True, empirical, or gross formula: As
Molecular weight: 74.922
Arsenic- (lat. Arsenicum; denoted by the symbol As) - a chemical element of the 15th group (according to obsolete classification- the main subgroup of the fifth group) of the fourth period of the periodic system; has atomic number 33. A simple substance is a brittle steel-colored semimetal with a greenish tint (in a gray allotropic modification). CAS number: 7440-38-2.
Story
Arsenic is one of the oldest elements used by man. Arsenic sulfides As 2 S 3 and As 4 S 4 , the so-called orpiment (“arsenic”) and realgar, were familiar to the Romans and Greeks. These substances are poisonous. Arsenic is one of the elements found in nature in its free form. It can be relatively easily isolated from compounds. Therefore, history does not know who first received elemental arsenic in a free state. Many attribute the role of the discoverer to the alchemist Albert the Great. The writings of Paracelsus also describe the production of arsenic as a result of the reaction of arsenic with eggshells. Many historians of science suggest that metallic arsenic was obtained much earlier, but it was considered to be representative of native mercury. This can be explained by the fact that arsenic sulfide was very similar to the mercury mineral. And the release from it was very easy, just like the release of mercury. Elemental arsenic has been known in Europe and Asia since the Middle Ages. The Chinese got it from ores. Unlike the Europeans, they could diagnose death from arsenic poisoning. But this method of analysis has not reached the present time. Europeans learned to determine the onset of death in case of arsenic poisoning much later, this was first done by D. Marchais. This reaction is still in use today.
Arsenic is sometimes found in tin ores. In Chinese literature of the Middle Ages, deaths of people who drank water or wine from tin vessels are described, due to the presence of arsenic in it. For a relatively long time, people confused arsenic itself and its oxide, took it for one substance. This misunderstanding was eliminated by G. Brandt and A. Lavoisier, who proved that these are different substances, and that arsenic is an independent chemical element. Arsenic oxide has long been used to kill rodents. Hence the origin of the Russian name of the element. It comes from the words "mouse" and "poison".
Etymology
The name of arsenic in Russian comes from the word "mouse", in connection with the use of its compounds for the extermination of mice and rats. The Greek name ἀρσενικόν comes from the Persian زرنيخ (zarnik) - "yellow orpiment". Folk etymology traces back to other Greek. ἀρσενικός - male.
The Latin name arsenicum is a direct borrowing from the Greek ἀρσενικόν. In 1789, A. Lavoisier included arsenic in the list of chemical elements under the name arsenic.
Being in nature
Arsenic is a trace element. Content in earth's crust 1.7 10−4% by weight. AT sea water 0.003 mg/l. This element is sometimes found in nature in its native form, the mineral has the form of metallic shiny gray shells or dense masses consisting of small grains.
About 200 arsenic-containing minerals are known. In small concentrations, it often accompanies lead, copper and silver ores. Two natural arsenic minerals are quite common in the form of sulfides (binary compounds with sulfur): orange-red transparent realgar AsS and lemon-yellow orpiment As 2 S 3 . A mineral of industrial importance for the production of arsenic is arsenopyrite (arsenic pyrites) FeAsS or FeS 2 FeAs 2 (46% As), arsenic pyrites are also processed - lollingite (FeAs 2) (72.8% As), scorodite FeAsO 4 (27 - 36% As). Most of the arsenic is mined incidentally during the processing of arsenic-containing gold, lead-zinc, copper pyrite and other ores.
Place of Birth
The main industrial mineral of arsenic is arsenopyrite FeAsS. There are large copper-arsenic deposits in Georgia, Central Asia and Kazakhstan, in the USA, Sweden, Norway and Japan, arsenic-cobalt - in Canada, arsenic-tin - in Bolivia and England. In addition, gold-arsenic deposits are known in the USA and France. Russia has numerous deposits of arsenic in Yakutia, the Urals, Siberia, Transbaikalia and Chukotka.
isotopes
33 isotopes and at least 10 excited states of nuclear isomers are known. Of these isotopes, only 75 As is stable, and natural arsenic consists of this isotope alone. The longest-lived radioactive isotope, 73 As, has a half-life of 80.3 days.
Receipt
The discovery of a method for obtaining metallic arsenic (gray arsenic) is attributed to the medieval alchemist Albert the Great, who lived in the 13th century. However, much earlier, Greek and Arab alchemists were able to obtain free arsenic by heating "white arsenic" (arsenic trioxide) with various organic substances.
There are many ways to obtain arsenic: sublimation of natural arsenic, thermal decomposition of arsenic pyrites, reduction of arsenic anhydride, etc. Currently, to obtain metallic arsenic, arsenopyrite is most often heated in muffle furnaces without air access. In this case, arsenic is released, the vapors of which condense and turn into solid arsenic in iron pipes coming from furnaces and in special ceramic receivers. The residue in the ovens is then heated with access to air, and then the arsenic is oxidized to As 2 O 3 . Metallic arsenic is obtained in rather small quantities, and the main part of arsenic-containing ores is processed into white arsenic, that is, into arsenic trioxide - arsenic anhydride As 2 O 3. The main production method is the roasting of sulfide ores, followed by the reduction of oxide with coal.
Application
Arsenic is used for alloying lead alloys used for the preparation of shot, since when shot is cast by the tower method, drops of an arsenic-lead alloy acquire a strictly spherical shape, and in addition, the strength and hardness of lead increase significantly.
High purity arsenic (99.9999%) is used to synthesize a number of useful and important semiconductor materials - arsenides (for example, gallium arsenide) and other semiconductor materials with a zinc blende-type crystal lattice.
Arsenic sulfide compounds - orpiment and realgar - are used in painting as paints and in the leather industry as a means to remove 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 nitrate burns (it forms a bright white flame when burned).
Some organoelement compounds of arsenic are chemical warfare agents, for example, lewisite.
At the beginning of the 20th century, some cacodyl derivatives, such as salvarsan, were used to treat syphilis, over time, these drugs were displaced from medical use for the treatment of syphilis by other, less toxic and more effective, pharmaceutical preparations that do not contain arsenic.
Many of the arsenic compounds in very small doses are used as drugs to combat anemia and a number of other serious diseases, as they have a clinically noticeable stimulating effect on a number of specific body functions, in particular, on hematopoiesis. Of the inorganic compounds of arsenic, arsenic 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 in everyday life and slang called "arsenic" and was used in dentistry for local necrosis of the dental nerve (see pulpitis). Currently (2015), arsenic preparations are rarely used in dental practice due to their toxicity. Now other methods of painless necrosis of the nerve of the tooth under local anesthesia have been developed and are being used.
Biological role and physiological action
Arsenic and all its compounds are poisonous. In acute arsenic poisoning, vomiting, abdominal pain, diarrhea, depression of the central nervous system are observed. nervous system. Similarities between the symptoms of arsenic poisoning and those of cholera long time allowed to mask the use of arsenic compounds (most often, arsenic trioxide, the so-called "white arsenic") as a deadly poison. In France, arsenic trioxide powder for its high efficiency received the common name "hereditary powder" (fr. poudre de succession). There is an assumption that Napoleon was poisoned with arsenic compounds on the island of St. Helena. In 1832, a reliable qualitative reaction for arsenic - the Marsh test, which significantly increased the efficiency of diagnosing poisoning. In areas where there is an excess of arsenic in soil and water, it accumulates in the thyroid gland of people and causes endemic goiter. Help and antidotes for arsenic poisoning: taking aqueous solutions of sodium thiosulfate Na 2 S 2 O 3, gastric lavage, taking milk and cottage cheese; specific antidote - unithiol. MPC in the air for arsenic is 0.5 mg/m³. Work with arsenic in sealed boxes, using protective clothing. Due to their high toxicity, arsenic compounds were used as poisonous substances in the First World War. AT Western countries arsenic was known mainly as a strong poison, while in traditional Chinese medicine it has been used for almost two thousand years to treat syphilis and psoriasis. Now doctors have proven that arsenic has a positive effect in the fight against leukemia. Chinese scientists have found that arsenic attacks proteins that are responsible for the growth of cancer cells. Arsenic in small doses is carcinogenic, its use as a "blood-improving" drug (the so-called "white arsenic", for example, "Blo's Arsenic Tablets", etc.) continued until the mid-1950s, and contributed its significant contribution to the development of cancer. Organic arsenic compounds are traditionally used to treat sleeping sickness. Recently, technogenic ecological catastrophy in southern India - due to excessive withdrawal of water from aquifers, arsenic began to enter drinking water. This caused toxic and oncological damage in tens of thousands of people. It was believed that "microdoses of arsenic, introduced with caution into a growing organism, contribute to the growth of human and animal bones in length and thickness, in some cases, bone growth can be caused by microdoses of arsenic during the period of growth completion." It was also believed that “With long-term consumption of small doses of arsenic, the body develops immunity: This fact has been established both for humans and for animals. There are cases when habitual users of arsenic immediately took doses several times higher than the lethal dose and remained healthy. Animal experiments have shown the originality of this habit. It turned out that an animal accustomed to arsenic when using it quickly dies if a much lower dose is injected into the blood or under the skin. However, such "addiction" is very limited, in relation to the so-called. "acute toxicity", and does not protect against neoplasms. However, the effect of microdoses of arsenic-containing drugs as an anticancer agent is currently being investigated. Extremophilic bacteria are known to be able to survive at high concentrations of arsenate in environment. It was suggested that in the case of the GFAJ-1 strain, arsenic replaces phosphorus in biochemical reactions, in particular, it is included in DNA, but this assumption was not confirmed.
In forensic science
The method of post-mortem detection of arsenic in cases of suspected poisoning was developed at the beginning of the 19th century. English chemist James Marsh.
Arsenic contamination
On the territory of the Russian Federation in Skopin Ryazan region As a result of the many years of work of the local metallurgical plant SMK Metallurg, about one and a half thousand tons of dusty waste with a high content of arsenic were buried in the burial grounds of the enterprise. Arsenic is a characteristic element of many gold deposits, which leads to additional environmental problems in gold mining countries such as Romania.
Arsenic is a chemical element with atomic number 33 in the periodic system, denoted by the symbol As. It is a brittle steel-colored semi-metal.Finding arsenic in nature
Arsenic is a trace element. Content in the earth's crust 1.7 10-4% by weight. This substance can occur in its native state, has the form of metallic lustrous gray shells or dense masses consisting of small grains. About 200 arsenic-containing minerals are known. In small concentrations, it is often found in lead, copper and silver ores. Quite often there are two natural compounds of arsenic with sulfur: orange-red transparent realgar AsS and lemon-yellow orpiment As2S3. A mineral of industrial importance - arsenopyrite (arsenic pyrite) FeAsS or FeS2 FeAs2, arsenic pyrite - löllingite (FeAs2) is also mined.Getting arsenic
There are many ways to obtain arsenic: sublimation of natural arsenic, thermal decomposition of arsenic pyrites, reduction of arsenic anhydride, etc. Currently, to obtain metallic arsenic, arsenopyrite is most often heated in muffle furnaces without air access. This releases arsenic, the vapors of which condense and turn into solid arsenic in iron pipes coming from furnaces and in special ceramic receivers. The residue in the furnaces is then heated with air access, and then the arsenic is converted into As2O3. Metallic arsenic is obtained in rather small quantities, and the main part of arsenic-containing ores is processed into white arsenic, that is, into arsenic trioxide - arsenic anhydride As2O3.Application of arsenic
- The use of arsenic in metallurgy - it is used for alloying lead alloys used for the preparation of shot, since when shot is cast by a tower method, drops of an arsenic alloy with lead acquire a strictly spherical shape, and in addition, the strength and hardness of lead increase.
- Application in electrical engineering - High purity arsenic (99.9999%) is used for the synthesis of a number of practically very valuable and important semiconductor materials - arsenides and complex diamond-like semiconductors.
- Application as a dye - arsenic sulfide compounds - orpiment and realgar - are used in painting as paints.
- Application in the leather industry - used as a means to remove hair from the skin.
- Application in pyrotechnics - realgar is used to obtain the "Greek" or "Indian" fire that occurs when burning a mixture of realgar with sulfur and nitrate (bright white flame).
- Use in medicine - many of the arsenic compounds in very small doses are used as drugs 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, on hematopoiesis. Of the inorganic compounds of arsenic, arsenic 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 (the same “arsenic” that is placed in the tooth canal before removing the nerve and filling). Currently, arsenic preparations are rarely used in dental practice due to toxicity and the possibility of painless tooth denervation under local anesthesia.
- Application in glass production - arsenic trioxide makes glass "deaf", i.e. opaque. However, small additions of this substance, on the contrary, lighten the glass. Arsenic is still included in the formulations of some glasses, for example, "Viennese" glass for thermometers and semi-crystal.
The most promising field of application of arsenic is undoubtedly semiconductor technology. Gallium arsenides GaAs and indium arsenides InAs acquired particular importance in it. Gallium arsenide is also needed for an important area of electronic technology - optoelectronics, which arose in 1963 ... 1965. at the intersection of solid state physics, optics and electronics. The same material helped create the first semiconductor lasers.
Why did arsenides turn out to be promising for semiconductor technology? To answer this question, let us briefly recall some of the basic concepts of semiconductor physics: "valence band", "forbidden band" and "conduction band".
Unlike a free electron, which can have any energy, an electron enclosed in an atom can only have certain, well-defined values of energy. From the possible values of the energy of electrons in an atom, energy bands are added. By virtue of the well-known Pauli principle, the number of electrons in each zone cannot exceed a certain certain maximum. If the band is empty, then, of course, it cannot participate in the creation of conductivity. The electrons of the completely filled band also do not participate in the conduction: since there are no free levels, the external electric field cannot cause a redistribution of electrons and thereby create electricity. Conductivity is possible only in a partially filled zone. Therefore, bodies with a partially filled band are referred to as metals, and bodies in which the energy spectrum of electronic states consists of filled and empty bands are referred to as dielectrics or semiconductors.
We also recall that completely filled bands in crystals are called valence bands, partially filled and empty bands are called conduction bands, and the energy interval (or barrier) between them is called the band gap.
The main difference between dielectrics and semiconductors lies precisely in the band gap: if an energy of more than 3 eV is needed to overcome it, then the crystal is referred to as dielectrics, and if less, to semiconductors.
Compared to classical group IV semiconductors, germanium and silicon, group III element arsenides have two advantages. The band gap and the mobility of charge carriers in them can be varied over a wider range. And the more mobile the charge carriers, the higher frequencies the semiconductor device can operate. The band gap is chosen depending on the purpose of the device.
So, for rectifiers and amplifiers designed to operate at elevated temperature, a material with a large bandgap is used, and for cooled infrared receivers - with a small one.
Gallium arsenide has gained particular popularity because it has good electrical characteristics, which it retains in a wide temperature range - from minus to plus 500 ° C. For comparison, we point out that indium arsenide, which is not inferior to GaAs in electrical properties, begins to lose them already at room temperature, germanium - at 70...80, and silicon - at 150...200°C.
Arsenic is also used as a dopant, which gives "classical" semiconductors (Si, Ge) a certain type of conductivity. In this case, a so-called transition layer is created in the semiconductor, and, depending on the purpose of the crystal, it is doped in such a way as to obtain a transition layer at different depths. In crystals intended for the manufacture of diodes, it is “hidden” deeper; if solar batteries are made from semiconductor crystals, then the depth of the transition layer is no more than one micrometer.
Arsenic as a valuable additive is also used in non-ferrous metallurgy. Thus, the addition of 0.2 ... 1% As to lead significantly increases its hardness. Shot, for example, is always made from lead alloyed with arsenic - otherwise you will not get a strictly spherical shape of shots.
The addition of 0.15 ... 0.45% arsenic to copper increases its tensile strength, hardness and corrosion resistance when working in a gassed environment. In addition, arsenic increases the fluidity of copper during casting, facilitates the process of wire drawing.
Arsenic is added to some grades of bronzes, brasses, babbits, printing alloys.
And at the same time, arsenic very often harms metallurgists. In the production of steel and many non-ferrous metals, they deliberately go to the complication of the process - just to remove all arsenic from the metal. The presence of arsenic in the ore makes production harmful. Harmful twice: first, for people's health; secondly, for a metal, significant impurities of arsenic worsen the properties of almost all metals and alloys.
All conn. arsenic, p-rimye in water and slightly acidic environments (eg, gastric juice), are extremely toxic; MPC in the air of arsenic and its Comm. (except AsH3) in terms of arsenic 0.5 mg/m3. Comm. As (III) are more poisonous than Comm. As(V). From inorg. conn. As2O3 and AsH3 are especially dangerous. When working with arsenic and its Comm. necessary: complete sealing of equipment, removal of dust and gases by intensive ventilation, personal hygiene (anti-dust clothing, glasses, gloves, gas mask), frequent medical monitoring; women and teenagers are not allowed to work. In acute arsenic poisoning, vomiting, abdominal pain, diarrhea, depression of the center are observed. nervous system. Help and antidotes for arsenic poisoning: taking aqueous solutions of Na2S2O3, gastric lavage, taking milk and cottage cheese; specific antidote - unithiol. A particular problem is the removal of arsenic from exhaust gases, technol. waters and by-products of processing ores and concentrates of non-ferrous and rare metals and iron. Naib. A promising way to bury arsenic is by converting it into practically insoluble sulfide glasses.
Arsenic has been known since ancient times. Even Aristotle mentioned his nature. sulfur compounds. It is not known who first obtained elemental arsenic, the achievement is usually attributed to Albertus Magnus c. 1250. Chem. Arsenic was recognized as an element by A. Lavoisier in 1789.
This is element #33, which has a well-deserved ill repute, and yet is very useful in many cases.
The content of arsenic in the earth's crust is only 0.0005%, but this element is quite active, and therefore there are more than 120 minerals containing arsenic. The main industrial mineral of arsenic is arsenopyrite FeAsS. There are large copper-arsenic deposits in the USA, Sweden, Norway and Japan, arsenic-cobalt deposits in Canada, arsenic-tin deposits in Bolivia and England. In addition, gold-yshyakovye deposits are known in the USA and France. Russia has numerous deposits of arsenic in Yakutia and the Caucasus, Central Asia and the Urals, Siberia and Chukotka, Kazakhstan and Transbaikalia. Arsenic is one of the few elements for which the demand is less than the ability to produce them. World production of arsenic (excluding socialist countries) in terms of As2O3 approx. 50 thousand tons (1983); ~11 tons of elemental arsenic of high purity are obtained from them for the synthesis of semiconductor compounds.
The X-ray fluorescent method for the analysis of arsenic is quite simple and safe, unlike the chemical method. Pure pulp is pressed into tablets and used as a reference. GOST 1293.4-83, GOST 1367.1-83, GOST 1429.10-77, GOST 2082.5-81, GOST 2604.11-85, GOST 6689.13-92, GOST 11739.14-99 The determination is made using an X-ray fluorescence spectrometer. The most proven in this area are the edx 3600 B and edx 600 spectrometers.
Arsenic(lat. arsenicum), as, a chemical element of the v group 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.
History reference. Natural compounds of M. with sulfur (orpiment as 2 s 3, realgar as 4 s 4) were known to the peoples ancient world who used these minerals as medicines and paints. The product of burning sulfides of M. was also known - the oxide of M. (iii) as 2 o 3 (“white M.”). The name arsenik o n is already found in Aristotle; it is derived from the Greek a rsen - strong, courageous and served to designate M. compounds (according to their strong effect on the body). The Russian name is believed to have come from "mouse" (according to the use of M.'s preparations for the extermination of mice and rats). Getting M. in a free state is attributed Albert the Great(about 1250). In 1789 A. Lavoisier included M. in the list of chemical elements.
distribution in nature. The average content of M. in the earth's crust (clarke) is 1.7 × 10 -4% (by mass), in such quantities it is present in most igneous rocks. Since M.'s compounds are volatile at high temperatures, the element does not accumulate during magmatic processes; it is concentrated by precipitating from hot deep waters (together with s, se, sb, fe, co, ni, cu, and other elements). During volcanic eruptions, M. in the form of its volatile compounds enters the atmosphere. Since M. is multivalent, its migration is greatly influenced by the redox environment. Under oxidizing conditions earth's surface arsenates (as 5+) and arsenites (as 3+) are formed. These are rare minerals found only in areas of mineral deposits. Native mineral and as 2+ minerals are even rarer. Of the numerous minerals of M. (about 180), only arsenopyrite feass is of major industrial importance.
Small amounts of M. are necessary for life. However, in the areas of the M. deposit and the activity of young volcanoes, soils in places contain up to 1% M., which is associated with livestock diseases and the death of vegetation. M.'s accumulation is especially characteristic of the landscapes of the steppes and deserts, in the soils of which M. is inactive. In a humid climate, M. is easily washed out of the soil.
In living matter, on average, 3 × 10 -5% M., in rivers 3 × 10 -7%. M., brought by rivers into the ocean, is relatively quickly precipitated. In sea water, only 1 10 -7% M., but in clays and shales 6.6 10 -4%. Sedimentary iron ores, ferromanganese nodules are often enriched in M.
Physical and chemical properties. M. has several allotropic modifications. Under normal conditions, the most stable is the so-called metallic, or gray, M. (a -as) - a gray-steel brittle crystalline mass; in a fresh fracture it has a metallic luster, quickly tarnishes in air, because it is covered with a thin film of as 2 o 3. The crystal lattice of gray M. is rhombohedral ( a= 4.123 a , angle a = 54°10", X= 0.226), layered. Density 5.72 g/cm 3(at 20°c), electrical resistivity 35 10 -8 ohm? m, or 35 10 -6 ohm? cm, temperature coefficient of electrical resistance 3.9 10 -3 (0°-100 °c), Brinell hardness 1470 MN/m 2, or 147 kgf/mm 2(3-4 according to Mohs); M. is diamagnetic. Under atmospheric pressure, M. sublimates at 615 ° C without melting, since the triple point a -as lies at 816 ° C and a pressure of 36 at. Steam M. up to 800 ° C consists of molecules as 4, above 1700 ° C - only from as 2. During the condensation of vapor M. on a surface cooled by liquid air, yellow M. is formed - transparent, wax-soft crystals, with a density of 1.97 g/cm 3, similar in properties to white phosphorus. Under the action of light or upon slight heating, it turns into gray M. Glassy-amorphous modifications are also known: black M. and brown M., which, when heated above 270 ° C, turn into gray M.
The configuration of the outer electrons of the atom M. 3 d 10 4 s 2 4 p 3 . In compounds, M. has the oxidation states + 5, + 3, and - 3. Gray M. is much less chemically active than phosphorus. When heated in air above 400 ° C, M. burns, forming as 2 o 3. M. connects to halogens directly; under normal conditions asf 5 - gas; asf 3 , ascl 3 , asbr 3 - colorless, easily volatile liquids; asi 3 and as 2 l 4 are red crystals. When M. is heated with sulfur, sulfides are obtained: orange-red as 4 s 4 and lemon-yellow as 2 s 3 . Pale yellow sulfide as 2 s 5 precipitates when h 2 s is passed into an ice-cooled solution of arsenic acid (or its salts) in fuming hydrochloric acid: 2h 3 aso 4 + 5h 2 s \u003d as 2 s 5 + 8h 2 o; around 500°c it decomposes into as 2 s 3 and sulfur. All M.'s sulfides are insoluble in water and dilute acids. Strong oxidizing agents (mixtures of hno 3 + hcl, hcl + kclo 3) convert them into a mixture of h 3 aso 4 and h 2 so 4. Sulfide as 2 s 3 is easily soluble in sulfides and polysulfides of ammonium and alkali metals, forming salts of acids - thioarsenous h 3 ass 3 and thioarsenic h 3 ass 4 . With oxygen, M. gives oxides: oxide M. (iii) as 2 o 3 - arsenic anhydride and oxide M. (v) as 2 o 5 - arsenic anhydride. The first of these is formed by the action of oxygen on M. or its sulfides, for example, 2as 2 s 3 + 9o 2 \u003d 2as 2 o 3 + 6so 2. Vapors as 2 o 3 condense into a colorless glassy mass, which becomes opaque over time due to the formation of small cubic crystals, density 3.865 g/cm 3. The vapor density corresponds to the formula as 4 o 6: above 1800°c, the vapor consists of as 2 o 3 . At 100 G water dissolves 2.1 G as 2 o 3 (at 25°c). Oxide M. (iii) is an amphoteric compound, with a predominance of acidic properties. Salts (arsenites) are known that correspond to orthoarsenic h 3 aso 3 and metaarsenic haso 2 acids; the acids themselves have not been obtained. Only alkali metal and ammonium arsenites are soluble in water. as 2 o 3 and arsenites are usually reducing agents (for example, as 2 o 3 + 2i 2 + 5h 2 o \u003d 4hi + 2h 3 aso 4), but they can also be oxidizing agents (for example, as 2 o 3 + 3c \u003d 2as + 3co ).
Oxide M. (v) is obtained by heating arsenic acid h 3 aso 4 (about 200°c). It is colorless, about 500°c decomposes into as 2 o 3 and o 2 . Arsenic acid is obtained by the action of concentrated hno 3 on as or as 2 o 3 . Salts of arsenic acid (arsenates) are insoluble in water, with the exception of alkali metal and ammonium salts. Salts corresponding to acids orthoarsenic h 3 aso 4 , metaarsenic haso 3 , and pyroarsenic h 4 as 2 o 7 are known; the last two acids have not been obtained in the free state. When fused with metals, M. for the most part forms compounds ( arsenides).
Getting and using . M. is obtained in industry by heating arsenic pyrites:
feass = fes + as
or (more rarely) as 2 o 3 reduction with charcoal. Both processes are carried out in refractory clay retorts connected to a receiver for condensing M vapor. Arsenic anhydride is obtained by oxidative roasting of arsenic ores or as a by-product of roasting polymetallic ores, which almost always contain M. During oxidative roasting, as 2 o 3 vapors are formed, which condense into capture chambers. Crude as 2 o 3 is purified by sublimation at 500-600°c. Purified as 2 o 3 is used for the production of M. and its preparations.
Small additives of M. (0.2-1.0% by weight) are introduced into lead used for the production of shotgun shot (M. increases the surface tension of molten lead, due to which the shot acquires a shape close to spherical; M. slightly increases the hardness of lead ). As a partial substitute for antimony, M. is part of some babbits and printing alloys.
Pure M. is not poisonous, but all its compounds that are soluble in water or that can go into solution under the action of gastric juice are extremely poisonous; especially dangerous arsenic hydrogen. Of the compounds used in the production of M., arsenic anhydride is the most toxic. Almost all sulfide ores of non-ferrous metals, as well as iron (sulfur) pyrite, contain an admixture of M.. Therefore, during their oxidative roasting, along with sulfur dioxide so 2, as 2 o 3 is always formed; most of it condenses in the smoke channels, but in the absence or low efficiency of treatment facilities, the exhaust gases of ore kilns entrain significant amounts of as 2 o 3 . Pure M., although not poisonous, is always covered with a coating of poisonous as 2 o 3 when stored in air. In the absence of proper ventilation, it is extremely dangerous to etch metals (iron, zinc) with technical sulfuric or hydrochloric acids containing an admixture of M., since arsenic hydrogen is formed in this case.
S. A. Pogodin.
M. in the body. As trace element M. is ubiquitous in wildlife. The average content of M. in soils is 4 10 -4%, in plant ash - 3 10 -5%. The content of M. in marine organisms is higher than in terrestrial ones (in fish 0.6-4.7 mg in 1 kg crude matter accumulates in the liver). The average content of M. in the human body is 0.08-0.2 mg/kg. In the blood, M. is concentrated in erythrocytes, where it binds to the hemoglobin molecule (moreover, the globin fraction contains twice as much of it as the heme). The largest number him (for 1 G tissue) is found in the kidneys and liver. A lot of M. is contained in the lungs and spleen, skin and hair; relatively little - in the cerebrospinal fluid, brain (mainly the pituitary gland), gonads, etc. In the tissues of M. is in the main protein fraction, much less - in the acid-soluble and only a small part of it is found in the lipid fraction. M. is involved in redox reactions: the oxidative breakdown of complex carbohydrates, fermentation, glycolysis, etc. M. compounds are used in biochemistry as specific inhibitors enzymes to study metabolic reactions.
M. in medicine. Organic compounds M. (aminarson, miarsenol, novarsenal, osarsol) are used mainly for the treatment of syphilis and protozoal diseases. Inorganic preparations M. - sodium arsenite (sodium arsenic acid), potassium arsenite (potassium arsenic acid), arsenic anhydride as 2 o 3, are prescribed as general tonic and tonic. When applied topically, inorganic preparations of M. can cause a necrotizing effect without previous irritation, which is why this process proceeds almost painlessly; this property, which is most pronounced in as 2 o 3 , is used in dentistry to destroy the dental pulp. M.'s inorganic preparations are also used to treat psoriasis.
Artificially obtained radioactive isotopes M. 74 as (t 1 / 2 = 17.5 day) and 76 as (t 1/2 = 26.8 h) are used for diagnostic and therapeutic purposes. With their help, the localization of brain tumors is clarified and the degree of radicalness of their removal is determined. Radioactive M. is sometimes used for blood diseases, etc.
According to the recommendations of the International Commission on Radiation Protection, the maximum allowable content of 76 as in the body is 11 microcurie. According to the sanitary standards adopted in the USSR, the maximum permissible concentrations of 76 as in water and open reservoirs are 1 10 -7 curie/l, in the air of working rooms 5 10 -11 curie/l. All M.'s preparations are very poisonous. In acute poisoning, they experience severe abdominal pain, diarrhea, kidney damage; possible collapse, convulsions. In chronic poisoning, the most common are gastrointestinal disorders, catarrhs of the mucous membranes of the respiratory tract (pharyngitis, laryngitis, bronchitis), skin lesions (exanthema, melanosis, hyperkeratosis), sensitivity disorders; possible development of aplastic anemia. In the treatment of poisoning with drugs M. highest value give unithiol.
Measures to prevent industrial poisoning should be aimed primarily at mechanization, sealing and dust removal of the technological process, at creating effective ventilation and providing workers with personal protective equipment against dust exposure. Regular medical examinations of workers are required. Preliminary medical examinations are carried out upon employment, and for employees - once every six months.
Lit.: Remi G., Course of inorganic chemistry, trans. from German, vol. 1, M., 1963, p. 700-712; Pogodin S. A., Arsenic, in the book: Brief Chemical Encyclopedia, vol. 3, M., 1964; Harmful substances in industry, under the total. ed. N. V. Lazareva, 6th ed., part 2, L., 1971.
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Arsenic
ARSENIC-a; m.
1. A chemical element (As) is a solid toxic substance of a brilliant gray color, which is part of many minerals. Arsenic oxide. Getting arsenic.
2. A drug containing this substance or its compounds (used as a tonic, antimicrobial, etc. agent). Arsenic treatment. The effect of arsenic on nerve endings.
◁ Arsenic, th, th. M connections. M-th acid. M. preparation. M-th poisoning. Arsenic, th, th. Obsolete Arsenic, th, th. ● The Russian name for this element comes from the word "mouse", because. arsenic was widely used in the destruction of rats and mice.
arsenic(lat. Arsenicum), a chemical element of group V of the periodic system. The Russian name is from "mouse" (arsenic preparations were used to exterminate mice and rats). Forms several modifications. Ordinary arsenic (the so-called metallic, or gray) - fragile crystals with a silvery sheen; density 5.74 g/cm 3 , sublimates at 615°C. It oxidizes and tarnishes in air. Mined from sulfide ores (minerals arsenopyrite, orpiment, realgar). Component of alloys with copper, lead, tin, etc. and semiconductor materials. Arsenic compounds are physiologically active and poisonous; served as one of the first insecticides (see, for example, Metal Arsenates). Inorganic arsenic compounds are used in medicine as general tonic, tonic, organic - as antimicrobial and antiprotozoal (in the treatment of syphilis, amoebiasis, etc.).
ARSENICARSENIC (lat. Arsenicum, from the Greek arsen - strong), As (read "arsenicum"), a chemical element with atomic number 33, atomic mass 74.9216. One stable isotope, 75 As, is found in nature. It is located in the VA group in the 4th period of the Periodic Table of the Elements. Electronic configuration of outer layer 4 s 2
p 3
. +3, +5, –3 oxidation states (valencies III, V).
The radius of the atom is 0.148 nm. The radius of the As 3+ ion is 0.191 nm, the As 3+ ion is 0.072 nm (coordination number 4), and the As 5+ ion is 0.047 nm (6). Sequential ionization energies 9.82, 18.62, 28.35, 50.1 and 62.6 eV. Pauling's electronegativity (cm. PAULING Linus) 2.1. Non-metal.
History reference
Arsenic has been known to mankind since ancient times, when orpiment minerals were used as dyes. (cm. AURPIGMENT) As 2 S 3 and realgar (cm. REALGAR) As 4 S 4 (they are mentioned by Aristotle) (cm. ARISTOTLE).
Alchemists, when calcining arsenic sulfides in air, noted that the formation of the so-called white oxide As 2 O 3:
2As 2 S 3 + 9O 2 \u003d 2As2O 3 + 6SO 2
This oxide is a strong poison, it dissolves in water and wine.
For the first time, As was obtained in free form by the German alchemist A. von Boldshtndt in the 13th century by heating arsenic oxide with coal:
As 2 O 3 + 3C \u003d 2As + 3CO
For the image of arsenic, the sign of a writhing snake with an open mouth was used.
Being in nature
Arsenic is a trace element. The content in the earth's crust is 1.7 10 -4% by weight. 160 arsenic-containing minerals are known. Rarely found in its native state. Mineral of industrial importance - arsenopyrite (cm. arsenopyrite) FeAsS. As is often found in lead, copper and silver ores.
Receipt
The enriched ore is subjected to oxidative roasting, then the volatile As 2 O 3 is sublimated. This oxide is reduced with carbon. To purify As, it is subjected to vacuum distillation, then converted to volatile chloride AsCl 3 , which is reduced with hydrogen (cm. HYDROGEN). The resulting arsenic contains 10 -5 -10 -6% impurities by weight.
Physical and chemical properties
Arsenic is a brittle substance gray with a metallic sheen (a-arsenic) with a rhombohedral crystal lattice, a= 0.4135 nm and a = 54.13°. Density 5.74 kg / dm 3.
When heated to 600°C, As sublimates. When the vapor is cooled, a new modification appears - yellow arsenic. Above 270°C, all As forms transform into black arsenic.
As can be melted only in sealed ampoules under pressure. Melting point 817°C at its saturated vapor pressure of 3.6 MPa.
The structure of gray arsenic is similar to the structure of gray antimony and resembles black phosphorus in structure.
Arsenic is reactive. When stored in air, powdered As ignites to form the acidic oxide As 2 O 3 . This oxide exists in vapor in the form of As 4 O 6 dimers.
With careful dehydration of arsenic acid H 3 AsO 4, the highest acidic arsenic oxide As 2 O 5 is obtained, which easily releases oxygen when heated (cm. OXYGEN), turning into As 2 O 3.
The As 2 O 3 oxide corresponds to the ortho-arsenic H 3 AsO 3 and meta-arsenic weak acids HAsO 2 that exist only in solutions. Their salts are arsenates.
Dilute nitric acid (cm. NITRIC ACID) oxidizes As to H 3 AsO 3 , concentrated nitric acid to H 3 AsO 4 . As does not react with alkalis, it dissolves in water.
When As and H 2 are heated, arsine gas is formed (cm. ARSENIC HYDRIDE) Ash 3 . With fluorine (cm. FLUORINE) and chlorine (cm. CHLORINE) As interacts with self-ignition. When As interacts with sulfur (cm. SULFUR), selenium (cm. SELENIUM) and tellurium (cm. TELLURIUM) chalcogenides are formed: (cm. CHALCOGENIDES) As 2 S 5, As 2 S 3, As 4 S 4, As 2 Se 3, As 2 Te 3, existing in a glassy state. They are semiconductors.
With many metals, As forms arsenides. (cm. ARSENIDES). Gallium arsenide GaAs and indium InAs - semiconductors (cm. SEMICONDUCTORS).
A large number of organic arsenic compounds are known, which contain chemical bond As - C: organoarsines R n AsH 3-n (n= 1.3), tetraorganodiarsines R 2 As - AsR 2 and others.
Application
As of high purity is used for the synthesis of semiconductor materials. Sometimes As is added to steels as an alloying addition.
In 1909 the German microbiologist P. Ehrlich (cm. ERLICH Paul) received "drug 606", an effective cure for malaria, syphilis, and relapsing fever.
Physiological action
Arsenic and all its compounds are poisonous. In acute arsenic poisoning, vomiting, abdominal pain, diarrhea, depression of the central nervous system are observed. Help and antidotes for arsenic poisoning: taking aqueous solutions of Na 2 S 2 O 3. Gastric lavage, intake of milk and cottage cheese; specific antidote - unithiol. MPC in the air for arsenic 0.5 mg / m 3. Work with arsenic in sealed boxes, using protective clothing. Due to the high toxicity of arsenic compounds, they were used by Germany as poisonous substances in the First World War.
In areas where there is an excess of arsenic in soil and water, it accumulates in the thyroid gland of people and causes endemic goiter.
encyclopedic Dictionary. 2009 .
Synonyms:See what "arsenic" is in other dictionaries:
ARSENIC- (Arsenum, Arsenium, Arseni cum), solid metalloid, symbol. As; at. in. 74.96. In the periodic system of elements, it occupies the 33rd place in order, in the 5th row of the V group. Natural compounds of M. with sulfur (realgar and orpiment) were known as early as ... ... Big Medical Encyclopedia
ARSENIC- see ARSENIC (As). Since arsenic and its compounds are widely used in the national economy, it is found in wastewater from various industries - metallurgical, chemical-pharmaceutical, textile, glass, leather, chemical ... Fish Diseases: A Handbook
Arsenic- (crude arsenic) is a solid extracted from natural arsenopyrites. It exists in two main forms: a) ordinary, the so-called metallic arsenic, in the form of shiny steel-colored crystals, fragile, not ... Official terminology
- (symbol As), a poisonous semi-metallic element of the fifth group of the periodic table; was probably obtained in 1250. Compounds containing arsenic are used as a poison for rodents, insects and as a weed killer. They also apply... Scientific and technical encyclopedic dictionary
- (Arsenium), As, a chemical element of group V of the periodic system, atomic number 33, atomic mass 74.9216; gray, yellow or black non-metal, mp 817 shC, sublimates at 615 shC. Arsenic is used to obtain semiconductor ... ... Modern Encyclopedia
Arsenic- (Arsenium), As, a chemical element of group V of the periodic system, atomic number 33, atomic mass 74.9216; gray, yellow or black non-metal, mp 817 °C, sublimes at 615 °C. Arsenic is used to obtain semiconductor ... ... Illustrated Encyclopedic Dictionary
ARSENIC- chem. element, symbol As (lat. Arsenicum), at. n. 33, at. m. 74.92; non-metal, exists in several allotropic modifications, density 5720 kg/m3. Under normal conditions, the most chemically resistant is the so-called metallic, or gray, arsenic. Great Polytechnic Encyclopedia
The atomic number of arsenic is 33, the atomic mass is 74.91. Arsenic can exist in three modifications:
1) metallic - crystalline modification from silver gray to black. This modification of arsenic, which crystallizes in a rhombohedral form, is formed by cooling arsenic vapor from a gas mixture superheated to a very high temperature;
2) amorphous - black-brown or gray, which is formed when arsenic vapors, overheated to a very high temperature, are deposited (cooled) on a plate heated to the evaporation temperature of arsenic;
3) yellow arsenic, which crystallizes in the cubic system and precipitates during sublimation in hydrogen. Yellow arsenic is the least stable modification; it turns into amorphous black arsenic when heated to 270-280 ° C or at ordinary temperature under the influence of light.
According to their physical properties, all three modifications of arsenic are different. Density of metallic arsenic 5.73; amorphous brown 4.7; crystal yellow 2.0 g/cm3. Metallic arsenic is brittle, crumbles (breaks) upon impact. The hardness of arsenic of this modification on a mineralogical scale is 3-4. Due to its high brittleness, its pressure treatment is impossible.
The melting point of arsenic lies in the range of 817-868 ° C. Significant evaporation of arsenic at atmospheric pressure begins at 554°C, but a noticeable elasticity of arsenic vapor is also observed at ordinary temperature. Therefore, arsenic is usually stored in sealed ampoules.
In vacuum, the sublimation of arsenic begins already at 90°C.
The value of arsenic vapor pressure depending on the temperature is expressed by the following figures:
Electrical Properties
The electrical resistivity of the metallic modification of arsenic at 0°C is 35*10 ohm*cm. Metal arsenic conducts electricity well, while the other two varieties are characterized by high electrical resistivity. Thus, the electrical resistivity at ordinary temperature of black (gray) amorphous arsenic is 10–11–10–12 ohm * cm, and at higher temperatures it decreases, as can be seen from the data below:
Above 250°C, the resistance of amorphous black arsenic changes significantly depending on its holding at the overheating temperature. So, for example, arsenic, heated to 260 ° C and kept at this temperature for 20 minutes, has a resistance of 3400 ohm * cm, aged 70 minutes 1000 ohm * cm; 90 min 2500 ohm * cm, and aged 170 min 11 ohm * cm.
Chemical properties of arsenic and its compounds
Arsenic has a relatively low chemical activity. At ordinary temperature in air, it oxidizes very slowly, but when crushed, and also when heated in a compact state, it quickly burns out in air, forming AS2O3.
Arsenic is insoluble in water; nitric acid and aqua regia oxidize it to arsenic acid. Hydrochloric acid acts on arsenic very slowly and only in the presence of air.
Arsenic and oxygen. There are two oxygen compounds of arsenic: As2O3 trioxide and As2O5 pentoxide. The vapor pressure of As2O3 at 300°C is 89 mm Hg. Art.
Hydrogen and carbon relatively easily reduce arsenic trioxide by the reactions:
As2O3 + 3H2 → 2As + 3H2O;
As2O3+ 3С → 2As + 3CO.
When arsenic trioxide interacts with metals during heating, arsenic is reduced and the metals are oxidized, which for zinc, potassium, sodium and aluminum is accompanied by a large release of heat and light.
Arsenic pentoxide (As2O5) is reduced to As2O3 when heated with a variety of reducing agents (phosphorus, arsenic itself, carbon, antimony, bismuth, sodium, potassium, silicon, zinc, iron, copper, tin, lead, manganese, cobalt, etc.). Therefore, in the processes of obtaining arsenic, pentoxide plays a very insignificant role, since, when formed, it quickly passes into trioxide.
Arsenic and hydrogen. Arsenic with hydrogen forms a number of compounds: As2H2; As4H2; AsH3. The As2H2 compound, when heated in vacuum, decomposes into arsenic and hydrogen. In air, this compound is stable at ordinary temperatures, but when heated, it oxidizes vigorously.
The As4H2 compound decomposes into arsenic, hydrogen, and AsH3 when heated. The AsH3 compound (arsine) is a colorless gas, very poisonous, slightly soluble in water.
Under normal conditions, this compound cannot be obtained by direct interaction of arsenic and hydrogen. Its formation requires high pressures and temperatures. Usually arsenic hydrogen is obtained by acting on arsenic with water vapor:
4As + 3H2O → As2O3 + 2AsH3.
The melting point of arsine is -113.5 ° C. The vapor pressure at 0 ° C is about 9 atm, and at 15 ° C 13 at.
When AsH3 is passed over a heated metal, arsine decomposes, releasing hydrogen and forming an arsenide of the corresponding metal, for example, potassium, sodium arsenide, etc.
Arsenic and phosphorus. When arsenic and phosphorus are heated together (to red heat), the As2P compound is formed. This compound is unstable - it decomposes and oxidizes in the light even under water.
Arsenic does not interact with carbon.
Halogen compounds of arsenic. Arsenic interacts with halides at ordinary temperatures. Some properties of arsenic halides are given in table. 61.
Arsenic and its compounds are highly toxic, so special safety precautions must be observed when working with them.
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