DEFINITION
Iron- element of the eighth group of the fourth period of the Periodic Table of Chemical Elements by D. I. Mendeleev.
And the volume number is 26. The symbol is Fe (Latin “ferrum”). One of the most common metals in the earth's crust (second place after aluminum).
Physical properties of iron
Iron is a gray metal. In its pure form it is quite soft, malleable and viscous. The electronic configuration of the outer energy level is 3d 6 4s 2. In its compounds, iron exhibits oxidation states “+2” and “+3”. The melting point of iron is 1539C. Iron forms two crystalline modifications: α- and γ-iron. The first of them has a body-centered cubic lattice, the second has a face-centered cubic lattice. α-Iron is thermodynamically stable in two temperature ranges: below 912 and from 1394C to the melting point. Between 912 and 1394C γ-iron is stable.
The mechanical properties of iron depend on its purity - the content of even very small quantities of other elements in it. Solid iron has the ability to dissolve many elements in itself.
Chemical properties of iron
In humid air, iron quickly rusts, i.e. covered with a brown coating of hydrated iron oxide, which, due to its friability, does not protect iron from further oxidation. In water, iron corrodes intensely; with abundant access to oxygen, hydrate forms of iron (III) oxide are formed:
2Fe + 3/2O 2 + nH 2 O = Fe 2 O 3 ×H 2 O.
With a lack of oxygen or difficult access, mixed oxide (II, III) Fe 3 O 4 is formed:
3Fe + 4H 2 O (v) ↔ Fe 3 O 4 + 4H 2.
Iron dissolves in hydrochloric acid of any concentration:
Fe + 2HCl = FeCl 2 + H 2.
Dissolution in dilute sulfuric acid occurs similarly:
Fe + H 2 SO 4 = FeSO 4 + H 2.
In concentrated solutions of sulfuric acid, iron is oxidized to iron (III):
2Fe + 6H 2 SO 4 = Fe 2 (SO 4) 3 + 3SO 2 + 6H 2 O.
However, in sulfuric acid, the concentration of which is close to 100%, iron becomes passive and practically no interaction occurs. Iron dissolves in dilute and moderately concentrated solutions of nitric acid:
Fe + 4HNO 3 = Fe(NO 3) 3 + NO + 2H 2 O.
At high concentrations of nitric acid, dissolution slows down and iron becomes passive.
Like other metals, iron reacts with simple substances. Reactions between iron and halogens (regardless of the type of halogen) occur when heated. The interaction of iron with bromine occurs at increased vapor pressure of the latter:
2Fe + 3Cl 2 = 2FeCl 3;
3Fe + 4I 2 = Fe 3 I 8.
The interaction of iron with sulfur (powder), nitrogen and phosphorus also occurs when heated:
6Fe + N 2 = 2Fe 3 N;
2Fe + P = Fe 2 P;
3Fe + P = Fe 3 P.
Iron is capable of reacting with non-metals such as carbon and silicon:
3Fe + C = Fe 3 C;
Among the reactions of interaction of iron with complex substances, the following reactions play a special role - iron is capable of reducing metals that are in the activity series to the right of it from salt solutions (1), reducing iron (III) compounds (2):
Fe + CuSO 4 = FeSO 4 + Cu (1);
Fe + 2FeCl 3 = 3FeCl 2 (2).
Iron, at elevated pressure, reacts with a non-salt-forming oxide - CO to form substances of complex composition - carbonyls - Fe (CO) 5, Fe 2 (CO) 9 and Fe 3 (CO) 12.
Iron, in the absence of impurities, is stable in water and in dilute alkali solutions.
Getting iron
The main method of obtaining iron is from iron ore (hematite, magnetite) or electrolysis of solutions of its salts (in this case, “pure” iron is obtained, i.e. iron without impurities).
Examples of problem solving
EXAMPLE 1
| Exercise | Iron scale Fe 3 O 4 weighing 10 g was first treated with 150 ml of hydrochloric acid solution (density 1.1 g/ml) with a mass fraction of hydrogen chloride of 20%, and then excess iron was added to the resulting solution. Determine the composition of the solution (in % by weight). |
| Solution | Let us write the reaction equations according to the conditions of the problem: 8HCl + Fe 3 O 4 = FeCl 2 + 2FeCl 3 + 4H 2 O (1); 2FeCl 3 + Fe = 3FeCl 2 (2). Knowing the density and volume of a hydrochloric acid solution, you can find its mass: m sol (HCl) = V(HCl) × ρ (HCl); m sol (HCl) = 150×1.1 = 165 g. Let's calculate the mass of hydrogen chloride: m(HCl) = m sol (HCl) ×ω(HCl)/100%; m(HCl) = 165×20%/100% = 33 g. Molar mass (mass of one mole) of hydrochloric acid, calculated using the table of chemical elements by D.I. Mendeleev – 36.5 g/mol. Let's find the amount of hydrogen chloride: v(HCl) = m(HCl)/M(HCl); v(HCl) = 33/36.5 = 0.904 mol. Molar mass (mass of one mole) of scale, calculated using the table of chemical elements by D.I. Mendeleev – 232 g/mol. Let's find the amount of scale substance: v(Fe 3 O 4) = 10/232 = 0.043 mol. According to equation 1, v(HCl): v(Fe 3 O 4) = 1:8, therefore, v(HCl) = 8 v(Fe 3 O 4) = 0.344 mol. Then, the amount of hydrogen chloride calculated by the equation (0.344 mol) will be less than that indicated in the problem statement (0.904 mol). Therefore, hydrochloric acid is in excess and another reaction will occur: Fe + 2HCl = FeCl 2 + H 2 (3). Let us determine the amount of ferric chloride substance formed as a result of the first reaction (we use indices to denote a specific reaction): v 1 (FeCl 2):v(Fe 2 O 3) = 1:1 = 0.043 mol; v 1 (FeCl 3):v(Fe 2 O 3) = 2:1; v 1 (FeCl 3) = 2 × v (Fe 2 O 3) = 0.086 mol. Let us determine the amount of hydrogen chloride that did not react in reaction 1 and the amount of iron (II) chloride formed during reaction 3: v rem (HCl) = v(HCl) – v 1 (HCl) = 0.904 – 0.344 = 0.56 mol; v 3 (FeCl 2): v rem (HCl) = 1:2; v 3 (FeCl 2) = 1/2 × v rem (HCl) = 0.28 mol. Let us determine the amount of FeCl 2 substance formed during reaction 2, the total amount of FeCl 2 substance and its mass: v 2 (FeCl 3) = v 1 (FeCl 3) = 0.086 mol; v 2 (FeCl 2): v 2 (FeCl 3) = 3:2; v 2 (FeCl 2) = 3/2× v 2 (FeCl 3) = 0.129 mol; v sum (FeCl 2) = v 1 (FeCl 2) + v 2 (FeCl 2) + v 3 (FeCl 2) = 0.043 + 0.129 + 0.28 = 0.452 mol; m(FeCl 2) = v sum (FeCl 2) × M(FeCl 2) = 0.452 × 127 = 57.404 g. Let us determine the amount of substance and mass of iron that entered into reactions 2 and 3: v 2 (Fe): v 2 (FeCl 3) = 1:2; v 2 (Fe) = 1/2× v 2 (FeCl 3) = 0.043 mol; v 3 (Fe): v rem (HCl) = 1:2; v 3 (Fe) = 1/2×v rem (HCl) = 0.28 mol; v sum (Fe) = v 2 (Fe) + v 3 (Fe) = 0.043+0.28 = 0.323 mol; m(Fe) = v sum (Fe) ×M(Fe) = 0.323 ×56 = 18.088 g. Let's calculate the amount of substance and the mass of hydrogen released in reaction 3: v(H 2) = 1/2×v rem (HCl) = 0.28 mol; m(H 2) = v(H 2) ×M(H 2) = 0.28 × 2 = 0.56 g. We determine the mass of the resulting solution m’ sol and the mass fraction of FeCl 2 in it: m’ sol = m sol (HCl) + m(Fe 3 O 4) + m(Fe) – m(H 2); |
Iron(Latin ferrum), fe, chemical element of group VIII of the periodic system of Mendeleev; atomic number 26, atomic mass 55.847; shiny silver-white metal. The element in nature consists of four stable isotopes: 54 fe (5.84%), 56 fe (91.68%), 57 fe (2.17%) and 58 fe (0.31%).
Historical reference. Iron was known back in prehistoric times, but it found widespread use much later, since it is extremely rare in nature in a free state, and its extraction from ores became possible only at a certain level of technological development. It was probably the first time that man became acquainted with meteorite iron, as evidenced by its names in the languages of ancient peoples: the ancient Egyptian “beni-pet” means “heavenly iron”; The ancient Greek sideros is associated with the Latin sidus (genitive case sideris) - star, celestial body. In Hittite texts of the 14th century. BC e. J. is mentioned as a metal that fell from the sky. Romance languages retain the root of the name given by the Romans (for example, French fer, Italian ferro).
The method of obtaining iron from ores was invented in western Asia in the 2nd millennium BC. e.; After that, the use of iron spread to Babylon, Egypt, and Greece; for changing Bronze Age came Iron Age. Homer (in the 23rd song of the Iliad) says that Achilles awarded a discus made of iron to the winner in a discus throwing competition. In Europe and Ancient Rus', for many centuries, women received cheese-making process. Iron ore was reduced with charcoal in a forge built in a pit; Air was pumped into the forge with bellows, the reduction product - the kritsa - was separated from the slag by hammer blows and various products were forged from it. As blowing methods improved and the height of the hearth increased, the temperature of the process increased and part of the iron was carburized, i.e., it was obtained cast iron; this relatively fragile product was considered a production waste. Hence the name of cast iron “pig iron”, “pig iron” - English pig iron. Later it was noticed that when loading cast iron rather than iron ore into the forge, a low-carbon iron crust was also obtained, and such a two-stage process turned out to be more profitable than the cheese-blowing process. In the 12th-13th centuries. the screaming method was already widespread. In the 14th century Cast iron began to be smelted not only as a semi-product for further processing, but also as a material for casting various products. The reconstruction of the hearth into a shaft furnace (“domnitsa”), and then into a blast furnace, also dates back to the same time. In the middle of the 18th century. in Europe, the crucible process for obtaining began to be used become, which was known in Syria in the early Middle Ages, but later turned out to be forgotten. In this method, steel was produced by melting metal charges in small vessels (crucibles) from a highly refractory mass. In the last quarter of the 18th century. The puddling process of converting pig iron into iron on the bottom of a fiery reverberatory furnace began to develop. The industrial revolution of the 18th and early 19th centuries, the invention of the steam engine, and the construction of railroads, large bridges, and a steam fleet created a huge demand for iron and its alloys. However, all existing methods of producing iron could not satisfy the needs of the market. Mass production of steel began only in the mid-19th century, when the Bessemer, Thomas and open-hearth processes were developed. In the 20th century The electric furnace melting process arose and became widespread, producing high-quality steel.
Prevalence in nature. In terms of content in the lithosphere (4.65% by mass), iron ranks second among metals (aluminum ranks first). It migrates vigorously in the earth's crust, forming about 300 minerals (oxides, sulfides, silicates, carbonates, titanates, phosphates, etc.). Iron takes an active part in magmatic, hydrothermal, and supergene processes, which are associated with the formation of various types of its deposits. Iron is a metal of the earth's depths; it accumulates at the early stages of magma crystallization, in ultrabasic (9.85%) and basic (8.56%) rocks (in granites it is only 2.7%). In the biosphere, iron accumulates in many marine and continental sediments, forming sedimentary ores.
An important role in the geochemistry of iron is played by redox reactions—the transition of 2-valent iron to 3-valent iron and vice versa. In the biosphere, in the presence of organic substances, fe 3+ is reduced to fe 2+ and easily migrates, and when it encounters atmospheric oxygen, fe 2+ is oxidized, forming accumulations of hydroxides of 3-valent iron. Widespread compounds of 3-valent iron are red, yellow, brown color. This determines the color of many sedimentary rocks and their name - “red-colored formation” (red and brown loams and clays, yellow sands, etc.).
Physical and chemical properties. The importance of iron in modern technology is determined not only by its wide distribution in nature, but also by a combination of very valuable properties. It is plastic, easily forged in both cold and heated states, and can be rolled, stamped and drawn. The ability to dissolve carbon and other elements serves as the basis for the production of various iron alloys.
Liquid can exist in the form of two crystal lattices: a - and g - body-centered cubic (bcc) and face-centered cubic (fcc). Below 910 °C, a - fe with a bcc lattice is stable (a = 2.86645 å at 20 °C). Between 910°C and 1400°C, the g-modification with an fcc lattice is stable (a = 3.64 å). Above 1400°C, the bcc d-fe lattice (a = 2.94 å) is formed again, stable up to the melting temperature (1539°C). a - fe is ferromagnetic up to 769°C (Curie point). Modification g -fe and d -fe are paramagnetic.
The polymorphic transformations of iron and steel upon heating and cooling were discovered in 1868 by D.K. Chernov. Carbon forms with J. solid solutions implantations in which C atoms, having a small atomic radius (0.77 å), are located in the interstices of the metal crystal lattice, consisting of larger atoms (atomic radius fe 1.26 å). A solid solution of carbon in g-fe is called. austenite, and in (a -fe- ferrite. Saturated solid solution of carbon in g - fe contains 2.0% C by weight at 1130°C; a -fe dissolves only 0.02-0.04% C at 723°C, and less than 0.01% at room temperature. Therefore, when hardening austenite is formed martensite - a supersaturated solid solution of carbon in a - fe, very hard and brittle. Combination of hardening with vacation(by heating to relatively low temperatures to reduce internal stresses) makes it possible to impart the required combination of hardness and ductility to steel.
The physical properties of iron depend on its purity. Industrial iron materials usually contain impurities of carbon, nitrogen, oxygen, hydrogen, sulfur, and phosphorus. Even at very low concentrations, these impurities greatly change the properties of the metal. So, sulfur causes the so-called. red brittleness, phosphorus (even 10 -20% P) - coldness; carbon and nitrogen reduce plastic, and hydrogen increases fragility G. (so-called hydrogen embrittlement). Reduction of impurity content to 10 -7 - 10 -9% leads to significant changes in the properties of the metal, in particular to an increase in ductility.
The following are the physical properties of iron, relating mainly to metal with a total impurity content of less than 0.01% by weight:
Atomic radius 1.26 å
Ionic radii fe 2+ o.80 å, fe 3+ o.67 å
Density (20 o c) 7.874 g/cm 3
t pl 1539°С
t kip about 3200 o C
Temperature coefficient of linear expansion (20°C) 11.7·10 -6
Thermal conductivity (25°C) 74.04 Tue/(m K)
The heat capacity of liquid depends on its structure and changes in a complex way with temperature; average specific heat capacity (0-1000 o c) 640.57 j/(kg·TO) .
Electrical resistivity (20°C)
9.7·10 -8 ohm m
Temperature coefficient of electrical resistance
(0-100°C) 6.51·10 -3
Young's modulus 190-210 10 3 Mn/m. 2
(19-21 10 3 kgf/mm 2)
Temperature coefficient of Young's modulus
Shear modulus 84.0 10 3 Mn/m 2
Short-term tensile strength
170-210 Mn/m 2
Elongation 45-55%
Brinell hardness 350-450 Mn/m 2
Yield strength 100 Mn/m 2
Impact strength 300 Mn/m 2
Configuration of the outer electron shell of the fe 3 atom d 6 4s 2 . Iron exhibits variable valency (compounds of 2- and 3-valent iron are the most stable). With oxygen, iron forms feo oxide, fe 2 o 3 oxide, and fe 3 o 4 oxide-oxide (a compound of feo with fe 2 o 3, which has the structure spinels) . In humid air at normal temperatures, iron becomes covered with loose rust (fe 2 o 3 n h 2 o). Due to its porosity, rust does not prevent the access of oxygen and moisture to the metal and therefore does not protect it from further oxidation. As a result of various types of corrosion, millions of tons of iron are lost annually. When iron is heated in dry air above 200°C, it becomes covered with a thin oxide film, which protects the metal from corrosion at normal temperatures; this is the basis of the technical method of protecting Zh. - bluing. When heated in water vapor, iron oxidizes to form fe 3 o 4 (below 570°C) or feo (above 570°C) and release hydrogen.
Fe(oh)2 hydroxide is formed in the form of a white precipitate when caustic alkalis or ammonia act on aqueous solutions of fe2+ salts in an atmosphere of hydrogen or nitrogen. When it comes into contact with air, fe(oh)2 first turns green, then turns black, and finally quickly turns into the red-brown hydroxide fe(oh)3. Feo oxide exhibits basic properties. Fe 2 o 3 oxide is amphoteric and has a weakly expressed acidic function; reacting with more basic oxides (for example, mgo), it forms ferrites - compounds of the fe 2 o 3 type n meo, which have ferromagnetic properties and are widely used in radio electronics. Acidic properties are also expressed in hexavalent iron, which exists in the form of ferrates, for example k 2 feo 4, salts of ferric acid not isolated in the free state.
F. easily reacts with halogens and hydrogen halides, giving salts, for example, the chlorides fecl 2 and fecl 3. When liquid is heated with sulfur, the sulfides fes and fes 2 are formed. Carbides Zh. - fe 3 c ( cementite) and fe 2 c (e-carbide) - precipitate from solid solutions of carbon in liquid upon cooling. fe 3 c is also released from solutions of carbon in liquid liquid at high concentrations of nitrogen. Nitrogen, like carbon, gives interstitial solid solutions from liquid; Of these, nitrides fe 4 n and fe 2 n are released. With hydrogen, iron produces only unstable hydrides, the composition of which has not been precisely established. When heated, iron reacts vigorously with silicon and phosphorus, forming silicides (for example, fe 3 si) and phosphides (for example, fe 3 p).
Liquid compounds with many elements (O, s, etc.) that form a crystalline structure have a variable composition (for example, the sulfur content in monosulfide can vary from 50 to 53.3 at.%). This is due to defects in the crystal structure. For example, in ferrous oxide, some of the fe 2+ ions at lattice sites are replaced by fe 3+ ions; to maintain electrical neutrality, some lattice sites that belonged to fe 2+ ions remain empty and the phase (wüstite) under normal conditions has the formula fe 0.947 o.
J.’s interaction with nitric acid. Concentrated hno 3 (density 1.45 g/cm 3) passivates the iron due to the appearance of a protective oxide film on its surface; a more dilute hno 3 dissolves liquid with the formation of fe 2+ or fe 3+ ions, being reduced to mh 3 or n 2 o and n 2.
Solutions of divalent iron salts in air are unstable - fe 2+ gradually oxidizes to fe 3+. Aqueous solutions of liquid salts due to hydrolysis have an acidic reaction. The addition of fe 3+ thiocyanate ions scn - to solutions of salts gives a bright blood-red color due to the appearance of fe (scn) 3, which makes it possible to discover the presence of 1 part fe 3+ in approximately 10 6 parts of water. J. is characterized by education complex compounds.
Receipt and application. Pure iron is obtained in relatively small quantities by electrolysis of aqueous solutions of its salts or by the reduction of its oxides with hydrogen. A method is being developed for the direct production of iron from ores by electrolysis of melts. The production of sufficiently pure iron is gradually increasing through its direct reduction from ore concentrates with hydrogen, natural gas, or coal at relatively low temperatures.
Iron is the most important metal of modern technology. In its pure form, iron is practically not used because of its low strength, although in everyday life steel or cast iron products are often called “iron.” The bulk of iron is used in the form of alloys with very different compositions and properties. Iron alloys account for approximately 95% of all metal products. Carbon-rich alloys (over 2% by weight) - cast irons - are smelted in blast furnaces from enriched iron ores. Steel of various grades (carbon content less than 2% by weight) is smelted from cast iron in open-hearth and electric furnaces and converters by oxidizing (burning out) excess carbon, removing harmful impurities (mainly s, P, O) and adding alloying elements. High-alloy steels (with a high content of nickel, chromium, tungsten and other elements) are smelted in electric arc and induction furnaces. For the production of steels and iron alloys for especially critical purposes, new processes are used - vacuum, electroslag remelting, plasma and electron beam melting, etc. Methods are being developed for steel smelting in continuously operating units that ensure high quality metal and automation of the process.
Based on iron, materials are created that can withstand the effects of high and low temperatures, vacuum and high pressures, aggressive environments, high alternating voltages, nuclear radiation, etc. The production of iron and its alloys is constantly growing. In 1971, 89.3 million were smelted in the USSR. T cast iron and 121 million T become.
L. A. Shvartsman, L. V. Vanyukova.
Iron as an artistic material has been used since antiquity in Egypt (head stand from the tomb of Tutankhamun near Thebes, mid-14th century BC, Ashmolean Museum, Oxford), Mesopotamia (daggers found near Carchemish, 500 BC, British Museum, London), India (iron column in Delhi, 415). Since the Middle Ages, numerous highly artistic products from iron and steel have been preserved in European countries (England, France, Italy, Russia, etc.) - forged fences, door hinges, wall brackets, weather vanes, chest frames, and lights. Forged through products made from rods and products made from expanded metal sheets (often with a mica lining) are distinguished by their flat shapes, a clear linear graphic silhouette, and are effectively visible against a light-airy background. In the 20th century Ferrous is used for the manufacture of gratings, fences, openwork interior partitions, candlesticks, and monuments.
T.L.
Iron in the body. Ferrous is present in the organisms of all animals and plants (on average about 0.02%); it is necessary mainly for oxygen metabolism and oxidative processes. There are organisms (so-called concentrators) capable of accumulating it in large quantities (for example, iron bacteria - up to 17-20% F.). Almost all fats in animal and plant organisms are associated with proteins. Lack of fat causes growth retardation and symptoms plant chlorosis, associated with reduced education chlorophyll. Excess iron also has a harmful effect on plant development, causing, for example, sterility of rice flowers and chlorosis. In alkaline soils, iron compounds are formed that are inaccessible for absorption by plant roots, and plants do not receive it in sufficient quantities; in acidic soils, iron passes into soluble compounds in excess quantities. When there is a deficiency or excess of assimilable iron compounds in the soil, plant diseases can occur over large areas.
Fiber enters the body of animals and humans with food (the richest sources in it are liver, meat, eggs, legumes, bread, cereals, spinach, and beets). Normally, a person receives 60-110 with a diet mg J., which significantly exceeds his daily requirement. Absorption of fertilization received from food occurs in the upper part of the small intestines, from where it enters the blood in a form bound with proteins and is carried with the blood to various organs and tissues, where it is deposited in the form of a fertilizing protein complex - ferritin. The main depot of fat in the body is the liver and spleen. Due to iron ferritin, all iron-containing compounds of the body are synthesized: respiratory pigment is synthesized in the bone marrow hemoglobin, in the muscles - myoglobin, in various tissues cytochromes and other iron-containing enzymes. Fat is excreted from the body mainly through the wall of the large intestine (in humans there are about 6-10 mg per day) and to a small extent by the kidneys. The body's need for fat changes with age and physical condition. For 1 kg of weight, children need - 0.6, adults - 0.1 and pregnant women - 0.3 mg J. per day. In animals, the need for fat is approximately (per 1 kg dry matter of the diet): for dairy cows - at least 50 mg, for young animals - 30-50 mg, for piglets - up to 200 mg, for pregnant pigs - 60 mg.
V. V. Kovalsky.
In medicine, medicinal preparations of iron (reduced iron, iron lactate, iron glycerophosphate, divalent iron sulfate, Blo tablets, malate solution, feramide, hemostimulin, etc.) are used in the treatment of diseases accompanied by iron deficiency. in the body (iron deficiency anemia), as well as as a general tonic (after infectious diseases, etc.). Isotopes of iron (52 fe, 55 fe and 59 fe) are used as indicators in biomedical research and diagnosis of blood diseases (anemia, leukemia, polycythemia, etc.).
Lit.: General metallurgy, M., 1967; Nekrasov B.V., Fundamentals of General Chemistry, vol. 3, M., 1970; Remi G., Course of inorganic chemistry, trans. from German, vol. 2, M., 1966; Brief chemical encyclopedia, vol. 2, M., 1963; Levinson N. R., [Products made of non-ferrous and ferrous metal], in the book: Russian decorative art, vol. 1-3, M., 1962-65; Vernadsky V.I., Biogeochemical essays. 1922-1932, M. - L., 1940; Granik S., Iron metabolism in animals and plants, in the collection: Microelements, trans. from English, M., 1962; Dixon M., Webb F., enzymes, trans. from English, M., 1966; neogi p., iron in ancient India, Calcutta, 1914; friend j. n., iron in antiquity, l., 1926; frank e. b., old French ironwork, camb. (mass.), 1950; Lister R., decorative wrought ironwork in great britain, l., 1960.
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The benefits of iron for the body
The main function of iron in the body is considered to be the formation of hemoglobin. This is not surprising, because it contains three-quarters of iron reserves. But in other protein structures the percentage of iron is relatively low - about 5%.
Why is hemoglobin needed? A protein containing a large amount of iron binds oxygen molecules, which are transported through the blood to working tissues and organs. That is why a decrease in the amount of hemoglobin in the blood immediately affects overall well-being and performance. So even a slight loss of blood is fraught with disorders for the body. For athletes, a lack of iron can impair recovery after intense physical activity.
Among other functions of iron, we can list the following:
- Energy replenishment of muscles. The cheapest source of fuel for muscles is oxygen. Thanks to its transformation through a series of chemical reactions, the muscle receives energy for contraction. In addition to oxygen, other energy sources are also used. These are phosphates contained in cells - creatine phosphate and ATP, as well as muscle and liver glycogen. However, their reserves are too small to support work lasting more than 1 minute. Creatine phosphate is enough for work lasting up to 10 seconds, ATP – for 2-3 seconds. The higher the concentration of hemoglobin in the blood, the more oxygen it is able to supply to working tissues and organs. But iron deficiency can cause muscle spasms that worsen during periods of rest (sleep, sitting).
- Energy replenishment of the brain. The brain needs oxygen just like the muscles. Moreover, iron deficiency is fraught with the development of Alzheimer's disease, dementia (acquired dementia) and other diseases caused by disorders of brain activity.
- Regulation of body temperature. This function is performed indirectly by iron. The stability of iron concentration in the blood determines the adequacy of all metabolic processes.
- Strengthening the immune system. The microelement is necessary for hematopoiesis. White (lymphocytes) and red (erythrocytes) blood cells are formed in the presence of iron. The former are responsible for immunity, and the latter supply the blood with oxygen. If the amount of iron in the body is normal, it is able to independently resist diseases. As soon as the iron concentration decreases, infectious diseases make themselves felt.
- Fetal development. During pregnancy, it is important to consume enough iron, since some is consumed during hematopoiesis in the fetus. But iron deficiency increases the risk of premature birth, provokes underweight in the newborn and developmental disorders.
How iron interacts in the body
In itself, a normal concentration of iron in the body does not guarantee good health, high immunity, absence of diseases and performance. No less important is the interaction of this trace element with other substances, because the functions of some can negatively affect the functions of others.
Avoid combining iron with:
- vitamin E and phosphates: the absorption of iron is impaired;
- Tetracycline and fluoroquinolones: the absorption process of the latter is inhibited;
- Calcium: the process of iron absorption is disrupted;
- milk, coffee and tea - iron absorption worsens;
- zinc and copper - the absorption process in the intestine is disrupted;
- soy protein – absorption is suppressed;
- chromium: iron inhibits its absorption.
But ascorbic acid, sorbitol, fructose and succinic acid improve the absorption of iron by the body.
These nuances must be taken into account when taking iron-containing drugs, since instead of improving your well-being, you can get the opposite effect.
The role of iron in the occurrence and course of various diseases
There are many diseases in which eating foods rich in iron can aggravate the situation.
People with high levels of iron in their bodies are more at risk of infections, heart disease, and some types of cancer (especially men).
In the form of free radicals, iron provokes the development of atherosclerosis. The same goes for rheumatoid arthritis. The use of iron in this disease provokes inflammation of the joints.
In case of individual iron intolerance, the consumption of certain foods causes heartburn, nausea, constipation and diarrhea.
During pregnancy, excess iron increases the risk of developing pathology of the placenta (free radical oxidation increases, resulting in the death of mitochondria - the oxygen “depots” of cells).
With pathological disorders of iron absorption, the risk of hemochromatosis is increased - accumulation of iron in the internal organs (liver, heart, pancreas).
What foods contain iron?
Iron reserves are replenished through foods of animal and plant origin. The former contain “heme” iron, the latter – “non-heme”.
To absorb heme, they consume products of animal origin - veal, beef, pork, rabbit meat and offal (liver, kidneys). To get the benefits of non-heme vitamins, you need to consume vitamin C at the same time as iron-containing foods.
The record holders for iron content are the following products of plant origin, mg Fe2+:
- peanuts – 200 g of product contains 120;
- soybean – per 200 g of product – 8.89;
- potatoes – per 200 g of product – 8.3;
- white beans – per 200 g of product – 6.93;
- beans – per 200 g of product – 6.61;
- lentils – per 200 g of product – 6.59;
- spinach – in 200 g of product – 6.43;
- beets (tops) – per 200 g of product – 5.4;
- chickpeas – per 100 g of product – 4.74;
- Brussels sprouts – per 200 g of product – 3.2;
- white cabbage – per 200 g of product – 2.2;
- green peas – per 200 g of product – 2.12.
Among cereals, it is better to include oatmeal and buckwheat, wholemeal flour, and wheat sprouts in the diet. Herbs include thyme, sesame (sesame). A lot of iron is found in dried porcini mushrooms and chanterelles, apricots, peaches, apples, plums, and quince. And also figs, pomegranate and dried fruits.
Among animal products, iron reserves are found in beef kidneys and liver, fish, and eggs (yolk). In meat products - veal, pork, rabbit, turkey. Seafood (clams, snails, oysters). Fish (mackerel, pink salmon).
Iron absorption
Interestingly, when eating meat products, iron is absorbed by 40-50%, and when eating fish products – by 10%. The record holder for iron absorption is the liver of animals.
From plant-based foods, the percentage of iron that is absorbed is even less. A person absorbs up to 7% from legumes, 6% from nuts, 3% from fruits and eggs, 1% from cooked cereals.
Advice! The body benefits from a diet that combines products of plant and animal origin. When adding 50 g of meat to vegetables, the absorption of iron doubles. When adding 100 g of fish - three times, when adding fruits containing vitamin C - five times
How to preserve iron in food and its combination with other substances
When cooked, foods lose some of their nutrients, and iron is no exception. Iron in animal products is more resistant to high temperatures. With vegetables and fruits, everything is more complicated - part of the iron passes into the water in which the food is cooked. The only way out is to minimize the heat treatment of plant products.
To increase the absorption of iron, eat iron-containing foods along with vitamin C. Half a grapefruit or orange is enough for the body to absorb three times more of it. The only caveat is that this rule only applies to iron-containing products of plant origin.
The diet requires vitamin A, the lack of which blocks the body's ability to use iron reserves to form red blood cells (red blood cells).
With a lack of copper, iron loses its “mobility”, as a result of which the process of transporting useful substances from “storages” to cells and organs is disrupted. To avoid this, include more legumes in your diet.
The combination of iron with B vitamins: the “performance” of the latter is greatly enhanced.
But it is better to consume dairy foods and grains separately from iron-containing foods, as they block the absorption of the microelement in the intestines.
Daily iron requirement
- up to 6 months – 0.3;
- 7-11 months – 11;
- up to 3 years – 7;
- up to 13 years old – 8–10.
Teenagers:
- from 14 to 18 years (boys) – 11; girls – 15.
Adults:
- men – 8–10;
- women under 50 years old – 15–18; over 50 years old – 8–10, pregnant women – 25–27.
Why is iron deficiency dangerous in the body?
A lack of iron in the body is dangerous due to the following conditions:
- acute anemia, or anemia - a decrease in the concentration of hemoglobin in the blood, which also reduces the number of red blood cells and changes their qualitative composition. The result of anemia is a decrease in the respiratory function of the blood and the development of oxygen starvation of tissues. Acute anemia can be recognized by pale skin and increased fatigue. Weakness, regular headaches and dizziness are signs of iron deficiency. Tachycardia (rapid heartbeat) and shortness of breath are harbingers of problems with the heart and lungs;
- fatigue and muscle weakness;
- excessive menstrual bleeding in women.
Lack of iron in the body leads to deterioration of the skin, brittle nails, and hair loss. Memory impairment and increased irritability are signs of iron deficiency. Decreased performance and constant drowsiness are harbingers of oxygen starvation.
Iron deficiency can be caused by the following factors:
- increased blood loss. The root cause of this scenario may be donor blood transfusion, excessive bleeding in women and soft tissue damage;
- intense aerobic and aerobic-strength physical activity (those that develop endurance). During such exercises, red blood cells have to carry oxygen faster, as a result of which the daily hemoglobin consumption can almost double;
- active mental activity. During creative work, not only iron reserves are actively consumed, but also glycogen stored in the liver and muscles;
- diseases of the gastrointestinal tract: gastritis with low acidity, duodenal ulcer, cirrhosis of the liver, autoimmune intestinal diseases provoke poor absorption of iron.
How to quickly replenish iron deficiency
To compensate for iron deficiency in the body, nutritionists recommend consuming foods of plant and animal origin. The former are a source of so-called “non-heme” iron, that is, iron that is not part of hemoglobin. In such products, iron is usually combined with vitamin C.
The best ways to replenish iron deficiency are non-heme foods such as legumes and green leafy vegetables, as well as whole grains.
“Heme” products contain iron, which is part of hemoglobin. The largest reserves of hemoglobin are characteristic of all foods of animal origin, as well as seafood. Unlike “non-heme” products, “heme” products replenish iron reserves faster, since the body absorbs them more easily.
Advice! Despite the fact that “heme” products are absorbed faster by the body, you should not get too carried away with them. To replenish iron stores, it is best to combine plant and animal foods, such as green leafy vegetables and red meats.
However, it is important to remember the secrets of cooking, because the final percentage of iron in food depends on the cooking methods. For example, whole grains lose about 75% of their iron reserves during processing. This is why whole grain flour has virtually no benefits for the body. Approximately the same thing happens when cooking food of plant origin by boiling - part of the iron remains in the water. If you cook spinach for 3 minutes, no more than 10% of your iron reserves will remain.
If you want to get the most benefit from plant-based foods, try to avoid long-term cooking and minimize the amount of water. The ideal cooking method is steamed.
With products of animal origin, everything is much simpler - iron, which is part of hemoglobin, is highly resistant to heat treatment.
What you need to know about excess iron in the body
It would be unfair to assume that the health hazard is solely due to iron deficiency. Its excess is also fraught with unpleasant symptoms. Due to excessive accumulation of iron in the body, the functioning of many functional systems is disrupted.
Causes of overdose. Most often, the cause of an increased concentration of a microelement is a genetic failure, as a result of which the absorption of iron by the intestine increases. Less commonly, large amounts of blood transfusion and uncontrolled use of iron-containing drugs. The latter happens when you independently increase the dose of an iron-containing drug when you miss the next dose.
When there is excess iron in the body, this usually happens:
- skin pigmentation changes (symptoms are often confused with hepatitis) - palms and armpits turn yellow, old scars darken. The sclera, roof of the mouth and tongue also acquire a yellowish tint;
- heart rhythm is disturbed, the liver enlarges;
- appetite decreases, fatigue increases, headache attacks become more frequent;
- the functioning of the digestive organs is disrupted - nausea and vomiting alternate with diarrhea, aching pain appears in the stomach area;
- immunity decreases;
- the likelihood of developing infectious and tumor pathologies increases, for example, liver and intestinal cancer, as well as the development of rheumatoid arthritis.
Preparations containing iron
Iron preparations include medications containing salts and complexes of microelement compounds, as well as its combinations with other minerals.
To avoid pathological conditions and complications, iron-containing drugs should be taken only as prescribed by a doctor after a series of tests. Otherwise, excess iron can lead to disruption of the heart, liver, stomach, intestines and brain.
- wash down with a small amount of water;
- incompatible with calcium supplements, Tetracycline, Levomycetin, as well as antacids (Almagel, Phosphalugel, etc.);
- taken in strict dosage. If for some reason the next dose of the drug was missed, the next dose remains unchanged. An overdose of iron (300 milligrams per day) can be fatal;
- The minimum course is two months. During the first month, hemoglobin and red blood cell levels normalize. In the future, taking medications is aimed at replenishing iron reserves (filling the “depot”). The dosage is reduced during the second month.
It should be remembered that even if all precautions are taken, taking iron-containing drugs can cause side effects such as skin flushing, nausea, loss of appetite, drowsiness, headache, digestive disorders (constipation, diarrhea, intestinal colic, heartburn and belching), metallic taste in the mouth. In some cases, teeth may darken (the oral cavity contains hydrogen sulfide, which, when interacting with iron, is converted into iron sulfide).
Advice! To avoid darkening of teeth (especially important for caries), immediately after taking iron-containing preparations, the mouth should be rinsed. If the drug is available in liquid dosage form, it is best to take it through a straw. If any of these symptoms occur, the medication should be stopped immediately
An overview of iron-containing products is given below.
Among the most frequently prescribed iron preparations are Conferon, Feracryl, Ferrum lek, Gemostimulin. Their advantages are the most accurate dosage and minimum side effects.
The dosage of the drug is calculated individually - 2 mg per 1 kg of the patient’s body weight (but not more than 250 mg per day). For better absorption, medications are taken with food, with a small amount of liquid.
Positive changes (an increase in the number of reticulocytes) are diagnosed within a week after starting to take the medication. After another two to three weeks, the hemoglobin concentration increases.
| A drug | Release form | Compound |
| Hemoferprolongatum | Film-coated tablets, weighing 325 mg | Ferrous sulfate, in one tablet – 105 mg Fe2+ |
| Tardiferon | Long-acting tablets | Mucoproteosis and ascorbic acid, in one tablet – 80 mg Fe2+ |
| Ferrogluconate and Ferronal | Tablets 300 mg | Iron gluconate, per tablet – 35 mg Fe2+ |
| Ferrogradumet | Film-coated tablets | Iron sulfate plus plastic matrix – gradumet, in one tablet – 105 mg Fe2+ |
| Heferol | 350 mg capsules | Fumaric acid, one tablet – 100 mg Fe2+ |
| Aktiferrin | Capsules, oral drops, syrup | Ferrous sulfate, D, L-serine (capsules and oral drops) and ferrous sulfate, D, L-serine, glucose, fructose, potassium sorbate (syrup). In 1 capsule and 1 ml of syrup - 38.2 mg Fe2+, in 1 ml drops, in 1 ml of syrup - and 34.2 mg Fe2+ |
| Gemsineral-TD | Capsules | Microgranules of iron fumarate, folic acid, cyanocobalamin. One capsule – 67 mg Fe2+ |
| Gyno-tardiferon | Pills | Ferrous sulfate, folic and ascorbic acids, mucoproteosis. One tablet contains 80 mg Fe2+ |
| Globiron | Gelatin capsules 300 mg | Iron fumarate, vitamins B6, B12, folic acid, sodium docusate. One capsule – 100 mg Fe2+ |
| Ranferon-12 | 300 mg capsules | Iron fumarate, ascorbic and folic acids, cyanocobalamin, zinc sulfate, iron ammonium citrate. One capsule – 100 mg Fe2+ |
| Sorbiferdurules | Film-coated tablets with prolonged release of iron ions | Iron sulfate, ascorbic acid, matrix (durules). One tablet contains 100 mg Fe2+ |
| Totema | Oral solution in ampoules of 10 ml | Iron gluconate, manganese, copper, as well as benzoate, sodium citrate and sucrose. One ampoule – 50 mg Fe2+ |
| Heferol | 350 mg capsules | Fumaric acid. One capsule – 100 mg Fe2+ |
| Fenyuls | Capsules | Iron sulfate, folic and ascorbic acids, thiamine. And also riboflavin, cyanocobalamin, pyridoxine, fructose, cysteine, calcium pantothenate, yeast. One capsule – 45 mg Fe2+ |
Contraindications to taking iron-containing drugs
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Conditional contraindications: |
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Iron injections and their features are described below. In addition to iron-containing capsules and tablets, injections are prescribed. Their use is necessary when:
- chronic pathologies of the digestive system, accompanied by reduced absorption of iron. Diagnoses: pancreatitis (inflammation of the pancreas), malabsorption syndrome, celiac disease, enteritis;
- ulcerative colitis of a nonspecific nature;
- intolerance to iron salts or hypersensitivity with allergic manifestations;
- peptic ulcer of the stomach and duodenum during periods of exacerbation;
- postoperative period after removal of part of the stomach or small intestine.
The advantage of injections is the rapid and maximum saturation with iron compared to other forms of drug release.
Important! When taking tablets and capsules, the maximum dose should not exceed 20-50 mg (lethal outcome is possible when taking 300 mg of iron). When injected, the maximum dose is considered to be 100 mg of iron.
Side effects when administering iron by injection: compaction (infiltrates) of tissue at the site of drug administration, phlebitis, abscesses, allergic reaction (in the worst case, anaphylactic shock immediately develops), disseminated intravascular coagulation syndrome, iron overdose.
Types of drugs are shown in the table
| A drug | Release form | Compound |
| Ferrum Lek (intramuscular) | Ampoules 2 ml | Iron hydroxide and dextran. One ampoule – 100 mg Fe2+ |
| Venofer (intravenous) | Ampoules 5 ml | Iron hydroxide sucrose complexes. One ampoule – 100 mg Fe2+ |
| Ferkoven (intravenously) | Ampoules 1 ml | Iron saccharate, carbohydrate solution and cobalt gluconate. One ampoule – 100 mg Fe2+ |
| Jectofer (intramuscular) | Ampoules 2 ml | Iron-sorbitol-citric acid complex |
| Ferrlecite (solution – intramuscular, ampoules – intravenous) | Solution for injection in ampoules of 1 and 5 ml | Iron gluconate complex |
| Ferbitol (intramuscular) | Ampoules 1 ml | Iron sorbitol complex |
DEFINITION
Iron- the twenty-sixth element of the Periodic Table. Designation - Fe from the Latin "ferrum". Located in the fourth period, VIIIB group. Refers to metals. The nuclear charge is 26.
Iron is the most common metal on the globe after aluminum: it makes up 4% (wt.) of the earth's crust. Iron is found in the form of various compounds: oxides, sulfides, silicates. Iron is found in its free state only in meteorites.
The most important iron ores include magnetic iron ore Fe 3 O 4 , red iron ore Fe 2 O 3 , brown iron ore 2Fe 2 O 3 × 3H 2 O and spar iron ore FeCO 3 .
Iron is a silvery (Fig. 1) ductile metal. It lends itself well to forging, rolling and other types of machining. The mechanical properties of iron strongly depend on its purity - on the content of even very small quantities of other elements in it.
Rice. 1. Iron. Appearance.
Atomic and molecular mass of iron
Relative molecular weight of the substance(M r) is a number showing how many times the mass of a given molecule is greater than 1/12 the mass of a carbon atom, and relative atomic mass of an element(A r) - how many times the average mass of atoms of a chemical element is greater than 1/12 of the mass of a carbon atom.
Since in the free state iron exists in the form of monatomic Fe molecules, the values of its atomic and molecular masses coincide. They are equal to 55.847.
Allotropy and allotropic modifications of iron
Iron forms two crystalline modifications: α-iron and γ-iron. The first of them has a body-centered cubic lattice, the second has a face-centered cubic lattice. α-Iron is thermodynamically stable in two temperature ranges: below 912 o C and from 1394 o C to the melting point. The melting point of iron is 1539 ± 5 o C. Between 912 o C and from 1394 o C γ-iron is stable.
The temperature ranges of stability of α- and γ-iron are determined by the nature of the change in the Gibbs energy of both modifications with temperature changes. At temperatures below 912 o C and above 1394 o C, the Gibbs energy of α-iron is less than the Gibbs energy of γ-iron, and in the range 912 - 1394 o C it is greater.
Isotopes of iron
It is known that in nature iron can be found in the form of four stable isotopes 54 Fe, 56 Fe, 57 Fe and 57 Fe. Their mass numbers are 54, 56, 57 and 58, respectively. The nucleus of an atom of the iron isotope 54 Fe contains twenty-six protons and twenty-eight neutrons, and the remaining isotopes differ from it only in the number of neutrons.
There are artificial isotopes of iron with mass numbers from 45 to 72, as well as 6 isomeric states of nuclei. The longest-lived among the above isotopes is 60 Fe with a half-life of 2.6 million years.
Iron ions
The electronic formula demonstrating the orbital distribution of iron electrons is as follows:
1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2 .
As a result of chemical interaction, iron gives up its valence electrons, i.e. is their donor, and turns into a positively charged ion:
Fe 0 -2e → Fe 2+ ;
Fe 0 -3e → Fe 3+.
Iron molecule and atom
In the free state, iron exists in the form of monoatomic Fe molecules. Here are some properties characterizing the iron atom and molecule:
Iron alloys
Until the 19th century, iron alloys were mainly known for their alloys with carbon, called steel and cast iron. However, later new iron-based alloys containing chromium, nickel and other elements were created. Currently, iron alloys are divided into carbon steels, cast irons, alloy steels and steels with special properties.
In technology, iron alloys are usually called ferrous metals, and their production is called ferrous metallurgy.
Examples of problem solving
EXAMPLE 1
| Exercise | The elemental composition of the substance is as follows: mass fraction of the iron element is 0.7241 (or 72.41%), mass fraction of oxygen is 0.2759 (or 27.59%). Derive the chemical formula. |
| Solution | The mass fraction of element X in a molecule of the composition NX is calculated using the following formula: ω (X) = n × Ar (X) / M (HX) × 100%. Let us denote the number of iron atoms in the molecule by “x”, the number of oxygen atoms by “y”. Let us find the corresponding relative atomic masses of the elements iron and oxygen (we will round the values of the relative atomic masses taken from D.I. Mendeleev’s Periodic Table to whole numbers). Ar(Fe) = 56; Ar(O) = 16. We divide the percentage content of elements into the corresponding relative atomic masses. Thus we will find the relationship between the number of atoms in the molecule of the compound: x:y= ω(Fe)/Ar(Fe) : ω(O)/Ar(O); x:y = 72.41/56: 27.59/16; x:y = 1.29: 1.84. Let’s take the smallest number as one (i.e., divide all numbers by the smallest number 1.29): 1,29/1,29: 1,84/1,29; Consequently, the simplest formula for the combination of iron and oxygen is Fe 2 O 3. |
| Answer | Fe2O3 |
Pure iron is obtained by various methods. The most important method is the thermal decomposition of iron pentacarbonyl (see § 193) and the electrolysis of aqueous solutions of its salts.
In humid air, iron quickly rusts, that is, it becomes covered with a brown coating of hydrated iron oxide, which, due to its friability, does not protect the iron from further oxidation. In water, iron corrodes intensely; with abundant access to oxygen, hydrate forms of iron(III) oxide are formed:
When there is a lack of oxygen or when its access is difficult, mixed oxide Fe 3 O 4 (FeO Fe 2 O 3) is formed:
Iron dissolves in hydrochloric acid of any concentration:
Dissolution in dilute sulfuric acid occurs similarly:
In concentrated solutions of sulfuric acid, iron is oxidized to iron(III):
However, in sulfuric acid, the concentration of which is close to 100%, iron becomes passive and practically no interaction occurs.
Iron dissolves in dilute and moderately concentrated solutions of nitric acid:
At high concentrations of HNO 3, dissolution slows down and iron becomes passive.
Iron is characterized by two series of compounds: iron(II) compounds and iron(III) compounds. The first correspond to iron (II) oxide, or ferrous oxide, FeO, the second - to iron (III) oxide, or iron oxide, Fe 2 O 3.
In addition, salts of iron acid H 2 FeO 4 are known, in which the oxidation state of iron is +6.
Iron(II) compounds.
Iron(II) salts are formed when iron is dissolved in dilute acids other than nitric acid. The most important of them is iron(II) sulfate, or ferrous sulfate, FeSO 4 · 7H 2 O, which forms light green crystals that are highly soluble in water. In air, iron sulfate gradually erodes and at the same time oxidizes from the surface, turning into a yellow-brown basic iron(III) salt.
Iron(II) sulfate is prepared by dissolving steel scraps in 20-30% sulfuric acid:
Iron(II) sulfate is used to control plant pests, in the production of inks and mineral paints, and in textile dyeing.
When ferrous sulfate is heated, water is released and a white mass of anhydrous salt FeSO 4 is obtained. At temperatures above 480°C, the anhydrous salt decomposes to release sulfur dioxide and sulfur trioxide; the latter in humid air forms heavy white vapors of sulfuric acid:
When a solution of an iron(II) salt reacts with an alkali, a white precipitate of iron(II) hydroxide Fe(OH) 2 precipitates, which in air due to oxidation quickly takes on a greenish and then brown color, turning into iron (III) hydroxide.
Anhydrous iron(II) oxide FeO can be obtained in the form of a black, easily oxidized powder by reducing iron(III) oxide with carbon(II) oxide at 500°C:
Alkali metal carbonates precipitate white iron(II) carbonate FeCO 3 from solutions of iron(II) salts. When exposed to water containing CO 2 , iron carbonate, like calcium carbonate, partially transforms into the more soluble acidic salt Fe(HCO 3) 2 . Iron is found in the form of this salt in natural ferruginous waters.
Iron (II) salts can easily be converted into iron (III) salts by the action of various oxidizing agents - nitric acid, potassium permanganate, chlorine, for example:
Due to their ability to oxidize easily, iron(II) salts are often used as reducing agents.
Iron (III) compounds.
Iron (III) chloride FeCl 3 is a dark brown crystal with a greenish tint. This substance is highly hygroscopic; absorbing moisture from the air, it turns into crystalline hydrates containing varying amounts of water and spreading in the air. In this state, iron (III) chloride has a brown-orange color. In a dilute solution, FeCl 3 hydrolyzes to basic salts. In vapor, iron (III) chloride has a structure similar to that of aluminum chloride (p. 615) and corresponds to the formula Fe 2 Cl 6; noticeable dissociation of Fe 2 Cl 6 into FeCl 3 molecules begins at temperatures around 500°C.
Iron (III) chloride is used as a coagulant in water purification, as a catalyst in the synthesis of organic substances, and in the textile industry.
Iron (III) sulfate Fe 2 (SO 4) 3 - very hygroscopic, white crystals that diffuse in air. Forms crystalline hydrate Fe 2 (SO 4) 3 · 9H 2 O (yellow crystals). In aqueous solutions, iron (III) sulfate is highly hydrolyzed. With alkali metal and ammonium sulfates, it forms double salts - alum, for example ferric ammonium alum (NH 4) Fe (SO 4) 2 · 12H 2 O - light purple crystals that are highly soluble in water. When heated above 500°C, iron (III) sulfate decomposes according to the equation:
Iron (III) sulfate is used, like FeCl 3 , as a coagulant in water purification, as well as for etching metals. A solution of Fe 2 (SO 4) 3 is capable of dissolving Cu 2 S and CuS to form copper(II) sulfate; this is used in the hydrometallurgical production of copper.
When alkalis act on solutions of iron (III) salts, red-brown iron (III) hydroxide Fe(OH) 3, insoluble in excess alkali, precipitates.
Iron (III) hydroxide is a weaker base than iron (II) hydroxide; this is expressed in the fact that iron (III) salts are strongly hydrolyzed, and with weak acids (for example, carbonic, hydrogen sulfide) Fe(OH) 3 salts do not form . Hydrolysis also explains the color of solutions of iron (III) salts: despite the fact that Fe 3+ is almost colorless, solutions containing it are colored yellow-brown, which is explained by the presence of hydroxo-ions of iron or Fe(OH) 3 molecules, which are formed due to hydrolysis:
When heated, the color darkens, and when acids are added it becomes lighter due to the suppression of hydrolysis.
When calcined, iron (III) hydroxide, losing water, turns into iron (III) oxide, or iron oxide, Fe 2 O 3. Iron(III) oxide occurs naturally in the form of red iron ore and is used as a brown paint - red lead, or mummy.
A characteristic reaction that distinguishes iron (III) salts from iron (II) salts is the effect of potassium thiocyanate KSCN or ammonium thiocyanate NH 4 SCN on iron salts. A solution of potassium thiocyanate contains colorless SCN - ions, which combine with Fe(III) ions, forming blood-red, weakly dissociated iron(III) thiocyanate Fe(SCN) 3 . When interacting with thiocyanates of iron (II) ions, the solution remains colorless.
Iron cyanide compounds. When solutions of iron (II) salts are exposed to soluble cyanides, for example potassium cyanide, a white precipitate of iron (II) cyanide is obtained:
In an excess of potassium cyanide, the precipitate dissolves due to the formation of the complex salt K 4 of potassium hexacyanoferrate (II)
Potassium hexacyanoferrate(II) K 4 ·3H 2 O crystallizes in the form of large light yellow prisms. This salt is also called yellow blood salt. When dissolved in water, salt dissociates into potassium ions and extremely stable complex 4- ions. In practice, such a solution does not contain Fe 2+ ions at all and does not give reactions characteristic of iron(II).
Potassium hexacyanoferrate (II) serves as a sensitive reagent for iron (III) ions, since 4- ions, interacting with Fe 3+ ions, form a water-insoluble salt of iron (III) hexacyanoferrate (III) Fe 4 3 of a characteristic blue color; This salt is called Prussian blue:
Prussian blue is used as a paint.
When chlorine or bromine acts on a solution of yellow blood salt, its anion is oxidized, turning into 3-
The salt K3 corresponding to this anion is called potassium hexacyanoferrate(III), or red blood salt. It forms red anhydrous crystals.
If you apply potassium hexacyanoferrate(III) to a solution of iron(II) salt, you get a precipitate of hexacyanoferrate(III), iron(I) (Turnboole blue), which looks very similar to Prussian blue, but has a different composition:
With iron (III) salts, K 3 forms a greenish-brown solution.
In most other complex compounds, as in the cyanoferrates considered, the coordination number of iron(II) and iron(III) is six.
Ferrites. When iron(III) oxide is fused with sodium or potassium carbonates, ferrites are formed - salts of ferrous acid HFeO 2 not obtained in a free state, for example sodium ferrite NaFeO 2:
When the alloy is dissolved in water, a red-violet solution is obtained, from which the water-insoluble barium ferrate BaFeO 4 can be precipitated by the action of barium chloride.
All ferrates are very strong oxidizing agents (stronger than permanganates). Iron acid H 2 FeO 4 corresponding to ferrates and its anhydride FeO 3 in the free state have not been obtained.
Iron carbonyls. Iron forms volatile compounds with carbon monoxide called iron carbonyls. Iron pentacarbonyl Fe(CO) 5 is a pale yellow liquid, boiling at 105°C, insoluble in water, but soluble in many organic solvents. Fe(CO) 5 is obtained by passing CO over iron powder at 150-200°C and a pressure of 10 MPa. The impurities contained in iron do not react with CO, resulting in a very pure product. When heated in a vacuum, iron pentacarbonyl decomposes into iron and CO; this is used to produce high-purity powdered iron - carbonyl iron (see § 193).
The nature of chemical bonds in the Fe(CO) 5 molecule is discussed on page 430.
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