What is the oxidation state of iron. Big encyclopedia of oil and gas

In the earth's crust, iron is widely distributed, accounting for about 4.1% of the mass. earth's crust(4th place among all elements, 2nd among metals). In the mantle and the earth's crust, iron is concentrated mainly in silicates, while its content is significant in basic and ultrabasic rocks, and low in acidic and intermediate rocks. A large number of ores and minerals containing iron are known. Of the greatest practical importance are red iron ore (hematite, Fe 2 O 3; contains up to 70% Fe), magnetic iron ore (magnetite, FeFe 2 O 4, Fe 3 O 4; contains 72.4% Fe), brown iron ore or limonite (goethite and hydrogoethite, respectively FeOOH and FeOOH nH 2 O) hematite magnetite limonite goethite

Siderite FeCO 3 contains approximately 35% iron. It has a yellowish white (with a gray or brown tint in case of contamination) color. Siderite Mispikel FeAsS contains 34.3% iron. Mispikel Löllingite FeAs 2 contains 27.2% iron Löllingite ilmenite FeTiO 3 ilmenite magnomagnetite (Fe, Mg) fibroferrite FeSO 4 (OH) 4.5H 2 O jarosite KFe 3 (SO 4) 2 (OH) 6 jarosite

The main oxidation states of iron are +2 and +3. When stored in air at temperatures up to 200 °C, iron is gradually covered with a dense film of oxide, which prevents further oxidation of the metal. In humid air, iron is covered with a loose layer of rust, which does not prevent the access of oxygen and moisture to the metal and its destruction. Rust has no permanent chemical composition, approximately chemical formula can be written as Fe 2 O 3 xH 2 O. rust oxide

Iron reacts with oxygen when heated. When iron is burned in air, oxide Fe 3 O 4 is formed, when combustion in pure oxygen, Fe 2 O 3 oxide. If oxygen or air is passed through molten iron, FeO oxide is formed. When sulfur and iron powder are heated, sulfide is formed, the approximate formula of which can be written as FeS. oxygenFe 3 O 4Fe 2 O 3 FeO sulfur

Story

Iron as an instrumental material has been known since ancient times. The oldest iron products found during archaeological excavations date back to the 4th millennium BC. e. and belong to the ancient Sumerian and ancient Egyptian civilizations. These are made of meteoric iron, that is, an alloy of iron and nickel (the content of the latter ranges from 5 to 30%), jewelry from Egyptian tombs (about 3800 BC) and a dagger from the Sumerian city of Ur (about 3100 BC). e.). Apparently, one of the names of iron in Greek and Latin: "sider" (which means "starry").

Products made of iron obtained by smelting have been known since the time of the settlement of the Aryan tribes from Europe to Asia, the islands mediterranean sea, and beyond (the end of the 4th and 3rd millennium BC). The oldest known iron tools are steel blades found in the masonry of the pyramid of Cheops in Egypt (built around 2530 BC). As excavations in the Nubian desert have shown, already in those days the Egyptians, trying to separate the mined gold from heavy magnetite sand, calcined ore with bran and similar substances containing carbon. As a result, a layer of doughy iron floated on the surface of the gold melt, which was processed separately. Tools were forged from this iron, including those found in the pyramid of Cheops. However, after the grandson of Cheops Menkaur (2471-2465 BC), turmoil occurred in Egypt: the nobility, led by the priests of the god Ra, overthrew the ruling dynasty, and a leapfrog of usurpers began, ending with the accession of the pharaoh of the next dynasty, Userkar, whom the priests declared to be the son and incarnation the god Ra himself (since then this has become the official status of the pharaohs). During this turmoil, the cultural and technical knowledge of the Egyptians fell into decay, and, just as the art of building the pyramids degraded, the technology of iron production was lost, to the point that later, while exploring the Sinai Peninsula in search of copper ore, the Egyptians did not pay any attention to iron ore deposits there, but received iron from neighboring Hittites and Mitannians.

The first mastered the production of iron Hatt, this is indicated by the oldest (2nd millennium BC) mention of iron in the texts of the Hittites, who founded their empire on the territory of the Hatt (modern Anatolia in Turkey). So, in the text of the Hittite king Anitta (about 1800 BC) it says:

When I went on a campaign to the city of Puruskhanda, a man from the city of Puruskhanda came to bow to me (...?) and he presented me with 1 iron throne and 1 iron scepter (?) as a sign of humility (?) ...

(source: Giorgadze G. G.// Bulletin ancient history. 1965. № 4.)

In ancient times, khalibs were reputed to be masters of iron products. The legend of the Argonauts (their campaign to Colchis took place about 50 years before the Trojan War) tells that the king of Colchis, Eet, gave Jason an iron plow to plow the field of Ares, and his subjects, the halibers, are described:

They do not plow the land, do not plant fruit trees, do not graze herds in rich meadows; they extract ore and iron from the uncultivated land and barter food for them. The day does not begin for them without hard work, they spend in the darkness of the night and thick smoke, working all day ...

Aristotle described their method of obtaining steel: “the Khalibs washed the river sand of their country several times - thereby separating black concentrate (a heavy fraction consisting mainly of magnetite and hematite), and melted it in furnaces; the metal thus obtained had a silvery color and was stainless."

Magnetite sands, which are often found along the entire coast of the Black Sea, were used as raw materials for steel smelting: these magnetite sands consist of a mixture of fine grains of magnetite, titanium-magnetite or ilmenite, and fragments of other rocks, so that the steel smelted by the Khalibs was alloyed, and had excellent properties. Such a peculiar way of obtaining iron suggests that the Khalibs only spread iron as a technological material, but their method could not be a method for the widespread industrial production of iron products. However, their production was the impetus for further development iron metallurgy.

In the deepest antiquity, iron was valued more than gold, and according to the description of Strabo, African tribes gave 10 pounds of gold for 1 pound of iron, and according to the studies of the historian G. Areshyan, the cost of copper, silver, gold and iron among the ancient Hittites was in the ratio 1: 160 : 1280: 6400. In those days, iron was used as a jewelry metal, thrones and other regalia of royal power were made from it: for example, in the biblical book Deuteronomy 3.11, an “iron bed” of the Rephaim king Og is described.

In the tomb of Tutankhamen (circa 1350 BC) was found a dagger made of iron in a gold frame - possibly a gift from the Hittites for diplomatic purposes. But the Hittites did not strive for the widespread dissemination of iron and its technologies, which is also evident from the correspondence that has come down to us. Egyptian pharaoh Tutankhamun and his father-in-law Hattusil, king of the Hittites. Pharaoh asks to send more iron, and the king of the Hittites evasively answers that the iron reserves have run out, and the blacksmiths are busy with agricultural work, so he cannot fulfill the request of the royal son-in-law, and sends only one dagger from “good iron” (that is, steel). As you can see, the Hittites tried to use their knowledge to achieve military advantages, and did not give others the opportunity to catch up with them. Apparently, therefore, iron products became widespread only after the Trojan War and the fall of the Hittites, when, thanks to the trading activity of the Greeks, iron technology became known to many, and new iron deposits and mines were discovered. So the Bronze Age was replaced by the Iron Age.

According to Homer's descriptions, although during the Trojan War (circa 1250 BC) weapons were mostly made of copper and bronze, iron was already well known and in great demand, although more as a precious metal. For example, in the 23rd song of the Iliad, Homer says that Achilles awarded the winner in a discus throwing competition with an iron cry disc. The Achaeans mined this iron from the Trojans and neighboring peoples (Iliad 7.473), including from the Khalibs, who fought on the side of the Trojans:

“Other men of the Achaeans bought wine with me,
Those for ringing copper, for gray iron changed,
Those for ox-skins or high-horned oxen,
Those for their captives. And a merry feast is prepared ... "

Perhaps iron was one of the reasons that prompted the Achaean Greeks to move to Asia Minor where they learned the secrets of its production. And excavations in Athens showed that already around 1100 BC. e. and later iron swords, spears, axes, and even iron nails were already widespread. The biblical book of Joshua 17:16 (cf. Judges 14:4) describes that the Philistines (biblical "PILISTIM", and these were proto-Greek tribes related to the later Hellenes, mainly Pelasgians) had many iron chariots, that is, in this iron has already become widely used in large quantities.

Homer in the Iliad and the Odyssey calls iron "a hard metal", and describes the hardening of tools:

“A quick forger, having made an ax or an ax,
Metal into the water, heating it up so that it doubles
He had a fortress, immerses ... "

Homer calls iron difficult, because in ancient times the main method of obtaining it was the raw-blowing process: alternating layers of iron ore and charcoal were calcined in special furnaces (forges - from the ancient "Horn" - a horn, a pipe, originally it was just a pipe dug in the ground , usually horizontally in the slope of a ravine). In the hearth, iron oxides are reduced to metal by hot coal, which takes away oxygen, oxidizing to carbon monoxide, and as a result of such calcination of ore with coal, doughy bloom (spongy) iron was obtained. Kritsu was cleaned of slag by forging, squeezing out impurities strong blows hammer. The first forges had relatively low temperature- noticeably less temperature melting cast iron, so the iron turned out to be relatively low-carbon. In order to obtain strong steel, it was necessary to calcinate and forge the iron bar with coal many times, while the surface layer of the metal was additionally saturated with carbon and hardened. That's how it turned out" good iron”- and although it required a lot of work, the products obtained in this way were significantly stronger and harder than bronze ones.

In the future, they learned how to make more efficient furnaces (in Russian - blast furnace, domnitsa) for the production of steel, and used furs to supply air to the furnace. Already the Romans were able to bring the temperature in the furnace to the melting of steel (about 1400 degrees, and pure iron melts at 1535 degrees). In this case, cast iron is formed with a melting point of 1100-1200 degrees, which is very brittle in the solid state (not even amenable to forging) and does not have the elasticity of steel. It was originally considered a harmful by-product. pig iron, in Russian, pig iron, ingots, where, in fact, the word cast iron comes from), but then it turned out that when remelted in a furnace with increased air blowing through it, cast iron turns into steel good quality, as excess carbon burns out. Such a two-stage process for the production of steel from cast iron turned out to be simpler and more profitable than bloomery, and this principle has been used without much change for many centuries, remaining to this day the main method for the production of iron materials.

Bibliography: Karl Bucks. Wealth of the earth's interior. M .: Progress, 1986, p. 244, chapter "Iron"

origin of name

There are several versions of the origin of the Slavic word "iron" (Belarusian zhalez, Ukrainian zalizo, old Slav. iron, bulg. iron, Serbohorv. zhezo, Polish. Zelazo, Czech železo, Slovenian zelezo).

One of the etymologies connects Praslav. *ZelEzo with the Greek word χαλκός , which meant iron and copper, according to another version *ZelEzo akin to words *zely"turtle" and *eye"rock", with the general seme "stone". The third version suggests an ancient borrowing from an unknown language.

The Germanic languages ​​borrowed the name iron (Gothic. eisarn, English iron, German Eisen, netherl. ijzer, dat. jern, swedish jarn) from Celtic.

Pra-Celtic word *isarno-(> OE iarn, OE Bret hoiarn), probably goes back to Proto-IE. *h 1 esh 2 r-no- "bloody" with the semantic development "bloody" > "red" > "iron". According to another hypothesis given word goes back to pra-i.e. *(H)ish 2ro- "strong, holy, possessing supernatural power" .

ancient greek word σίδηρος , may have been borrowed from the same source as the Slavic, Germanic, and Baltic words for silver.

The name of natural iron carbonate (siderite) comes from lat. sidereus- stellar; indeed, the first iron that fell into the hands of people was of meteoric origin. Perhaps this coincidence is not accidental. In particular, the ancient Greek word sideros (σίδηρος) for iron and latin sidus, meaning "star", probably have a common origin.

isotopes

Natural iron consists of four stable isotopes: 54 Fe (isotopic abundance 5.845%), 56 Fe (91.754%), 57 Fe (2.119%) and 58 Fe (0.282%). More than 20 unstable iron isotopes with mass numbers from 45 to 72 are also known, the most stable of which are 60 Fe (half-life according to data updated in 2009 is 2.6 million years), 55 Fe (2.737 years), 59 Fe ( 44.495 days) and 52 Fe (8.275 hours); the remaining isotopes have half-lives of less than 10 minutes.

The iron isotope 56 Fe is among the most stable nuclei: all of the following elements can reduce the binding energy per nucleon by decay, and all previous elements, in principle, could reduce the binding energy per nucleon due to fusion. It is believed that a series of synthesis of elements in the cores of normal stars ends with iron (see Iron star), and all subsequent elements can be formed only as a result of supernova explosions.

Geochemistry of iron

Hydrothermal source with ferruginous water. Iron oxides turn water brown

Iron is one of the most abundant elements in solar system, especially on the terrestrial planets, in particular on Earth. A significant part of the iron of the terrestrial planets is located in the cores of the planets, where its content is estimated to be about 90%. The content of iron in the earth's crust is 5%, and in the mantle about 12%. Of the metals, iron is second only to aluminum in terms of abundance in the crust. At the same time, about 86% of all iron is in the core, and 14% in the mantle. The content of iron increases significantly in the igneous rocks of the basic composition, where it is associated with pyroxene, amphibole, olivine and biotite. In industrial concentrations, iron accumulates during almost all exogenous and endogenous processes occurring in the earth's crust. IN sea ​​water iron is contained in very small quantities of 0.002-0.02 mg / l. In river water, it is slightly higher - 2 mg / l.

Geochemical properties of iron

The most important geochemical feature of iron is the presence of several oxidation states. Iron in a neutral form - metallic - composes the core of the earth, possibly present in the mantle and very rarely found in the earth's crust. Ferrous iron FeO is the main form of iron in the mantle and the earth's crust. Oxide iron Fe 2 O 3 is characteristic of the uppermost, most oxidized, parts of the earth's crust, in particular, sedimentary rocks.

In terms of crystal chemical properties, the Fe 2+ ion is close to the Mg 2+ and Ca 2+ ions, other main elements that make up a significant part of all terrestrial rocks. Due to their crystal chemical similarity, iron replaces magnesium and, in part, calcium in many silicates. The content of iron in minerals of variable composition usually increases with decreasing temperature.

iron minerals

A large number of ores and minerals containing iron are known. Of the greatest practical importance are red iron ore (hematite, Fe 2 O 3; contains up to 70% Fe), magnetic iron ore (magnetite, FeFe 2 O 4, Fe 3 O 4; contains 72.4% Fe), brown iron ore or limonite (goethite and hydrogoethite, FeOOH and FeOOH nH 2 O, respectively). Goethite and hydrogoethite are most often found in weathering crusts, forming the so-called "iron hats", the thickness of which reaches several hundred meters. They can also be of sedimentary origin, falling out of colloidal solutions in lakes or coastal areas of the seas. In this case, oolitic, or legume, iron ores are formed. Vivianite Fe 3 (PO 4) 2 8H 2 O is often found in them, forming black elongated crystals and radial-radiant aggregates.

Iron sulfides are also widespread in nature - pyrite FeS 2 (sulfur or iron pyrite) and pyrrhotite. They are not iron ore - pyrite is used to produce sulfuric acid, and pyrrhotite often contains nickel and cobalt.

In terms of iron ore reserves, Russia ranks first in the world. The content of iron in sea water is 1·10 −5 -1·10 −8%.

Other common iron minerals are:

• Siderite - FeCO 3 - contains approximately 35% iron. It has a yellowish-white (with a gray or brown tint in case of contamination) color. The density is 3 g / cm³ and the hardness is 3.5-4.5 on the Mohs scale.
• Marcasite - FeS 2 - contains 46.6% iron. It occurs in the form of yellow, like brass, bipyramidal rhombic crystals with a density of 4.6-4.9 g / cm³ and a hardness of 5-6 on the Mohs scale.
• Lollingite - FeAs 2 - contains 27.2% iron and occurs in the form of silver-white bipyramidal rhombic crystals. Density is 7-7.4 g / cm³, hardness is 5-5.5 on the Mohs scale.
• Mispikel - FeAsS - contains 34.3% iron. It occurs in the form of white monoclinic prisms with a density of 5.6-6.2 g / cm³ and a hardness of 5.5-6 on the Mohs scale.
• Melanterite - FeSO 4 7H 2 O - is less common in nature and is a green (or gray due to impurities) monoclinic crystals with a vitreous luster, fragile. The density is 1.8-1.9 g / cm³.
• Vivianite - Fe 3 (PO 4) 2 8H 2 O - occurs in the form of blue-gray or green-gray monoclinic crystals with a density of 2.95 g / cm³ and a hardness of 1.5-2 on the Mohs scale.

In addition to the above iron minerals, there are, for example:

Main deposits

According to the US Geological Survey (2011 estimate), the world's proven reserves of iron ore are about 178 billion tons. The main iron deposits are in Brazil (1st place), Australia, USA, Canada, Sweden, Venezuela, Liberia, Ukraine, France, India. In Russia, iron is mined at the Kursk Magnetic Anomaly (KMA), the Kola Peninsula, Karelia and Siberia. significant role in Lately they acquire bottom ocean deposits, in which iron, together with manganese and other valuable metals, is found in nodules.

Receipt

In industry, iron is obtained from iron ore, mainly from hematite (Fe 2 O 3) and magnetite (FeO Fe 2 O 3).

Exist various ways extraction of iron from ores. The most common is the domain process.

The first stage of production is the reduction of iron with carbon in a blast furnace at a temperature of 2000 ° C. In a blast furnace, carbon is in the form of coke, iron ore in the form of agglomerate or pellets and flux (for example, limestone) are fed from above, and from below they are met by a stream of injected hot air.

In the furnace, carbon in the form of coke is oxidized to carbon monoxide. This oxide is formed during combustion in a lack of oxygen:

In turn, carbon monoxide recovers iron from the ore. In order for this reaction to proceed faster, heated carbon monoxide passed through iron(III) oxide:

Calcium oxide combines with silicon dioxide, forming a slag - calcium metasilicate:

Slag, unlike silicon dioxide, is melted in a furnace. Lighter than iron, slag floats on the surface - this property allows you to separate the slag from the metal. The slag can then be used in construction and agriculture. Iron melt obtained in a blast furnace contains quite a lot of carbon (cast iron). Except in such cases, when cast iron is used directly, it requires further processing.

Excess carbon and other impurities (sulphur, phosphorus) are removed from cast iron by oxidation in open-hearth furnaces or in converters. Electric furnaces are also used for smelting alloyed steels.

In addition to the blast furnace process, the process of direct production of iron is common. In this case, pre-crushed ore is mixed with special clay to form pellets. The pellets are roasted and treated in a shaft furnace with hot methane conversion products that contain hydrogen. Hydrogen easily reduces iron:

while there is no contamination of iron with impurities such as sulfur and phosphorus, which are common impurities in coal. Iron is obtained in solid form, and then melted down in electric furnaces.

Chemically pure iron is obtained by electrolysis of solutions of its salts.

Physical Properties

The phenomenon of polymorphism is extremely important for steel metallurgy. It is thanks to the α-γ transitions of the crystal lattice that the heat treatment of steel occurs. Without this phenomenon, iron as the basis of steel would not have received such widespread use.

Iron is a moderately refractory metal. In a series of standard electrode potentials, iron stands before hydrogen and easily reacts with dilute acids. Thus, iron belongs to the metals of medium activity.

The melting point of iron is 1539 °C, the boiling point is 2862 °C.

Chemical properties

Characteristic oxidation states

• Acid does not exist in its free form - only its salts have been obtained.

For iron, the oxidation states of iron are characteristic - +2 and +3.

The oxidation state +2 corresponds to black oxide FeO and green hydroxide Fe(OH) 2 . They are basic. In salts, Fe(+2) is present as a cation. Fe(+2) is a weak reducing agent.

+3 oxidation states correspond to red-brown Fe 2 O 3 oxide and brown Fe(OH) 3 hydroxide. They are amphoteric in nature, although their acidic and basic properties are weakly expressed. Thus, Fe 3+ ions are completely hydrolyzed even in an acidic environment. Fe (OH) 3 dissolves (and even then not completely), only in concentrated alkalis. Fe 2 O 3 reacts with alkalis only when fused, giving ferrites (formal salts of an acid that does not exist in a free form of acid HFeO 2):

Iron (+3) most often exhibits weak oxidizing properties.

The +2 and +3 oxidation states easily transition between themselves when the redox conditions change.

In addition, there is Fe 3 O 4 oxide, the formal oxidation state of iron in which is +8/3. However, this oxide can also be considered as iron (II) ferrite Fe +2 (Fe +3 O 2) 2 .

There is also an oxidation state of +6. The corresponding oxide and hydroxide do not exist in free form, but salts - ferrates (for example, K 2 FeO 4) have been obtained. Iron (+6) is in them in the form of an anion. Ferrates are strong oxidizing agents.

Properties of a simple substance

When stored in air at temperatures up to 200 ° C, iron is gradually covered with a dense film of oxide, which prevents further oxidation of the metal. In moist air, iron is covered with a loose layer of rust, which does not prevent the access of oxygen and moisture to the metal and its destruction. Rust does not have a constant chemical composition; approximately its chemical formula can be written as Fe 2 O 3 xH 2 O.

Iron(II) compounds

Iron oxide (II) FeO has basic properties, it corresponds to the base Fe (OH) 2. Salts of iron (II) have a light green color. When stored, especially in moist air, they turn brown due to oxidation to iron (III). The same process occurs during storage of aqueous solutions of iron(II) salts:

Of the iron (II) salts in aqueous solutions, Mohr's salt is stable - double ammonium and iron (II) sulfate (NH 4) 2 Fe (SO 4) 2 6H 2 O.

Potassium hexacyanoferrate (III) K 3 (red blood salt) can serve as a reagent for Fe 2+ ions in solution. When Fe 2+ and 3− ions interact, turnbull blue precipitates:

For the quantitative determination of iron (II) in solution, phenanthroline Phen is used, which forms a red FePhen 3 complex with iron (II) (light absorption maximum - 520 nm) in a wide pH range (4-9).

Iron(III) compounds

Iron(III) compounds in solutions are reduced by metallic iron:

Iron (III) is able to form double sulfates with singly charged alum-type cations, for example, KFe (SO 4) 2 - potassium iron alum, (NH 4) Fe (SO 4) 2 - iron ammonium alum, etc.

For qualitative detection of iron(III) compounds in solution, the qualitative reaction of Fe 3+ ions with thiocyanate ions SCN − is used. When Fe 3+ ions interact with SCN − anions, a mixture of bright red iron thiocyanate complexes 2+ , + , Fe(SCN) 3 , - is formed. The composition of the mixture (and hence the intensity of its color) depends on various factors, so this method is not applicable for the accurate qualitative determination of iron.

Another high-quality reagent for Fe 3+ ions is potassium hexacyanoferrate (II) K 4 (yellow blood salt). When Fe 3+ and 4− ions interact, a bright blue precipitate of Prussian blue precipitates:

Iron(VI) compounds

Oxidizing properties Ferrates are used to disinfect water.

Iron compounds VII and VIII

There are reports on the electrochemical preparation of iron(VIII) compounds. , , , however, there are no independent works confirming these results.

Application

Iron ore

Iron is one of the most used metals, accounting for up to 95% of the world's metallurgical production.

• Iron is the main component of steels and cast irons - the most important structural materials.
• Iron can be part of alloys based on other metals - for example, nickel.
• Magnetic iron oxide (magnetite) is an important material in the manufacture of long-term computer memory devices: hard drives, floppy disks, etc.
• Ultrafine magnetite powder is used in many black and white laser printers mixed with polymer granules as a toner. It uses both the black color of magnetite and its ability to adhere to a magnetized transfer roller.
• The unique ferromagnetic properties of a number of iron-based alloys contribute to their widespread use in electrical engineering for magnetic circuits of transformers and electric motors.
• Iron (III) chloride (ferric chloride) is used in amateur radio practice for etching printed circuit boards.
• Ferrous sulfate (iron sulfate) mixed with copper sulphate is used to control harmful fungi in gardening and construction.
• Iron is used as an anode in iron-nickel batteries, iron-air batteries.
• Aqueous solutions of ferrous and ferric chlorides, as well as its sulfates, are used as coagulants in the purification of natural and Wastewater in the water treatment of industrial enterprises.

The biological significance of iron

In living organisms, iron is an important trace element that catalyzes the processes of oxygen exchange (respiration). The body of an adult contains about 3.5 grams of iron (about 0.02%), of which 78% are the main active element of blood hemoglobin, the rest is part of the enzymes of other cells, catalyzing the processes of respiration in cells. Iron deficiency manifests itself as a disease of the body (chlorosis in plants and anemia in animals).

Normally, iron enters enzymes as a complex called heme. In particular, this complex is present in hemoglobin, the most important protein that ensures the transport of oxygen with blood to all organs of humans and animals. And it is he who stains the blood in a characteristic red color.

Iron complexes other than heme are found, for example, in the enzyme methane monooxygenase, which oxidizes methane to methanol, in the important enzyme ribonucleotide reductase, which is involved in DNA synthesis.

Inorganic iron compounds are found in some bacteria and are sometimes used by them to bind atmospheric nitrogen.

Iron enters the body of animals and humans with food (liver, meat, eggs, legumes, bread, cereals, beets are the richest in it). Interestingly, once spinach was erroneously included in this list (due to a typo in the analysis results - the “extra” zero after the decimal point was lost).

An excess dose of iron (200 mg or more) may cause toxic effect. An overdose of iron depresses the body's antioxidant system, so use iron supplements healthy people Not recommended.

Notes

Sources (to the History section)

• G. G. Giorgadze."Text of Anitta" and some questions of the early history of the Hittites
• R. M. Abramishvili. On the issue of the development of iron in the territory of Eastern Georgia, VGMG, XXII-B, 1961.
• Khakhutayshvili D. A. On the history of ancient Colchian iron metallurgy. Questions of ancient history (Caucasian-Middle Eastern collection, issue 4). Tbilisi, 1973.
• Herodotus."History", 1:28.
• Homer. Iliad, Odyssey.
• Virgil."Aeneid", 3:105.
• Aristotle."On Incredible Rumors", II, 48. VDI, 1947, No. 2, p. 327.
• Lomonosov M.V. The first foundations of metallurgy.

see also

• Category: Iron compounds

Links

• Diseases caused by deficiency and excess of iron in the human body

13. CHROME SUB-GROUP ELEMENTS.

atomic number	Name	Electronic configuration	ρ g/cm 3	tpl. 0C	tboiling 0C	EO	Atomic radius, nm	Degree oxidation
26	Iron Fe	3d64s2	7,87	1535	2750	1,64	0,128	+2,+3
27	Cobalt Co	3d74s2	8,9	1495	2870	1,7	0,125	+2,+3
28	Nickel Ni	3d8 4s2	8,9	1453	2732	1,75	0,124	+1,+2,+3,+4

Receipt
iron subgroup metals

Recovery from oxides with carbon or carbon monoxide (II)

FeO + C Fe + CO
Fe 2 O 3 + 3CO 2Fe + 3CO 2
NiO + C Ni + CO
Co 2 O 3 + 3C 2Co + 3CO

Fe
d- element of group VIII; serial number – 26; atomic mass- 56; (26p; 30n), 26e

Medium activity metal, reducing agent.
Main oxidation states - +2, +3

Iron and its compounds

Chemical properties

In air, iron is easily oxidized in the presence of moisture (rusting):

4Fe + 3O 2 + 6H 2 O 4Fe(OH) 3

A heated iron wire burns in oxygen, forming scale - iron oxide (II, III):

3Fe + 2O 2 Fe 3 O 4

At high temperature(700–900 0 C) iron reacts with water vapor:

3Fe + 4H 2 O Fe 3 O 4 + 4H 2
Iron reacts with non-metals when heated:

2Fe + 3Br 2 2FeBr 3
Fe + S FeS
Iron readily dissolves in hydrochloric and dilute sulfuric acids:

Fe + 2HCl FeCl 2 + H 2
Fe + H 2 SO 4 (razb.) FeSO 4 + H 2

In concentrated oxidizing acids, iron dissolves only when heated.

2Fe + 6H 2 SO 4 (conc.) Fe 2 (SO 4) 3 + 3SO 2 + 6H 2 O
Fe + 6HNO 3 (conc.) Fe(NO 3) 3 + 3NO 2 + 3H 2 O

(in the cold, concentrated nitric and sulfuric acids passivate iron).
Iron displaces metals to the right of it in the series of stresses from solutions of their salts.

Fe + CuSO 4 FeSO 4 + Cu

Connections ferrous iron

Iron(II) hydroxide

It is formed by the action of alkali solutions on iron (II) salts without air access:

FeCl + 2KOH 2KCl + Fe(OH) 2

Fe (OH) 2 - weak base, soluble in strong acids:

Fe(OH) 2 + H 2 SO 4 FeSO 4 + 2H 2 O

When Fe (OH) 2 is calcined without air access, iron oxide (II) FeO is formed:

Fe(OH) 2 FeO + H 2 O

In the presence of atmospheric oxygen, a white precipitate Fe (OH) 2, oxidizing, turns brown - forming iron (III) hydroxide Fe (OH) 3:

4Fe(OH) 2 + O 2 + 2H 2 O 4Fe(OH) 3

Iron (II) compounds have reducing properties, they are easily converted into iron (III) compounds under the action of oxidizing agents:

10FeSO 4 + 2KMnO 4 + 8H 2 SO 4 5Fe 2 (SO 4) 3 + K 2 SO 4 + 2MnSO 4 + 8H 2 O
6FeSO 4 + 2HNO 3 + 3H 2 SO 4 3Fe 2 (SO 4) 3 + 2NO + 4H 2 O

Iron compounds are prone to complex formation (coordination number = 6):

FeCl 2 + 6NH 3 Cl 2
Fe(CN)2 + 4KCN K4(yellow blood salt)

Qualitative reaction for Fe 2+

Under the action of potassium hexacyanoferrate (III) K 2 (red blood salt) on solutions of ferrous salts, a blue precipitate (turnbull blue) is formed:

3FeSO 4 + 2K 3 Fe 3 + 3K 2 SO 4

Ferric compounds

Iron(III) oxide

It is formed during the combustion of iron sulfides, for example, during the firing of pyrite:

4FeS 2 + 11O 2 2Fe 2 O 3 + 8SO 2

or when calcining iron salts:

2FeSO 4 Fe 2 O 3 + SO 2 + SO 3

Fe 2 O 3 - basic oxide, slightly amphoteric

Fe 2 O 3 + 6HCl 2FeCl 3 + 3H 2 O

Fe 2 O 3 + 2NaOH + 3H 2 O 2Na

Iron(III) hydroxide

It is formed by the action of alkali solutions on ferric iron salts: it precipitates as a red-brown precipitate

Fe(NO 3) 3 + 3KOH Fe(OH) 3 + 3KNO 3

Fe (OH) 3 is a weaker base than iron (II) hydroxide.
This is explained by the fact that Fe 2+ has a smaller ion charge and a larger radius than Fe 3+ , and therefore, Fe 2+ holds hydroxide ions weaker, i.e. Fe(OH) 2 dissociates more easily.
In this regard, iron (II) salts are hydrolyzed slightly, and iron (III) salts are very strongly hydrolyzed. The color of solutions of Fe(III) salts is also explained by hydrolysis: despite the fact that the Fe3+ ion is almost colorless, the solutions containing it are colored yellow-brown, which is explained by the presence of iron hydroxoions or Fe(OH)3 molecules, which are formed due to hydrolysis:

Fe 3+ + H 2 O 2 + + H +
2 + + H 2 O + + H +
+ + H2O Fe(OH) 3 + H +

When heated, the color darkens, and when acids are added, it becomes lighter due to the suppression of hydrolysis. Fe (OH) 3 has a weakly pronounced amphotericity: it dissolves in dilute acids and in concentrated alkali solutions:

Fe(OH) 3 + 3HCl FeCl 3 + 3H 2 O

Fe(OH) 3 + NaOH Na

Iron (III) compounds are weak oxidizing agents, they react with strong reducing agents:

2FeCl 3 + H2S S + 2FeCl 2 + 2HCl

Qualitative reactions on Fe3+

Page 3

On fig. V.8 shows a correlation scheme that gives an idea of ​​the intervals of 57Fe isomeric shifts for iron compounds. The oxidation state of iron can vary from 0 to 6, and it is not so easy to characterize it by the 57Fe isomeric shift.

A reducing atmosphere causes a decrease in the degree of oxidation of iron in the slag, while in an oxidizing atmosphere under the action of high temperatures the flame continues to decompose the higher oxides of iron. An increase in the degree of oxidation of iron in slag by the action of an oxidizing atmosphere is possible only at a flame temperature below 1200 C and a large slag surface.

The content of Al2O3 and alkalis changes quite sharply in the rocks. The oxidation state of iron remains constant.

Sample C with an oxidation state of 13% has no plastic region, and the slag behaves like glass. With an increase in the degree of oxidation of iron to 30 or 56%, a bend appears in the viscosity curves of samples B and A, indicating that the slag in the place of the bend passes into a plastic state.

But the degree of oxidation of sulfur, which is part of these ions, is different. In the first case, the oxidation state of iron coincides with the charge of a simple Fe2 ion and with the valency of iron. Thus, the valency of a given element in a complex compound is called the total amount of bonds that the central atom, the complexing agent, has in this compound.

The tendency to complex formation is also confirmed by the existence of typical double salts such as shenites and alums. In this compound, the oxidation state of iron 2 stabilizes, while sulfate FeSO4 in aqueous solution prone to oxidation by atmospheric oxygen. Nickel does not form such compounds, since the oxidation state 3 for this element is so uncharacteristic that it does not even stabilize in double salts.

This increase in the degree of oxidation of iron in the slag continues up to a temperature of about 1,200 C. With a further increase in the temperature of the slag, the degree of oxidation of iron drops significantly.

As indicated, the central iron atom lies in the plane of the 16-membered porphyry ring, and it is bonded to the nitrogen atoms of the pyrrole rings by four of the six available valences, and therefore two valences remain to complete the octahedral complex; these valences are above and below the drawing plane of the model shown. In addition, the degree of oxidation of iron must also be taken into account; when the iron is in the ferrous state, as shown in the figure, the protoporphyrin is called thema or, more clearly, ferrogem. If the heme is in the free state in solution and is not bound to the protein, then it is assumed that two water molecules are in coordination with the fifth and sixth positions of the valence of iron. George designates this ferrogem as follows: H2O - Fep-H. When oxidized, it goes into H O Fep NaO with one positive charge. This ferriheme can coordinate the chlorine ion with the transition to H2O - Fep-Cl and in this case is called hemin; with a coordinated hydroxyl ion, ferrigem is designated as hematin H2O - Pep-OH, although these terms are sometimes used less specifically, only to indicate the presence of iron oxide. Coordination of other molecules is also possible, and coordination with hydrogen peroxide plays a role in the first place. Ferrohem easily coordinates nitrogenous bases, such as pyridine, forming hemochromogees B-Fp-B. The same compound with ferriheme B-Fep-B is called parahematin.

By means of the magnetic method, the presence and quantitative assessment of valence bonds between neighboring positive ions was established. Thus, in Fe203 on an A1203 support, the oxidation state of iron is three, but at the same time, neighboring iron atoms form a covalent bond with each other.

By means of the magnetic method, the presence and a quantitative assessment of valence bonds between neighboring positive ions were established. Thus, in Fe2O3 on an A12O3 carrier, the oxidation state of iron is three, but at the same time, neighboring iron atoms form a covalent bond with each other.

If we consider the hydroxides Fe (OH) 2 and Fe (OH) 3, then from the standpoint of the Kossel scheme, the acidic properties of the second hydroxide should be more pronounced than the first. This follows from the fact that the higher the degree of oxidation of iron (even if we assume that the radii of the Fe2 and Fe3 ions are the same), the higher the repulsion of the proton and the more pronounced the acidic properties of the corresponding hydroxide. If we take into account that the radius of the Fe3 ion is somewhat smaller than that of the Fe2 ion, then the greater repulsion of the proton in the Fe (OH) 3 compound in comparison with Fe (OH) 2 becomes even more obvious.

Part of the iron oxides is reduced to metallic iron, the other part to [nitrous oxide]; in addition, carbon is released on them. The amount of oxygen still contained in the ore characterizes the degree of oxidation of iron.

If, after preliminary tests, there remains doubt whether an iron ion is present, verification reactions can be carried out. But it should be remembered that with this test it is no longer possible to establish the initial degree of oxidation of iron in the analyzed sample.

Only in the presence of strong oxidizing agents, it is possible to obtain rather fragile derivatives of iron acid H2FeO4 with an iron oxidation state of 6, however, it was not possible to isolate the corresponding oxide. If RuO4 is a low-stable substance that is obtained indirectly, then OsO4 is a completely stable compound formed during the oxidation of a metal in air.