Arsenic is a chemical element with atomic number 33 in the periodic table of chemical elements D.I. Mendeleev, is designated by the symbol As. It is a brittle, steel-colored semi-metal.
origin of name
The name of arsenic in Russian is associated with the use of its compounds to exterminate mice and rats. The Greek name ἀρσενικόν comes from the Persian زرنيخ (zarnik) - “yellow orpiment.” Folk etymology dates back to ancient Greek. ἀρσενικός - male.
In 1789, A.L. Lavoisier isolated metallic arsenic from arsenic trioxide (“white arsenic”), proved that it was an independent simple substance, and assigned the name “arsenicum” to the element.
Receipt
The discovery of a method for producing metallic arsenic (gray arsenic) is attributed to the medieval alchemist Albertus Magnus, who lived in the 13th century. However, much earlier, Greek and Arab alchemists were able to obtain arsenic in free form by heating “white arsenic” (arsenic trioxide) with various organic substances.
There are many ways to obtain arsenic: by sublimation of natural arsenic, by thermal decomposition of arsenic pyrite, by reduction of arsenic anhydride, etc.
Currently, to obtain arsenic metal, arsenopyrite is most often heated in muffle furnaces without access to air. At the same time, arsenic is released, the vapors of which condense and turn into solid arsenic in iron tubes coming from the furnaces and in special ceramic receivers. The residue in the furnaces is then heated with access to air, and then the arsenic turns into As 2 O 3. Metallic arsenic is obtained in rather small quantities, and main part arsenic-containing ores are processed into white arsenic, that is, into arsenic trioxide - arsenous anhydride As 2 O 3.
Application
Arsenic is used to alloy lead alloys used to prepare shot, since when shot is cast using the tower method, drops of the arsenic-lead alloy acquire a strictly spherical shape, and in addition, the strength and hardness of lead increases.
Arsenic of special purity (99.9999%) is used for the synthesis of a number of valuable and important semiconductor materials - arsenides and complex diamond-like semiconductors.
Arsenic sulfide compounds - orpiment and realgar - are used in painting as paints and in the leather industry as means for removing hair from the skin.
In pyrotechnics, realgar is used to produce “Greek” or “Indian” fire, which occurs when a mixture of realgar with sulfur and saltpeter burns (a bright white flame).
Many of the arsenic compounds in very small doses are used as medicines to combat anemia and a number of serious diseases, as they have a clinically significant stimulating effect on a number of body functions, in particular, hematopoiesis. Of the inorganic arsenic compounds, arsenous anhydride can be used in medicine for the preparation of pills and in dental practice in the form of a paste as a necrotizing drug. This drug was called “arsenic” and was used in dentistry to remove a nerve. Currently, arsenic preparations are rarely used in dental practice due to toxicity. Other methods of painless tooth denervation under local anesthesia have been developed and are used.
ARSENIC(possibly from the word “mouse”; in Ancient Rus', the emergence of such a name could be associated with the use of arsenic compounds to exterminate mice and rats; lat. Arsenicura, from the Greek arsen-strong, powerful) As, chemical. element V gr. periodic
Content in the earth's crust is 1.7. 10 -4% by weight. Belongs to the dispersed elements, but forms St. 160 own minerals Rarely found in its native form.
Naib. common minerals having industrial meaning, arsenopyrite FeAsS, realgar As 4 S 4 and orpiment As 2 S 3. Practical Arsenic ores containing at least 2-5% arsenic are important. In rich deposits, the arsenic content in the ore reaches 25-35%. Means. Amounts of arsenic are concentrated in most polymetallic materials. non-ferrous metal ores. First of all, it is genetically associated with the ores of W, Sn, Pb, Sb, Zn, Cu, Ni and Co. With almost all of these metals, arsenic forms simple and complex arsenide minerals, for example. sperrshsht PbAs 2, shmaltin CoAs 2, tennatite 3Cu 2 S. As 2 S 3 . Arsenic minerals are also found in deposits of the noble metals Au and Ag. Basic mass of arsenic and its components. (more than 90%) are obtained by processing polymetallic materials.3.7 MPa; air temperature - 615°C; dense liquid 5.24 g/cm 3 (817°C); C 0 p 25.05 J/(mol K); DH 0 pl 28 kJ/mol, DH 0 sub 150 kJ/mol (for As 4); S 0 298 35.6 JDmol K); level of temperature dependence of steam pressure: logp (mm Hg) = 11.160 - 7357/T (623 -1090 K); temperature coefficient linear expansion 4. 10 -6 K -1 (293-573 K); tcrit 1400 °C, pcrit 22.0 MPa, drit 2.65 g/cm3.
Arsenic vapor is colorless, consists of As 4 molecules up to 800 ° C, above 1700 ° C from As 2, in the range of 800-1700 ° C from a mixture of As 2 and As 4. Gray arsenic is very fragile and breaks down along the cleavages; Brinell hardness ~ 1500 MPa, Mohs hardness 3.5. Arsenic is diamagnetic, magnesium susceptibility is 5.5. 10 -6 ;
has a metal lich. conductivity; p 3.3. 10 -5 Ohm. cm, temperature coefficient p 3.9. 10 -3 K -1 (273-373 K).
Ortho arsenic acid (arsenic acid) H 3 AsO 4 x x 0.5H 2 O, colorless. crystals; m.p. 36 °C (with decomposition); sol. in water (88% by weight at 20 °C); hygroscopic; in aqueous solutions, tribasic acid: K a1 = 5.6. 10 -3, K a2 =1.7. 10 -7, K a3 = 3.0. 10 -12 ; when heated OK. 100 °C loses water, turning into pyroarsenic acid H 4 As 2 O 7, at higher temperatures it turns into metaarsenic acid HAsO 3. Obtained by oxidation of As or As 2 O 3 conc. HNO3. Used to produce As 2 O 5 , arsenates (V), arsenic. com., as an antiseptic for wood. Orthomous acid (arsenic acid) H 3 AsO, exists only in aqueous solution; weak, K a1 = 8. 10 -16 (25 °C); obtained by dissolving As 2 O 3 in water; intermittent product in the preparation of arsenates (III) and other compounds.
Receipt. Arsenic-containing ores are subjected to oxidation. roasting and arsenic is recovered in the form of As 2 O 3 .
It is sublimated and a product with a purity of more than 98% is obtained. Almost all connections arsenic in industry is produced based on As 2 O 3. Metallic arsenic is also obtained from As 2 O 3 by reducing it with carbon-containing reducing agents (most often charcoal). Arsenic is purified by sublimation. High purity arsenic for the synthesis of semiconductor compounds. obtained from pre-purified AsH 3 or AsCl 3 chemical. by vapor deposition. Arsine decomposes at 300-400 °C in a stream of H 2 or Ar. The chloride is reduced with high purity H2 (which is purified by diffusion through Pd alloys). Naib.mirrors." The Gutzeit method is sensitive; H 2 with traces of AsH 3 released (during the reduction of arsenic compounds) is passed over a strip of dry filter paper impregnated with HgCl 2 or, better, HgBr 2; this method can also be used as a quantitative The neutron activation method for detecting arsenic in the form of 76 As (T 1/2 26.6 h) has a very high sensitivity (~5.10 -12 g);10 -8 -10 -10% arsenic.
Arsenic is determined quantitatively after distilling it from hydrochloric acid solution in the form of AsCl 3 . According to the Ledebour method, AsCl 3 captured in water is titrated with KBrO 3 in hydrochloric acid solution in the presence. methyl orange or fluorescein. According to the hypophosphite method, As(III) is reduced to elemental arsenic in a strongly acidic medium (2As 3+ + 3H 2 PO - 2 +ZN 2 O -> 2As + ZN 2 PO - 3 + 6H +);
the resulting arsenic is filtered off, washed with dil. hydrochloric acid and NH 4 Cl solution and dissolve in an excess of a known amount of 0.01-0.1 N. solution I 2. Excess I 2 is titrated with H 3 AsO 3 solution in the presence of NaHCO3.
Gravimetric methods, arsenic is determined in the form
Arsenic is a classic poison of medieval and modern poisoners
and medicine in modern sports and rehabilitation medicine Toxic and poisonous stones and minerals
Arsenic
(lat. Arsenicum), As, chemical element of group V of the periodic system of Mendeleev, atomic number 33, atomic mass 74.9216; steel-gray crystals. The element consists of one stable isotope 75 As. Poisonous in any form, medicine.
Historical reference.
Natural compounds of arsenic with sulfur (orpiment As 2 S 3, realgar As 4 S 4) were known to the peoples of the ancient world, who used these minerals as medicines and paints. The product of burning arsenic sulfides was also known - arsenic (III) oxide As 2 O 3 (“white arsenic”).
The name arsenikon is found already at the beginning of our era; it is derived from the Greek arsen - strong, courageous and served to designate arsenic compounds (based on their effect on the body). The Russian name is believed to have come from “mysh” (“death” - after the use of arsenic preparations to kill yaks, as well as exterminate mice and rats). The chemical production of free arsenic is attributed to 1250 AD. In 1789, A. Lavoisier included arsenic in the list of chemical elements.
The average arsenic content in the earth's crust (clarke) is 1.7 * 10 -4% (by mass), in such quantities it is present in most igneous rocks. Since arsenic compounds are volatile at high temperatures (dry volcanic sublimation on batholiths), the element sublimes into the atmosphere and air in the form of metal vapors (mirages - the air below ripples) does not accumulate during magmatic lava processes sublimating through cracks and tubes; it is concentrated, deposited from vapors and hot deep waters on crystal formation catalysts - metallic iron (together with S, Se, Sb, Fe, Co, Ni, Cu and other elements).
During volcanic eruptions (during dry sublimation of arsenic), arsenic in the form of its volatile compounds enters the atmosphere. Since arsenic is multivalent, its migration is 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 in areas of arsenic deposits. Native arsenic and As 2+ minerals are even less common. Of the minerals and arsenic compounds (about 180), arsenopyrite FeAsS is of industrial importance (the iron atom is the center of pyrite formation, the formula of the starting “single crystal” is Fe + (As + S)).
Arsenopyrite vein. Trifonovskaya mine, Kochkarskoye deposit (Au), Plast, South Ural, Russia. Arsenics. Photo: A.A. Evseev.
Small amounts of arsenic are essential for life. However, in areas of arsenic deposits and the activity of young volcanoes, soils in some places contain up to 1% arsenic, which is associated with livestock diseases and death of vegetation. The accumulation of arsenic is especially typical for landscapes of steppes and deserts, in the soils of which arsenic is inactive. In humid climates and when plants and soils are watered, arsenic is washed out of the soil.
In living matter there is an average of 3·10 -5% arsenic, in rivers 3·10 -7%. Arsenic carried by rivers into the ocean precipitates relatively quickly. In sea water there is 1 * 10 -7% arsenic (there is a lot of gold there, which displaces it), but in clays and shales there is arsenic (along the banks of rivers and reservoirs, in clayey black formations and along the edges of quarries) - 6.6 * 10 - 4 %. Sedimentary iron ores, ferromanganese and other iron nodules are often enriched in arsenic.
Physical properties of arsenic.
Arsenic has several allotropic modifications. Under normal conditions, the most stable is the so-called metallic, or gray, arsenic (α-As) - steel gray fragile crystalline mass (according to properties - like pyrite, gold blende, iron pyrite); when freshly fractured, it has a metallic luster; in air it quickly becomes dull, as it is covered with a thin film of As 2 O 3 .
Arsenic is rarely called silver blende - the case of the Tsar's Clerks A.M. Romanov in the middle of the 17th century, “silver”, not malleable, comes in powder, can be ground - poison for the Tsar of All Rus'. The most famous Spanish scandal in the poisoners' tavern near the Don Quixote mill on the road to Almaden, Spain, where red cinnabar is mined on the European continent (scandals about the sale of virgins in the Krasnodar Territory of the Russian Federation, the village of Novy, crystalline red cinnabar, do not want to work) .
Arsenopyrite. Druze of prismatic crystals with calcite spherulites. Freiberg, Saxony, Germany. Photo: A.A. Evseev.
The crystal lattice of gray arsenic is rhombohedral (a = 4.123Å, angle α = 54 o 10", x = 0.226), layered. Density 5.72 g/cm 3 (at 20 o C), electrical resistivity 35 * 10 -8 ohm *m, or 35*10 -6 ohm*cm, temperature coefficient of electrical resistance 3.9·10 -3 (0 o -100 o C), Brinell hardness 1470 MN/m 2, or 147 kgf/mm 2 (3- 4 according to Moocy); arsenic is diamagnetic.
Under atmospheric pressure, arsenic sublimes at 615 o C without melting, since the triple point of α-As lies at 816 o C and a pressure of 36 at.
Arsenic vapor consists of As 4 molecules up to 800 o C, above 1700 o C - only As 2. When arsenic vapor condenses on a surface cooled by liquid air, yellow arsenic is formed - transparent, wax-soft crystals with a density of 1.97 g/cm 3, similar in properties to white phosphorus.
When exposed to light or low heat, it turns into gray arsenic. Glassy-amorphous modifications are known: black arsenic and brown arsenic, which, when heated above 270 o C, turn into gray arsenic
Chemical properties of arsenic.
The configuration of the outer electrons of the arsenic atom is 3d 10 4s 2 4p 3. In compounds, arsenic has oxidation states +5, +3 and -3. Gray arsenic is less chemically active than phosphorus. When heated in air above 400 o C, arsenic burns, forming As 2 O 3.
Arsenic combines directly with halogens; under normal conditions, AsF 5 is a gas; AsF 3 , AsCl 3 , AsBr 3 - colorless volatile liquids; AsI 3 and As 2 I 4 are red crystals. When arsenic is heated with sulfur, sulfides are obtained: orange-red As 4 S 4 and lemon-yellow As 2 S 3.
Pale yellow silver sulfide As 2 S 5 ( arsenopyrite) is deposited by passing H 2 S into an ice-cooled solution of arsenic acid (or its salts) in fuming hydrochloric acid: 2H 3 AsO 4 + 5H 2 S = As 2 S 5 + 8H 2 O; At about 500 o C it decomposes into As 2 S 3 and sulfur.
All arsenic sulfides are insoluble in water and dilute acids. Strong oxidizing agents (mixtures of HNO 3 + HCl, HCl + KClO 3) convert them into a mixture of H 3 AsO 4 and H 2 SO 4.
As 2 S 3 sulfide 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, arsenic produces oxides: arsenic oxide (III) As 2 O 3 - arsenous anhydride and arsenic oxide (V) As 2 O 5 - arsenic anhydride. The first of them is formed by the action of oxygen on arsenic or its sulfides, for example 2As 2 S 3 + 9O 2 = 2As 2 O 3 + 6SO 2.
As 2 O 3 vapors condense into a colorless 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 o C the steam consists of As 2 O 3.
2.1 g of As 2 O 3 dissolves in 100 g of water (at 25 o C). Arsenic (III) oxide 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 ).
Arsenic (V) oxide is prepared by heating arsenic acid H 3 AsO 4 (about 200 o C). It is colorless, at about 500 o 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 H 4 As 2 O 7 ; the last two acids were not obtained in a free state. When alloyed with metals, arsenic mostly forms compounds (arsenides).
Obtaining arsenic.
Arsenic 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 condensing arsenic vapor.
Arsenic anhydride is obtained by oxidative roasting of arsenic ores or as a by-product of roasting polymetallic ores, which almost always contain arsenic. During oxidative roasting, As 2 O 3 vapors are formed, which condense in the collection chambers.
Crude As 2 O 3 is purified by sublimation at 500-600 o C. Purified As 2 O 3 is used for the production of arsenic and its preparations.
Use of arsenic.
Small additions of arsenic (0.2-1.0% by weight) are introduced into lead used for the production of gun shot (arsenic increases the surface tension of molten lead, due to which the shot takes on a shape close to spherical; arsenic slightly increases the hardness of lead). As a partial substitute for antimony, arsenic is included in some babbitt and printing alloys.
Pure arsenic 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; Arsenic hydrogen is especially dangerous. Of the arsenic compounds used in production, arsenic anhydride is the most toxic.
Almost all sulfide ores of non-ferrous metals, as well as iron (sulfur) pyrite, contain an admixture of arsenic. Therefore, during their oxidative roasting, along with sulfur dioxide SO 2, As 2 O 3 is always formed; Most of it condenses in the smoke channels, but in the absence or low efficiency of treatment facilities, the exhaust gases of ore kilns carry away noticeable amounts of As 2 O 3.
Pure arsenic, although not poisonous, is always covered with a coating of toxic As 2 O 3 when stored in air. In the absence of properly performed ventilation, etching of metals (iron, zinc) with industrial sulfuric or hydrochloric acids containing arsenic is extremely dangerous, since this produces arsenous hydrogen.
Arsenic in the body.
As a trace element, arsenic is ubiquitous in wildlife. The average arsenic content in soils is 4*10 -4%, in plant ash - 3*10 -5%. The arsenic content in marine organisms is higher than in terrestrial ones (in fish 0.6-4.7 mg per 1 kg of raw material, accumulates in the liver).
The largest amount of it (per 1 g of tissue) is found in the kidneys and liver (when ingested, it does not accumulate in the brain). A lot of arsenic is found in the lungs and spleen, skin and hair; relatively little - in the cerebrospinal fluid, brain (mainly in the pituitary gland), gonads and others.
In tissues, arsenic is found mainly protein fraction(“the stone of bodybuilders and athletes”), much less - in the acid-soluble and only a small part of it is found in the lipid fraction. It is used to treat progressive muscular dystrophy - it does not accumulate in the brain and bones (sports doping, treated for hostages and prisoners of concentration camps such as "Auschwitz" in Poland, EU, 1941-1944).
Arsenic is involved in redox reactions: oxidative breakdown of complex biological carbohydrates and sugars, fermentation, glycolysis, etc. Improves mental abilities (promotes the process of breaking down sugars in the brain). Arsenic compounds are used in biochemistry as specific enzyme inhibitors to study metabolic reactions. Promotes the breakdown of biological tissues (accelerates). It is actively used in dentistry and oncology - to eliminate rapidly growing and early aging cancer cells and tumors.
Mixture (hard sulfide alloy) of thallium, arsenic and lead: Hutchinsonite (Hutchinsonite)
The mineral formula is (Pb, Tl)S` Ag2S * 5 As2 S5 - complex sulfide and adsenide carbide salt. Rhombus. The crystals are prismatic to needle-shaped. Cleavage perfect according to (010). The aggregates are radial-needle-shaped, granular. Hardness 1.5-2. Specific gravity 4.6. Red. Diamond shine. In hydrothermal deposits with dolomite, with sulfides and arsenides of Zn, Fe, As and sulfoarsenides. The result of dry sulfuric and arsenic sublimation of magma through calderas and open volcanic vents, as well as dry sublimation through cracks in deep magmatic plutonites from the hot magma of the Earth. Contains silver. It is one of the ten very dangerous to human and animal health and carcinogenic stones and minerals that crystallize in modern conditions among other rocks in the form of harmful, hazardous to health (if handled without permission) and deceptive ore beauty. In the photo - Hutchinsonite with orpiment.
Poisonous minerals. Hutchinsonite - named after the mineralogist Hutchinson from the University of Cambridge and resembles lead in appearance (it can be used for protection against radiation). Opened in 1861. A deadly mixture (hard alloy) of thallium, arsenic and lead. Contact with this mineral can lead to hair loss (alopecia, baldness, baldness), complex skin diseases and death. All of its main components are poisonous. Very similar to lead, native silver, pyrite ("dry pyrite") and arsenopyrite. It is also similar to stibnite (an antimony compound, also very poisonous). Also similar to zeolites. Hutchinsonite is a dangerous and striking carbide mixture of thallium, lead and arsenic. Three rare, very expensive and valuable ore metals form a toxic, lethal cocktail of minerals that must be handled with the utmost care. Affects the brain, heart and liver simultaneously.
Thallium is lead's dark counterpart. This dense, fatty metal is similar in atomic mass to lead, but is even more deadly. Thallium is a rare metal that appears in highly toxic compounds consisting of strange combinations of elements (hard alloys). The effects of thallium exposure are more dangerous than lead, and include hair loss (alopecia, baldness), serious illness from skin contact, and in many cases death. Hutchinsonite was named after John Hutchinson, a famous mineralogist at the University of Cambridge. This mineral can be found in mountainous regions of Europe, most often in ore deposits. A mineral popular in medical dentistry, etc. Alcoholics are afraid of the mineral.
Hutchinsonite (Hutchinsonite) is sometimes jokingly called “dry” or “solid alcohol”, “solid alcohol” (and not only for the harmful effects of intoxicating poisoning on the body and human health). The chemical formula of food alcohol (alcohol) is C2 H5 (OH). Hutchinsonite (Hutchinsonite) has a chemical formula - 5 As2 S5 * (Pb, Tl) S` Ag2 S or 5 As2 S5 * (Pb, Tl) S` Ag Ag S. The formula of Hutchinsonite (Hutchinsonite) is sometimes rewritten differently - As2 S5 * ( Pb) + As2 S5 * (Tl) + As2 S5 * S + As2 S5 * Ag + As2 S5 * AgS. Chemical separation of components in production is also carried out according to the type of different alcohols (layers of mechanical enrichment, different in mass and weight, which are crushed by ultrasound and separated in a centrifuge or on a vibration platform - the horror movie "Aliens"). Other similar variations of the chemical formula are possible (composition varies).
ADR 6.1
Toxic substances (poison)
Risk of poisoning through inhalation, skin contact or ingestion. Hazardous to the aquatic environment or sewer system
Use a mask when leaving a vehicle in an emergency
ADR 3
Flammable liquids
Fire risk. Risk of explosion. Containers can explode when heated (extremely dangerous - burn easily)
ADR 2.1
Flammable gases
Fire risk. Risk of explosion. May be under pressure. Risk of suffocation. May cause burns and/or frostbite. Containers can explode when heated (extremely dangerous - practically do not burn)
Use cover. Avoid low surface areas (holes, lowlands, trenches)
Red diamond, ADR number, black or white flame
ADR 2.2
Gas cylinder Non-flammable, non-toxic gases.
Risk of suffocation. May be under pressure. They can cause frostbite (similar to a burn - pallor, blisters, black gas gangrene - creaking). Containers can explode when heated (extremely dangerous - explosion from a spark, flame, match, practically do not burn)
Use cover. Avoid low surface areas (holes, lowlands, trenches)
Green diamond, ADR number, black or white gas cylinder (cylinder, thermos type)
ADR 2.3
Toxic gases. Skull and crossbones
Danger of poisoning. May be under pressure. May cause burns and/or frostbite. Containers can explode when heated (extremely dangerous - instantaneous spread of gases throughout the surrounding area)
Use a mask when leaving a vehicle in an emergency. Use cover. Avoid low surface areas (holes, lowlands, trenches)
White diamond, ADR number, black skull and crossbones
| Name of particularly dangerous cargo during transportation | Number UN | Class ADR |
| Arsenic (III) oxide ARSENE TRIOXIDE | 1561 | 6.1 |
| 1685 | 6.1 | |
| 1557 | 6.1 | |
| 1561 | 6.1 | |
| Calcium arsenic acid ARSENATE COMPOUND, SOLID, N.Z.K. inorganic including: Arsenati, n.c.c., Arsenite, n.c.c., Arsene sulfides, n.c.c. | 1557 | 6.1 |
| Calcium arsenate CALCIUM ARSENATE | 1573 | 6.1 |
| CALCIUM ARSENATE | 1573 | 6.1 |
| CALCIUM ARSENATE AND CALCIUM ARSENITE MIXTURE, SOLID | 1574 | 6.1 |
| Calcium arsenite | 1557 | 6.1 |
| AMMONIUM ARSENATE | 1546 | 6.1 |
| Arsenic anhydride ARSENE TRIOXIDE | 1561 | 6.1 |
| ARSEN | 1558 | 6.1 |
| ARSENIC DUST | 1562 | 6.1 |
| Hydrogen arsene Arsine | 2188 | 2 |
| Arsene-soda solution | 1556 | 6.1 |
| ARSENE BROMIDE | 1555 | 6.1 |
| ARSENE PENTOOXIDE | 1559 | 6.1 |
| ARSEN COMPOUND, LIQUID, N.Z.K. inorganic, including: Arsenati, n.c.c., Arsenite, n.c.c., but Arsene sulfides, n.c.c. | 1556 | 6.1 |
| ARSEN COMPOUND, SOLID, N.Z.K. inorganic, including: Arsenati, n.c.c., Arsenite, n.c.c., but Arsene sulfides, n.c.c. | 1557 | 6.1 |
| ARSENE TRIOXIDE | 1561 | 6.1 |
| ARSENE TRICHLORIDE | 1560 | 6.1 |
| ARSINE | 2188 | 2 |
| IRON(II) ARSENATE | 1608 | 6.1 |
| IRON(III) ARSENATE | 1606 | 6.1 |
| IRON(III) ARSENITE | 1607 | 6.1 |
| POTASSIUM ARSENATE | 1677 | 6.1 |
| POTASSIUM ARSENITE | 1678 | 6.1 |
| ARSENIC ACID, SOLID | 1554 | 6.1 |
| ARSENIC ACID, LIQUID | 1553 | 6.1 |
| MAGNESIUM ARSENATE | 1622 | 6.1 |
| COPPER ARSENITE | 1586 | 6.1 |
| COPPER ACETOARSENITE | 1585 | 6.1 |
| Sodium arsenic acid SODIUM ARSENITE SOLID | 2027 | 6.1 |
| Sodium arsenic acid SODIUM ARSENATE | 1685 | 6.1 |
| SODIUM AZIDE | 1687 | 6.1 |
| SODIUM ARSENATE | 1685 | 6.1 |
| SODIUM ARSENITE SOLID | 2027 | 6.1 |
| SODIUM ARSENITE AQUEOUS SOLUTION | 1686 | 6.1 |
| Tin arsenide | 1557 | 6.1 |
| Arsenic tin Tin arsenite | 1557 | 6.1 |
| 2760 | 3 | |
| ARSENE-CONTAINING PESTICIDE LIQUID, FLAMMABLE, TOXIC with a flash point less than 23 o C | 2760 | 3 |
| ARSENE-CONTAINING PESTICIDE, SOLID, TOXIC | 2759 | 6.1 |
| ARSENE-CONTAINING PESTICIDE, LIQUID, TOXIC | 2994 | 6.1 |
| ARSENE-CONTAINING PESTICIDE, LIQUID, TOXIC, FLAMMABLE, with a flash point of at least 23 o C | 2993 | 6.1 |
| MERCURY (II) ARSENATE | 1623 | 6.1 |
| LEAD ARSENATHI | 1617 | 6.1 |
| LEAD ARSENITE | 1618 | 6.1 |
| ARSENE-ORGANIC COMPOUND, LIQUID, N.Z.K. | 3280 | 6.1 |
| ARSENE-ORGANIC COMPOUND, SOLID, N.Z.K.* | 3465 | 6.1 |
| SILVER ARSENITE | 1683 | 6.1 |
| STRONTIUM ARSENITE | 1691 | 6.1 |
| ZINC ARSENATE, ZINC ARSENITE or ZINC ARSENATE AND ZINC ARSENITE MIXTURE | 1712 | 6.1 |
The content of the article
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 a half-life from several minutes to several months have also been artificially obtained. Typical oxidation states in compounds are –3, +3, +5. The name of arsenic in Russian is associated with the use of its compounds to exterminate mice and rats; 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 was smelted with special valuable properties– it was cast better and forged easier. 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. So, in Ancient China m, the solid mineral realgar (sulfide with the composition As 4 S 4, realgar in Arabic means “mine dust”) was used for stone carving, but when heated or in the 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, arsenogauchecornite 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 the 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 managed 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; it is not without reason that it is called “ubiquitous”. Arsenic distribution over different regions the globe was largely determined in the processes of formation of the lithosphere by the volatility of its compounds at high temperatures, as well as by the processes of sorption and desorption in soils and sedimentary rocks. Arsenic migrates easily, which is facilitated by the 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. Drink one or two glasses of “arsenic” mineral water They will not bring harm to a person: 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 clean waters algae from Norwegian fjords can contain arsenic in amounts up to 0.1 g/kg. 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 substance is obtained yellow color, resembling yellow phosphorus, its density (2.03 g/cm3) 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. Reactions of arsenic with sulfur form sulfides of various compositions– 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 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.
