What color is iron. III

The first products made of iron and its alloys were found during excavations and date back to about the 4th millennium BC. That is, even the ancient Egyptians and Sumerians used meteorite deposits of this substance to make jewelry and household items, as well as weapons.

Today, various kinds of iron compounds, as well as pure metal, are the most common and used substances. No wonder the 20th century was considered iron. After all, before the advent and widespread use of plastic and related materials, it was this compound that was of decisive importance for humans. What is this element and what substances it forms, we will consider in this article.

Chemical element iron

If we consider the structure of the atom, then first of all we should indicate its location in the periodic system.

1. Ordinal number - 26.
2. The period is the fourth big one.
3. The eighth group, the secondary subgroup.
4. The atomic weight is 55.847.
5. The structure of the outer electron shell is denoted by the formula 3d 6 4s 2 .
6. - Fe.
7. The name is iron, the reading in the formula is "ferrum".
8. In nature, there are four stable isotopes of the element in question with mass numbers 54, 56, 57, 58.

The chemical element iron also has about 20 different isotopes that are not stable. The possible oxidation states that a given atom can exhibit are:

Not only the element itself is important, but also its various compounds and alloys.

Physical properties

As a simple substance, iron has a pronounced metallicity. That is, it is a silvery-white metal with a gray tint, which has a high degree of ductility and ductility and a high melting and boiling point. If we consider the characteristics in more detail, then:

• melting point - 1539 0 С;
• boiling - 2862 0 С;
• activity - average;
• refractoriness - high;
• exhibits pronounced magnetic properties.

Depending on the conditions and different temperatures, there are several modifications that iron forms. Their physical properties differ from the fact that the crystal lattices differ.

All modifications have different types of structure of crystal lattices, and also differ in magnetic properties.

Chemical properties

As mentioned above, the simple substance iron exhibits medium chemical activity. However, in a finely dispersed state, it is capable of self-ignition in air, and the metal itself burns out in pure oxygen.

The corrosion ability is high, so the alloys of this substance are coated with alloying compounds. Iron is able to interact with:

• acids;
• oxygen (including air);
• gray;
• halogens;
• when heated - with nitrogen, phosphorus, carbon and silicon;
• with salts of less active metals, reducing them to simple substances;
• with sharp water vapor;
• with iron salts in the oxidation state +3.

It is obvious that, showing such activity, the metal is able to form various compounds, diverse and polar in properties. And so it happens. Iron and its compounds are extremely diverse and are used in various branches of science, technology, and industrial human activity.

Distribution in nature

Natural iron compounds are quite common, because it is the second most common element on our planet after aluminum. At the same time, in its pure form, the metal is extremely rare, as part of meteorites, which indicates its large accumulations in space. The main mass is contained in the composition of ores, rocks and minerals.

If we talk about the percentage of the element in question in nature, then the following figures can be given.

1. The cores of the terrestrial planets - 90%.
2. In the earth's crust - 5%.
3. In the Earth's mantle - 12%.
4. In the earth's core - 86%.
5. In river water - 2 mg/l.
6. In the sea and ocean - 0.02 mg / l.

The most common iron compounds form the following minerals:

• magnetite;
• limonite or brown iron ore;
• vivianite;
• pyrrhotite;
• pyrite;
• siderite;
• marcasite;
• lellingite;
• mispikel;
• milanterite and others.

This is still a long list, because there are really a lot of them. In addition, various alloys that are created by man are widespread. These are also such iron compounds, without which it is difficult to imagine the modern life of people. These include two main types:

• cast irons;
• become.

Iron is also a valuable addition to many nickel alloys.

Iron(II) compounds

These include those in which the oxidation state of the forming element is +2. They are quite numerous, because they include:

• oxide;
• hydroxide;
• binary compounds;
• complex salts;
• complex compounds.

The formulas of chemical compounds in which iron exhibits the indicated degree of oxidation are individual for each class. Consider the most important and common of them.

1. Iron(II) oxide. Black powder, insoluble in water. The nature of the connection is basic. It is able to quickly oxidize, however, it can also be easily reduced to a simple substance. It dissolves in acids to form the corresponding salts. Formula - FeO.
2. Iron(II) hydroxide. It is a white amorphous precipitate. Formed by the reaction of salts with bases (alkalis). It shows weak basic properties, is able to quickly oxidize in air to iron compounds +3. Formula - Fe (OH) 2.
3. The salts of an element in the specified oxidation state. As a rule, they have a pale green color of the solution, oxidize well even in air, acquiring and turning into iron salts 3. They dissolve in water. Examples of compounds: FeCL 2 , FeSO 4 , Fe(NO 3) 2 .

   

   Several compounds are of practical importance among the designated substances. First, (II). This is the main supplier of ions to the human body with anemia. When such an ailment is diagnosed in a patient, he is prescribed complex preparations, which are based on the compound in question. This is how iron deficiency in the body is replenished.

   Secondly, that is, iron (II) sulfate, together with copper, is used to destroy agricultural pests in crops. The method has been proving its effectiveness for more than a dozen years, therefore it is very much appreciated by gardeners and gardeners.

   Mora Salt

   This is a compound that is a crystalline hydrate of iron and ammonium sulfate. Its formula is written as FeSO 4 * (NH 4) 2 SO 4 * 6H 2 O. One of the iron (II) compounds, which has been widely used in practice. The main areas of human use are as follows.

   1. Pharmaceutics.
   2. Scientific research and laboratory titrimetric analyzes (to determine the content of chromium, potassium permanganate, vanadium).
   3. Medicine - as an additive to food with a lack of iron in the patient's body.
   4. For impregnation of wooden products, as Mora salt protects against decay processes.

   There are other areas in which this substance finds application. It got its name in honor of the German chemist who first discovered the manifested properties.

   Substances with an oxidation state of iron (III)

   The properties of iron compounds, in which it exhibits an oxidation state of +3, are somewhat different from those discussed above. Thus, the nature of the corresponding oxide and hydroxide is no longer basic, but pronounced amphoteric. We give a description of the main substances.

   
   

   Among the examples given, from a practical point of view, such a crystalline hydrate as FeCL 3 * 6H 2 O, or iron (III) chloride hexahydrate, is important. It is used in medicine to stop bleeding and replenish iron ions in the body with anemia.

   Iron(III) sulfate pentahydrate is used to purify drinking water, as it behaves as a coagulant.

   Iron(VI) compounds

   The formulas of the chemical compounds of iron, where it exhibits a special oxidation state of +6, can be written as follows:

   • K 2 FeO 4 ;
   • Na 2 FeO 4 ;
   • MgFeO 4 and others.

   All of them have a common name - ferrates - and have similar properties (strong reducing agents). They are also able to disinfect and have a bactericidal effect. This allows them to be used for the treatment of drinking water on an industrial scale.

   Complex compounds

   Special substances are very important in analytical chemistry and not only. Those that form in aqueous solutions of salts. These are complex compounds of iron. The most popular and well-studied of them are as follows.

   1. Potassium hexacyanoferrate (II) K 4 . Another name for the compound is yellow blood salt. It is used for qualitative determination of iron ion Fe 3+ in solution. As a result of exposure, the solution acquires a beautiful bright blue color, since another complex is formed - Prussian blue KFe 3+. Since ancient times it has been used as
   2. Potassium hexacyanoferrate (III) K 3 . Another name is red blood salt. It is used as a qualitative reagent for the determination of iron ions Fe 2+ . As a result, a blue precipitate is formed, which is called Turnbull blue. Also used as a dye for fabric.

   

   Iron in organic matter

   Iron and its compounds, as we have already seen, are of great practical importance in the economic life of man. However, in addition to this, its biological role in the body is no less great, on the contrary.

   There is one very important protein, which includes this element. This is hemoglobin. It is thanks to him that oxygen is transported and uniform and timely gas exchange is carried out. Therefore, the role of iron in the vital process - respiration - is simply enormous.

   

   In total, the human body contains about 4 grams of iron, which must be constantly replenished through the food consumed.

Iron(Latin ferrum), fe, a chemical element of group viii of Mendeleev's periodic system; atomic number 26, atomic mass 55.847; shiny silvery 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%).

History reference. Iron was known as early as prehistoric times, but it found wide application much later, since it is extremely rare in nature in the free state, and its production from ores became possible only at a certain level of technological development. Probably, for the first time, a person became acquainted with meteoric 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 sideris) - a star, a celestial body. In Hittite texts of the 14th century. BC e. Zh. is mentioned as a metal that fell from the sky. In the Romance languages, the root of the name given by the Romans has been preserved (for example, French fer, Italian ferro).

The method of obtaining iron from ores was invented in the western part of Asia in the 2nd millennium BC. e.; after that, the use of Zh. spread in Babylon, Egypt, and Greece; for changing Bronze Age came iron age. Homer (in the 23rd canto of the Iliad) relates that Achilles awarded the winner of a discus-throwing competition with an iron cry discus. In Europe and Ancient Russia for many centuries, Zh. received cheese process. Iron ore was reduced with charcoal in a furnace built in a pit; air was pumped into the furnace with bellows, the reduction product - kritsu was separated from the slag by hammer blows and various products were forged from it. As the methods of blowing were improved and the height of the hearth increased, the temperature of the process increased and part of the iron became carburized, i.e., it turned out cast iron; this relatively fragile product was considered a waste product. Hence the name pig iron, pig iron - English pig iron. Later it was noticed that when not iron ore, but cast iron is loaded into the furnace, low-carbon iron bloom is also obtained, and such a two-stage process turned out to be more profitable than raw-dough. 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-finished 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 become, which was known on the territory of Syria in the early period of the Middle Ages, but later turned out to be forgotten. With this method, steel was obtained by melting metal mixtures in small vessels (crucibles) from a highly refractory mass. In the last quarter of the 18th century The puddling process of redistribution of cast iron into iron began to develop on the hearth of a fiery reverberatory furnace. 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 an enormous demand for iron and its alloys. However, all existing methods of producing iron could not meet the needs of the market. Mass production of steel began only in the middle of the 19th century, when the Bessemer, Thomas, and open-hearth processes were developed. In the 20th century the electric steelmaking process arose and became widespread, giving high-quality steel.

distribution in nature. In terms of content in the lithosphere (4.65% by weight), aluminum ranks second among metals (aluminum is in first place). It migrates vigorously in the earth's crust, forming about 300 minerals (oxides, sulfides, silicates, carbonates, titanates, phosphates, etc.). Zh. takes an active part in magmatic, hydrothermal, and supergene processes, which are associated with the formation of various types of its deposits. Zh. - metal of the earth's depths, it accumulates in 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 trivalent 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 have red, yellow, brown colors. 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. Zh.'s value 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 both in a cold and heated state, can be rolled, stamped and drawn. The ability to dissolve carbon and other elements serves as the basis for obtaining various iron alloys.

Zh. 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 is stable with a bcc lattice (a = 2.86645 å at 20 °C). Between 910°C and 1400°C, the g-modification with the fcc lattice is stable (a = 3.64 å). Above 1400°C, the bcc lattice d-fe (a = 2.94 å) is again formed, which is stable up to the melting point (1539°C). a - fe ferromagnetic up to 769°C (Curie point). Modification g -fe and d -fe are paramagnetic.

Polymorphic transformations of iron and steel during heating and cooling were discovered in 1868 by D.K. Chernov. Carbon forms with J. solid solutions interstitials, in which C atoms with a small atomic radius (0.77 å) are located in the interstices of the metal crystal lattice, which consists of larger atoms (atomic radius fe 1.26 å). A solid solution of carbon in g -fe called. austenite, and in (a -fe- ferrite. Saturated solid solution of carbon in g - fe contains 2.0% C by mass 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 - 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) allows you to give the steel the required combination of hardness and ductility.

The physical properties of zinc depend on its purity. As a rule, industrial iron materials are accompanied by 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) - cold brittleness; carbon and nitrogen reduce plastic, and hydrogen increases fragility Zh. (so-called hydrogen brittleness). Reducing the content of impurities 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 zinc, relating mainly to a 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°C) 7.874 g/cm 3

t pl 1539°C

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 a liquid depends on its structure and varies with temperature in a complex way; 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

Relative elongation 45-55%

Brinell hardness 350-450 MN/m 2

Yield strength 100 MN/m 2

Impact strength 300 MN/m 2

The configuration of the outer electron shell of the atom fe 3 d 6 4s 2 . Zh. exhibits variable valency (the most stable compounds are 2- and 3-valent Zh.). With oxygen, iron forms feo oxide, fe 2 o 3 oxide, and fe 3 o 4 oxide (feo compound with fe 2 o 3 , having the structure spinels) . In humid air at ordinary temperatures, iron becomes covered with loose rust (fe 2 o 3 n h2o). 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 every year. When iron is heated in dry air above 200°C, it is covered with a very thin oxide film, which protects the metal from corrosion at ordinary temperatures; this is the basis of the technical method of protecting J. - bluing. When heated in water vapor, iron is oxidized to form fe 3 o 4 (below 570°C) or feo (above 570°C) and release hydrogen.

Hydroxide fe (oh) 2 is formed as a white precipitate by the action of caustic alkalis or ammonia on aqueous solutions of fe 2+ salts in an atmosphere of hydrogen or nitrogen. Upon contact with air, fe (oh) 2 first turns green, then blackens, and finally quickly turns into red-brown hydroxide fe (oh) 3 . Feo oxide exhibits basic properties. Oxide fe 2 o 3 amphoteric and has a weakly acidic function; reacting with more basic oxides (for example, with mgo), it forms ferrites - compounds of the type fe 2 o 3 n meo, which have ferromagnetic properties and are widely used in radio electronics. Acidic properties are also expressed in 6-valent iron, which exists in the form of ferrates, for example k 2 feo 4 , salts of iron acid not isolated in the free state.

Zh. easily reacts with halogens and hydrogen halides, giving salts, for example chlorides fecl 2 and fecl 3. When iron is heated with sulfur, 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 iron at high concentrations of carbon. Nitrogen, like carbon, gives interstitial solid solutions with iron; nitrides fe 4 n and fe 2 n stand out from them. With hydrogen, hydrogen gives 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).

Zh. compounds with many elements (O, s, etc.), which form a crystal structure, have a variable composition (for example, the sulfur content in monosulfide can range from 50 to 53.3 at.%). This is due to defects in the crystal structure. For example, in iron oxide, some of the fe 2+ ions at the lattice sites are replaced by fe 3+ ions; to maintain electrical neutrality, some lattice sites belonging to fe 2+ ions remain empty and the phase (wustite) under normal conditions has the formula fe 0.947 o.

Peculiarly, Zh.'s interaction with nitric acid. Concentrated hno 3 (density 1.45 g/cm 3) passivates iron due to the appearance of a protective oxide film on its surface; more dilute hno 3 dissolves iron with the formation of fe 2+ or fe 3+ ions, recovering to mh 3 or n 2 o and n 2 .

Solutions of salts of 2-valent iron are unstable in air - fe 2+ gradually oxidizes to fe 3+. Aqueous solutions of salts Zh. due to hydrolysis have an acid reaction. The addition of thiocyanate ions scn - to solutions of salts fe 3+ gives a bright blood-red color due to the appearance of fe (scn) 3, which makes it possible to reveal the presence of 1 part fe 3+ in about 10 6 parts of water. Zh. is characterized by education complex compounds.

Receipt and application. Pure iron is obtained in relatively small quantities by the 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 by means of its direct reduction from ore concentrates with hydrogen, natural gas, or coal at relatively low temperatures.

Zh. - the most important metal of modern technology. Iron is practically never used in its pure form 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 that are very different in composition and properties. Iron alloys account for approximately 95% of all metal products. Carbon-rich alloys (over 2% by weight) - cast iron, 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. New processes such as vacuum remelting, electroslag remelting, plasma and electron beam melting, etc., are used for the production of steels and iron alloys of particular importance. Methods are being developed for smelting steel in continuously operating units that ensure high quality of the metal and process automation.

On the basis of iron, materials are created that can withstand the effects of high and low temperatures, vacuum and high pressures, aggressive media, high alternating voltages, nuclear radiation, etc. The production of iron and its alloys is constantly growing. In 1971, 89.3 million tons were smelted in the USSR. t pig iron and 121 mln. t become.

L. A. Shvartsman, L. V. Vanyukova.

Iron as an artistic material has been used since antiquity in Egypt (a headstand from the tomb of Tutankhamen 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 items made of Zh. have been preserved in European countries (England, France, Italy, Russia, etc.) - forged fences, door hinges, wall brackets, weather vanes, chest fittings, svetets. Forged end-to-end products made of rods and products made of perforated sheet iron (often with a mica lining) are distinguished by planar forms, a clear linear graphic silhouette, and are effectively visible against a light-air background. In the 20th century Zh. is used for the manufacture of lattices, fences, openwork interior partitions, candlesticks, and monuments.

T. L.

Iron in the body. Zh. is present in the organisms of all animals and in plants (an average of about 0.02%); it is necessary mainly for oxygen exchange and oxidative processes. There are organisms (the so-called concentrators) that can accumulate it in large quantities (for example, iron bacteria - up to 17-20% W.). Almost all iron in animal and plant organisms is associated with proteins. Lack of Zh. causes a growth retardation and the phenomenon plant chlorosis, associated with lower education chlorophyll. Excess iron also has a harmful effect on the development of plants, causing, for example, sterility of rice flowers and chlorosis. In alkaline soils, iron compounds inaccessible to plant roots are formed, and the plants do not receive it in sufficient quantities; in acidic soils, iron passes into soluble compounds in excess. With a deficiency or excess of assimilable compounds in soils, plant diseases can be observed in large areas.

Zh. enters the body of animals and humans with food (liver, meat, eggs, legumes, bread, cereals, spinach, and beets are the richest in it). Normally, a person receives with a diet of 60-110 mg Zh., which significantly exceeds its daily requirement. Absorption of iron taken with food occurs in the upper part of the small intestines, from where it enters the bloodstream in a protein-bound form and is carried with blood to various organs and tissues, where it is deposited in the form of iron - a protein complex - ferritin. The main depot of iron in the body is the liver and spleen. Due to G. ferritin, the synthesis of all iron-containing compounds of the body occurs: a respiratory pigment is synthesized in the bone marrow hemoglobin, in the muscles myoglobin, in various tissues cytochromes and other iron-containing enzymes. Zh. is excreted from the body mainly through the wall of the large intestine (in humans, 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 F. per day. In animals, the need for fat is approximately (per 1 kg dry matter of the ration): 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, Zh. medicines (reconstituted Zh., lactate Zh., glycerophosphate Zh., sulfate of 2-valent Zh., Blo tablets, malic acid solution, feramid, hemostimulin, etc.) are used in the treatment of diseases accompanied by a lack of Zh. in the body (iron deficiency anemia), as well as general tonic (after infectious diseases, etc.). Zh. isotopes (52 fe, 55 fe, and 59 fe) are used as indicators in biomedical research and in the diagnosis of blood diseases (anemia, leukemia, polycythemia, etc.).

Lit.: General metallurgy, Moscow, 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, v. 2, M., 1963; Levinson N. R., [Products from 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: Trace elements, 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.

download abstract

DEFINITION

Iron is 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% (mass) of the earth's crust. Iron occurs in the form of various compounds: oxides, sulfides, silicates. Iron is found in the free state only in meteorites.

The most important ores of iron 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 amounts of other elements in it.

Rice. 1. Iron. Appearance.

Atomic and molecular weight of iron

Relative molecular weight of a substance(M r) is a number showing how many times the mass of a given molecule is greater than 1/12 of 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 are the same. 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 cubic body-centered lattice, the second - a cubic face-centered one. 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 1394 o C, γ-iron is stable.

The temperature ranges of stability of α- and γ-iron are due to the nature of the change in the Gibbs energy of both modifications with a change in temperature. 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 - more.

Isotopes of iron

It is known that iron can occur in nature in the form of four stable isotopes 54Fe, 56Fe, 57Fe, and 57Fe. 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 most long-lived among the above isotopes is 60 Fe with a half-life of 2.6 million years.

iron ions

The electronic formula showing the distribution of iron electrons over the orbits 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+.

Molecule and atom of iron

In the free state, iron exists in the form of monatomic Fe molecules. Here are some properties that characterize the atom and molecule of iron:

iron alloys

Until the 19th century, iron alloys were mainly known for their alloys with carbon, which received the names of steel and cast iron. However, in the future, new iron-based alloys containing chromium, nickel and other elements were created. At present, 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: the mass fraction of the iron element is 0.7241 (or 72.41%), the mass fraction of oxygen is 0.2759 (or 27.59%). Derive the chemical formula.
Solution	The mass fraction of the element X in the molecule of the HX composition is calculated by the following formula: ω (X) = n × Ar (X) / M (HX) × 100%. Let us denote the number of iron atoms in the molecule as "x", the number of oxygen atoms as "y". Let us find the corresponding relative atomic masses of the elements of iron and oxygen (the values ​​of the relative atomic masses taken from the Periodic Table of D.I. Mendeleev will be rounded to integers). Ar(Fe) = 56; Ar(O) = 16. We divide the percentage of elements by 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; Therefore, the simplest formula for the combination of iron with oxygen is Fe 2 O 3.
Answer	Fe2O3

Do you know that iron protects the planet from "space attacks"? Due to the huge accumulations of this element, the Earth's magnetic field is formed. Like a shield, the field protects her from asteroids...

Iron plays a role not only in such global things, but also in our daily life: steel and most alloys are created on the basis of this element. Thus, everything from cutlery to cars and microelectronics could not work without iron.

Finally, our life would be impossible without it, since this mineral is part of hemoglobin, the content of red blood cells, thanks to which tissues are able to use oxygen. There are many more useful properties hidden in this wonderful element. Read more about what the functions of iron for our health are in this article.

Iron content in foods (per 100 g):

Liver 10-20 mg
Yeast 18 mg
Seaweed 16 mg
Lentils 12 mg
Buckwheat 8.2 mg
Yolk 7.2 mg
Rabbit 4.4 mg
Black caviar 2.5 mg

What is iron?

This is metal. In the composition of organs and tissues, iron is in the approximate amount of 3-5 grams. This is not much, but such a small dose is quite enough for the body in order to successfully continue its existence. Four-fifths of all iron is in hemoglobin, the rest is dispersed throughout the body and distributed in the liver, muscles, bones, etc. Some of the internal iron is part of the enzymes.

Over time, there is a natural loss of the mineral, and therefore a person needs a constant supply of certain dosages of iron. It is lost in the urine and sweat fluid, and in women, iron consumption is also associated with monthly losses during menstruation.

Foods rich in iron

The element is so common in nature that iron is present in most foods. The best sources are animals - meat and liver. In them, iron is in the most digestible form. It is usually less in plant foods than in animal foods, but it is also an important source of the mineral. It is present in citrus fruits, pomegranates, beets, buckwheat, legumes, nuts, pumpkin, apples, sea kale, persimmons.

daily iron requirement

As a rule, men need more vitamins and minerals than women, but in this case, this is not the case: women need higher dosages of iron. They need 18 mg of the mineral, while men need about 10 mg. For children, the norm is not precisely defined, according to various sources, it can be from 4 to 15 mg.

Increased need for iron

An increased need for iron is inherent in the following groups of people:

Women during the period after menstruation. Blood loss, albeit small, requires compensation for the hemoglobin content in the blood.
. Pregnant and lactating. During pregnancy, there is a significant consumption of iron to build the body of the fetus, and nursing mothers spend their iron on feeding the child (it penetrates into breast milk). Literally every second pregnant woman has signs of iron deficiency, which indicates a significant increase in the need for this element in expectant mothers.
. After injuries, blood loss, major surgical operations.

Iron is a very valuable element. In this regard, the body has learned to use it repeatedly. With the natural destruction of old red blood cells, special carrier proteins capture the released iron and transfer it to the hematopoietic organs, where it is used again.

However, the loss of the mineral is still quite large, so that in everyday life, many people require additional use of iron. If you have an increased need for this element, you should start taking nutritional supplements containing this element.

Absorption of iron from food

Even under ideal conditions, no more than 10% of the incoming iron is absorbed from food. There are a number of factors that further reduce this figure. At the same time, there are certain factors that increase the absorption of the mineral. What determines the degree of absorption of iron?

1. Source. In animal products, iron is found in an easy-to-absorb bivalent form. In plants, it is trivalent. In order to assimilate it and “put it into motion”, the body must spend energy to restore the mineral to a divalent form. That is why most of the iron that came with buckwheat or pomegranate juice does not benefit the body.
2. Digestive health. With low acidity of gastric juice, gastritis and enteritis, the absorption of iron is significantly reduced. With a healthy digestive tract, it is optimal.
3. Composition of food.

4. Iron is better absorbed in the presence of vitamin C, vegetable and fruit organic acids, the amino acids lysine and histidine, and certain carbohydrates such as fructose and sorbitol. Thus, meat and liver should always be paired with a fresh vegetable salad.

5. Iron is absorbed worse in the presence of tannins, dietary fiber (they “collect” iron molecules on themselves and remove them from the body), phytin, oxalic acid. This means that if you're looking to get more iron, it's a good idea to avoid eating foods like legumes, sorrel, spinach, and bran too often. Calcium is a fairly strong antagonist of iron; products containing it (mainly dairy) inhibit its absorption.

The biological role of iron

The functions of iron are:

It is an indispensable element for hematopoiesis, a raw material for the formation of the respiratory pigment hemoglobin and the formation of red blood cells.
. Important for the synthesis of thyroid hormones
. Strengthens the immune system, increases the body's defenses
. Improves the work of some vitamins, such as vitamin B6, B12, B9
. Improves the effects of a number of trace elements such as cobalt, manganese, copper
. It is part of the enzymes that ensure the neutralization of harmful substances in the body
. Provides the possibility of tissue breathing, and this gives not only a health-improving, but also a cosmetic effect. With a normal intake of iron in the human body, the condition of the skin, hair, nails remains good
. Protects against overwork, chronic fatigue
. It is of great importance in the functioning of the nervous system.

Signs of iron deficiency

The lack of a mineral and the need for regular use of iron is an extremely common occurrence. The very first and main sign of an element deficiency in the body is anemia.

A decrease in the number of red blood cells and the level of hemoglobin in the blood leads to such symptoms: weakness, rapid onset of fatigue, instability to physical exertion, constipation or diarrhea, disturbances in appetite and taste, numbness and chilliness in the limbs, pallor and dry skin, deterioration of nails, hair loss , weakened immunity, etc. Often, it is these signs that allow us to guess about iron deficiency in the body. A person goes to the doctor, he is examined and anemia is detected.

Signs of excess iron

Even when eating foods containing high concentrations of iron, there is no excess of it. This is due to the fact that the body independently “filters” excess mineral compounds and takes exactly as much iron as it needs.

It is much more difficult for him to resist the ultra-high dosages of iron that come with the drugs. If you use iron products and nutritional supplements too intensively, poisoning may occur. It makes itself felt with vomiting, headache, stool disorders and other symptoms.

Excess iron is also seen in a rare condition called hemochromatosis. With this disease, the body carries out a pathological accumulation of iron, which is manifested by serious disorders of the liver and other organs.

Factors affecting the content of iron in foods

If food is cooked for a long time, the content of digestible iron in them decreases, as it passes into a form that is inaccessible for absorption. So if you're buying meat or liver, choose the highest quality products that won't be too tough and won't take too long to boil or fry.

DEFINITION

Iron- an element of the eighth group of the fourth period of the Periodic system of chemical elements of D. I. Mendeleev.

And the languid number is 26. The symbol is Fe (lat. “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 ductile. The electronic configuration of the external energy level is 3d 6 4s 2 . In its compounds, iron exhibits the 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 cubic body-centered lattice, the second has a cubic face-centered one. 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 in it of even very small amounts of other elements. Solid iron has the ability to dissolve many elements in itself.

Chemical properties of iron

In moist 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 intensively; with abundant access of oxygen, hydrated forms of iron oxide (III) are formed:

2Fe + 3/2O 2 + nH 2 O = Fe 2 O 3 × H 2 O.

With a lack of oxygen or with difficult access, a 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 \u003d FeCl 2 + H 2.

Similarly, dissolution occurs in dilute sulfuric acid:

Fe + H 2 SO 4 \u003d FeSO 4 + H 2.

In concentrated solutions of sulfuric acid, iron is oxidized to iron (III):

2Fe + 6H 2 SO 4 \u003d 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 there is practically no interaction. In dilute and moderately concentrated solutions of nitric acid, iron dissolves:

Fe + 4HNO 3 \u003d 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. The reactions of the interaction of iron with halogens (regardless of the type of halogen) proceed when heated. The interaction of iron with bromine proceeds at an increased vapor pressure of the latter:

2Fe + 3Cl 2 \u003d 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 able to react 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 able to reduce metals that are in the activity series to the right of it, from salt solutions (1), to reduce iron (III) compounds (2):

Fe + CuSO 4 \u003d 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 way to obtain 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 an excess of iron was added to the resulting solution. Determine the composition of the solution (in % by weight).

Solution

We write the reaction equations according to the condition of the problem: 8HCl + Fe 3 O 4 \u003d 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) \u003d 150 × 1.1 \u003d 165 g. Calculate the mass of hydrogen chloride: m(HCl)=msol(HCl)×ω(HCl)/100%; m(HCl) = 165 x 20%/100% = 33 g. The molar mass (mass of one mol) of hydrochloric acid, calculated using the table of chemical elements of D.I. Mendeleev - 36.5 g / mol. Find the amount of hydrogen chloride substance: v(HCl) = m(HCl)/M(HCl); v (HCl) \u003d 33 / 36.5 \u003d 0.904 mol. Molar mass (mass of one mole) of scale, calculated using the table of chemical elements of D.I. Mendeleev - 232 g/mol. Find the amount of scale substance: v (Fe 3 O 4) \u003d 10/232 \u003d 0.043 mol. According to equation 1, v(HCl): v(Fe 3 O 4) \u003d 1: 8, therefore, v (HCl) \u003d 8 v (Fe 3 O 4) \u003d 0.344 mol. Then, the amount of hydrogen chloride substance calculated according to the equation (0.344 mol) will be less than that indicated in the condition of the problem (0.904 mol). Therefore, hydrochloric acid is in excess and another reaction will proceed: Fe + 2HCl = FeCl 2 + H 2 (3). Let's determine the amount of iron chloride substance formed as a result of the first reaction (indices 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's determine the amount of hydrogen chloride that did not react in reaction 1 and the amount of iron (II) chloride substance formed during reaction 3: v rem (HCl) \u003d v (HCl) - v 1 (HCl) \u003d 0.904 - 0.344 \u003d 0.56 mol; v 3 (FeCl 2): ​​v rem (HCl) = 1:2; v 3 (FeCl 2) \u003d 1/2 × v rem (HCl) \u003d 0.28 mol. Let's 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) \u003d v 1 (FeCl 2) + v 2 (FeCl 2) + v 3 (FeCl 2) \u003d 0.043 + 0.129 + 0.28 \u003d 0.452 mol; m (FeCl 2) \u003d v sum (FeCl 2) × M (FeCl 2) \u003d 0.452 × 127 \u003d 57.404 g. Let us determine the amount of substance and the mass of iron that entered into reactions 2 and 3: v 2 (Fe): v 2 (FeCl 3) = 1:2; v 2 (Fe) \u003d 1/2 × v 2 (FeCl 3) \u003d 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) \u003d v 2 (Fe) + v 3 (Fe) \u003d 0.043 + 0.28 \u003d 0.323 mol; m(Fe) = v sum (Fe) ×M(Fe) = 0.323 ×56 = 18.088 g. Let us calculate the amount of substance and the mass of hydrogen released in reaction 3: v (H 2) \u003d 1/2 × v rem (HCl) \u003d 0.28 mol; m (H 2) \u003d v (H 2) × M (H 2) \u003d 0.28 × 2 \u003d 0.56 g. We determine the mass of the resulting solution m ' sol and the mass fraction of FeCl 2 in it: m’ sol \u003d m sol (HCl) + m (Fe 3 O 4) + m (Fe) - m (H 2);