Characteristics of arsenic by position in the periodic table. Mendeleev's periodic table of elements - arsenic

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ARSENIC– a chemical element of group V of the 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 half-lives 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 to exterminate 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 to produce paints and medicines. Particularly interesting is the use of arsenic in metallurgy.

Several thousand years 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-Euphrates valley, somewhere between the 30th and 25th centuries. BC. In some regions, bronze with especially valuable properties was smelted - it was better cast and easier to forge. As modern scientists have found, 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 the search, we used the property of such minerals to give off a specific garlic odor 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. Thus, in Ancient China, the solid mineral realgar (a sulfide of the composition As 4 S 4, realgar in Arabic means “mine dust”) was used for stone carving, but when heated or exposed to light it “deteriorated”, as it turned into As 2 S 3. In the 4th century. BC. Aristotle described this mineral under the name "sandarac". 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 (As 2 O 3 oxide), yellow arsenic (As 2 S 3 sulfide) and red arsenic (As 4 S 4 sulfide). 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 settled in the form of a white coating. 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; This may have been the first example of arsenic in the form of a simple substance obtained artificially. But this substance violated the mystical “connection” of the seven known metals with the seven planets; This is probably why alchemists considered arsenic a “bastard metal.” At the same time, they discovered its property of giving copper a white color, which gave rise to calling it “a Venus (i.e. copper) bleaching agent.”

Arsenic was clearly identified as an individual substance in the mid-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 organic compounds containing arsenic were discovered.

Arsenic in nature.

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

The composition of minerals formed by arsenic (and about 200 of them are known) 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 (ionic radii S–2, Sb–3 and As–3 are close and are 0.182, 0.208 and 0.191 nm, respectively), on the other – metal atoms. In the first case, arsenic atoms have a rather negative oxidation state, in the second - a positive one.

The electronegativity of arsenic (2.0) is small, but higher than that of antimony (1.9) and most metals, therefore the –3 oxidation state is observed for arsenic only in metal arsenides, as well as in stibarsen SbAs and intergrowths of this mineral with pure crystals antimony or arsenic (mineral allemontite). Many arsenic compounds with metals, judging by their composition, are intermetallic compounds rather than arsenides; some of them have variable arsenic content. Arsenides may simultaneously contain several metals, the atoms of which, at close ion radii, 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, and their hardness is low.

Examples 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 nickel skutterudite NiAs 2–3, nickel (red nickel pyrite) NiAs, rammelsbergite (white nickel pyrite) NiAs 2 , safflorite (speys 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 classify many of them as “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 FeS 2 pyrite with arsenic atoms (ordinary pyrite also always contains a little arsenic). Such compounds are called sulfosalts. Similarly, the minerals cobaltine (cobalt luster) CoAsS, glaucodote (Co,Fe)AsS, gersdorfite (nickel luster) NiAsS, enargite and luzonite of the same composition, but different structures Cu 3 AsS 4, proustite Ag 3 AsS 3 - an important silver ore, which Sometimes called "ruby silver" because of its bright red color, it is often found in the upper layers of silver veins, where magnificent large crystals of this mineral are found. Sulfosalts may also contain noble metals of the platinum group; These are the minerals 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 seinajokite (Fe,Ni)(Sb,As) 2, arsenopalladinite Pd 8 (As,Sb) 3, arsene polybasite (Ag,Cu) 16 (Ar,Sb) 2 S 11.

The structure of minerals is interesting, in which arsenic is present simultaneously with sulfur, but plays rather the role of a metal, grouping together with other metals. These are the minerals arsenosulvanite Cu 3 (As,V)S 4, arsenogauchekornite 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, gyrodite (Cu,Zn,Ag) 12 (As,Sb) 4 (Se,S) 13 . You 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 , as well as in colorless oxide As 2 O 3, which occurs as the minerals arsenolite and claudetite with different crystal structures (they are formed as a result of weathering of other arsenic minerals). Typically these minerals are found in the form of small inclusions. But in the 30s of the 20th century. In the southern part of the Verkhoyansk Range, huge crystals of orpiment measuring 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 include 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 goernesite 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 arsenic acid H 3 AsO 3 - are very rare.

In central Sweden there are the famous Langbanov iron-manganese quarries, in which more than 50 samples of arsenate minerals were 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. Typically, arsenates are oxidation products of sulfide ores. They, as a rule, have no industrial use, but some of them are very beautiful and adorn mineralogical collections.

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

An interesting ancient name for the mineral nickel (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 was able to 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 these are Sb, Bi, Ag, Fe, Ni, Co. It is easy to grind into powder. In Russia, geologists found native arsenic 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, and it is not for nothing that it is called “ubiquitous.” The distribution of arsenic over different regions of the globe was largely determined during the 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 fairly 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 arsenic content in rivers is 3 µg/l, in surface waters – about 10 µg/l, in sea and ocean waters – only about 1 µg/l. This is explained by 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 from 0.1 to 40 mg/kg. But in areas where arsenic ores occur, as well as in volcanic areas, 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 compared to the average content - they contain four times more arsenic than the average. In our country, the maximum permissible concentration of arsenic in soil is 2 mg/kg.

Arsenic can be carried out of the soil not only by water, but also by wind. But to do 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 to form 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 in both 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 also occur in nature. Using 14 C-labeled methylcobalamin and 74 As-labeled sodium hydroarsenate Na 2 HAsO 4 it was shown that one of the strains of methanobacteria 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 of arsenic, in cities where there is 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 arsenic content, etc.) the concentration of arsenic in the air can exceed 1 μg/m 3 . The intensity of arsenic deposition in the areas where industrial centers are located is 40 kg/km 2 per year.

The formation of volatile arsenic compounds (trimethylarsine, for example, boils at only 51 ° C) caused in the 19th century. numerous poisonings, since arsenic was contained in plaster and even green wallpaper paint. Scheele greens were previously used in the form of paint Cu 3 (AsO 3) 2 n H 2 O and Parisian or Schweyfurt 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 the last years of his life (as is known, arsenic was found in Napoleon's hair a century and a half after his death).

Arsenic is found in noticeable quantities in some mineral waters. Russian standards establish that arsenic in medicinal table mineral waters should not exceed 700 µg/l. IN 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 such water cannot be drunk constantly instead of ordinary water.

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

Living matter contains an average of 6·10–6% arsenic, that is, 6 µg/kg. Some seaweeds can concentrate arsenic to such an extent that they become dangerous to humans. Moreover, these algae can grow and reproduce in pure solutions of arsenic acid. Such algae are used in some Asian countries as a remedy against 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, and it accumulates in hair and nails.

Properties of arsenic.

Although arsenic looks like 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 is very similar to phosphorus. The most stable of them is gray arsenic, a very brittle substance that, when freshly fractured, has a metallic sheen (hence the name “metallic arsenic”); its density is 5.78 g/cm3. When heated strongly (up to 615° C), it sublimes without melting (the same behavior is characteristic of iodine). Under a pressure of 3.7 MPa (37 atm), arsenic melts at 817 ° C, which is significantly 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. As the temperature increases, its electrical conductivity, like that of typical metals, decreases - to approximately the same extent as that of copper.

If arsenic vapor is very quickly cooled to the temperature of liquid nitrogen (–196 ° C), a transparent soft yellow substance is obtained, reminiscent of yellow phosphorus, its density (2.03 g/cm 3) is significantly lower than that of gray arsenic. Arsenic vapor 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, and at 1700° C only As 2 molecules remain. When heated and exposed to ultraviolet light, yellow arsenic quickly turns gray with the release of heat. When arsenic vapor condenses in an inert atmosphere, another amorphous form of this element, black in color, 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 (4s 2 4p 3 configuration), leaving a 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 a lone pair in complex formation is significantly more difficult for arsenic compared to nitrogen and phosphorus.

If d orbitals are involved in the As atom, pairing of 4s electrons is possible 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 fades and becomes covered with black oxide. During sublimation, arsenic vapor easily burns in air with a blue flame to form heavy white vapor 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.

The oxidation of As 2 O 3 produces an acidic oxide - arsenic anhydride:

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

When it reacts with soda, sodium hydroarsenate 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 quite inert; water, alkalis and acids that do not have oxidizing properties do not affect it. Dilute nitric acid oxidizes it to orthoarsenic acid H 3 AsO 3 , and concentrated nitric acid oxidizes it to orthoarsenic acid 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 a medium-strength acid, slightly weaker than phosphoric acid. 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. Arsenous 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 that fumes in air; hydrolyzed with water: AsCl 3 + 2H 2 O ® HAsO 2 + 3HCl. AsBr 3 bromide and AsI 3 iodide are known, which also decompose with 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 ammonium sulfide solution 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 occurs especially quickly in an acidic environment 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 decomposes slowly 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. Back in 1760, the director of the Serves porcelain factory, Louis Claude Cadet de Gassicourt, distilling potassium acetate with arsenic(III) oxide, unexpectedly received a fuming liquid containing arsenic with a disgusting odor, which was called alarsine, or Cadet's liquid. As it was later found out, 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 . Kakodyl (from the Greek “kakos” - bad) was one of the first radicals discovered in organic compounds.

In 1854, Parisian chemistry professor 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 irritant and blister effects. Currently, tens of thousands of organoarsenic compounds have been synthesized.

Obtaining arsenic.

Arsenic is obtained mainly as a by-product of the processing of copper, lead, zinc and cobalt ores, as well as during 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 sublimes, and when heated in air, volatile oxide As 2 O 3 is formed - “white arsenic”. It is condensed and heated with coal, and arsenic is reduced. Producing 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 on neighboring fields and forests. The exhaust gases of arsenic plants contain from 20 to 250 mg/m 3 As 2 O 3, while usually the air contains approximately 0.00001 mg/m 3. The average daily permissible concentration of arsenic in the air is considered to be only 0.003 mg/m3. Paradoxically, even now it is not the factories that produce arsenic that pollute the environment much more heavily, but non-ferrous metallurgy enterprises and power plants that burn coal. Bottom sediments near copper smelters contain huge amounts of arsenic – up to 10 g/kg. Arsenic can also enter the soil with phosphorus fertilizers.

And another paradox: they receive more arsenic than is required; This is quite a rare case. In Sweden, “unnecessary” arsenic was even forced to be buried in reinforced concrete containers in deep abandoned mines.

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

Determination 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 March reaction or the Gutzeit method: strips of paper soaked in HgCl 2 darken in the presence of arsine, which reduces sublimate to mercury.

In recent decades, various sensitive analytical methods have been developed that can quantify minute 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 necessary. Using such concentration, a group of Kharkov scientists from the National Academy of Sciences of Ukraine developed in 1999 an extraction-X-ray fluorescence method for determining 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 first separated from each other using well-known extraction and chromatographic methods, as well as using selective hydrogenation. Extraction is usually carried out using 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 converted back into the aqueous phase by oxidation with nitric acid. In the second sample, arsenate is converted to arsenite using a reducing agent, and then a similar extraction is performed. This is how “total arsenic” is determined, and then by subtracting the first result from the second, As(III) and As(V) are determined separately. If there are organic arsenic compounds in water, they are usually converted to methyldiodarsine CH 3 AsI 2 or dimethyliodarsine (CH 3) 2 AsI, which are determined by one or another chromatographic method. Thus, using high-performance liquid chromatography, nanogram quantities of a substance can be determined.

Many arsenic compounds can be analyzed using the so-called hydride method. It involves the selective reduction of the analyte into volatile arsine. Thus, inorganic arsenites are reduced to AsH 3 at pH 5 – 7, and at pH

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

Use of arsenic.

About 97% of mined arsenic is used in the form of its compounds. Pure arsenic is rarely used. Only a few hundred tons of arsenic metal are produced and used annually throughout the world. In an amount of 3%, arsenic improves the quality of bearing alloys. Additions of arsenic to lead significantly increase its hardness, which is used in the production of lead batteries and cables. Small additions of arsenic increase corrosion resistance and improve the thermal properties of copper and brass. Highly purified arsenic is used in the production 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 is also used as a valuable additive 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 when casting shot, balls of the correct spherical shape are obtained. The addition of 0.15...0.45% arsenic to copper increases its tensile strength, hardness and corrosion resistance when working in a gaseous environment. In addition, arsenic increases the fluidity of copper during casting and facilitates the process of wire drawing. Arsenic is added to some types of bronze, brass, babbitt, and printing alloys. And at the same time, arsenic very often harms metallurgists. In the production of steel and many non-ferrous metals, they deliberately complicate the process in order to remove all arsenic from the metal. The presence of arsenic in ore makes production harmful. Harmful twice: firstly, for human health; secondly, for metals - significant arsenic impurities worsen the properties of almost all metals and alloys.

Various arsenic compounds, which are produced annually in tens of thousands of tons, are more widely used. As 2 O 3 oxide is used in glass making as a glass brightener. Even the ancient glassmakers knew that white arsenic makes glass “dull”, 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, “Vienna” glass for thermometers.

Arsenic compounds are used as an antiseptic to protect against spoilage and preserve skins, furs and stuffed animals, to impregnate wood, and as a component of antifouling paints for the bottoms of ships. For this purpose, salts of arsenic and arsenous 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 sanitary and epidemiological service specialists. As a result, arsenic-containing stimulants for the growth and productivity of livestock, anthelmintic agents, and medicines for the prevention of diseases in young animals on livestock farms appeared. Arsenic compounds (As 2 O 3, Ca 3 As 2, Na 3 As, Parisian green) are used to control insects, rodents, and weeds. Previously, such uses were widespread, especially in fruit trees, tobacco and cotton plantations, for ridding livestock of lice and fleas, for promoting growth in poultry and pig production, and for drying cotton before harvest. 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 is limited.

Important areas of application of arsenic compounds are the production of semiconductor materials and microcircuits, fiber optics, growing single crystals for lasers, and film electronics. Arsine gas is used to introduce small, strictly dosed amounts of this element into semiconductors. 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 hours, 17.8 days and 26.3 hours, respectively) are used to diagnose various diseases.

Ilya Leenson



Arsenic(Latin arsenicum), as, 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.

Historical reference. Natural compounds of minerals 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 M. sulfides was also known - M. oxide (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 come from “mouse” (from the use of M. preparations for the extermination of mice and rats). The receipt of M. in a free state is attributed to Albert the Great(about 1250). In 1789 A. Lavoisier included M. in the list of chemical elements.

Distribution in nature. The average content of metal in the earth's crust (clarke) is 1.7 × 10 -4% (by mass); it is present in such quantities in most igneous rocks. Since M. compounds are volatile at high temperatures, the element does not accumulate during magmatic processes; it concentrates, precipitating from hot deep waters (together with s, se, sb, fe, co, ni, cu and other elements). During volcanic eruptions, minerals enter the atmosphere in the form of their volatile compounds. Since M. is multivalent, its migration is greatly influenced by the redox environment. Under 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 less common. Of the numerous minerals of M. (about 180), only arsenopyrite feass is of primary industrial importance.

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

In living matter there is an average of 3 × 10 -5% M, in rivers 3 × 10 -7%. M., brought by rivers to the ocean, settles out relatively quickly. In sea water there is only 1 x 10 -7% M, but in clays and shales it is 6.6 x 10 -4%. Sedimentary iron ores and 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 steel-gray brittle crystalline mass; when freshly fractured, it has a metallic luster; in air it quickly fades 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. diamagnetic. Under atmospheric pressure, metal sublimes at 615 °C without melting, since the triple point a -as lies at 816 °C and a pressure of 36 at. M. steam consists of as 4 molecules up to 800 ° C, above 1700 ° C - only of as 2. When vapor of metal condenses on a surface cooled by liquid air, yellow metal is formed - transparent crystals, soft like wax, with a density of 1.97 g/cm 3, similar in properties to white phosphorus. When exposed to light or weak heating, it turns into gray M. Glassy-amorphous modifications are also known: black M. and brown M., which turn into gray M when heated above 270°c.

Configuration of the outer electrons of the atom M. 3 d 10 4 s 2 4 p 3. In compounds, M has oxidation states of + 5, + 3, and – 3. Gray M is significantly less chemically active than phosphorus. When heated in air above 400°c, M burns, forming as 2 o 3. M combines directly with halogens; under normal conditions asf 5 - gas; asf 3, ascl 3, asbr 3 - colorless, highly volatile liquids; asi 3 and as 2 l 4 - red crystals. When M. is heated with sulfur, the following sulfides are 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 = as 2 s 5 + 8h 2 o; At about 500°c it decomposes into as 2 s 3 and sulfur. All M. sulfides are insoluble in water and dilute acids. Strong oxidizing agents (mixtures 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 thioarsenic h 3 ass 4. With oxygen, M. produces oxides: M. oxide (iii) as 2 o 3 - arsenic anhydride and M. oxide (v) as 2 o 5 - arsenic anhydride. The first of them is formed by the action of oxygen on metal 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 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 steam consists of as 2 o 3. At 100 G water dissolves 2.1 G as 2 o 3 (at 25°c). M. oxide (iii) is an amphoteric compound, with a predominance of acidic properties. Salts (arsenites) corresponding to orthoarsenic acids h 3 aso 3 and metaarsenic haso 2 are known; 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 = 4hi + 2h 3 aso 4), but can also be oxidizing agents (for example, as 2 o 3 + 3c = 2as + 3co ).

M. oxide (v) is obtained by heating arsenic acid h 3 aso 4 (about 200°c). It is colorless, at about 500°c it 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. Arsenic acid salts (arsenates) are insoluble in water, with the exception of alkali metal and ammonium salts. Salts are known that correspond to the acids orthoarsenic h 3 aso 4 , metaarsenic haso 3 , and pyroarsenic acid h 4 as 2 o 7 ; the last two acids were not obtained in a free state. When fused with metals, metal mostly forms compounds ( arsenides).

Receipt and use . M. is produced industrially by heating arsenic pyrites:

feass = fes + as

or (less often) reduction of as 2 o 3 with coal. Both processes are carried out in retorts made of refractory clay, connected to a receiver for condensation of M vapors. 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 catch 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 gun 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 included in some babbitts and printing alloys.

Pure M. is not poisonous, but all its compounds that are soluble in water or can go into solution under the influence of gastric juice are extremely poisonous; especially dangerous arsenic hydrogen. Of the M compounds used in production, arsenous anhydride is the most toxic. Almost all sulfide ores of non-ferrous metals, as well as iron (sulfur) pyrite, contain metal admixtures. 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 carry away noticeable 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, etching of metals (iron, zinc) with industrial sulfuric or hydrochloric acids containing an admixture of metals is extremely dangerous, since this produces arsenous hydrogen.

S. A. Pogodin.

M. in the body. As trace element M. is ubiquitous in living nature. The average content of M in soils is 4 · 10 -4%, in plant ashes - 3 · 10 -5%. The M content in marine organisms is higher than in terrestrial organisms (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 (and the globin fraction contains twice as much as heme). The largest amount of it (per 1 G tissue) is found in the kidneys and liver. A lot of M. is found in the lungs and spleen, skin and hair; relatively little - in the cerebrospinal fluid, brain (mainly the pituitary gland), gonads, etc. In tissues, M. is found in the main protein fraction, much less in the acid-soluble fraction, and only a small part of it is found in the lipid fraction. M. participates in redox reactions: oxidative breakdown of complex carbohydrates, fermentation, glycolysis, etc. M. compounds are used in biochemistry as specific inhibitors enzymes for studying metabolic reactions.

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

Artificially obtained radioactive isotopes M. 74 as (t 1 / 2 = 17.5 days) and 76 as (t 1 / 2 = 26.8 h) are used for diagnostic and therapeutic purposes. With their help, the location of brain tumors is clarified and the degree of radicality 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 permissible content of 76 as in the body is 11 mccurie. According to 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 premises 5 10 -11 curie/l. All M. preparations are very poisonous. In case of acute poisoning, severe abdominal pain, diarrhea, and kidney damage are observed; Collapse and convulsions are possible. In chronic poisoning, the most common are gastrointestinal disorders, catarrh of the mucous membranes of the respiratory tract (pharyngitis, laryngitis, bronchitis), skin lesions (exanthema, melanosis, hyperkeratosis), and sensitivity disorders; the development of aplastic anemia is possible. In the treatment of poisoning with M. drugs, unithiol is of greatest importance.

Measures to prevent industrial poisonings should be aimed primarily at mechanization, sealing and dust removal of the technological process, creating effective ventilation and providing workers with personal protective equipment from exposure to dust. Regular medical examinations of workers are necessary. Preliminary medical examinations are carried out upon hiring, 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 general. ed. N. V. Lazareva, 6th ed., part 2, Leningrad, 1971.

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Arsenic compounds (English and French Arsenic, German Arsen) have been known for a very long time. In the III - II millennia BC. e. already knew how to produce copper alloys with 4 - 5% arsenic. Aristotle's student, Theophrastus (IV-III centuries BC), called red arsenic sulfide found in nature as realgar; Pliny calls yellow arsenic sulphide As 2 S 3 orpiment (Auripigmentum) - golden in color, and later it received the name orpiment. The ancient Greek word arsenicon, as well as sandarac, refer mainly to sulfur compounds. In the 1st century Dioscorides described the burning of orpiment and the resulting product - white arsenic (As 2 O 3). In the alchemical period of the development of chemistry, it was considered undeniable that arsenic (Arsenik) has a sulfurous nature, and since sulfur (Sulfur) was revered as the “father of metals,” masculine properties were attributed to arsenic. It is unknown when exactly arsenic metal was first obtained. This discovery is usually attributed to Albert the Great (13th century). Alchemists considered the coloring of copper with the addition of arsenic to a white silver color as the transformation of copper into silver and attributed such a “transmutation” to the powerful power of arsenic. In the Middle Ages and in the first centuries of modern times, the toxic properties of arsenic became known. However, even Dioscorides (Iv.) recommended that asthma patients inhale the vapors of the product obtained by heating realgar with resin. Paracelsus already widely used white arsenic and other arsenic compounds for treatment. Chemists and miners of the 15th - 17th centuries. knew about the ability of arsenic to sublimate and form vaporous products with a specific odor and toxic properties. Vasily Valentin mentions what was well known to metallurgists of the 16th century. blast furnace smoke (Huttenrauch) and its specific smell. The Greek (and Latin) name for arsenic, referring to arsenic sulfides, is derived from the Greek masculine. There are other explanations for the origin of this name, for example from the Arabic arsa paki, meaning “an unfortunate poison penetrating deep into the body”; the Arabs probably borrowed this name from the Greeks. The Russian name arsenic has been known for a long time. It has appeared in literature since the time of Lomonosov, who considered arsenic to be a semimetal. Along with this name in the 18th century. the word arsenic was used, and arsenic was called As 2 O 3. Zakharov (1810) proposed the name arsenic, but it did not catch on. The word arsenic was probably borrowed by Russian artisans from the Turkic peoples. In Azerbaijani, Uzbek, Persian and other eastern languages, arsenic was called margumush (mar - kill, mush - mouse); Russian arsenic, probably a corruption of mouse-poison, or mouse-venom.

Arsenic is a chemical element of group 5 of the 4th period of the periodic table with atomic number 33. It is a brittle semi-metal of steel color with a greenish tint. Today we will take a closer look at what arsenic is and get acquainted with the basic properties of this element.

general characteristics

The uniqueness of arsenic lies in the fact that it is found literally everywhere - in rocks, water, minerals, soil, flora and fauna. Therefore, it is often called nothing less than the omnipresent element. Arsenic is distributed unhindered throughout all geographic regions of planet Earth. The reason for this is the volatility and solubility of its compounds.

The name of the element is associated with its use for the extermination of rodents. The Latin word Arsenicum (arsenic formula in the periodic table is As) is derived from the Greek Arsen, meaning “strong” or “powerful.”

The body of the average adult contains about 15 mg of this element. It is mainly concentrated in the small intestine, liver, lungs and epithelium. Absorption of the substance is carried out by the stomach and intestines. Antagonists of arsenic are sulfur, phosphorus, selenium, some amino acids, as well as vitamins E and C. The element itself impairs the absorption of zinc, selenium, as well as vitamins A, C, B9 and E.

Like many other substances, arsenic can be both a poison and a medicine, it all depends on the dose.

Among the useful functions of such an element as arsenic are:

1. Stimulating the absorption of nitrogen and phosphorus.
2. Improvement of hematopoiesis.
3. Interaction with cysteine, proteins and lipoic acid.
4. Weakening of oxidative processes.

The daily requirement for arsenic for an adult is from 30 to 100 mcg.

Historical reference

One of the stages of human development is called “bronze”, since during this period people replaced stone weapons with bronze ones. This metal is an alloy of tin and copper. Once, when smelting bronze, craftsmen accidentally used weathering products of the copper-arsenic sulfide mineral instead of copper ore. The resulting alloy was easy to cast and excellent forging. In those days, no one yet knew what arsenic was, but deposits of its minerals were deliberately sought for the production of high-quality bronze. Over time, this technology was abandoned, apparently due to the fact that poisoning often occurred with its use.

In Ancient China they used a hard mineral called realgar (As 4 S 4). It was used for stone carving. Since under the influence of temperature and light realgar turned into another substance - As 2 S 3, it was also soon abandoned.

In the 1st century BC, the Roman scientist Pliny the Elder, along with the botanist and physician Dioscorides, described the arsenic mineral called orpiment. Its name is translated from Latin as “golden paint”. The substance was used as a yellow dye.

In the Middle Ages, alchemists classified three forms of the element: yellow (As 2 S 3 sulfide), red (As 4 S 4 sulfide) and white (As 2 O 3 oxide). In the 13th century, by heating yellow arsenic with soap, alchemists obtained a metal-like substance. Most likely, it was the first example of a pure element obtained artificially.

What arsenic is in its pure form was discovered at the beginning of the 17th century. This happened when Johann Schröder, reducing the oxide with charcoal, isolated this element. A few years later, the French chemist Nicolas Lemery managed to obtain the substance by heating its oxide in a mixture with soap and potash. In the next century, arsenic was already well known in its semimetal status.

Chemical properties

In the periodic table of Mendeleev, the chemical element arsenic is located in the fifth group and belongs to the nitrogen family. Under natural conditions, it is the only stable nuclide. More than ten radioactive isotopes of the substance are produced artificially. Their half-life range is quite wide - from 2-3 minutes to several months.

Although arsenic is sometimes called a metal, it is more likely to be a non-metal. In combination with acids, it does not form salts, but is itself an acid-forming substance. This is why the element is identified as a semimetal.

Arsenic, like phosphorus, can be found in various allotropic configurations. One of them, gray arsenic, is a brittle substance that has a metallic sheen when broken. The electrical conductivity of this semimetal is 17 times lower than that of copper, but 3.6 times higher than that of mercury. As the temperature increases, it decreases, which is typical for typical metals.

By rapidly cooling arsenic vapor to the temperature of liquid nitrogen (-196 °C), a soft yellowish substance resembling yellow phosphorus can be obtained. When heated and exposed to ultraviolet light, yellow arsenic instantly turns gray. The reaction is accompanied by the release of heat. When vapors condense in an inert atmosphere, another form of matter is formed - amorphous. If arsenic vapor is precipitated, a mirror film appears on the glass.

The outer electron shell of this substance has the same structure as phosphorus and nitrogen. Like phosphorus, arsenic forms three covalent bonds. In dry air it has a stable shape, and with increasing humidity it becomes dull and becomes covered with a black oxide film. When the vapor is ignited, the substances burn with a blue flame.

Since arsenic is inert, it is not affected by water, alkalis and acids, which do not have oxidizing properties. When a substance comes into contact with dilute nitric acid, orthoarsenic acid is formed, and with concentrated acid, orthoarsenic acid is formed. Arsenic also reacts with sulfur, forming sulfides of different compositions.

Being in nature

Under natural conditions, a chemical element such as arsenic is often found in compounds with copper, nickel, cobalt and iron.

The composition of the minerals that the substance forms is due to its semi-metallic properties. To date, more than 200 minerals of this element are known. Since arsenic can exist in negative and positive oxidation states, it easily interacts with many other substances. During positive oxidation of arsenic, it functions as a metal (in sulfides), and during negative oxidation, it functions as a nonmetal (in arsenides). Minerals containing this element have a rather complex composition. In a crystal lattice, a semimetal can replace atoms of sulfur, antimony and metals.

From a compositional point of view, many metal compounds with arsenic are more likely to belong not to arsenides, but to intermetallic compounds. Some of them are distinguished by variable content of the main element. Arsenides can simultaneously contain several metals, the atoms of which can replace each other at close ion radii. All minerals classified as arsenides have a metallic luster, are opaque, heavy and durable. Among the natural arsenides (there are about 25 in total) the following minerals can be noted: skutterudite, rammelsbreggite, nickelin, lellingrite, clinosafflorite and others.

Interesting from a chemical point of view are those minerals in which arsenic is present simultaneously with sulfur and plays the role of a metal. They have a very complex structure.

Natural salts of arsenic acid (arsenates) can have different colors: erythritol - cobalt; simplesite, annabergite and scoride are green, and rooseveltite, kettigite and gernessite are colorless.

In terms of its chemical properties, arsenic is quite inert, so it can be found in its native state in the form of fused cubes and needles. The content of impurities in the nugget does not exceed 15%.

In soil, the arsenic content ranges from 0.1-40 mg/kg. In areas of volcanoes and places where arsenic ore occurs, this figure can reach up to 8 g/kg. Plants in such places die and animals get sick. A similar problem is typical for steppes and deserts, where the element is not washed out from the soil. Clay rocks are considered enriched, since they contain four times more arsenic substances than ordinary rocks.

When a pure substance is converted into a volatile compound through the process of biomethylation, it can be carried out of the soil not only by water, but also by wind. In normal areas, the concentration of arsenic in the air averages 0.01 μg/m 3 . In industrial areas where factories and power plants operate, this figure can reach 1 μg/m3.

Mineral water may contain a moderate amount of arsenic substances. In medicinal mineral waters, according to generally accepted standards, the concentration of arsenic should not exceed 70 µg/l. It is worth noting here that even at higher rates, poisoning can only occur with regular consumption of such water.

In natural waters, the element can be found in various forms and compounds. Trivalent arsenic, for example, is much more toxic than pentavalent arsenic.

Obtaining arsenic

The element is obtained as a by-product of the processing of lead, zinc, copper and cobalt ores, as well as during gold mining. In some polymetallic ores, the arsenic content can reach up to 12%. When they are heated to 700 °C, sublimation occurs - the transition of a substance from a solid to a gaseous state, bypassing the liquid state. An important condition for this process to occur is the absence of air. When arsenic ores are heated in air, a volatile oxide is formed, called “white arsenic.” By subjecting it to condensation with coal, pure arsenic is recovered.

The formula for getting an element is as follows:

• 2As 2 S 3 +9O 2 =6SO 2 +2As 2 O 3;
• As 2 O 3 +3C=2As+3CO.

Arsenic mining is a hazardous industry. Paradoxical is the fact that the greatest pollution of the environment by this element occurs not near the enterprises that produce it, but near power plants and non-ferrous metallurgy plants.

Another paradox is that the volume of production of metallic arsenic exceeds the need for it. This is a very rare occurrence in the metal mining industry. Excess arsenic must be disposed of by burying metal containers in old mines.

The largest deposits of arsenic ores are concentrated in the following countries:

1. Copper-arsenic - USA, Georgia, Japan, Sweden, Norway and Central Asian states.
2. Gold-arsenic - France and USA.
3. Arsenic-cobalt - Canada and New Zealand.
4. Arsenic-tin - England and Bolivia.

Definition

Laboratory determination of arsenic is carried out by precipitation of yellow sulfides from hydrochloric acid solutions. Traces of the element are determined using the Gutzeit method or the Marsh reaction. Over the past half century, all sorts of sensitive analysis techniques have been created that can detect even very small amounts of this substance.

Some arsenic compounds are analyzed using the selective hybrid method. It involves the reduction of the test substance into the volatile element arsine, which is then frozen in a container cooled with liquid nitrogen. Subsequently, when the contents of the container are slowly heated, the various arsines begin to evaporate separately from each other.

Industrial use

Almost 98% of mined arsenic is not used in its pure form. Its compounds are widely used in various industries. Hundreds of tons of arsenic are mined and processed annually. It is added to bearing alloys to improve their quality, used to increase the hardness of cables and lead batteries, and is also used in the production of semiconductor devices along with germanium or silicon. And these are just the most ambitious areas.

As a dopant, arsenic imparts conductivity to some “classical” semiconductors. Its addition to lead significantly increases the strength of the metal, and to copper - fluidity, hardness and corrosion resistance. Arsenic is also sometimes added to some grades of bronzes, brasses, babbitts and type alloys. However, metallurgists often try to avoid using this substance, since it is unsafe for health. For some metals, large amounts of arsenic are also harmful because they degrade the properties of the original material.

Arsenic oxide has found use in glass making as a glass brightener. It was used in this direction by ancient glassblowers. Arsenic compounds are a strong antiseptic, so they are used to preserve furs, stuffed animals and skins, and also to create antifouling paints for water transport and impregnation for wood.

Due to the biological activity of some arsenic derivatives, the substance is used in the production of plant growth stimulants, as well as medicines, including anthelmintics for livestock. Products containing this element are used to control weeds, rodents and insects. Previously, when people did not think about whether arsenic could be used for food production, the element had wider uses in agriculture. However, after its toxic properties were discovered, a replacement had to be found.

Important areas of application of this element are: the production of microcircuits, fiber optics, semiconductors, film electronics, as well as the growth of microcrystals for lasers. For these purposes, gaseous arsines are used. And the production of lasers, diodes and transistors is not complete without gallium and indium arsenides.

Medicine

In human tissues and organs, the element is presented mainly in the protein fraction, and to a lesser extent in the acid-soluble fraction. It is involved in fermentation, glycolysis and redox reactions, and also ensures the breakdown of complex carbohydrates. In biochemistry, compounds of this substance are used as specific enzyme inhibitors, which are necessary for the study of metabolic reactions. Arsenic is necessary for the human body as a trace element.

The use of the element in medicine is less extensive than in production. Its microscopic doses are used to diagnose all kinds of diseases and pathologies, as well as to treat dental diseases.

In dentistry, arsenic is used to remove pulp. A small portion of a paste containing arsenous acid ensures the death of the tooth literally within a day. Thanks to its action, pulp removal is painless and unhindered.

Arsenic is also widely used in the treatment of mild forms of leukemia. It allows you to reduce or even suppress the pathological formation of leukocytes, as well as stimulate red hematopoiesis and the release of red blood cells.

Arsenic is like poison

All compounds of this element are poisonous. Acute arsenic poisoning results in abdominal pain, diarrhea, nausea, and central nervous system depression. The symptoms of intoxication with this substance resemble those of cholera. Therefore, earlier cases of intentional arsenic poisoning were often encountered in judicial practice. For criminal purposes, the element was most often used in the form of trioxide.

Symptoms of intoxication

At first, arsenic poisoning manifests itself as a metallic taste in the mouth, vomiting and abdominal pain. If measures are not taken, convulsions and even paralysis may occur. In the worst case, poisoning can be fatal.

The cause of poisoning can be:

1. Inhalation of dust containing arsenic compounds. Occurs, as a rule, in arsenic production plants where labor safety rules are not followed.
2. Consuming poisoned food or water.
3. Use of certain medications.

First aid

The most widely available and well-known antidote for arsenic intoxication is milk. The casein protein it contains forms insoluble compounds with the toxic substance that cannot be absorbed into the blood.

In case of acute poisoning, to quickly help the victim, he needs to undergo gastric lavage. In hospital settings, hemodialysis is also carried out, aimed at cleansing the kidneys. Among medications, a universal antidote is used - Unithiol. Additionally, antagonist substances can be used: selenium, zinc, sulfur and phosphorus. In the future, the patient is required to be prescribed a complex of amino acids and vitamins.

Arsenic deficiency

Answering the question: “What is arsenic?”, it is worth noting that the human body needs it in small quantities. The element is considered immunotoxic, conditionally essential. It takes part in almost all the most important biochemical processes of the human body. A deficiency of this substance may be indicated by the following signs: a decrease in the concentration of triglycerides in the blood, deterioration in the development and growth of the body.

As a rule, in the absence of serious health problems, there is no need to worry about a lack of arsenic in the diet, since the element is found in almost all products of plant and animal origin. Seafood, cereals, grape wine, juices, and drinking water are especially rich in this substance. Within 24 hours, 34% of consumed arsenic is eliminated from the body.

In case of anemia, the substance is taken to increase appetite, and in case of selenium poisoning, it acts as an effective antidote.

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The site provides reference information for informational purposes only. Diagnosis and treatment of diseases must be carried out under the supervision of a specialist. All drugs have contraindications. Consultation with a specialist is required!

General information

Uniqueness arsenic is that it can be found everywhere - in rocks, minerals, water, soil, animals and plants. It is even called the omnipresent element. Arsenic is distributed over different geographic regions of the Earth due to the volatility of its compounds and their high solubility in water. If the region's climate is humid, the element is washed out of the ground and then carried away by groundwater. Surface waters and the depths of rivers contain from 3 µg/l to 10 µg/l of the substance, and sea and ocean water contain much less, about 1 µg/l.

Arsenic occurs in the adult human body in amounts of approximately 15 mg. Most of it is found in the liver, lungs, small intestine and epithelium. Absorption of the substance occurs in the stomach and intestines.
The antagonists of the substance are phosphorus, sulfur, selenium, vitamins E, C, as well as some amino acids. In turn, the substance impairs the body’s absorption of selenium, zinc, vitamins A, E, C, and folic acid.
The secret of its benefits is in its quantity: in a small dose it performs a number of useful functions; and in large ones it is a powerful poison.

Functions:

• Improving the absorption of phosphorus and nitrogen.
• Stimulation of hematopoiesis.
• Weakening of oxidative processes.
• Interaction with proteins, lipoic acid, cysteine.

The daily need for this substance is small - from 30 to 100 mcg.

Arsenic as a chemical element

Arsenic is classified as a chemical element of group V of the periodic table and belongs to the nitrogen family. Under natural conditions, this substance is represented by the only stable nuclide. More than a dozen radioactive isotopes of arsenic have been artificially obtained, with a wide range of half-life values ​​- from a couple of minutes to a couple of months. The formation of the term is associated with its use for the extermination of rodents - mice and rats. Latin name Arsenicum (As) derived from the Greek word " arsen", What means: powerful, strong.

Historical information

Arsenic in its pure form was discovered during alchemical experiments in the Middle Ages. And its compounds have been known to people for a long time; they were used to produce medicines and paints. Today, arsenic is used in a particularly versatile manner in metallurgy.

Historians called one of the periods of human development the bronze period. At this time, people switched from stone weapons to improved bronze weapons. Bronze is a compound ( alloy) tin with copper. According to historians, the first bronze was cast in the Tigris and Euphrates valley, around the 30th century. BC. Depending on the percentage composition of the components included in the alloy, bronze cast by different blacksmiths could have different properties. Scientists have found that the best bronze with valuable properties is a copper alloy that contains up to 3% tin and up to 7% arsenic substances. Such bronze was easy to cast and forged better. Probably, during smelting, copper ore was confused with weathering products of copper-arsenic sulfide minerals, which had a similar appearance. Ancient craftsmen appreciated the good properties of the alloy and then purposefully searched for deposits of arsenic minerals. To find them, we used the specific property of these minerals to give off a garlicky odor when heated. But over time, the smelting of bronze containing arsenic compounds ceased. Most likely, this happened due to the fact that poisoning very often occurred when firing arsenic-containing substances.

Of course, in the distant past this element was known only in the form of its minerals. In ancient China, they knew a solid mineral called realgar, which, as is now known, is a sulfide with the composition As4S4. Word " realgar" translated from Arabic means " mine dust" This mineral was used for stone carving, but it had one significant drawback: in the light or when heated, realgar “spoiled”, because under the influence of a thermal reaction it turned into a completely different substance, As2S3.

Scientist and philosopher Aristotle in the 4th century BC. gave its name to this mineral - “ sandarac" Three centuries later, the Roman scientist and writer Pliny the Elder together with a doctor and a botanist Dioscorides described another mineral called orpiment. The Latin name of the mineral is translated “ gold paint" This mineral was used as a yellow dye.

In the Middle Ages, alchemists isolated three forms of the substance: yellow arsenic ( being a sulfide of As2S3), red ( sulfide As4S4) and white ( oxide As2O3). White is formed by the sublimation of some arsenic impurities during the roasting of copper ores that contain this element. It condensed from the gas phase and settled in the form of a white coating, after which it was collected.

In the 13th century, alchemists heated yellow arsenic and soap to produce a metal-like substance that may have been the first example of a pure substance produced artificially. But the resulting substance violated the alchemists’ ideas about the mystical “connection” of the seven metals known to them with the seven astronomical objects - the planets; that is why alchemists called the resulting substance “illegitimate metal.” They noticed one interesting property about it - the substance could give copper a white color.

Arsenic was clearly identified as an independent substance at the beginning of the 17th century, when a pharmacist Johann Schröder when reducing the oxide with charcoal, I obtained it in its pure form. A few years later, a French physician and chemist Nicola Lemery managed to obtain this substance by heating its oxide in a mixture with potash and soap. In the next century it was already well known and called an unusual “semi-metal”.

Swedish scientist Scheele experimentally obtained arsenous hydrogen gas and arsenic acid. In the same time A.L. Lavoisier recognized this substance as an independent chemical element.

Being in natural conditions

The element is often found in natural conditions in compounds with copper, cobalt, nickel, and iron. There is not much of it in the earth's crust - about 5 grams per ton, which is about the same amount as tin, molybdenum, germanium, tungsten and bromine.

The composition of minerals that this chemical element forms ( today there are more than 200 of them), due to the “semi-metallic” properties of the element. It can be in both negative and positive oxidation states and therefore combines easily with many other elements; in positive oxidation, arsenic plays the role of a metal ( for example, in sulfides), if negative – non-metal ( in arsenides). Arsenic-containing minerals have a complex composition. The element itself can replace antimony, sulfur, and metal atoms in the crystal lattice.

Many compounds of metals and arsenic, judging by their composition, are more likely to be intermetallic compounds than arsenides; Some of them are distinguished by variable content of the main element. Several metals can be simultaneously present in arsenides, and the atoms of these metals, with close ion radii, can replace each other in the crystal lattice in arbitrary ratios. All minerals classified as arsenides have a metallic luster. They are opaque, heavy, and their hardness is low.

An example of natural arsenides ( there are approximately 25 of them) can serve such minerals as skutterudite, safflorite, rammelsbergite, nickelskutterudite, nickelin, löllingite, sperrylite, maucherite, algodonite, langisite, clinosafflorite. These arsenides have a high density and belong to the group of “superheavy” minerals.

The most common mineral is arsenopyrite ( or, as it is also called, arsenic pyrite). What seems interesting to chemists is the structure of those minerals in which arsenic is present simultaneously with sulfur, and in which it plays the role of a metal, since it is grouped together with other metals. These minerals are arsenosulvanite, gyrodite, arsenogauchekornite, freibergite, goldfieldite, tennantite, argentotennantite. The structure of these minerals is very complex.

Natural sulfides such as realgar, orpiment, dimorphite, getchellite, have a positive oxidation state As ( lat. arsenic designation). These minerals appear as small inclusions, although crystals of large size and weight have occasionally been mined in some areas.

An interesting fact is that natural salts of arsenic acid, called arsenates, look very different. Erythritol has a cobalt color, while scorodite, annabergite and simplesite are green. And görnesite, köttigitite, and rooseveltite are completely colorless.

In the central region of Sweden there are quarries in which ferromanganese ore is mined. More than fifty samples of minerals that are arsenates were found and described in these quarries. Some of these arsenates have not been found anywhere else. Experts believe that these minerals were formed at low temperatures as a result of the interaction of arsenic acid with other substances. Arsenates are oxidation products of certain sulfide ores. They usually have no value other than aesthetic value. Such minerals are decorations of mineralogical collections.

The names of the minerals were given in different ways: some of them were named after scientists and prominent political figures; others were named after the locality in which they were found; still others were named by Greek terms denoting their basic properties ( for example color); the fourth were named with abbreviations that denoted the initial letters of the names of other elements.

For example, the formation of the ancient name for such a mineral as nickel is interesting. Previously it was called kupfernickel. German miners who worked to develop copper five to six centuries ago were superstitiously afraid of an evil mountain spirit, which they called Nickel. German word " kupfer" meant " copper" They called “damn” or “fake” copper Kupfernickel. This ore was very similar to copper, but copper could not be obtained from it. But it has found its application in glass making. With its help, glass was painted green. Subsequently, a new metal was isolated from this ore and called nickel.

Pure arsenic is quite inert in its chemical properties and can be found in its native state. It looks like fused needles or cubes. Such a nugget is easy to grind into powder. It contains up to 15% impurities ( cobalt, iron, nickel, silver and other metals).

As a rule, the As content in soil ranges from 0.1 mg/kg to 40 mg/kg. In areas where arsenic ore occurs and in the area of ​​volcanoes, the soil can contain very large amounts of As - up to 8 g/kg. This is exactly the rate found in some areas of New Zealand and Switzerland. In such areas, flora dies and animals get sick. The same situation is typical for deserts and steppes, where arsenic is not washed out of the soil. Compared to the average content, clayey rocks are also considered enriched, since they contain four times more arsenic substances.

If a pure substance is converted as a result of biomethylation into a volatile organoarsenic compound, then it is carried out of the soil not only by water, but also by wind. Biomethylation is the addition of a methyl group to form a C–As bond. This process is carried out with the participation of the substance methylcobalamin - a methylated derivative of vitamin B12. Biomethylation of As occurs in both seawater and freshwater. This leads to the formation of organoarsenic compounds such as methylarsonic and dimethylarsinic acids.

In those areas where there is no specific pollution, the arsenic concentration is 0.01 μg/m3, and in industrial areas where power plants and factories are located, the concentration reaches a level of 1 μg/m3. In areas where industrial centers are located, arsenic deposition is intense and amounts to up to 40 kg/sq. km per year.

Volatile arsenic compounds, when their properties had not yet been fully studied, brought a lot of trouble to people. Mass poisonings were not uncommon even in the 19th century. But the doctors did not know the reasons for the poisoning. And the toxic substance was contained in green wallpaper paint and plaster. High humidity led to the formation of mold. Under the influence of these two factors, volatile organoarsenic substances were formed.

There is an assumption that the process of formation of volatile organoarsenic derivatives could have caused the delayed poisoning of the emperor Napoleon which led to his death. This assumption is based on the fact that 150 years after his death, traces of arsenic were found in his hair.

Arsenic substances are found in moderate quantities in some mineral waters. Generally accepted standards establish that in medicinal mineral waters the concentration of arsenic should be no more than 70 µg/l. In principle, even if the concentration of the substance is higher, it can lead to poisoning only with constant, long-term use.

Arsenic can be found in natural waters in various compounds and forms. Trivalent arsenic, for example, is many times more toxic than pentavalent arsenic.

Some seaweeds can accumulate arsenic in such concentrations that they are dangerous to humans. Such algae can easily grow and even reproduce in an acidic arsenic environment. In some countries they are used as pest control agents ( against rats).

Chemical properties

Arsenic is sometimes called a metal, but in reality it is more of a non-metal. It does not form salts when combined with acids, but in itself it is an acid-forming substance. That's why it is also called a semimetal. Like phosphorus, arsenic can exist in different allotropic forms.

One of these forms is gray arsenic, a rather fragile substance. Its fracture has a bright metallic sheen ( therefore, its second name is “arsenic metal”). The electrical conductivity of this semimetal is 17 times less than that of copper, but at the same time 3.6 times greater than that of mercury. The higher the temperature, the lower the electrical conductivity. This typical property of metals is also characteristic of this semimetal.

If arsenic vapor is cooled for a short time to a temperature of –196 degrees ( this is the temperature of liquid nitrogen), you will get a soft, transparent, yellow substance that looks like yellow phosphorus. The density of this substance is much lower than that of arsenic metal. Yellow arsenic and arsenic vapors consist of molecules that have the shape of a tetrahedron ( those. pyramid shape with four bases). Phosphorus molecules have the same shape.

Under the influence of ultraviolet radiation, as well as when heated, yellow arsenic instantly turns into gray; This reaction releases heat. If vapors condense in an inert atmosphere, then another form of this element is formed - amorphous. If arsenic vapor is deposited on glass, a mirror film is formed.

The structure of the electronic outer shell of this element is the same as that of phosphorus and nitrogen. Arsenic, like phosphorus, can form three covalent bonds.

If the air is dry, then As has a stable form. It becomes dull from humid air and becomes covered with black oxide on top. When ignited, arsenic vapor easily burns with a blue flame.

As in its pure form is quite inert; alkalis, water and various acids that do not have oxidizing properties do not affect it in any way. If you take dilute nitric acid, it will oxidize pure As to orthoarsenous acid, and if you take concentrated nitric acid, it will oxidize it to orthoarsenic acid.

As reacts with sulfur and halogens. In reactions with sulfur, sulfides of different compositions are formed.

Arsenic is like poison

All arsenic compounds are poisonous.

Acute poisoning by these substances is manifested by abdominal pain, diarrhea, vomiting, and central nervous system depression. The symptoms of intoxication with this substance are very similar to the symptoms of cholera. Therefore, in judicial practice, cases of the use of arsenic as a poison were often encountered in the past. The most successfully used poisonous compound for criminal purposes is arsenic trioxide.

In those areas where there is an excess of the substance in water and soil, it accumulates in the thyroid glands of people. As a result, they develop an endemic goiter.

Arsenic poisoning

Symptoms of arsenic poisoning include a metallic taste in the mouth, vomiting, and severe abdominal pain. Later, seizures or paralysis may occur. Poisoning can lead to death. The most widely available and well-known antidote for arsenic intoxication is milk. The main protein of milk is casein. It forms an insoluble compound with arsenic that is not absorbed into the blood.

Poisoning occurs:
1. When inhaling arsenic compounds in the form of dust ( most often - in unfavorable production conditions).
2. When drinking poisoned water and food.
3. When using certain medications. Excess substance is deposited in the bone marrow, lungs, kidneys, skin, and intestinal tract. There is a large body of evidence that inorganic arsenic compounds are carcinogenic. Due to long-term consumption of arsenic-poisoned water or medications, low-grade skin cancer may develop ( Bowen's cancer) or liver hemangioendothelioma.

In case of acute poisoning, gastric lavage is required as first aid. In stationary conditions, hemodialysis is performed to cleanse the kidneys. For use in acute and chronic poisoning, Unithiol is used - a universal antidote. Additionally, antagonist substances are used: sulfur, selenium, zinc, phosphorus; and a complex of vitamins and amino acids is mandatory.

Symptoms of overdose and deficiency

Possible signs of arsenic deficiency are manifested by a decrease in the concentration of triglycerides in the blood, an increase in fertility, and a deterioration in the development and growth of the body.

Arsenic is a highly toxic substance; a single dose of 50 mg can be fatal. An overdose is manifested by irritability, allergies, headaches, dermatitis, eczema, conjunctivitis, depression of respiratory function and the nervous system, and impaired liver function. An overdose of a substance increases the risk of developing cancer.

The source of the element is considered to be: plant and animal products, seafood, grains, cereals, tobacco, wine, and even drinking water.

There is no need to worry about getting this microelement into our diet - it is found in almost all products of animal and plant origin, except in refined sugar. It comes to us in sufficient quantities with food. Products especially rich in it, such as shrimp, lobster, lobsters - in order to avoid an overdose, you should eat in moderation so as not to ingest an excessive amount of poison.

Arsenic compounds can enter the human body with mineral water, seafood, juices, grape wines, medications, herbicides and pesticides. This substance accumulates mainly in the reticuloendothelial system, as well as in the lungs, skin, and kidneys. An insufficient daily intake of a substance into the body is considered to be 1 mcg/day. The toxicity threshold is approximately 20 mg.

A large amount of the element is found in fish oil and, oddly enough, in wines. In normal drinking water, the content of the substance is low and not hazardous to health - approximately 10 µg/l. Some regions of the world ( Mexico, Taiwan, India, Bangladesh) are notorious for having high levels of arsenic in their drinking water ( 1 mg/l), and therefore mass poisonings of citizens sometimes occur there.

Arsenic prevents the body from losing phosphorus. Vitamin D is a regulating factor in the course of phosphorus-calcium metabolism, and arsenic, in turn, regulates phosphorus metabolism.

It is also known that some forms of allergies develop due to arsenic deficiency in the body.

The trace element is used to increase appetite in case of anemia. For selenium poisoning, arsenic is an excellent antidote. Experimental studies on mice have shown that precisely calculated doses of the substance help reduce the incidence of cancer.

When the concentration of an element in soil or food increases, intoxication occurs. Severe intoxication can lead to serious diseases such as laryngeal cancer or leukemia. Moreover, the number of deaths will also increase.

It is known that 80% of the substance that enters the body with food is sent to the gastrointestinal tract and from there enters the blood, and the remaining 20% ​​reaches us through the skin and lungs.

A day after entering the body, more than 30% of the substance is excreted from it along with urine and about 4% along with feces. According to the classification, arsenic is classified as an immunotoxic, conditionally essential, element. It has been proven that the substance takes part in almost all important biochemical processes.

Arsenic in dentistry

This substance is often used to treat dental diseases such as caries. Caries begins when the calcareous salts of tooth enamel begin to break down and the weakened tooth is attacked by pathogens. By affecting the soft inner part of the tooth, microbes form a carious cavity.
If at this stage of the disease the carious cavity is cleaned and filled with filling material, the tooth will remain “alive”. And if you let the process take its course, the carious cavity reaches the tissue that contains blood, nerve and lymphatic vessels. It's called pulp.

Inflammation of the pulp develops, after which the only way to prevent further spread of the disease is to remove the nerve. It is for this manipulation that arsenic is needed.

The pulp is exposed with a dental instrument, a grain of paste containing arsenous acid is placed on it, and it diffuses into the pulp almost instantly. A day later the tooth dies. Now the pulp can be removed completely painlessly, the root canals and pulp chamber can be filled with a special antiseptic paste, and the tooth can be sealed.

Arsenic in the treatment of leukemia

Arsenic is quite successfully used to treat mild forms of leukemia, as well as during the period of primary exacerbation, in which a sharp enlargement of the spleen and lymph nodes has not yet been observed. It reduces or even suppresses the pathological formation of leukocytes, stimulates red hematopoiesis and the release of red blood cells to the periphery.

Obtaining arsenic

It is obtained as a by-product of the processing of lead, copper, cobalt and zinc ores, as well as during gold mining. Some of the polymetallic ores contain up to 12% arsenic. If they are heated to 650 - 700 degrees, then in the absence of air sublimation occurs. If heated in air, “white arsenic” is formed, which is a volatile oxide. It is condensed and heated with coal, during which arsenic is reduced. Obtaining this element is a harmful production.

Previously, before the development of ecology as a science, “white arsenic” was released into the atmosphere in large quantities, and subsequently it settled on trees and plants. The permissible concentration in the air is 0.003 mg/m3, while near industrial facilities the concentration reaches 200 mg/m3. Oddly enough, the environment is most polluted not by those factories that produce arsenic, but by power plants and non-ferrous metallurgy enterprises. Bottom sediments near copper smelters contain large amounts of the element - up to 10 g/kg.

Another paradox is that this substance is produced in greater quantities than it is required. This is a rare occurrence in the metal mining industry. Excess it has to be disposed of in large metal containers, hiding them in disused old mines.

Arsenopyrite is a valuable industrial mineral. Large copper-arsenic deposits are found in Central Asia, Georgia, USA, Japan, Norway, Sweden; gold-arsenic - in the USA, France; arsenic-cobalt - in New Zealand, Canada; arsenic-tin - in England and Bolivia.

Determination of arsenic

The qualitative reaction to arsenic consists of the precipitation of yellow sulfides from hydrochloric acid solutions. Traces are determined by the Gutzeit method or the Marsh reaction: paper strips soaked in HgCl2 change color to dark in the presence of arsine, which reduces sublimate to mercury.

Over the past half century, a variety of sensitive analytical techniques have been developed ( spectrometry), thanks to which even small amounts of arsenic can be detected. If there is very little substance in the water, then the samples are pre-concentrated.

Some compounds are analyzed by the selective hydride method. This method involves selective reduction of the analyte to the volatile compound arsine. Volatile arsines are frozen in a container cooled with liquid nitrogen. Then, by slowly heating the contents of the container, you can ensure that different arsines evaporate separately from each other.

Industrial Application

About 98% of all arsenic mined is not used in its pure form. But its compounds have gained popularity and are used in various industries. Hundreds of tons of the substance are mined and used annually. It is added to bearing alloys to improve quality, used in the creation of cables and lead batteries to increase hardness, and used in alloys with germanium or silicon in the production of semiconductor devices. Arsenic is used as a dopant that imparts a certain type of conductivity to “classical” semiconductors.

Arsenic is a valuable material in non-ferrous metallurgy. When added to lead in an amount of 1%, the hardness of the alloy increases. If you add a little arsenic to molten lead, then in the process of casting the shot, spherical balls of regular shape come out. Additives to copper enhance its strength, corrosion resistance and hardness. Thanks to this additive, the fluidity of copper increases, which facilitates the process of wire drawing.

As is added to some types of brass, bronze, printing alloys, and babbitts. But still, metallurgists are trying to exclude this additive from the production process, since it is very harmful to humans. Moreover, it is also harmful to metals, since the presence of arsenic in large quantities impairs the properties of many alloys and metals.

Oxides are used in glass making as glass brighteners. Even ancient glassblowers knew that white arsenic contributes to the opacity of glass. However, small additions of it, on the contrary, brighten the glass. Arsenic is still included in the recipe for making some glasses, for example, “Vienna” glass, used to create thermometers.

Arsenic compounds are used as an antiseptic to protect against spoilage, as well as for preserving furs, skins, stuffed animals; for creating antifouling paints for water transport; for impregnation of wood.

The biological activity of some As derivatives has interested agronomists, sanitary and epidemiological service workers, and veterinarians. As a result, arsenic-containing drugs were created, which were stimulants of productivity and growth; medicines for the prevention of livestock diseases; anthelmintic agents.

Landowners in ancient China treated rice crops with arsenic oxide to protect them from fungal diseases and rats, and thus protect the crop. Now, due to the toxicity of arsenic-containing substances, their use in agriculture is limited.

The most important areas of use of arsenic-containing substances are the production of microcircuits, semiconductor materials and fiber optics, film electronics, as well as the growth of special single crystals for lasers. In these cases, as a rule, gaseous arsine is used. Indium and gallium arsenides are used in the manufacture of diodes, transistors, and lasers.

In tissues and organs, the element is mainly found in the protein fraction, much less of it is in the acid-soluble fraction, and only a small part of it is in the lipid fraction. It is a participant in redox reactions; without it, the oxidative breakdown of complex carbohydrates is impossible. It is involved in fermentation and glycolysis. Compounds of this substance are used in biochemistry as specific enzyme inhibitors, which are needed to study metabolic reactions. It is necessary for the human body as a trace element.