled sodium hydrogen arsenate Na 2 HAsO 4, it was shown that one of the methanobacteria strains reduces and methylates this salt to volatile dimethylarsine. As a result, the air in rural areas contains an average of 0.001 - 0.01 μg / m 3 arsenic, in cities where there are no specific pollution - up to 0.03 μg / m 3, and near sources of pollution (non-ferrous metal smelting plants, power plants, working on coal with a high content of arsenic, etc.) the concentration of arsenic in the air can exceed 1 µg/m 3 . The intensity of arsenic fallout in the areas of industrial centers is 40 kg/km 2 per year.

The formation of volatile compounds of arsenic (trimethylarsine, for example, boils at only 51 ° C) caused in the 19th century. numerous poisonings, since arsenic was contained in plaster and even in green wallpaper paint. In the form of paint, Scheele greens Cu 3 (AsO 3) 2 were used earlier. n H 2 O and Parisian or Schweifurt greens Cu 4 (AsO 2) 6 (CH 3 COO) 2. In conditions of high humidity and the appearance of mold, volatile organoarsenic derivatives are formed from such paint. It is believed that this process could be the reason for the slow poisoning of Napoleon in last years his life (as you know, arsenic was found in Napoleon's hair a century and a half after his death).

Arsenic is found in significant amounts in some mineral waters. Russian standards establish that arsenic in medicinal table mineral waters should not exceed 700 µg/l. AT Jermuk it may be several times larger. Drinking one or two glasses of “arsenic” mineral water will not bring harm to a person: in order to be fatally poisoned, you need to drink three hundred liters at once ... But it is clear that you cannot drink such water all the time instead of ordinary water.

Chemists have found that arsenic in natural waters can be found in different forms, which is significant in terms of its analysis, migration methods, and different toxicity of these compounds; thus, trivalent arsenic compounds are 25–60 times more toxic than pentavalent ones. As(III) compounds in water are usually present in the form of weak arsenic acid H 3 AsO 3 ( RK a = 9.22), while the As(V) compounds are in the form of a much stronger arsenic acid H 3 AsO 4 ( RK a = 2.20) and its deprotonated anions H 2 AsO 4 – and HAsO 4 2–.

The living matter of arsenic contains on average 6 10 -6%, that is, 6 μg / kg. Some seaweeds are able to concentrate arsenic to such an extent that they become dangerous to humans. Moreover, these algae can grow and multiply in pure solutions of arsenic acid. Such algae are used in some Asian countries as a remedy for rats. Even in the clear waters of the Norwegian fjords, algae can contain up to 0.1 g/kg of arsenic. In humans, arsenic is found in brain tissue and muscles, it accumulates in hair and nails.

Arsenic properties.

Although in appearance arsenic resembles a metal, it is still rather a non-metal: it does not form salts, for example, with sulfuric acid, but is itself an acid-forming element. Therefore, this element is often called a semimetal. Arsenic exists in several allotropic forms and in this respect closely resembles phosphorus. The most stable of them is gray arsenic, a very fragile substance that has a metallic sheen when freshly fractured (hence the name "metallic arsenic"); its density is 5.78 g/cm 3 . With strong heating (up to 615 ° C), it sublimates without melting (the same behavior is typical for iodine). Under a pressure of 3.7 MPa (37 atm), arsenic melts at 817°C, which is much higher than the sublimation temperature. The electrical conductivity of gray arsenic is 17 times less than that of copper, but 3.6 times higher than that of mercury. With increasing temperature, its electrical conductivity, like that of typical metals, decreases - approximately to the same extent as that of copper.

If arsenic vapor is cooled very quickly to the temperature of liquid nitrogen (-196 ° C), a transparent soft yellow substance is obtained, resembling yellow phosphorus, its density (2.03 g / cm 3) is much lower than that of gray arsenic. Pairs of arsenic and yellow arsenic consist of As 4 molecules that have the shape of a tetrahedron - and here the analogy with phosphorus. At 800°C, a noticeable dissociation of vapor begins with the formation of As 2 dimers, while at 1700°C only As 2 molecules remain. When heated and under the action of ultraviolet, yellow arsenic quickly turns into gray with heat release. When arsenic vapor condenses in an inert atmosphere, another amorphous black form of this element is formed. If arsenic vapor is deposited on glass, a mirror film is formed.

The structure of the outer electron shell of arsenic is the same as that of nitrogen and phosphorus, but unlike them, it has 18 electrons in the penultimate shell. Like phosphorus, it can form three covalent bonds (configuration 4s 2 4p 3), leaving an lone pair on the As atom. The sign of the charge on the As atom in compounds with covalent bonds depends on the electronegativity of neighboring atoms. The participation of the lone pair in the complex formation is much more difficult for arsenic than for nitrogen and phosphorus.

If d orbitals are involved in the As atom, the 4s electrons can be depaired to form five covalent bonds. This possibility is practically realized only in combination with fluorine - in pentafluoride AsF 5 (pentachloryl AsCl 5 is also known, but it is extremely unstable and quickly decomposes even at –50 ° C).

In dry air, arsenic is stable, but in humid air it tarnishes and becomes covered with black oxide. During sublimation, arsenic vapor easily burns in air with a blue flame to form heavy white vapors of arsenic anhydride As 2 O 3 . This oxide is one of the most common arsenic-containing reagents. It has amphoteric properties:

As 2 O 3 + 6HCl ® 2AsCl 3 + 3H 2 O,

2 O 3 + 6NH 4 OH ® 2 (NH 4) 3 AsO 3 + 3H 2 O.

When As 2 O 3 is oxidized, an acid oxide is formed - arsenic anhydride:

As 2 O 3 + 2HNO 3 ® As 2 O 5 + H 2 O + NO 2 + NO.

When it interacts with soda, sodium hydrogen arsenate is obtained, which is used in medicine:

As 2 O 3 + 2Na 2 CO 3 + H 2 O ® 2Na 2 HAsO 4 + 2CO 2.

Pure arsenic is rather inert; water, alkalis and acids that do not have oxidizing properties do not act on it. Dilute nitric acid oxidizes it to ortho-arsenic acid H 3 AsO 3, and concentrated - to ortho-arsenic H 3 AsO 4:

3As + 5HNO 3 + 2H 2 O ® 3H 3 AsO 4 + 5NO.

Arsenic(III) oxide reacts similarly:

3As 2 O 3 + 4HNO 3 + 7H 2 O ® 6H 3 AsO 4 + 4NO.

Arsenic acid is an acid of medium strength, slightly weaker than phosphoric. In contrast, arsenic acid is very weak, corresponding in strength to boric acid H 3 BO 3. In its solutions, there is an equilibrium H 3 AsO 3 HAsO 2 + H 2 O. Arsenic acid and its salts (arsenites) are strong reducing agents:

HAsO 2 + I 2 + 2H 2 O ® H 3 AsO 4 + 2HI.

Arsenic reacts with halogens and sulfur. AsCl 3 chloride is a colorless oily liquid fuming in air; hydrolyzes with water: AsCl 3 + 2H 2 O ® HAsO 2 + 3HCl. Bromide AsBr 3 and iodide AsI 3 are known, which are also decomposed by water. In the reactions of arsenic with sulfur, sulfides of various compositions are formed - up to Ar 2 S 5. Arsenic sulfides dissolve in alkalis, in a solution of ammonium sulfide and in concentrated nitric acid, for example:

As 2 S 3 + 6KOH ® K 3 AsO 3 + K 3 AsS 3 + 3H 2 O,

2 S 3 + 3 (NH 4) 2 S ® 2 (NH 4) 3 AsS 3,

2 S 5 + 3 (NH 4) 2 S ® 2 (NH 4) 3 AsS 4,

As 2 S 5 + 40HNO 3 + 4H 2 O ® 6H 2 AsO 4 + 15H 2 SO 4 + 40NO.

In these reactions, thioarsenites and thioarsenates are formed - salts of the corresponding thioacids (similar to thiosulfuric acid).

In the reaction of arsenic with active metals, salt-like arsenides are formed, which are hydrolyzed by water. The reaction proceeds especially quickly in an acidic medium with the formation of arsine: Ca 3 As 2 + 6HCl ® 3CaCl 2 + 2AsH 3. Arsenides of low-active metals - GaAs, InAs, etc. have a diamond-like atomic lattice. Arsine is a colorless, odorless, highly poisonous gas, but impurities give it the smell of garlic. Arsine slowly decomposes into elements already at room temperature and quickly when heated.

Arsenic forms many organoarsenic compounds, for example, tetramethyldiarsine (CH 3) 2 As–As(CH 3) 2 . As early as 1760, the director of the Servian porcelain factory, Louis Claude Cade de Gassicourt, distilling potassium acetate with arsenic (III) oxide, unexpectedly obtained a smoking liquid containing arsenic with a disgusting smell, which was called alarsin, or Cade liquid. As it turned out later, this liquid contained the first obtained organic derivatives of arsenic: the so-called cacodyl oxide, which was formed as a result of the reaction

4CH 3 COOK + As 2 O 3 ® (CH 3) 2 As–O–As(CH 3) 2 + 2K 2 CO 3 + 2CO 2 , and dicacodyl (CH 3) 2 As–As(CH 3) 2 . Kakodil (from the Greek "kakos" - bad) was one of the first radicals discovered in organic compounds.

In 1854, the Parisian professor of chemistry Auguste Kaur synthesized trimethylarsine by the action of methyl iodide on sodium arsenide: 3CH 3 I + AsNa 3 ® (CH 3) 3 As + 3NaI.

Subsequently, arsenic trichloride was used for syntheses, for example,

(CH 3) 2 Zn + 2AsCl 3 ® 2(CH 3) 3 As + 3ZnCl 2 .

In 1882, aromatic arsines were obtained by the action of metallic sodium on a mixture of aryl halides and arsenic trichloride: 3C 6 H 5 Cl + AsCl 3 + 6Na ® (C 6 H 5) 3 As + 6NaCl. The chemistry of organic derivatives of arsenic developed most intensively in the 20s of the 20th century, when some of them had antimicrobial, as well as irritating and blistering effects. At present, tens of thousands of organoarsenic compounds have been synthesized.

Getting arsenic.

Arsenic is obtained mainly as a by-product of the processing of copper, lead, zinc and cobalt ores, as well as gold mining. Some polymetallic ores contain up to 12% arsenic. When such ores are heated to 650–700°C in the absence of air, arsenic sublimates, and when heated in air, volatile oxide As 2 O 3, “white arsenic,” is formed. It is condensed and heated with coal, and arsenic is reduced. Obtaining arsenic is a harmful production. Previously, when the word "ecology" was known only to narrow specialists, "white arsenic" was released into the atmosphere, and it settled in neighboring fields and forests. The exhaust gases of arsenic plants contain between 20 and 250 mg/m 3 of As 2 O 3 , while the air usually contains about 0.00001 mg/m 3 . The average daily allowable concentration of arsenic in the air is considered to be only 0.003 mg / m 3. Paradoxically, even now it is not the plants for its production that pollute the environment with arsenic, but non-ferrous metallurgy enterprises and power plants that burn coal. Bottom sediments near copper smelters contain a huge amount of arsenic - up to 10 g/kg. Arsenic can also get into the soil with phosphate fertilizers.

And another paradox: they get more arsenic than they need; this is a rather rare occurrence. In Sweden, "unnecessary" arsenic was even forced to be buried in reinforced concrete containers in deep abandoned mines.

The main industrial mineral of arsenic is arsenopyrite FeAsS. There are large copper-arsenic deposits in Georgia, Central Asia and Kazakhstan, in the USA, Sweden, Norway and Japan, arsenic-cobalt - in Canada, arsenic-tin - in Bolivia and England. In addition, gold-arsenic deposits are known in the USA and France. Russia has numerous deposits of arsenic in Yakutia, the Urals, Siberia, Transbaikalia and Chukotka.

Definition of arsenic.

A qualitative reaction to arsenic is the precipitation of yellow sulfide As 2 S 3 from hydrochloric acid solutions. Traces are determined by the Marsh reaction or the Gutzeit method: strips of paper moistened with HgCl 2 darken in the presence of arsine, which reduces sublimate to mercury.

In recent decades, various sensitive methods of analysis have been developed with which it is possible to quantify negligible concentrations of arsenic, for example, in natural waters. These include flame atomic absorption spectrometry, atomic emission spectrometry, mass spectrometry, atomic fluorescence spectrometry, neutron activation analysis... If there is very little arsenic in the water, pre-concentration of the samples may be required. Using this concentration, a group of Kharkov scientists from the National Academy of Sciences of Ukraine developed in 1999 an X-ray extraction method for the determination of arsenic (as well as selenium) in drinking water with a sensitivity of up to 2.5–5 µg/l.

For the separate determination of As(III) and As(V) compounds, they are preliminarily separated from each other using well-known extraction and chromatographic methods, as well as using selective hydrogenation. The extraction is usually carried out with sodium dithiocarbamate or ammonium pyrrolidine dithiocarbamate. These compounds form water-insoluble complexes with As(III), which can be extracted with chloroform. The arsenic can then be brought back into the aqueous phase by oxidation with nitric acid. In the second sample, arsenate is converted to arsenite with the help of a reducing agent, and then a similar extraction is performed. This is how “total arsenic” is determined, and then As (III) and As (V) are determined separately by subtracting the first result from the second. If there are organic arsenic compounds in water, they are usually converted into methyldiodarsine CH 3 AsI 2 or dimethyliodarsine (CH 3) 2 AsI, which are determined by one or another chromatographic method. Thus, nanogram amounts of a substance can be determined using high performance liquid chromatography.

Many arsenic compounds can be analyzed by the so-called hydride method. It consists in the selective reduction of the analyte to volatile arsine. So, inorganic arsenites are reduced to AsH 3 at pH 5 - 7, and at pH

The neutron activation method is also sensitive. It consists in irradiating the sample with neutrons, while the 75 As nuclei capture neutrons and turn into the 76 As radionuclide, which is detected by characteristic radioactivity with a half-life of 26 hours. In this way, up to 10–10% of arsenic in a sample can be detected, i.e. 1 mg per 1000 tons of substance

The use of arsenic.

About 97% of the mined arsenic is used in the form of its compounds. Pure arsenic is rarely used. Only a few hundred tons of metallic arsenic are produced and used annually throughout the world. In the amount of 3% arsenic improves the quality of bearing alloys. Additives of arsenic to lead significantly increase its hardness, which is used in the production of lead batteries and cables. Small additions of arsenic increase the corrosion resistance and improve the thermal properties of copper and brass. Highly purified arsenic is used in the manufacture of semiconductor devices, in which it is alloyed with silicon or germanium. Arsenic is also used as a dopant, which gives "classical" semiconductors (Si, Ge) a certain type of conductivity.

Arsenic as a valuable additive is also used in non-ferrous metallurgy. Thus, the addition of 0.2 ... 1% As to lead significantly increases its hardness. It has long been noticed that if a little arsenic is added to molten lead, then balls of the correct spherical shape are obtained when casting shot. The addition of 0.15 ... 0.45% arsenic to copper increases its tensile strength, hardness and corrosion resistance when working in a gassed environment. In addition, arsenic increases the fluidity of copper during casting, facilitates the process of wire drawing. Arsenic is added to some grades of bronzes, brasses, babbits, printing alloys. And at the same time, arsenic very often harms metallurgists. In the production of steel and many non-ferrous metals, they deliberately go to the complication of the process - just to remove all arsenic from the metal. The presence of arsenic in the ore makes production harmful. Harmful twice: first, for people's health; secondly, for a metal, significant impurities of arsenic worsen the properties of almost all metals and alloys.

More wide application have various arsenic compounds, which are produced annually by tens of thousands of tons. Oxide As 2 O 3 is used in glassmaking as a glass clarifier. Even the ancient glassmakers knew that white arsenic makes the glass "deaf", i.e. opaque. However, small additions of this substance, on the contrary, lighten the glass. Arsenic is still included in the formulations of some glasses, for example, "Viennese" glass for thermometers.

Arsenic compounds are used as an antiseptic to protect against spoilage and preserve skins, furs and stuffed animals, to impregnate wood, as a component of antifouling paints for the bottoms of ships. In this capacity, salts of arsenic and arsenic acids are used: Na 2 HAsO 4, PbHAsO 4, Ca 3 (AsO 3) 2, etc. The biological activity of arsenic derivatives has interested veterinarians, agronomists, and specialists in the sanitary and epidemiological service. As a result, arsenic-containing stimulators of growth and productivity of livestock, antihelminthics, drugs for the prevention of diseases of young animals on livestock farms appeared. Arsenic compounds (As 2 O 3 , Ca 3 As 2 , Na 3 As, Parisian greens) are used to control insects, rodents, and also weeds. In the past, such use was widespread, especially in the cultivation of fruit trees, tobacco and cotton plantations, to rid livestock of lice and fleas, to stimulate growth in poultry and pig production, and to dry cotton before harvesting. Even in ancient China, rice crops were treated with arsenic oxide to protect them from rats and fungal diseases and thus increase the yield. And in South Vietnam, American troops used cacodylic acid (Agent Blue) as a defoliant. Now, due to the toxicity of arsenic compounds, their use in agriculture limited.

Important areas of application of arsenic compounds are the production of semiconductor materials and microcircuits, fiber optics, the growth of single crystals for lasers, and film electronics. To introduce small, strictly metered amounts of this element into semiconductors, gaseous arsine is used. Gallium arsenides GaAs and indium InAs are used in the manufacture of diodes, transistors, and lasers.

Arsenic also finds limited use in medicine. . Arsenic isotopes 72 As, 74 As, and 76 As with half-lives convenient for research (26 h, 17.8 days, and 26.3 h, respectively) are used to diagnose various diseases.

Ilya Leenson

Arsenic - the classic poison of medieval and modern poisoners
and medicine in modern sports and rehabilitation medicine
Toxic and poisonous stones and minerals

Arsenic(lat. Arsenicum), As, a chemical element of group V of the periodic system of Mendeleev, atomic number 33, atomic mass 74.9216; steel gray crystals. The element consists of one stable isotope, 75 As. Poisonous in any form, medicine.

History reference.

Natural compounds of arsenic with sulfur (orpiment As 2 S 3 , realgar As 4 S 4) were known to the peoples of the ancient world, who used these minerals as medicines and paints. The product of burning arsenic sulfides was also known - arsenic oxide (III) As 2 O 3 ("white arsenic").

The name arsenikon is found already at the beginning of our era; it is derived from the Greek arsen - strong, courageous and served to designate arsenic compounds (according to their effect on the body). The Russian name is believed to have come from "mouse" ("death" - according to the use of arsenic preparations for killing yaks, as well as the extermination of mice and rats). The chemical preparation of free arsenic is attributed to 1250 AD. In 1789, A. Lavoisier included arsenic in the list of chemical elements.

Arsenic. Belorechenskoe deposit, Sev. Caucasus, Russia. ~10x7 cm. Photo: A.A. Evseev.

Distribution of arsenic in nature.

The average content of arsenic in the earth's crust (clarke) is 1.7 * 10 -4% (by mass), in such quantities it is present in most igneous rocks. Since arsenic compounds are volatile at high temperatures (dry volcanic sublimation on batholiths), the element is sublimated into the atmosphere and air in the form of metal vapors (mirages - the air below ripples) does not accumulate during sublimation through cracks and tubes magmatic lava processes; it is concentrated, precipitating from vapors and hot deep waters on crystal formation catalysts - metallic iron (together with S, Se, Sb, Fe, Co, Ni, Cu and other elements).

During volcanic eruptions (during the dry sublimation of arsenic), arsenic in the form of its volatile compounds enters the atmosphere. Since arsenic is polyvalent, its migration is affected by the redox environment. Under the oxidizing conditions of the earth's surface, arsenates (As 5+) and arsenites (As 3+) are formed.

These are rare minerals found in areas of arsenic deposits. Native arsenic and As 2+ minerals are even rarer. Of the minerals and arsenic compounds (about 180), arsenopyrite FeAsS is of industrial importance (the iron atom is the center of pyrite formation, the formula of the starting "single crystal" is Fe + (As + S)).

Arsenopyrite vein. Trifonovskaya shkh., Kochkarskoye deposit (Au), Plast, Yu. Ural, Russia. Arsenic. Photo: A.A. Evseev.

Small amounts of arsenic are essential for life. However, in the areas of arsenic deposits and the activity of young volcanoes, soils in places contain up to 1% arsenic, which is associated with livestock diseases and the death of vegetation. The accumulation of arsenic is especially characteristic of the landscapes of steppes and deserts, in the soils of which arsenic is inactive. In humid climates and when watering plants and soils, arsenic is washed out of the soil.

In living matter, on average, 3·10 -5% arsenic, in rivers 3·10 -7%. Arsenic, brought by rivers into the ocean, settles relatively quickly. In sea water, 1 * 10 -7% arsenic (there is a lot of gold that displaces it), but in clays and arsenic shales (along the banks of rivers and reservoirs, in clay black formations and along the edges of quarries) - 6.6 * 10 - four %. Sedimentary iron ores, ferromanganese and other iron nodules are often enriched in arsenic.

Physical properties of arsenic.

Arsenic has several allotropic modifications. Under normal conditions, the most stable is the so-called metallic, or gray, arsenic (α-As) - gray steel fragile crystalline mass (according to properties - like pyrite, gold blende, iron pyrite); on a fresh fracture it has a metallic luster, it quickly tarnishes in air, as it is covered with a thin film of As 2 O 3 .

Arsenic is rarely referred to as silver blende - the case of the Clerks of Tsar A.M. Romanov in the middle of the 17th century, "silver", not malleable, sometimes in powder, can be ground - poison for the Tsar of All Russia. The most famous Spanish scandal in the tavern of poisoners at the Don Quixote mill on the way to Almaden, Spain, where red cinnabar is mined on the European continent (scandals about the sale of virgins Krasnodar Territory RF, pos. New, crystal red cinnabar, do not want to work).

Arsenopyrite. Druse of prismatic crystals with calcite spherulites. Freiberg, Saxony, Germany. Photo: A.A. Evseev.

The crystal lattice of gray arsenic is rhombohedral (a \u003d 4.123Å, angle α \u003d 54 o 10 ", x \u003d 0.226), layered. Density 5.72 g / cm 3 (at 20 o C), electrical resistivity 35 * 10 -8 ohm * m, or 35 * 10 -6 ohm * cm, temperature coefficient of electrical resistance 3.9 10 -3 (0 o -100 o C), Brinell hardness 1470 MN / m 2, or 147 kgf / mm 2 (3- 4 according to Moocy); arsenic is diamagnetic.

Under atmospheric pressure, arsenic sublimates at 615 o C without melting, since the triple point of α-As lies at 816 o C and a pressure of 36 at.

Arsenic vapor consists up to 800 o C of As 4 molecules, above 1700 o C - only of As 2. When arsenic vapor condenses on a surface cooled by liquid air, yellow arsenic is formed - transparent, wax-soft crystals, with a density of 1.97 g / cm 3, similar in properties to white phosphorus.

Under the action of light or with slight heating, it turns into gray arsenic. Glassy-amorphous modifications are known: black arsenic and brown arsenic, which, when heated above 270 o C, turn into gray arsenic

Chemical properties of arsenic.

The configuration of the outer electrons of the arsenic atom is 3d 10 4s 2 4p 3 . In compounds, arsenic has oxidation states +5, +3 and -3. Gray arsenic is less chemically active than phosphorus. When heated in air above 400 o C, arsenic burns, forming As 2 O 3 .

Arsenic combines directly with halogens; under normal conditions, AsF 5 - gas; AsF 3 , AsCl 3 , AsBr 3 - colorless volatile liquids; AsI 3 and As 2 I 4 are red crystals. When arsenic is heated with sulfur, sulfides are obtained: orange-red As 4 S 4 and lemon-yellow As 2 S 3 .

Pale yellow silver sulfide As 2 S 5 ( arsenopyrite) is deposited by passing H 2 S into an ice-cooled solution of arsenic acid (or its salts) in fuming hydrochloric acid: 2H 3 AsO 4 + 5H 2 S \u003d As 2 S 5 + 8H 2 O; around 500 o C it decomposes into As 2 S 3 and sulfur.

All arsenic sulfides are insoluble in water and dilute acids. Strong oxidizers (mixtures of HNO 3 + HCl, HCl + KClO 3) convert them into a mixture of H 3 AsO 4 and H 2 SO 4 .

Sulfide As 2 S 3 easily dissolves in sulfides and polysulfides of ammonium and alkali metals, forming salts of acids - thioarsenic H 3 AsS 3 and thiomarsenic H 3 AsS 4 .

With oxygen, arsenic gives oxides: arsenic oxide (III) As 2 O 3 - arsenic anhydride and arsenic oxide (V) As 2 O 5 - arsenic anhydride. The first of them is formed by the action of oxygen on arsenic or its sulfides, for example 2As 2 S 3 + 9O 2 = 2As 2 O 3 + 6SO 2.

As 2 O 3 vapors condense into a colorless vitreous mass, which becomes opaque over time due to the formation of small cubic crystals, density 3.865 g/cm 3 . The vapor density corresponds to the formula As 4 O 6 ; above 1800 o C vapor consists of As 2 O 3 .

In 100 g of water, 2.1 g of As 2 O 3 is dissolved (at 25 o C). Arsenic (III) oxide is an amphoteric compound, with a predominance of acidic properties. Salts (arsenites) are known that correspond to orthoarsenic H 3 AsO 3 and metaarsenic HAsO 2 acids; the acids themselves have not been obtained. Only alkali metal and ammonium arsenites are soluble in water.

As 2 O 3 and arsenites are usually reducing agents (for example, As 2 O 3 + 2I 2 + 5H 2 O \u003d 4HI + 2H 3 AsO 4), but they can also be oxidizing agents (for example, As 2 O 3 + 3C \u003d 2As + ZSO ).

Arsenic (V) oxide is obtained by heating arsenic acid H 3 AsO 4 (about 200 o C). It is colorless, about 500 o C decomposes into As 2 O 3 and O 2 . Arsenic acid is obtained by the action of concentrated HNO 3 on As or As 2 O 3 .

Salts of arsenic acid (arsenates) are insoluble in water, with the exception of alkali metal and ammonium salts. Salts corresponding to acids orthoarsenic H 3 AsO 4 , metaarsenic HAsO 3 and pyromensic H 4 As 2 O 7 are known; the last two acids have not been obtained in the free state. When fused with metals, arsenic mostly forms compounds (arsenides).

Getting arsenic.

Arsenic is obtained in industry by heating arsenic pyrites:

FeAsS = FeS + As

or (more rarely) reduction of As 2 O 3 with coal. Both processes are carried out in refractory clay retorts connected to a receiver for arsenic vapor condensation.

Arsenic anhydride is produced by the oxidative roasting of arsenic ores or as a by-product of the roasting of polymetallic ores, which almost always contain arsenic. During oxidative roasting, As 2 O 3 vapors are formed, which condense in the trapping chambers.

Raw As 2 O 3 is purified by sublimation at 500-600 o C. Purified As 2 O 3 is used for the production of arsenic and its preparations.

The use of arsenic.

Small additions of arsenic (0.2-1.0% by weight) are introduced into lead used for the production of shotgun shot (arsenic increases the surface tension of molten lead, due to which the shot takes on a shape close to spherical; arsenic slightly increases the hardness of lead). As a partial substitute for antimony, arsenic is found in some babbits and printing alloys.

Pure arsenic is not poisonous, but all of its compounds, which are soluble in water or can go into solution under the action of gastric juice, are extremely poisonous; arsenic hydrogen is especially dangerous. Of the arsenic compounds used in production, arsenic anhydride is the most toxic.

Almost all sulfide ores of non-ferrous metals, as well as iron (sulfur) pyrite, contain an admixture of arsenic. Therefore, during their oxidative roasting, along with sulfur dioxide SO 2, As 2 O 3 is always formed; most of it condenses in the smoke channels, but in the absence or low efficiency of treatment facilities, the exhaust gases of ore kilns entrain significant amounts of As 2 O 3 .

Pure arsenic, although not toxic, is always coated with poisonous As 2 O 3 when stored in air. In the absence of properly performed ventilation, it is extremely dangerous to etch metals (iron, zinc) with technical sulfuric or hydrochloric acids containing an admixture of arsenic, since arsenic hydrogen is formed in this case.

Arsenic in the body.

As a trace element, arsenic is ubiquitous in wildlife. The average content of arsenic in soils is 4 * 10 -4%, in plant ash - 3 * 10 -5%. The content of arsenic in marine organisms is higher than in terrestrial organisms (in fish, 0.6-4.7 mg per 1 kg of raw matter accumulates in the liver).

The largest amount of it (per 1 g of tissue) is found in the kidneys and liver (when ingested, it does not accumulate in the brain). A lot of arsenic is found in the lungs and spleen, skin and hair; relatively little - in the cerebrospinal fluid, brain (mainly in the pituitary gland), sex glands and others.

In tissues, arsenic is in the main protein fraction("stone of bodybuilders and athletes"), much less - in acid-soluble and only a small part of it is found in the lipid fraction. They are treated with progressive muscular dystrophy - it does not accumulate in the brain and bones (sport doping, they treat hostages and prisoners of concentration camps like "Ausvents" in Poland, the EU, 1941-1944).

Arsenic is involved in redox reactions: oxidative breakdown of complex biological carbohydrates and sugars, fermentation, glycolysis, etc. Improves mental abilities (contributes to the process of breaking down sugars in the brain). Arsenic compounds are used in biochemistry as specific enzyme inhibitors for studying metabolic reactions. Promotes the disintegration of biological tissues (accelerates). It is actively used in dentistry and oncology - to eliminate rapidly growing and early aging cancer cells and tumors.

Mixture (hard sulfide alloy) of thallium, arsenic and lead: Hutchinsonite (Hutchinsonite)

Mineral formula (Pb, Tl)S` Ag2S * 5 As2 S5 is a complex sulfide and adsenide carbide salt. Rhombus. Crystals prismatic to acicular. Cleavage perfect according to (010). The aggregates are radially acicular, granular. Hardness 1.5-2. Specific gravity 4.6. Red. Diamond glitter. In hydrothermal deposits with dolomite, with sulfides and arsenides of Zn, Fe, As and sulfoarsenides. The result of dry sulfuric and arsenic sublimation of magma through calderas and open volcanic vents, as well as dry sublimation through cracks in deep-seated igneous plutonites from the Earth's red-hot magma. Contains silver. It is one of the ten very dangerous for human and animal health and carcinogenic stones and minerals that crystallize under modern conditions among other rocks in the form of harmful, dangerous to health (with unauthorized handling) and deceptive ore beauty. In the photo - Hutchinsonite with orpiment.

Poisonous minerals. Hutchinsonite - named after the mineralogist Hutchinson from the University of Cambridge and looks like lead (it can be used to protect against radiation). Opened in 1861. A deadly mixture (hard alloy) of thallium, arsenic and lead. Contact with this mineral can lead to hair loss (alopecia, baldness, baldness), complex skin diseases and death. All of its main components are poisonous. Very similar to lead, native silver, pyrite ("dry pyrite") and arsenopyrite. It also looks like antimonite (antimony compound, also very poisonous). It also looks like zeolites. Gutchinsonite is a dangerous and amazing hardmetal mixture of thallium, lead and arsenic. Three rare, very expensive and valuable ore metals form a poisonous, deadly cocktail of minerals that must be handled with the utmost care. They affect the brain, heart and liver at the same time.

Thallium is the gloomy twin of lead. This dense, fatty metal is similar in atomic weight to lead, but even more lethal. Thallium is a rare metal that appears in highly toxic compounds made up of strange combinations of elements (hard alloys). The effects of thallium exposure are more dangerous than lead, and include hair loss (alopecia, alopecia), serious illness through skin contact, and in many cases death. Hutchinsonite was named after John Hutchinson, a renowned mineralogist at the University of Cambridge. This mineral can be found in the mountainous regions of Europe, most often in ore deposits. A mineral popular in medical dentistry, etc. Alcoholics are afraid of the mineral.

Hutchinsonite (Hatchinsonite) is sometimes jokingly called "dry" or "hard alcohol", "hard alcohol" (and not only for the harmful effects of intoxicating poisoning on the body and human health). The chemical formula of food alcohol (alcohol) is C2 H5 (OH). Hutchinsonite (Hatchinsonite) has a chemical formula - 5 As2 S5 * (Pb, Tl) S` Ag2 S or 5 As2 S5 * (Pb, Tl) S` Ag Ag S. The formula of Hutchinsonite (Hatchinsonite) is sometimes rewritten differently - As2 S5 * ( Pb) + As2 S5 * (Tl) + As2 S5 * S + As2 S5 * Ag + As2 S5 * AgS. The chemical separation of components in production is also carried out according to the type of different alcohols (layers of mechanical enrichment, different in mass and weight, which are crushed by ultrasound and separated in a centrifuge or on a vibrating platform - horror film "Aliens"). Other similar variants of the chemical formula are possible (composition varies).

ADR 6.1
Toxic substances (poison)
Risk of poisoning by inhalation, skin contact or if swallowed. Hazardous to the aquatic environment or the sewerage system
Use an emergency escape mask vehicle

ADR 3
Flammable liquids
Fire risk. Risk of explosion. Containers may explode when heated (super hazardous - easy to burn)

ADR 2.1
flammable gases
Fire risk. Risk of explosion. May be under pressure. Choking risk. May cause burns and/or frostbite. Capacities can explode when heated (super-dangerous - practically do not burn)
Use cover. Avoid low surface areas (holes, lowlands, trenches)
Red diamond, ADR number, black or white flame

ADR 2.2
gas cylinder Non-flammable, non-toxic gases.
Choking risk. May be under pressure. May cause frostbite (similar to a burn - pallor, blisters, black gas gangrene - creaking). Containers can explode when heated (super-dangerous - an explosion from a spark, flame, match, practically does not burn)
Use cover. Avoid low surface areas (holes, lowlands, trenches)
Green rhombus, ADR number, black or white gas cylinder (such as "cylinder", "thermos")

ADR 2.3
Toxic gases. Skull and crossbones
Danger of poisoning. May be under pressure. May cause burns and/or frostbite. Containers can explode when heated (super-dangerous - instant spread of gases around the area)
Use an emergency exit mask. Use cover. Avoid low surface areas (holes, lowlands, trenches)
White diamond, ADR number, black skull and crossbones

Natural compounds of Arsenic with sulfur (orpiment As 2 S 3 , realgar As 4 S 4) were known to the peoples of the ancient world, who used these minerals as medicines and paints. The product of burning Arsenic sulfides was also known - Arsenic oxide (III) As 2 O 3 ("white Arsenic"). The name arsenikon is found already in Aristotle; it is derived from the Greek arsen - strong, courageous and served to designate Arsenic compounds (according to their strong effect on the body). The Russian name is believed to have come from "mouse" (for the use of Arsenic preparations for the extermination of mice and rats). Getting Arsenic in a free state is attributed to Albert the Great (about 1250). In 1789, A. Lavoisier included Arsenic in the list of chemical elements.

Distribution of Arsenic in nature. The average content of Arsenic in the earth's crust (clarke) is 1.7·10 -4% (by mass), in such quantities it is present in most igneous rocks. Because Arsenic compounds are volatile at high temperatures, the element does not accumulate in magmatic processes; it is concentrated by precipitating from hot deep waters (together with S, Se, Sb, Fe, Co, Ni, Cu and other elements). During volcanic eruptions, Arsenic in the form of its volatile compounds enters the atmosphere. Since Arsenic is polyvalent, its migration is greatly influenced by the redox environment. Under the oxidizing conditions of the earth's surface, arsenates (As 5+) and arsenites (As 3+) are formed. These are rare minerals found only in areas of Arsenic deposits. Native Arsenic and As 2+ minerals are even rarer. Of the numerous Arsenic minerals (about 180), only arsenopyrite FeAsS is of major industrial importance.

Small amounts of Arsenic are essential for life. However, in the areas of Arsenic deposits and the activity of young volcanoes, soils in places contain up to 1% Arsenic, which is associated with livestock diseases and the death of vegetation. The accumulation of Arsenic is especially characteristic of the landscapes of steppes and deserts, in the soils of which Arsenic is inactive. In humid climates Arsenic is easily washed out of the soil.

In living matter, on average, 3·10 -5% Arsenic, in rivers 3·10 -7%. Arsenic, brought by rivers into the ocean, settles relatively quickly. In sea water, only 1 10 -7% Arsenic, but in clays and shales 6.6 10 -4%. Sedimentary iron ores, ferromanganese nodules are often enriched in Arsenic.

Physical properties of Arsenic. Arsenic has several allotropic modifications. Under normal conditions, the most stable is the so-called metallic, or gray, Arsenic (α-As) - a grey-steel brittle crystalline mass; in a fresh fracture it has a metallic luster, it quickly tarnishes in air, as it is covered with a thin film of As 2 O 3 . The crystal lattice of gray Arsenic is rhombohedral (a \u003d 4.123Å, angle α \u003d 54 ° 10 ", x \u003d\u003d 0.226), layered. Density 5.72 g / cm 3 (at 20 ° C), electrical resistivity 35 10 -8 ohm m, or 35 10 -6 ohm cm, temperature coefficient of electrical resistance 3.9 10 -3 (0 ° -100 ° C), Brinell hardness 1470 MN / m 2, or 147 kgf / mm 2 (3 -4 according to Moocy); Arsenic is diamagnetic. Under atmospheric pressure, Arsenic sublimates at 615 ° C without melting, since the α-As triple point lies at 816 ° C and a pressure of 36 at. Arsenic vapor consists up to 800 ° C of As 4 molecules, above 1700 ° C - only from As 2. When Arsenic vapor condenses on a surface cooled by liquid air, yellow Arsenic is formed - transparent, wax-soft crystals, with a density of 1.97 g / cm 3, similar in properties to white phosphorus. under light or on slight heating it transforms into gray arsenic.There are also glassy-amorphous modifications: black arsenic and brown arsenic, which, when heated above 270 ° C, turn into gray arsenic. yak

Chemical properties of Arsenic. The configuration of the outer electrons of the Arsenic atom is 3d 10 4s 2 4p 3 . In compounds Arsenic has oxidation states +5, +3 and -3. Gray Arsenic is much less chemically active than phosphorus. When heated in air above 400 °C, Arsenic burns, forming As 2 O 3 . Arsenic combines with halogens directly; under normal conditions, AsF 5 - gas; AsF 3 , AsCl 3 , AsBr 3 - colorless, easily volatile liquids; AsI 3 and As 2 I 4 are red crystals. When Arsenic was heated with sulfur, sulfides were obtained: orange-red As 4 S 4 and lemon-yellow As 2 S 3 . Pale yellow sulfide As 2 S 5 is precipitated by passing H 2 S into an ice-cooled solution of arsenic acid (or its salts) in fuming hydrochloric acid: 2H 3 AsO 4 + 5H 2 S \u003d As 2 S 5 + 8H 2 O; around 500 °C it decomposes into As 2 S 3 and sulfur. All Arsenic sulfides are insoluble in water and dilute acids. Strong oxidizers (mixtures of HNO 3 + HCl, HCl + KClO 3) convert them into a mixture of H 3 AsO 4 and H 2 SO 4 . Sulfide As 2 S 3 easily dissolves in sulfides and polysulfides of ammonium and alkali metals, forming salts of acids - thioarsenic H 3 AsS 3 and thiomarsenic H 3 AsS 4 . Arsenic gives oxides with oxygen: Arsenic (III) oxide As 2 O 3 - arsenic anhydride and Arsenic (V) oxide As 2 O 5 - arsenic anhydride. The first of these is formed by the action of oxygen on Arsenic or its sulfides, for example, 2As 2 S 3 + 9O 2 = 2As 2 O 3 + 6SO 2 . As 2 O 3 vapors condense into a colorless vitreous mass, which becomes opaque over time due to the formation of small cubic crystals, density 3.865 g/cm 3 . The vapor density corresponds to the formula As 4 O 6 ; above 1800 °C the vapor consists of As 2 O 3 . 2.1 g As 2 O 3 dissolves in 100 g of water (at 25 °C). Oxide Arsenic (III) is an amphoteric compound, with a predominance of acidic properties. Salts (arsenites) are known that correspond to orthoarsenic H 3 AsO 3 and metaarsenic HAsO 2 acids; the acids themselves have not been obtained. Only alkali metal and ammonium arsenites are soluble in water. As 2 O 3 and arsenites are usually reducing agents (for example, As 2 O 3 + 2I 2 + 5H 2 O \u003d 4HI + 2H 3 AsO 4), but they can also be oxidizing agents (for example, As 2 O 3 + 3C \u003d 2As + ZSO ).

Arsenic (V) oxide is obtained by heating arsenic acid H 3 AsO 4 (about 200 ° C). It is colorless, about 500 °C decomposes into As 2 O 3 and O 2 . Arsenic acid is obtained by the action of concentrated HNO 3 on As or As 2 O 3 . Salts of arsenic acid (arsenates) are insoluble in water, with the exception of alkali metal and ammonium salts. Salts corresponding to acids orthoarsenic H 3 AsO 4 , metaarsenic HAsO 3 and pyromensic H 4 As 2 O 7 are known; the last two acids have not been obtained in the free state. When fused with metals, Arsenic mostly forms compounds (arsenides).

Getting Arsenic. Arsenic is obtained in industry by heating arsenic pyrites:

FeAsS = FeS + As

or (more rarely) reduction of As 2 O 3 with coal. Both processes are carried out in refractory clay retorts connected to a receiver for Arsenic vapor condensation. Arsenic anhydride is produced by the oxidative roasting of arsenic ores or as a by-product of the roasting of polymetallic ores, which almost always contain arsenic. During oxidative roasting, As 2 O 3 vapors are formed, which condense in the trapping chambers. Raw As 2 O 3 is purified by sublimation at 500-600 °C. Purified As 2 O 3 is used for the production of Arsenic and its preparations.

Application of Arsenic. Small additives of Arsenic (0.2-1.0% by weight) are introduced into lead used for the production of shotgun shot (Arsenic increases the surface tension of molten lead, due to which the shot takes on a shape close to spherical; Arsenic slightly increases the hardness of lead). As a partial substitute for antimony, arsenic is included in some babbits and printing alloys.

Pure Arsenic is not poisonous, but all of its compounds, which are soluble in water or can go into solution under the action of gastric juice, are extremely poisonous; arsenic hydrogen is especially dangerous. Of the Arsenic compounds used in production, arsenic anhydride is the most toxic. Almost all sulfide ores of non-ferrous metals, as well as iron (sulfur) pyrite, contain an admixture of arsenic. Therefore, during their oxidative roasting, along with sulfur dioxide SO 2, As 2 O 3 is always formed; most of it condenses in the smoke channels, but in the absence or low efficiency of treatment facilities, the exhaust gases of ore kilns entrain significant amounts of As 2 O 3 . Pure Arsenic, although not poisonous, is always coated with poisonous As 2 O 3 when stored in air. In the absence of proper ventilation, it is extremely dangerous to pickle metals (iron, zinc) with technical sulfuric or hydrochloric acids containing an admixture of Arsenic, since arsenic hydrogen is formed in this case.

Arsenic in the body. As a trace element, arsenic is ubiquitous in wildlife. The average content of Arsenic in soils is 4·10 -4%, in the ashes of plants - 3·10 -5%. The content of Arsenic in marine organisms is higher than in terrestrial organisms (in fish, 0.6-4.7 mg per 1 kg of raw material accumulates in the liver). The average content of Arsenic in the human body is 0.08-0.2 mg/kg. In the blood, arsenic is concentrated in erythrocytes, where it binds to the hemoglobin molecule (moreover, the globin fraction contains twice as much of it as the heme). The largest amount of it (per 1 g of tissue) is found in the kidneys and liver. A lot of Arsenic is found in the lungs and spleen, skin and hair; relatively little - in the cerebrospinal fluid, brain (mainly the pituitary gland), sex glands and others. In tissues, arsenic is found in the main protein fraction, much less in the acid-soluble fraction, and only an insignificant part of it is found in the lipid fraction. Arsenic is involved in redox reactions: oxidative breakdown of complex carbohydrates, fermentation, glycolysis, etc. Arsenic compounds are used in biochemistry as specific inhibitors of enzymes to study metabolic reactions.