Element characteristic

6 C 1s 2 2s 2 2p 2

Isotopes: 12 C (98.892%); 13 C (1.108%); 14 C (radioactive)

Clark in the earth's crust 0.48% by weight. Location forms:

in free form (coal, diamonds);

in the composition of carbonates (CaCO 3, MgCO 3, etc.);

in the composition of fossil fuels (coal, oil, gas);

in the form of CO 2 - in the atmosphere (0.03% by volume);

in the oceans - in the form of HCO 3 - anions;

in the composition of living matter (-18% carbon).

The chemistry of carbon compounds is basically organic chemistry. In the course of inorganic chemistry, the following C-containing substances are studied: free carbon, oxides (CO and CO 2), carbonic acid, carbonates and bicarbonates.

Free carbon. Allotropy.

In the free state, carbon forms 3 allotropic modifications: diamond, graphite and artificially obtained carbine. These modifications of carbon differ in crystal-chemical structure and physical characteristics.

Diamond

In a diamond crystal, each carbon atom is bound by strong covalent bonds to four others placed at equal distances around it.

All carbon atoms are in a state of sp 3 hybridization. The atomic crystal lattice of diamond has a tetrahedral structure.

Diamond is a colorless, transparent, highly refractive substance. It has the highest hardness among all known substances. Diamond is brittle, refractory, poorly conducts heat and electricity. Small distances between adjacent carbon atoms (0.154 nm) determine the rather high density of diamond (3.5 g/cm 3 ).

Graphite

In the crystal lattice of graphite, each carbon atom is in a state of sp 2 hybridization and forms three strong covalent bonds with carbon atoms located in the same layer. Three electrons of each atom, carbon, participate in the formation of these bonds, and the fourth valence electrons form n-bonds and are relatively free (mobile). They determine the electrical and thermal conductivity of graphite.

The length of the covalent bond between adjacent carbon atoms in the same plane is 0.152 nm, and the distance between C atoms in different layers is 2.5 times greater, so the bonds between them are weak.

Graphite is an opaque, soft, greasy to the touch substance of a gray-black color with a metallic sheen; conducts heat and electricity well. Graphite has a lower density than diamond and is easily split into thin flakes.

The disordered structure of fine-crystalline graphite underlies the structure of various forms of amorphous carbon, the most important of which are coke, brown and black coals, soot, and activated (active) carbon.

Carbine

This allotropic modification of carbon is obtained by catalytic oxidation (dehydropolycondensation) of acetylene. Carbyne is a chain polymer that has two forms:

C=C-C=C-... and...=C=C=C=

Carbin has semiconductor properties.

Chemical properties of carbon

At ordinary temperature, both modifications of carbon (diamond and graphite) are chemically inert. Fine-crystalline forms of graphite - coke, soot, Activated carbon- more reactive, but, as a rule, after their preliminary heating to a high temperature.

C - active reducing agent:

1. Interaction with oxygen

C + O 2 \u003d CO 2 + 393.5 kJ (in excess O 2)

2C + O 2 \u003d 2CO + 221 kJ (with a lack of O 2)

Coal combustion is one of the most important sources of energy.

2. Interaction with fluorine and sulfur.

C + 2F 2 = CF 4 carbon tetrafluoride

C + 2S \u003d CS 2 carbon disulfide

3. Coke is one of the most important reducing agents used in industry. In metallurgy, it is used to produce metals from oxides, for example:

ZS + Fe 2 O 3 \u003d 2Fe + ZSO

C + ZnO = Zn + CO

4. When carbon interacts with oxides of alkali and alkaline earth metals, the reduced metal combines with carbon to form carbide. For example: 3C + CaO \u003d CaC 2 + CO calcium carbide

5. Coke is also used to obtain silicon:

2C + SiO 2 \u003d Si + 2CO

6. With an excess of coke, silicon carbide (carborundum) SiC is formed.

Obtaining "water gas" (solid fuel gasification)

By passing water vapor through hot coal, a combustible mixture of CO and H 2 is obtained, called water gas:

C + H 2 O \u003d CO + H 2

7. Reactions with oxidizing acids.

Activated or charcoal, when heated, restores NO 3 - and SO 4 2- anions from concentrated acids:

C + 4HNO 3 \u003d CO 2 + 4NO 2 + 2H 2 O

C + 2H 2 SO 4 \u003d CO 2 + 2SO 2 + 2H 2 O

8. Reactions with molten nitrates alkali metals

In KNO 3 and NaNO 3 melts, crushed coal burns intensively with the formation of a blinding flame:

5C + 4KNO 3 \u003d 2K 2 CO 3 + ZSO 2 + 2N 2

C - low-active oxidizing agent:

1. Formation of salt-like carbides with active metals.

A significant weakening of the non-metallic properties of carbon is expressed in the fact that its functions as an oxidizing agent are manifested to a much lesser extent than the reducing functions.

2. Only in reactions with active metals, carbon atoms pass into negatively charged ions C -4 and (C \u003d C) 2-, forming salt-like carbides:

ZS + 4Al \u003d Al 4 C 3 aluminum carbide

2C + Ca \u003d CaC 2 calcium carbide

3. Ionic type carbides are very unstable compounds, they easily decompose under the action of acids and water, which indicates the instability of negatively charged carbon anions:

Al 4 C 3 + 12H 2 O \u003d ZSN 4 + 4Al (OH) 3

CaC 2 + 2H 2 O \u003d C 2 H 2 + Ca (OH) 2

4. Formation of covalent compounds with metals

In melts of mixtures of carbon with transition metals, carbides are formed predominantly with a covalent type of bond. Their molecules have a variable composition, and substances in general are close to alloys. Such carbides are highly resistant, they are chemically inert with respect to water, acids, alkalis and many other reagents.

5. Interaction with hydrogen

At high T and P, in the presence of a nickel catalyst, carbon combines with hydrogen:

C + 2HH 2 → CNN 4

The reaction is very reversible and has no practical significance.

Structure of a diamond (a) and graphite (b)

Carbon(Latin carboneum) - C, a chemical element of the IV group of the periodic system of Mendeleev, atomic number 6, atomic mass 12.011. It occurs in nature in the form of crystals of diamond, graphite or fullerene and other forms and is part of organic (coal, oil, animal and plant organisms, etc.) and not organic matter(limestone, baking soda and etc.). Carbon is widespread, but its content in the earth's crust is only 0.19%.

Carbon is widely used in the form of simple substances. In addition to precious diamonds, which are the subject jewelry, great importance have industrial diamonds - for the manufacture of grinding and cutting tools. Charcoal and other amorphous forms of carbon are used for decolorization, purification, adsorption of gases, in areas of technology where adsorbents with a developed surface are required. Carbides, compounds of carbon with metals, as well as with boron and silicon (for example, Al 4 C 3, SiC, B 4 C) are highly hard and are used to make abrasive and cutting tools. Carbon is present in steels and alloys in the elemental state and in the form of carbides. Saturation of the surface of steel castings with carbon at high temperature(cementation) significantly increases the surface hardness and wear resistance.

History reference

Graphite, diamond and amorphous carbon have been known since antiquity. It has long been known that other material can be marked with graphite, and the very name "graphite", which comes from Greek word, meaning "to write", was proposed by A. Werner in 1789. However, the history of graphite is confused, often substances with similar external physical properties, such as molybdenite (molybdenum sulfide), at one time considered graphite. Among other names of graphite, "black lead", "iron carbide", "silver lead" are known.

In 1779, K. Scheele found that graphite can be oxidized with air to form carbon dioxide. For the first time, diamonds found use in India, and in Brazil, precious stones acquired commercial importance in 1725; deposits in South Africa were opened in 1867.

In the 20th century The main diamond producers are South Africa, Zaire, Botswana, Namibia, Angola, Sierra Leone, Tanzania and Russia. Artificial diamonds, the technology of which was created in 1970, are produced for industrial purposes.

Properties

Four crystalline modifications of carbon are known:

• graphite,
• diamond,
• carbine,
• lonsdaleite.

Graphite- gray-black, opaque, greasy to the touch, scaly, very soft mass with a metallic sheen. At room temperature and normal pressure (0.1 MN/m2, or 1 kgf/cm2), graphite is thermodynamically stable.

Diamond- very solid, crystalline substance. Crystals have a cubic face-centered lattice. At room temperature and normal pressure, diamond is metastable. A noticeable transformation of diamond into graphite is observed at temperatures above 1400°C in vacuum or in an inert atmosphere. At atmospheric pressure and a temperature of about 3700 ° C, graphite sublimates.

Liquid carbon can be obtained at pressures above 10.5 MN/m2 (105 kgf/cm2) and temperatures above 3700°C. Solid carbon (coke, soot, charcoal) is also characterized by a state with a disordered structure - the so-called "amorphous" carbon, which is not an independent modification; its structure is based on the structure of fine-grained graphite. Heating some varieties of "amorphous" carbon above 1500-1600 ° C without air causes their transformation into graphite.

The physical properties of "amorphous" carbon depend very strongly on the dispersion of particles and the presence of impurities. Density, heat capacity, thermal conductivity and electrical conductivity of "amorphous" carbon is always higher than graphite.

Carbine obtained artificially. It is a finely crystalline powder of black color (density 1.9-2 g / cm 3). Built from long chains of atoms FROM laid parallel to each other.

Lonsdaleite found in meteorites and obtained artificially; its structure and properties have not been finally established.

Properties of carbon
atomic number		6
Atomic mass		12,011
Isotopes:	stable	12, 13
	unstable	8, 9, 10, 11, 14, 15, 16, 17, 18, 19, 20, 21, 22
Melting temperature		3550°С
Boiling temperature		4200°C
Density		1.9-2.3 g / cm 3 (graphite) 3.5-3.53 g / cm 3 (diamond)
Hardness (Mohs)		1-2
Content in the earth's crust (mass.)		0,19%
Oxidation states		-4; +2; +4

Alloys

Steel

Coke is used in metallurgy as a reducing agent. Charcoal - in forges, to obtain gunpowder (75% KNO 3 + 13% C + 12% S), to absorb gases (adsorption), as well as in everyday life. Soot is used as a rubber filler, for the manufacture of black paints - printing ink and ink, as well as in dry galvanic cells. Glassy carbon is used for the manufacture of equipment for highly aggressive environments, as well as in aviation and astronautics.

Activated charcoal absorbs harmful substances from gases and liquids: they fill gas masks, purification systems, it is used in medicine for poisoning.

Carbon is the basis of all organic substances. Every living organism is made up largely of carbon. Carbon is the basis of life. The source of carbon for living organisms is usually CO 2 from the atmosphere or water. As a result of photosynthesis, it enters the biological food chains, in which living beings eat each other or the remains of each other and thereby extract carbon for the construction of their own body. biological cycle carbon ends up either oxidized and re-released into the atmosphere, or buried as coal or oil.

The use of the radioactive isotope 14 C contributed to the success of molecular biology in studying the mechanisms of protein biosynthesis and transmission hereditary information. Determination of the specific activity of 14 C in carbonaceous organic remains makes it possible to judge their age, which is used in paleontology and archeology.

Sources

Chemical elements and materials
Chemical elements	Nitrogen. Argon. Hydrogen. Helium. Iron . Calcium. Oxygen. Silicon. Magnesium. Manganese.

Organic life on Earth is represented by carbon compounds. The element is part of the main components cell structures: proteins, carbohydrates and fats, and also forms the basis of the substance of heredity - deoxyribonucleic acid. In inorganic nature, carbon is one of the most common elements that form the earth's crust and the atmosphere of the planet. Organic chemistry as a section of chemical science is completely devoted to the properties of the chemical element carbon and its compounds. Our article will consider the physicochemical characteristics of carbon and the features of its properties.

The place of the element in the periodic system of Mendeleev

The carbon subgroup is the main subgroup of group IV, which, in addition to carbon, also includes silicon, germanium, tin and lead. All of the listed elements have the same structure of the external energy level, on which four electrons are located. This determines the similarity of their chemical properties. In the normal state, the elements of the subgroup are divalent, and when their atoms go into an excited state, they exhibit a valence equal to 4. Physical and Chemical properties carbon depend on the state of the electron shells of its atom. Thus, in reaction with oxygen, an element whose particles are in an unexcited state forms an indifferent oxide CO. Carbon atoms in the excited state are oxidized to carbon dioxide, which exhibits acidic properties.

Forms of carbon in nature

Diamond, graphite and carbine are three allotropic modifications of carbon as a simple substance. Clear crystals with a high degree refraction of light rays, which are the hardest compounds in nature - these are diamonds. They are poor conductors of heat and are dielectrics. The crystal lattice is atomic, very strong. In it, each atom of an element is surrounded by four other particles, forming a regular tetrahedron.

Completely different physicochemical properties of carbon forming graphite. It is greasy to the touch crystalline substance of dark gray color. It has a layered structure, the distances between the layers of atoms are quite large, while their attractive forces are weak. Therefore, when pressing on a graphite rod, the substance is stratified into thin flakes. They leave a dark mark on paper. Graphite is thermally conductive and slightly inferior to metals in electrical conductivity.

The ability to conduct electric current is explained by the structure of the crystal of a substance. In it, carbon particles are bound to three others using strong covalent bonds. chemical bonds. The fourth valence electron of each atom remains free and is able to move in the thickness of the substance. Directed movement of negatively charged particles and causes the appearance electric current. The fields of application of graphite are diverse. So, it is used for the manufacture of electrodes in electrical engineering and for carrying out the electrolysis process, with the help of which, for example, pure alkali metals are obtained. Graphite has found application in nuclear reactors to control the rate of chain reactions taking place in them as a neutron moderator. It is known to use the substance as slate rods or lubricants in the rubbing parts of mechanisms.

What is carbin?

The black crystalline powder with a glassy sheen is carbine. It was synthesized in the middle of the 20th century in Russia. The substance surpasses graphite in hardness, is chemically passive, has the properties of a semiconductor and is the most stable modification of carbon. The connection is stronger than graphite. There are also such forms of carbon, the chemical properties of which differ from each other. These are soot, charcoal and coke.

Various characteristics allotropic modifications of carbon are explained by the structure of their crystal lattices. It is a refractory substance, colorless and odorless. AT organic solvents insoluble, but capable of forming solid solutions - alloys, for example, with iron.

Chemical properties of carbon

Depending on the substance with which carbon reacts, it can exhibit dual properties: both a reducing agent and an oxidizing agent. For example, by fusing coke with metals, their compounds are obtained - carbides. In reaction with hydrogen, hydrocarbons are formed. These are organic compounds, for example, methane, ethylene, acetylene, in which, as in the case of metals, carbon has an oxidation state of -4. Recovery chemical reactions carbon, the properties of which we are studying, are manifested during its interaction with oxygen, halogens, water and basic oxides.

Oxides of carbon

By burning coal in air with a low oxygen content, carbon monoxide- oxide of bivalent carbon. It is colorless, odorless and highly toxic. Combining with blood hemoglobin during respiration, carbon monoxide is distributed throughout human body, causing poisoning and then death by asphyxiation. In the classification, a substance takes the place of indifferent oxides, does not react with water, and neither a base nor an acid corresponds to it. The chemical properties of carbon having a valency of 4 differ from the previously discussed characteristics.

Carbon dioxide

A colorless gaseous substance at a temperature of 15 and a pressure of one atmosphere passes into a solid phase. It's called dry ice. CO 2 molecules are non-polar, although the covalent bond between oxygen and carbon atoms is polar. The compound belongs to acidic oxides. When interacting with water, it forms carbonic acid. Reactions between carbon dioxide and simple substances are known: metals and non-metals, for example, with magnesium, calcium or coke. In them, it plays the role of an oxidizing agent.

Qualitative reaction to carbon dioxide

To make sure that the gas under study is really carbon monoxide CO 2, the following experiment is carried out in inorganic chemistry: the substance is passed through a transparent solution of lime water. Observation of the cloudiness of the solution due to the precipitation of a white precipitate of calcium carbonate confirms the presence of carbon dioxide molecules in the reagent mixture. With further passage of gas through a solution of calcium hydroxide, the CaCO 3 precipitate dissolves due to its transformation into calcium bicarbonate, a water-soluble salt.

The role of carbon in the blast furnace process

The chemical properties of carbon are used in industrial production iron from its ores: magnetic, red or brown iron ore. Chief among them will be the reducing properties of carbon and oxides - carbon monoxide and carbon dioxide. The processes occurring in the blast furnace can be represented as the following sequence of reactions:

• First, coke burns in a stream of air heated to 1,850 °C with the formation of carbon dioxide: C + O 2 = CO 2.
• Passing through hot carbon, it is reduced to carbon monoxide: CO 2 + C = 2CO.
• Carbon monoxide reacts with iron ore, resulting in iron oxide: 3Fe 2 O 3 + CO \u003d 2Fe 3 O 4 + CO 2, Fe 3 O 4 + CO \u003d 3FeO + CO 2.
• The iron production reaction will have the following form: FeO + CO \u003d Fe + CO 2

Molten iron dissolves a mixture of carbon and carbon monoxide in itself, resulting in a substance - cementite.

Cast iron smelted in a blast furnace, in addition to iron, contains up to 4.5% carbon and other impurities: manganese, phosphorus, sulfur. Steel, which differs from cast iron in a number of ways, such as the ability to roll and forge, has only 0.3 to 1.7% carbon in its composition. Steel products found wide application in almost all industries: mechanical engineering, metallurgy, medicine.

In our article, we found out what chemical properties of carbon and its compounds are used in various fields human activity.

In this book, the word "carbon" appears quite often: in stories about the green leaf and about iron, about plastics and crystals, and in many other stories. Carbon - "bearing coal" - one of the most amazing chemical elements. Its history is the history of the emergence and development of life on Earth, because it is part of all life on Earth.

What does carbon look like?

Let's do some experiments. Take sugar and heat it without air. It will first melt, turn brown, and then turn black and turn into coal, releasing water. If we now heat this coal in the presence of , it will burn without residue and turn into . So, sugar consisted of coal and water (sugar, by the way, is called a carbohydrate), and "sugar" coal - this, apparently, is pure carbon because carbon dioxide is a combination of carbon and oxygen. So carbon is a black, soft powder.

Let's take a gray soft graphite stone, well known to you thanks to pencils. If it is heated in oxygen, it will also burn without residue, although a little more slowly than coal, and carbon dioxide will remain in the device where it burned. So graphite is also pure carbon? Of course, but that's not all.

If a diamond is heated in the same apparatus in oxygen, a transparent sparkling gem, the hardest of all minerals, it will also burn to become carbon dioxide. If you heat a diamond without access to oxygen, it will turn into graphite, and at very high pressures and temperatures, it is possible to obtain diamond from graphite.

So, coal, graphite and diamond are various forms the existence of one and the same element - carbon.

Even more surprising is the ability of carbon to "take part" in a huge number of different compounds (which is why the word "carbon" appears so often in this book).

104 elements of the periodic system form more than forty thousand studied compounds. And over a million compounds are already known, the basis of which is carbon!

The reason for this diversity is that carbon atoms can combine with each other and with other atoms. strong bond, forming complex in the form of chains, rings and other shapes. No element in the table, except carbon, is capable of this.

There is an infinite number of figures that can be built from carbon atoms, and therefore an infinite number of possible compounds. This may be very simple substances, for example, the lighting gas methane, in the molecule of which four atoms are bonded to one carbon atom, and so complex that the structure of their molecules has not yet been established. Such substances include

Carbon (C) is a typical non-metal; in periodic system is in the 2nd period of the IV group, the main subgroup. Ordinal number 6, Ar = 12.011 amu, nuclear charge +6.

Physical properties: carbon forms many allotropic modifications: diamond one of the hardest substances graphite, coal, soot.

A carbon atom has 6 electrons: 1s 2 2s 2 2p 2 . The last two electrons are located in separate p-orbitals and are unpaired. In principle, this pair could occupy one orbital, but in this case the interelectron repulsion strongly increases. For this reason, one of them takes 2p x, and the other, either 2p y , or 2p z-orbitals.

The difference between the energies of the s- and p-sublevels of the outer layer is small, therefore, the atom quite easily passes into an excited state, in which one of the two electrons from the 2s-orbital passes to a free 2r. A valence state arises having the configuration 1s 2 2s 1 2p x 1 2p y 1 2p z 1 . It is this state of the carbon atom that is characteristic of the diamond lattice - tetrahedral spatial arrangement hybrid orbitals, the same length and bond energy.

This phenomenon is known to be called sp 3 -hybridization, and the resulting functions are sp 3 -hybrid . The formation of four sp 3 bonds provides the carbon atom with a more stable state than three rr- and one s-s-bond. In addition to sp 3 hybridization, sp 2 and sp hybridization are also observed at the carbon atom . In the first case, there is a mutual overlap s- and two p-orbitals. Three equivalent sp 2 - hybrid orbitals are formed, located in the same plane at an angle of 120 ° to each other. The third orbital p is unchanged and directed perpendicular to the plane sp2.

In sp hybridization, the s and p orbitals overlap. An angle of 180° arises between the two equivalent hybrid orbitals formed, while the two p-orbitals of each of the atoms remain unchanged.

Allothropy of carbon. diamond and graphite

In a graphite crystal, carbon atoms are located in parallel planes, occupying the vertices of regular hexagons in them. Each of the carbon atoms is linked to three adjacent sp 2 hybrid bonds. Between parallel planes, the connection is carried out due to van der Waals forces. Free p-orbitals of each of the atoms are directed perpendicular to the planes of covalent bonds. Their overlap explains the additional π-bond between carbon atoms. So from the valence state in which carbon atoms are in a substance, the properties of this substance depend.

Chemical properties of carbon

The most characteristic oxidation states: +4, +2.

At low temperatures carbon is inert, but when heated, its activity increases.

Carbon as a reducing agent:

- with oxygen
C 0 + O 2 - t ° \u003d CO 2 carbon dioxide
with a lack of oxygen - incomplete combustion:
2C 0 + O 2 - t° = 2C +2 O carbon monoxide

- with fluorine
C + 2F 2 = CF 4

- with steam
C 0 + H 2 O - 1200 ° \u003d C + 2 O + H 2 water gas

— with metal oxides. In this way metal is smelted from ore.
C 0 + 2CuO - t ° \u003d 2Cu + C +4 O 2

- with acids - oxidizing agents:
C 0 + 2H 2 SO 4 (conc.) \u003d C +4 O 2 + 2SO 2 + 2H 2 O
С 0 + 4HNO 3 (conc.) = С +4 O 2 + 4NO 2 + 2H 2 O

- forms carbon disulfide with sulfur:
C + 2S 2 \u003d CS 2.

Carbon as an oxidizing agent:

- forms carbides with some metals

4Al + 3C 0 \u003d Al 4 C 3

Ca + 2C 0 \u003d CaC 2 -4

- with hydrogen - methane (as well as a huge amount of organic compounds)

C 0 + 2H 2 \u003d CH 4

- with silicon, forms carborundum (at 2000 ° C in an electric furnace):

Finding carbon in nature

Free carbon occurs as diamond and graphite. In the form of compounds, carbon is found in minerals: chalk, marble, limestone - CaCO 3, dolomite - MgCO 3 *CaCO 3; bicarbonates - Mg (HCO 3) 2 and Ca (HCO 3) 2, CO 2 is part of the air; carbon is the main integral part natural organic compounds - gas, oil, coal, peat, is part of organic substances, proteins, fats, carbohydrates, amino acids that are part of living organisms.

Inorganic carbon compounds

Neither C 4+ ions, nor C 4- - under any normal chemical processes are not formed: in carbon compounds there are covalent bonds of different polarity.

Carbon monoxide (II) SO

Carbon monoxide; colorless, odorless, sparingly soluble in water, soluble in organic solvents, poisonous, bp = -192°C; t sq. = -205°C.

Receipt
1) In industry (in gas generators):
C + O 2 = CO 2

2) In the laboratory - thermal decomposition of formic or oxalic acid in the presence of H 2 SO 4 (conc.):
HCOOH = H2O + CO

H 2 C 2 O 4 \u003d CO + CO 2 + H 2 O

Chemical properties

At normal conditions CO is inert; when heated - reducing agent; non-salt-forming oxide.

1) with oxygen

2C +2 O + O 2 \u003d 2C +4 O 2

2) with metal oxides

C +2 O + CuO \u003d Cu + C +4 O 2

3) with chlorine (in the light)

CO + Cl 2 - hn \u003d COCl 2 (phosgene)

4) reacts with alkali melts (under pressure)

CO + NaOH = HCOONa (sodium formate)

5) forms carbonyls with transition metals

Ni + 4CO - t° = Ni(CO) 4

Fe + 5CO - t° = Fe(CO) 5

Carbon monoxide (IV) CO2

Carbon dioxide, colorless, odorless, solubility in water - 0.9V CO 2 dissolves in 1V H 2 O (at normal conditions); heavier than air; t°pl.= -78.5°C (solid CO 2 is called "dry ice"); does not support combustion.

Receipt

1. Thermal decomposition of salts of carbonic acid (carbonates). Limestone firing:

CaCO 3 - t ° \u003d CaO + CO 2

1. The action of strong acids on carbonates and bicarbonates:

CaCO 3 + 2HCl \u003d CaCl 2 + H 2 O + CO 2

NaHCO 3 + HCl \u003d NaCl + H 2 O + CO 2

ChemicalpropertiesCO2
Acid oxide: reacts with basic oxides and bases to form carbonic acid salts

Na 2 O + CO 2 \u003d Na 2 CO 3

2NaOH + CO 2 \u003d Na 2 CO 3 + H 2 O

NaOH + CO 2 \u003d NaHCO 3

At elevated temperature may exhibit oxidizing properties

C +4 O 2 + 2Mg - t ° \u003d 2Mg +2 O + C 0

Qualitative reaction

Turbidity of lime water:

Ca(OH) 2 + CO 2 = CaCO 3 ¯( white precipitate) + H2O

It disappears when CO 2 is passed through lime water for a long time, because. insoluble calcium carbonate is converted to soluble bicarbonate:

CaCO 3 + H 2 O + CO 2 \u003d Ca (HCO 3) 2

carbonic acid and itssalt

H2CO3 — Weak acid, exists only in aqueous solution:

CO 2 + H 2 O ↔ H 2 CO 3

Dual base:
H 2 CO 3 ↔ H + + HCO 3 - Acid salts - bicarbonates, bicarbonates
HCO 3 - ↔ H + + CO 3 2- Medium salts - carbonates

All properties of acids are characteristic.

Carbonates and bicarbonates can be converted into each other:

2NaHCO 3 - t ° \u003d Na 2 CO 3 + H 2 O + CO 2

Na 2 CO 3 + H 2 O + CO 2 \u003d 2NaHCO 3

Metal carbonates (except alkali metals) decarboxylate when heated to form an oxide:

CuCO 3 - t ° \u003d CuO + CO 2

Qualitative reaction- "boiling" under the action of a strong acid:

Na 2 CO 3 + 2HCl \u003d 2NaCl + H 2 O + CO 2

CO 3 2- + 2H + = H 2 O + CO 2

Carbides

calcium carbide:

CaO + 3 C = CaC 2 + CO

CaC 2 + 2 H 2 O \u003d Ca (OH) 2 + C 2 H 2.

Acetylene is released when zinc, cadmium, lanthanum and cerium carbides react with water:

2 LaC 2 + 6 H 2 O \u003d 2La (OH) 3 + 2 C 2 H 2 + H 2.

Be 2 C and Al 4 C 3 are decomposed by water to form methane:

Al 4 C 3 + 12 H 2 O \u003d 4 Al (OH) 3 \u003d 3 CH 4.

Titanium carbides TiC, tungsten W 2 C (hard alloys), silicon SiC (carborundum - as an abrasive and material for heaters) are used in technology.

cyanides

obtained by heating soda in an atmosphere of ammonia and carbon monoxide:

Na 2 CO 3 + 2 NH 3 + 3 CO \u003d 2 NaCN + 2 H 2 O + H 2 + 2 CO 2

Hydrocyanic acid HCN is an important chemical industry product widely used in organic synthesis. Its world production reaches 200 thousand tons per year. The electronic structure of the cyanide anion is similar to carbon monoxide (II), such particles are called isoelectronic:

C = O:[:C = N:]-

Cyanides (0.1-0.2% water solution) are used in gold mining:

2 Au + 4 KCN + H 2 O + 0.5 O 2 \u003d 2 K + 2 KOH.

When cyanide solutions are boiled with sulfur or when solids are fused, thiocyanates:
KCN + S = KSCN.

When cyanides of low-active metals are heated, cyanide is obtained: Hg (CN) 2 \u003d Hg + (CN) 2. cyanide solutions are oxidized to cyanates:

2KCN + O2 = 2KOCN.

Cyanic acid exists in two forms:

H-N=C=O; H-O-C = N:

In 1828, Friedrich Wöhler (1800-1882) obtained urea from ammonium cyanate: NH 4 OCN \u003d CO (NH 2) 2 by evaporating an aqueous solution.

This event is usually seen as the victory of synthetic chemistry over "vitalistic theory".

There is an isomer of cyanic acid - fulminic acid

H-O-N=C.
Its salts (mercury fulminate Hg(ONC) 2) are used in impact igniters.

Synthesis urea(carbamide):

CO 2 + 2 NH 3 \u003d CO (NH 2) 2 + H 2 O. At 130 0 C and 100 atm.

Urea is an amide of carbonic acid, there is also its "nitrogen analogue" - guanidine.

Carbonates

The most important inorganic compounds of carbon are salts of carbonic acid (carbonates). H 2 CO 3 is a weak acid (K 1 \u003d 1.3 10 -4; K 2 \u003d 5 10 -11). Carbonate buffer supports carbon dioxide balance in the atmosphere. The oceans have a huge buffer capacity because they are an open system. The main buffer reaction is the equilibrium during the dissociation of carbonic acid:

H 2 CO 3 ↔ H + + HCO 3 -.

With a decrease in acidity, additional absorption of carbon dioxide from the atmosphere occurs with the formation of acid:
CO 2 + H 2 O ↔ H 2 CO 3.

With an increase in acidity, carbonate rocks (shells, chalk and limestone deposits in the ocean) dissolve; this compensates for the loss of hydrocarbonate ions:

H + + CO 3 2- ↔ HCO 3 -

CaCO 3 (tv.) ↔ Ca 2+ + CO 3 2-

Solid carbonates are converted into soluble hydrocarbons. It is this process of chemically dissolving excess carbon dioxide that counteracts the "greenhouse effect" - global warming due to the absorption of the Earth's thermal radiation by carbon dioxide. Approximately one third of the world's production of soda (sodium carbonate Na 2 CO 3) is used in the manufacture of glass.