Iron exhibits the highest degree of oxidation in the compound. Great encyclopedia of oil and gas

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In Fig. V.8 shows a correlation diagram that gives an idea of ​​the ranges of isomeric shifts of 57Fe 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 isomer shift of 57Fe.

A reducing atmosphere causes a decrease in the degree of oxidation of iron in the slag, while in an oxidizing atmosphere under the influence high temperatures The flame continues to decompose higher iron oxides. Increasing the degree of oxidation of iron in the slag by exposure to an oxidizing atmosphere is only possible at a flame temperature below 1,200 C and a large slag surface.

The content of Al2O3 and alkalis in the rocks changes quite sharply. 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 iron oxidation to 30 or 56%, a bend appears in the viscosity curves of samples B and A, indicating that the slag at 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 the simple Fe2 ion and with the valence of iron. Thus, the valence of a given element in a complex compound is the total amount of bonds that the central atom, the complexing agent, has in a given compound.

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

This increase in the degree of oxidation of iron in the slag continues until a temperature of about 1200 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 porphyrip 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 oxidation state of iron must also be taken into account; when iron is in the ferrous state, as shown in the figure, then protoporphyrin is called theme or, more clearly, ferroheme. If heme is in a free state in solution and is not associated with protein, then it is assumed that two water molecules are in a coordination bond with the fifth and sixth valency positions of iron. George designates this ferrogem as follows: H2O - Fep-H. Upon oxidation, it turns into H O Fep NaO with one positive charge. This ferrigem can coordinate a chlorine ion to form 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, with coordination with hydrogen peroxide playing a primary role. Ferrohem easily coordinates nitrogenous bases, such as pyridine, forming hemochromogeum B-Pbr - B. The same compound with ferrigem B-Fep-B is called parahematin.

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

Using the magnetic method, the presence and quantitative assessment of valence bonds between neighboring positive ions was established. Thus, in Fe2O3 on the A12O3 support, 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 oxidation state of iron (even if we assume that the radii of the Fe2 and Fe3 ions are the same), the higher the proton repulsion and the more pronounced the acidic properties of the corresponding hydroxide. If we take into account that the radius of the Fe3 ion is slightly smaller than that of the Fe2 ion, then the greater repulsion of the proton in the Fe (OH) 3 compound compared to Fe (OH) 2 becomes even more obvious.

Some of the iron oxides are reduced to metallic iron, the other part to [nitrous oxide]; In addition, they release carbon. The amount of oxygen still contained in the ore characterizes the degree of oxidation of iron.

If after preliminary tests there is still doubt as to whether an iron ion is present, verification reactions can be performed. 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 is it possible to obtain rather weak derivatives of iron acid H2FeO4 with an oxidation state of iron of 6, but the corresponding oxide could not be isolated. 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.

Story

Iron, as a tool material, has been known since ancient times. The oldest iron objects 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 from meteorite 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 languages: “sider” (which means “starry”).

Products made from iron obtained by smelting have been known since the settlement of Aryan tribes from Europe to Asia, the islands Mediterranean Sea, onwards (late 4th and 3rd millennium BC). The oldest known iron tools are steel blades found in the masonry of the Cheops Pyramid 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 the heavy magnetite sand, calcined the 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 Cheops pyramid. However, after the grandson of Cheops Menkaur (2471-2465 BC), turmoil ensued 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 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 decline, and, just as the art of building pyramids degraded, the technology of iron production was lost, to the point that later, when exploring the Sinai Peninsula in search of copper ore, the Egyptians did not pay any attention to the deposits of iron ore that existed there, and received iron from the neighboring Hittites and Mitannians.

The first to master the production of iron were the Hutts, 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 Hutts (modern Anatolia in Turkey). Thus, the text of the Hittite king Anitta (circa 1800 BC) 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 submission (?) ...

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

In ancient times, the Khalibs were known as masters of iron products. The legend of the Argonauts (their campaign in Colchis took place about 50 years before the Trojan War) tells that the king of Colchis, Eet, gave Jason an iron plow so that he could plow the field of Ares, and his subjects, the Calibers, are described:

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

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

As a raw material for steel smelting, magnetite sands were used, which are often found along the entire Black Sea coast: these magnetite sands consist of a mixture of small grains of magnetite, titano-magnetite or ilmenite, and fragments of other rocks, so that the steel smelted by the Khalibans was alloyed, and had excellent properties. This unique method 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 served as an impetus for further development iron metallurgy.

In ancient times, iron was valued more than gold, and according to Strabo’s description, African tribes gave 10 pounds of gold for 1 pound of iron, and according to the research of 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, the biblical book of Deuteronomy 3.11 describes the “iron bed” of the Rephaim king Og.

In the tomb of Tutankhamun (circa 1350 BC) an iron dagger in a gold frame was found - 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 clear from the correspondence that has reached us. Egyptian pharaoh Tutankhamun and his father-in-law Hattusil, the king of the Hittites. The pharaoh asks to send more iron, and the king of the Hittites evasively replies that iron reserves have dried up, 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 made of “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, this is why iron products became widespread only after the Trojan War and the fall of the Hittite power, 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 mainly 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 a discus made of iron to the winner in a discus throwing competition. The Achaeans mined this iron from the Trojans and neighboring peoples (Iliad 7.473), including the Khalibs, who fought on the side of the Trojans:

“Other Achaean men bought wine with barter,
They exchanged them for ringing copper, for gray iron,
Those for oxhide or steep-horned oxen,
Those for their full ones. And a joyful feast has been 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 At the time, iron had already become widely used in large quantities.

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

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

Homer calls iron difficult because in ancient times the main method of its production was the cheese-blowing process: alternating layers of iron ore and charcoal were calcined in special furnaces (furnaces - from the ancient “Horn” - horn, pipe, originally it was just a pipe dug in the ground , usually horizontally in the slope of a ravine). In the forge, iron oxides are reduced to metal by hot coal, which takes up oxygen, oxidizing to carbon monoxide, and as a result of such calcination of ore with coal, dough-like krichine (sponge) iron was obtained. Kritsa was cleaned of slag by forging, squeezing out impurities with 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. To obtain strong steel, it was necessary to calcinate and forge the iron core with coal many times, while the surface layer of the metal was additionally saturated with carbon and strengthened. This is how it turned out" good iron“- and although this required a lot of work, the products obtained in this way were significantly stronger and harder than bronze ones.

Later they learned to make more efficient furnaces (in Russian - blast furnace, domna) for steel production, and used bellows to supply air to the furnace. Already the Romans knew how to bring the temperature in the furnace to melting steel (about 1400 degrees, and pure iron melts at 1535 degrees). This produces cast iron with a melting point of 1100-1200 degrees, which is very brittle in the solid state (not even forgeable) and does not have the elasticity of steel. It was initially considered a harmful by-product. pig iron, in Russian, pig iron, ingots, where, in fact, the word cast iron comes from), but then it was discovered that when re-melted in a furnace with intensive air blowing through it, cast iron turns into steel good quality, as excess carbon burns out. This two-stage process for producing steel from cast iron turned out to be simpler and more profitable than the critical one, and this principle has been used without much change for many centuries, remaining to this day the main method of producing iron materials.

Bibliography: Carl Bax. The riches 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 zaleza, Ukrainian zalizo, Old Slav. iron, Bulgarian Zhelyazo, Serbohorv. zhejezo, Polish żelazo, Czech železo, Slovenian. železo).

One of the etymologies connects Praslav. *želězo with the Greek word χαλκός , which meant iron and copper, according to another version *želězo akin to words *žely"turtle" and *glazъ“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, Netherlands ijzer, dat. jern, Swedish järn) from Celtic.

Pre-Celtic word *isarno-(> Old Irish iarn, Old Brett hoiarn), probably goes back to the ancestral I.e. *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 2 ro- "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 the Latin. sidereus- starry; Indeed, the first iron that fell into the hands of people was of meteorite 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 isotopes of iron are also known with mass numbers from 45 to 72, 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 one of 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 through fusion. It is believed that iron ends the series of synthesis of elements in the cores of normal stars (see Iron Star), and all subsequent elements can only be formed as a result of supernova explosions.

Geochemistry of iron

Hydrothermal spring with ferruginous water. Iron oxides color water brown.

Iron is one of the most common 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 iron content in the earth's crust is 5%, and in the mantle about 12%. Of the metals, iron is second only to aluminum in abundance in the bark. At the same time, about 86% of all iron is found in the core, and 14% in the mantle. The iron content increases significantly in mafic igneous rocks, where it is associated with pyroxene, amphibole, olivine and biotite. In industrial concentrations, iron accumulates during almost all exogenous and endogenous processes occurring in earth's crust. IN sea ​​water iron is contained in very small quantities 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 - makes up the core of the earth, is possibly present in the mantle and is very rarely found in the earth's crust. Ferrous iron FeO is the main form of iron found in the mantle and 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 earthly rocks. Due to crystal chemical similarity, iron replaces magnesium and, partially, calcium in many silicates. In this case, the iron content in minerals of variable composition usually increases with decreasing temperature.

Iron minerals

A large number of ores and minerals containing iron are known. Of 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). Goethite and hydrogoethite are most often found in weathering crusts, forming 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 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 make sulfuric acid, and pyrrhotite often contains nickel and cobalt.

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

Other commonly found iron minerals:

• Siderite - FeCO 3 - contains approximately 35% iron. It has a yellowish-white (with a gray or brown tint if dirty) 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, brass-like, bipyramidal rhombic crystals with a density of 4.6-4.9 g/cm³ and a hardness of 5-6 on the Mohs scale.
• Löllingite - FeAs 2 - contains 27.2% iron and occurs in the form of silvery-white bipyramidal rhombic crystals. Density is 7-7.4 g/cm³, hardness 5-5.5 on the Mohs scale.
• Mispickel - 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.
• Melantherite - FeSO 4 · 7H 2 O - is less common in nature and is green (or gray due to impurities) monoclinic crystals with a glassy luster and fragile. 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 iron minerals described above, 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 located in Brazil (1st place), Australia, USA, Canada, Sweden, Venezuela, Liberia, Ukraine, France, India. In Russia, iron is mined in the Kursk Magnetic Anomaly (KMA), the Kola Peninsula, Karelia and Siberia. Significant role in Lately 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) is supplied from above, and from below they are met by a stream of forced 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 reduces iron from the ore. To make this reaction go faster, heated carbon monoxide passed through iron(III) oxide:

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

Slag, unlike silicon dioxide, is melted in a furnace. Slag, lighter than iron, 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. Melted iron produced in a blast furnace contains quite a lot of carbon (cast iron). Except in cases where cast iron is used directly, it requires further processing.

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

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

in this case, the iron does not become contaminated with such impurities as sulfur and phosphorus, which are common impurities in coal. Iron is obtained in solid form and is subsequently melted 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 α-γ transitions of the crystal lattice that 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 the series of standard electrode potentials, iron is ranked before hydrogen and easily reacts with dilute acids. Thus, iron belongs to the metals of intermediate 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 free form - only its salts are obtained.

Iron is characterized by oxidation states of iron - +2 and +3.

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

The oxidation state +3 corresponds to the red-brown oxide Fe 2 O 3 and the brown hydroxide Fe(OH) 3. They are amphoteric in nature, although acidic, and their 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 upon fusion, giving ferrites (formal acid salts of the acid HFeO 2, which does not exist in free form):

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

Oxidation states +2 and +3 easily change between each other when redox conditions change.

In addition, there is the oxide Fe 3 O 4, 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 are obtained - ferrates (for example, K 2 FeO 4). Iron (+6) is present 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 humid air, iron becomes 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 her chemical formula can be written as Fe 2 O 3 xH 2 O.

Iron(II) compounds

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

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

Potassium hexacyanoferrate(III) K3 (red blood salt) can serve as a reagent for Fe 2+ ions in solution. When Fe 2+ and 3− ions interact, a Turnboole blue precipitate forms:

For the quantitative determination of iron (II) in solution, phenanthroline Phen is used, which forms a red complex FePhen 3 with iron (II) (maximum light absorption - 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 capable of forming double sulfates with singly charged cations such as alum, for example, KFe(SO 4) 2 - iron-potassium alum, (NH 4)Fe(SO 4) 2 - iron-ammonium alum, etc.

For qualitative detection of iron(III) compounds in solution, use qualitative reaction Fe 3+ ions with thiocyanate ions SCN − . 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 therefore the intensity of its color) depends on various factors, therefore this method is not applicable for 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 is formed:

Iron(VI) compounds

Oxidative properties Ferrates are used to disinfect water.

Iron compounds VII and VIII

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

Application

Iron ore

Iron is one of the most used metals, accounting for up to 95% of global 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 production 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. This uses both the black color of the magnetite and its ability to stick to the magnetized transfer roller.
• The unique ferromagnetic properties of a number of iron-based alloys contribute to their wide application 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 heptate (ferrous sulfate) mixed with copper sulfate is used to combat harmful fungi in gardening and construction.
• Iron is used as an anode in iron-nickel batteries and iron-air batteries.
• Aqueous solutions chlorides of divalent and trivalent iron, as well as its sulfates, are used as coagulants in the purification processes of natural and Wastewater in water treatment of industrial enterprises.

Biological significance of iron

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

Typically, iron enters enzymes in the form of a complex called heme. In particular, this complex is present in hemoglobin, the most important protein that ensures the transport of oxygen in the blood to all organs of humans and animals. And it is he who colors the blood in its 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 fix air nitrogen.

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

Excessive doses of iron (200 mg or more) may have toxic effect. An overdose of iron inhibits the body's antioxidant system, so take 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.
• Khakhutaishvili 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

17. d -elements. Iron, general characteristics, properties. Oxides and hydroxides, CO and OM characteristics, biorole, ability to form complexes.

1. General characteristics.

Iron - d-element of the side subgroup of the eighth group of the fourth period of PSHE with atomic number 26.

One of the most common metals in the earth's crust (second place after aluminum).

A simple substance, iron, is a malleable silver-white metal with high chemical reactivity: iron quickly corrodes at high temperatures or high humidity in the air.

4Fe + 3O2 + 6H2O = 4Fe(OH)3

Iron burns in pure oxygen, and in a finely dispersed state it spontaneously ignites in air.

3Fe + 2O2 = FeO + Fe2O3

3Fe + 4H2O = FeO*Fe2O3

FeO*Fe2O3 = Fe3O4 (iron scale)

Actually, iron is usually called its alloys with a low impurity content (up to 0.8%), which retain the softness and ductility of pure metal. But in practice, alloys of iron with carbon are more often used: steel (up to 2.14 wt.% carbon) and cast iron (more than 2.14 wt.% carbon), as well as stainless (alloy) steel with the addition of alloying metals (chrome, manganese, nickels, etc.). The combination of specific properties of iron and its alloys make it “metal No. 1” in importance for humans.

In nature, iron is rarely found in its pure form; most often it is found in iron-nickel meteorites. The abundance of iron in the earth's crust is 4.65% (4th place after O, Si, Al). Iron is also believed to make up most of the earth's core.

2.Properties

1.Physical St. Iron is a typical metal; in its free state it is silvery-white in color with a grayish tint. Pure metal is ductile; various impurities (in particular carbon) increase its hardness and brittleness. It has pronounced magnetic properties. The so-called “iron triad” is often distinguished - a group of three metals (iron Fe, cobalt Co, nickel Ni) with similar physical properties, atomic radii and electronegativity values.

2.Chemical St.

Iron is characterized by oxidation states of iron - +2 and +3.

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

The oxidation state +3 corresponds to the red-brown oxide Fe 2 O 3 and the brown hydroxide Fe(OH) 3. They are amphoteric in nature, although acidic, and their basic properties are weakly expressed. Thus, Fe 3+ ions are completely hydrolyze 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 upon fusion, giving ferrites(formal acid salts of the acid HFeO 2, which does not exist in free form):

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

Oxidation states +2 and +3 easily change between each other when redox conditions change.

In addition, there is the oxide Fe 3 O 4, 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 are obtained - ferrates (for example, K 2 FeO 4). Iron (+6) is present in them in the form of an anion. Ferrates are strong oxidizing agents.

Pure metallic iron is stable in water and in dilute solutions alkalis. Iron does not dissolve in cold concentrated sulfuric and nitric acids due to passivation of the metal surface by a strong oxide film. Hot concentrated sulfuric acid, being a stronger oxidizing agent, interacts with iron.

WITH salt and diluted (approximately 20%) sulfur acids iron reacts to form iron(II) salts:

When iron reacts with approximately 70% sulfuric acid upon heating, the reaction proceeds to form iron(III) sulfate:

3.Oxides and hydroxides, CO and OM characteristics...

Iron(II) compounds

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

Stable from iron(II) salts in aqueous solutions Mohr's salt- double ammonium and iron(II) sulfate (NH 4) 2 Fe(SO 4) 2 6H 2 O.

A reagent for Fe 2+ ions in solution can be potassium hexacyanoferrate(III) K 3 (red blood salt). When Fe 2+ and 3− ions interact, a precipitate forms turnbull blue:

For the quantitative determination of iron (II) in solution, use phenanthroline, forming a red complex FePhen 3 with iron (II) in a wide pH range (4-9)

Iron(III) compounds

Iron(III) oxide Fe 2 O 3 weak amphoteric, it is answered by an even weaker base than Fe(OH) 2, Fe(OH) 3, which reacts with acids:

Fe 3+ salts are prone to the formation of crystalline hydrates. In them, the Fe 3+ ion is usually surrounded by six water molecules. Such salts have a pink or purple color. The Fe 3+ ion is completely hydrolyzed even in an acidic environment. At pH>4 this ion is almost completely precipitated as Fe(OH) 3:

With partial hydrolysis of the Fe 3+ ion, polynuclear oxo- and hydroxocation cations are formed, which is why the solutions turn brown. The main properties of iron(III) hydroxide Fe(OH) 3 are very weakly expressed. It is capable of reacting only with concentrated solutions of alkalis:

The resulting hydroxo complexes of iron(III) are stable only in strongly alkaline solutions. When solutions are diluted with water, they are destroyed, and Fe(OH) 3 precipitates.

When alloyed with alkalis and oxides of other metals, Fe 2 O 3 forms a variety of ferrites:

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

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

For qualitative detection of iron(III) compounds in solution, a qualitative reaction of Fe 3+ ions with thiocyanate ions is used SCN − . 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 therefore the intensity of its color) depends on various factors, therefore this method is not applicable for 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 forms Prussian blue:

Iron(VI) compounds

Ferratas- salts of iron acid H 2 FeO 4, which does not exist in free form. These are connections purple, which are reminiscent of permanganates in their oxidative properties and sulfates in their solubility. Ferrates are produced by the action of gaseous chlorine or ozone for suspended Fe(OH) 3 in alkali , for example, potassium ferrate(VI) K 2 FeO 4 . Ferrates are colored purple.

Ferratas can also be obtained electrolysis 30% alkali solution on an iron anode:

Ferrates are strong oxidizing agents. In an acidic environment they decompose with the release of oxygen:

The oxidizing properties of ferrates are used for water disinfection.

4.Biorole

1) In living organisms, iron is an important trace element that catalyzes the processes of oxygen exchange (respiration).

2) Iron is usually included in enzymes in the form of a complex. In particular, this complex is present in hemoglobin, the most important protein that ensures the transport of oxygen in the blood to all organs of humans and animals. And it is he who colors the blood in its characteristic red color.

4) An excessive dose of iron (200 mg and above) can have a toxic effect. An overdose of iron inhibits the body's antioxidant system, so it is not recommended for healthy people to take iron supplements.

In the earth's crust, iron is quite widespread; it accounts for about 4.1% of the mass of the earth's crust (4th place among all elements, 2nd among metals). In the mantle and 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 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 color (with a gray or brown tint if dirty). Siderite Mispickel FeAsS contains 34.3% iron. Mispickel Löllingite FeAs 2 contains 27.2% iron Löllingite ilmenite FeTiO 3 ilmenite magnetite (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 becomes 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. rust oxide

Iron reacts with oxygen when heated. When iron burns in air, Fe 3 O 4 oxide is formed, when burned in pure oxygen, Fe 2 O 3 oxide is formed. 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