Oxygen has a high chemical activity. Many substances react with oxygen at room temperature. So, for example, a fresh cut of an apple quickly acquires a brown color, this is due to chemical reactions between the organic substances contained in the apple and the oxygen contained in the air.
With simple substances, oxygen, as a rule, reacts when heated. We place a piece of coal in a metal spoon for burning substances, heat it red-hot in the flame of an alcohol lamp and lower it into a vessel with oxygen. We observe the bright combustion of coal in oxygen. Coal is a simple substance made up of the element carbon. The reaction of oxygen with carbon produces carbon dioxide:
C + O2 = CO2
It is worth noting that many chemicals have trivial names. Carbon dioxide is a trivial name for a substance. Trivial names of substances are used in Everyday life, many of which are ancient. For example, baking soda, Bertolet salt. However, each chemical substance also has a systematic chemical name, the compilation of which is regulated by international rules - the systematic chemical nomenclature. Thus, carbon dioxide has a systematic name carbon monoxide (IV).
Carbon dioxide is a complex substance, a binary compound, which includes oxygen.
We put sulfur in a spoon for burning substances and heat it. Sulfur melts, then ignites. In air, sulfur burns with a pale, almost imperceptible, blue flame. We introduce sulfur into a vessel with oxygen - sulfur burns with a bright blue flame. In the reaction of sulfur with oxygen, sulfur dioxide is formed:
S + O2 = SO2
Sulfur dioxide, like carbon dioxide, belongs to the group of oxides. It's sulfur oxide(IV) is a colorless gas with a pungent pungent odor.
Now let's add ignited red phosphorus to a vessel with oxygen. Phosphorus burns with a bright, dazzling flame. The vessel is filled with white smoke. White smoke is a reaction product, fine particulate matter phosphorus (V) oxide:
4P + 5O2 = 2P2O5
Not only non-metals can burn in oxygen. Metals also interact vigorously with oxygen. For example, magnesium burns in oxygen and in air with a dazzling white flame. The reaction product is magnesium oxide:
2Mg + O2 = 2MgO
Let's try to burn iron in oxygen. We heat a steel wire in the flame of an alcohol lamp and quickly lower it into a vessel with oxygen. Iron burns in oxygen, producing many sparks. The substance resulting from the reaction is called iron oxide:
3Fe + 2O2 = Fe3O4.
Sheaves of sparks formed during the burning of a Bengal fire are explained by the combustion of iron powder, which is part of these pyrotechnic products.
After the reactions considered, important conclusions can be drawn: oxygen reacts with both metals and non-metals; often these reactions are accompanied by combustion of substances. The reaction products of oxygen with simple substances are oxides.
Please note that when oxygen interacts with simple substances - metals and non-metals, complex substances - oxides are formed. This type of chemical reaction is called connection reactions.
Connection reaction - a reaction in which two or more less complex substances are formed, as a result of which more complex substances are formed
The interaction of oxygen with complex substances
Oxygen is able to react with complex substances. As an example, consider the reaction that occurs during the combustion of household gas, which consists of methane CH4.
According to the combustion of methane in the burner of the furnace, it can be concluded that the reaction proceeds with the release of energy in the form of heat and light. What are the products of this reaction?
CH4 + 2O2 = CO2 + 2H2O.
The reaction products are oxides: carbon dioxide (carbon (IV) oxide) and water (hydrogen oxide).
In the reaction of oxygen with the mineral pyrite FeS2 (an important mineral of iron and sulfur), oxides of sulfur and iron are obtained. The reaction occurs when heated:
4FeS2 + 11O2 = 8SO2 + 2Fe2O3
Oxidation - combustion and slow oxidation
Combustion- this is the first chemical reaction that the person has met. Fire... Is it possible to imagine our existence without fire? He entered our life, became inseparable from it. Without fire, a person cannot cook food, steel; without it, transport is impossible. Fire has become our friend and ally, a symbol of glorious deeds, good deeds, a memory of the past.
From a chemical point of view, combustion- This is a chemical reaction, accompanied by the release of a stream of hot gases and energy in the form of heat and light. We can say that oxygen, reacting with simple substances, oxidizes them:
Simple substance + Oxygen oxidation → Oxidation products (oxides) + Energy.
Oxidation of substances may not be accompanied by combustion, that is, the release of a flame. Such processes are called slow oxidation. Slow oxidation is a process of gradual interaction of substances with oxygen, with a slow release of heat, not accompanied by combustion. So, for example, carbon dioxide is formed not only during the combustion of carbon in oxygen, but also during slow oxidation organic matter air oxygen (rotting, decay).
- In the reaction of simple substances with oxygen, oxides
- Reactions of simple substances with oxygen proceed, as a rule, when heated
- Reactions of simple substances with oxygen are compound reactions
- Trivial names chemical substances do not reflect the chemical composition of substances, are used in everyday practice, many of them have developed historically
- Systematic names of chemicals reflect the chemical composition of the substance, correspond to the international systematic nomenclature
- Connection reaction- a reaction in which, from two or more less complex substances, more complex substances are formed
- Oxygen is able to react with complex substances
- Combustion- a chemical reaction accompanied by the release of energy in the form of heat and light
- slow oxidation- the process of gradual interaction of substances with oxygen, with a slow release of heat, not accompanied by combustion
8 O 1s 2 2s 2 2p 4 ; A r = 15.999 Isotopes: 16 O (99.759%); 17 O (0.037%); 18 O (0.204%); EO - 3.5
Clark in earth's crust 47% by weight; in the hydrosphere 85.82% by weight; in the atmosphere 20.95% by volume.
The most common element.
Forms of finding the element: a) in free form - O 2, O 3;
b) in bound form: O 2- anions (mainly)
Oxygen is a typical non-metal, p-element. Valency = II; oxidation state -2 (except for H 2 O 2, OF 2, O 2 F 2)
Physical properties of O 2
Molecular oxygen O 2 at normal conditions is in a gaseous state, has no color, smell and taste, slightly soluble in water. When deep cooling under pressure, it condenses into a pale blue liquid (Tbp - 183 ° C), which at -219 ° C turns into crystals of blue - blue color.
How to get
1. Oxygen is formed in nature in the process of photosynthesis mCO 2 + nH 2 O → mO 2 + Cm (H 2 O) n
2. Industrial production
a) rectification of liquid air (separation from N 2);
b) water electrolysis: 2H 2 O → 2H 2 + O 2
3. In the laboratory, they are obtained by thermal redox decomposition of salts:
a) 2KSlO 3 \u003d 3O 2 + 2KCI
b) 2KMnO 4 \u003d O 2 + MnO 2 + K 2 MnO 4
c) 2KNO 3 \u003d O 2 + 2KNO 2
d) 2Cu (NO 3) O 2 \u003d O 2 + 4NO 2 + 2CuO
e) 2AgNO 3 \u003d O 2 + 2NO 2 + 2Ag
4. In hermetically sealed rooms and in autonomous breathing apparatus, oxygen is obtained by the reaction:
2Na 2 O 2 + 2СO 2 \u003d O 2 + 2Na 2 CO 3
Chemical properties of oxygen
Oxygen is a strong oxidizing agent. In terms of chemical activity, it is second only to fluorine. Forms compounds with all elements except He, Ne and Ar. Reacts directly with most simple substances under normal conditions or when heated, as well as in the presence of catalysts (with the exception of Au, Pt, Hal 2, noble gases). Reactions involving O 2 are in most cases exothermic, often proceeding in the combustion mode, sometimes in an explosion. As a result of reactions, compounds are formed in which oxygen atoms, as a rule, have C.O. -2:
Alkali metal oxidation
4Li + O 2 = 2Li 2 O lithium oxide
2Na + O 2 \u003d Na 2 O 2 sodium peroxide
K + O 2 \u003d KO 2 potassium superoxide
Oxidation of all metals except Au, Pt
Me + O 2 = Me x O y oxides
Oxidation of non-metals, except halogens and noble gases
N 2 + O 2 \u003d 2NO - Q
S + O 2 \u003d SO 2;
C + O 2 \u003d CO 2;
4P + 5O 2 \u003d 2P 2 O 5
Si + O 2 \u003d SiO 2
Oxidation hydrogen compounds non-metals and metals
4HI + O 2 \u003d 2I 2 + 2H 2 O
2H 2 S + 3O 2 \u003d 2SO 2 + 2H 2 O
4NH 3 + 3O 2 \u003d 2N 2 + 6H 2 O
4NH 3 + 5O 2 \u003d 4NO + 6H 2 O
2PH 3 + 4O 2 \u003d P 2 O 5 + 3H 2 O
SiH 4 + 2O 2 \u003d SiO 2 + 2H 2 O
C x H y + O 2 = CO 2 + H 2 O
MeH x + 3O 2 \u003d Me x O y + H 2 O
Oxidation of lower oxides and hydroxides of polyvalent metals and nonmetals
4FeO + O 2 \u003d 2Fe 2 O 3
4Fe(OH) 2 + O 2 + 2H 2 O = 4Fe(OH) 3
2SO 2 + O 2 = 2SO 3
4NO 2 + O 2 + 2H 2 O \u003d 4HNO 3
Oxidation of metal sulfides
4FeS 2 + 11О 2 = 8SO 2 + 2Fe 2 О 3
Oxidation of organic substances
All organic compounds burn when oxidized by atmospheric oxygen.
The products of oxidation of various elements included in their molecules are:
In addition to reactions of complete oxidation (combustion), partial oxidation reactions are also possible.
Examples of reactions of incomplete oxidation of organic substances:
1) catalytic oxidation of alkanes
2) catalytic oxidation of alkenes
3) oxidation of alcohols
2R-CH 2 OH + O 2 → 2RCOH + 2H 2 O
4) oxidation of aldehydes
Ozone
Ozone O 3 is a stronger oxidizing agent than O 2, since during the reaction its molecules decompose to form atomic oxygen.
Pure O 3 is a blue gas, very toxic.
K + O 3 \u003d KO 3 potassium ozonide, red.
PbS + 2O 3 \u003d PbSO 4 + O 2
2KI + O 3 + H 2 O \u003d I 2 + 2KOH + O 2
The latter reaction is used for the qualitative and quantitative determination of ozone.
Ministry of Education and Science of the Russian Federation
"OXYGEN"
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General characteristics of oxygen.
OXYGEN (lat. Oxygenium), O (read "o"), chemical element with atomic number 8, atomic mass 15.9994. IN periodic system elements of Mendeleev oxygen is located in the second period in group VIA.
Natural oxygen consists of a mixture of three stable nuclides with mass numbers 16 (dominates in the mixture, it is 99.759% by mass), 17 (0.037%) and 18 (0.204%). The radius of the neutral oxygen atom is 0.066 nm. The configuration of the outer electron layer of the neutral unexcited oxygen atom is 2s2р4. The energies of sequential ionization of the oxygen atom are 13.61819 and 35.118 eV, the electron affinity is 1.467 eV. The radius of the O 2 ion is at different coordination numbers from 0.121 nm (coordination number 2) to 0.128 nm (coordination number 8). In compounds, it exhibits an oxidation state of -2 (valency II) and, less commonly, -1 (valency I). According to the Pauling scale, the electronegativity of oxygen is 3.5 (second place among non-metals after fluorine).
In its free form, oxygen is a colorless, odorless and tasteless gas.
Features of the structure of the O 2 molecule: atmospheric oxygen consists of diatomic molecules. The interatomic distance in the O 2 molecule is 0.12074 nm. Molecular oxygen (gaseous and liquid) is a paramagnetic substance, in each O 2 molecule there are 2 unpaired electron. This fact can be explained by the fact that each of the two antibonding orbitals in the molecule contains one unpaired electron.
The energy of dissociation of the O 2 molecule into atoms is quite high and amounts to 493.57 kJ / mol.
Physical and Chemical properties
Physical and chemical properties: in free form it occurs in the form of two modifications of O 2 (“ordinary” oxygen) and O 3 (ozone). O 2 is a colorless and odorless gas. At normal conditions oxygen gas density 1.42897 kg/m 3 . The boiling point of liquid oxygen (the liquid is blue) is -182.9°C. At temperatures from –218.7°C to –229.4°C there is solid oxygen with a cubic lattice (-modification), at temperatures from –229.4°C to –249.3°C - a modification with a hexagonal lattice and at temperatures below -249.3 ° C - cubic - modification. Other modifications of solid oxygen have also been obtained at elevated pressure and low temperatures.
At 20°C, the solubility of gas O 2 is: 3.1 ml per 100 ml of water, 22 ml per 100 ml of ethanol, 23.1 ml per 100 ml of acetone. There are organic fluorine-containing liquids (for example, perfluorobutyltetrahydrofuran) in which the solubility of oxygen is much higher.
High strength chemical bond between atoms in the O2 molecule leads to the fact that at room temperature, gaseous oxygen is chemically rather inactive. In nature, it slowly enters into transformations during the processes of decay. In addition, oxygen at room temperature is able to react with blood hemoglobin (more precisely, with heme iron II), which ensures the transfer of oxygen from the respiratory system to other organs.
Oxygen reacts with many substances without heating, for example, with alkaline and alkaline earth metals(corresponding oxides such as Li 2 O, CaO, etc., peroxides such as Na 2 O2, BaO 2, etc. and superoxides such as KO 2, RbO 2, etc. are formed), causes rust to form on the surface of steel products. Without heating, oxygen reacts with white phosphorus, with some aldehydes and other organic substances.
When heated, even a little, the chemical activity of oxygen increases dramatically. When ignited, it reacts explosively with hydrogen, methane, other combustible gases, a large number simple and complex substances. It is known that when heated in an oxygen atmosphere or in air, many simple and complex substances burn out, and various oxides are formed, for example:
S + O 2 \u003d SO 2; C + O 2 \u003d CO 2
4Fe + 3O 2 \u003d 2Fe 2 O 3; 2Cu + O 2 \u003d 2CuO
4NH 3 + 3O 2 = 2N 2 + 6H 2 O; 2H 2 S + 3O 2 \u003d 2H 2 O + 2SO 2
If a mixture of oxygen and hydrogen is stored in a glass vessel at room temperature, then the exothermic reaction of water formation
2H 2 + O 2 \u003d 2H 2 O + 571 kJ
proceeds extremely slowly; by calculation, the first droplets of water should appear in the vessel in about a million years. But when platinum or palladium (which play the role of a catalyst) is introduced into a vessel with a mixture of these gases, as well as when ignited, the reaction proceeds with an explosion.
Oxygen reacts with nitrogen N 2 either at high temperature (about 1500-2000°C) or by passing an electric discharge through a mixture of nitrogen and oxygen. Under these conditions, nitric oxide (II) is reversibly formed:
N 2 + O 2 \u003d 2NO
The resulting NO then reacts with oxygen to form a brown gas (nitrogen dioxide):
2NO + O 2 = 2NO2
From non-metals, oxygen under no circumstances directly interacts with halogens, from metals - with noble metals - silver, gold, platinum, etc.
Binary compounds of oxygen, in which the oxidation state of oxygen atoms is -2, are called oxides (the former name is oxides). Examples of oxides: carbon monoxide (IV) CO 2, sulfur oxide (VI) SO 3, copper oxide (I) Cu 2 O, aluminum oxide Al 2 O 3, manganese oxide (VII) Mn 2 O 7.
Oxygen also forms compounds in which its oxidation state is -1. These are peroxides (the old name is peroxides), for example, hydrogen peroxide H 2 O 2, barium peroxide BaO 2, sodium peroxide Na 2 O 2 and others. These compounds contain a peroxide group - O - O -. With active alkali metals, for example, with potassium, oxygen can also form superoxides, for example, KO 2 (potassium superoxide), RbO 2 (rubidium superoxide). In superoxides, the oxidation state of oxygen is –1/2. It can be noted that superoxide formulas are often written as K 2 O 4 , Rb 2 O 4 , etc.
With the most active non-metal fluorine, oxygen forms compounds in positive oxidation states. So, in the O 2 F 2 compound, the oxidation state of oxygen is +1, and in the O 2 F compound - +2. These compounds do not belong to oxides, but to fluorides. Oxygen fluorides can be synthesized only indirectly, for example, by acting with fluorine F 2 on dilute aqueous solutions of KOH.
Discovery history
The history of the discovery of oxygen, like nitrogen, is connected with the study of atmospheric air that lasted several centuries. The fact that air is not homogeneous in nature, but includes parts, one of which supports combustion and breathing, and the other does not, was known back in the 8th century by the Chinese alchemist Mao Hoa, and later in Europe by Leonardo da Vinci. In 1665, the English naturalist R. Hooke wrote that air consists of a gas contained in saltpeter, as well as an inactive gas, which makes up most of the air. The fact that air contains an element that supports life was known to many chemists in the 18th century. The Swedish pharmacist and chemist Karl Scheele began to study the composition of air in 1768. For three years, he decomposed saltpeter (KNO 3 , NaNO 3) and other substances by heating and received "fiery air" that supported breathing and combustion. But Scheele published the results of his experiments only in 1777 in the book “Chemical Treatise on Air and Fire”. In 1774, the English priest and naturalist J. Priestley obtained a combustion-supporting gas by heating "burnt mercury" (mercury oxide HgO). While in Paris, Priestley, who did not know that the gas he received was part of the air, reported his discovery to A. Lavoisier and other scientists. By this time, nitrogen was also discovered. In 1775, Lavoisier came to the conclusion that ordinary air consists of two gases - a gas necessary for breathing and supporting combustion, and a gas of an "opposite nature" - nitrogen. Lavoisier called the combustion-supporting gas oxygene - “forming acids” (from the Greek oxys - sour and gennao - I give birth; hence Russian name"oxygen"), since he then believed that all acids contain oxygen. It has long been known that acids can be both oxygen-containing and anoxic, but the name given to the element by Lavoisier has remained unchanged. For almost a century and a half, 1/16 of the mass of an oxygen atom served as a unit for comparing the masses of various atoms with each other and was used in the numerical characterization of the masses of atoms of various elements (the so-called oxygen scale of atomic masses).
Occurrence in nature: oxygen is the most common element on Earth, its share (as part of various compounds, mainly silicates), accounts for about 47.4% of the mass of the solid earth's crust. Marine and fresh water contain a huge amount of bound oxygen - 88.8% (by mass), in the atmosphere the content of free oxygen is 20.95% (by volume). The element oxygen is part of more than 1500 compounds of the earth's crust.
Receipt:
Currently, oxygen in industry is obtained by air separation at low temperatures. First, the air is compressed by the compressor, while the air is heated. The compressed gas is allowed to cool to room temperature and then allowed to expand freely. As the gas expands, the temperature drops sharply. Cooled air, the temperature of which is several tens of degrees lower than the temperature environment, again subjected to compression up to 10-15 MPa. Then the released heat is again taken away. After several cycles of "compression-expansion" the temperature drops below the boiling point of both oxygen and nitrogen. Liquid air is formed, which is then subjected to distillation (distillation). The boiling point of oxygen (-182.9°C) is more than 10 degrees higher than the boiling point of nitrogen (-195.8°C). Therefore, nitrogen evaporates first from the liquid, and oxygen accumulates in the remainder. Due to the slow (fractional) distillation, it is possible to obtain pure oxygen, in which the nitrogen impurity content is less than 0.1 volume percent.
Oxygen is a chemical element whose properties will be discussed in the next few paragraphs. Let us turn to the Periodic System of chemical elements of D.I. Mendeleev. The element oxygen is located in period 2, group VI, the main subgroup.
It also states that the relative atomic mass of oxygen is 16.
By the serial number of oxygen in the Periodic System, one can easily determine the number of electrons contained in its atom, the nuclear charge of the oxygen atom, the number of protons.
The valency of oxygen in most compounds is II. An oxygen atom can attach two electrons and turn into an ion: O0 + 2ē = O−2.
It is worth noting that oxygen is the most common element on our planet. Oxygen is part of the water. Marine and fresh waters are 89% oxygen by mass. Oxygen is found in many minerals and rocks. The mass fraction of oxygen in the earth's crust is about 47%. Air contains about 23% oxygen by mass.
Physical properties of oxygen
When two oxygen atoms interact, a stable molecule of a simple oxygen substance O2 is formed. This simple substance, like the element, is called oxygen. Do not confuse oxygen as an element and oxygen as a simple substance!
By physical properties oxygen It is a colorless, odorless and tasteless gas. Practically insoluble in water (at room temperature and normal atmospheric pressure, the solubility of oxygen is about 8 mg per liter of water).
Oxygen is soluble in water - 31 ml of oxygen (0.004% by mass) dissolves in 1 liter of water at a temperature of 20 ° C. However, this amount is sufficient for the respiration of fish living in water bodies. Gaseous oxygen is slightly heavier than air: 1 liter of air at 0°C and normal pressure weighs 1.29 g, and 1 liter of oxygen weighs 1.43 g.
Oxygen exhibits interesting properties when strongly cooled. So, at a temperature -183°C oxygen condenses into a clear mobile liquid of a pale blue color.
If liquid oxygen is cooled even more, then at a temperature -218°C oxygen "freezes" in the form of blue crystals. If the temperature is gradually raised, then -218°С, solid oxygen will begin to melt, and when -183°C- boil. Therefore, the boiling and condensation points, as well as the freezing and melting points for substances, are the same.
Dewar vessels are used to store and transport liquid oxygen.. Dewar flasks are used for storage and transportation of liquids, the temperature of which should long time stay constant. The Dewar vessel bears the name of its inventor, the Scottish physicist and chemist James Dewar.
The simplest Dewar vessel is a household thermos. The device of the vessel is quite simple: it is a flask placed in a large flask. Air is evacuated from the sealed space between the flasks. Due to the absence of air between the walls of the flasks, the liquid poured into the inner flask does not cool or heat up for a long time.
Oxygen is a paramagnetic substance, that is, in liquid and solid states, it is attracted by a magnet.
In nature, there is another simple substance, consisting of oxygen atoms. This is ozone. Chemical formula ozone O3. Ozone, like oxygen, is a gas under normal conditions. Ozone is formed in the atmosphere during lightning discharges. The characteristic smell of freshness after a thunderstorm is the smell of ozone.
If ozone is obtained in the laboratory and a significant amount of it is collected, then in high concentrations ozone will have a sharp unpleasant odor. Ozone is obtained in the laboratory in special devices - ozonators. Ozonator- a glass tube into which a current of oxygen is supplied, and an electric discharge is created. An electrical discharge turns oxygen into ozone:
Unlike colorless oxygen, ozone is a blue gas. The solubility of ozone in water is about 0.5 liters of gas per 1 liter of water, which is much higher than that of oxygen. Given this property, ozone is used for disinfection drinking water, as it has a detrimental effect on pathogens.
At low temperatures, ozone behaves similarly to oxygen. At a temperature of -112°C, it condenses into a violet liquid, and at a temperature of -197°C, it crystallizes in the form of dark purple, almost black crystals.
Thus, we can conclude that atoms of the same chemical element can form different simple substances.
The phenomenon of the existence of a chemical element in the form of several simple substances is called allotropy.
Simple substances formed by the same element are called allotropic modifications
Means, oxygen and ozone are allotropic modifications of the chemical element oxygen. There is evidence that at ultra-low temperatures, in a liquid or solid state, oxygen can exist in the form of O4 and O8 molecules.
The oxygen cycle in nature
The amount of oxygen in the atmosphere is constant. Consequently, the expended oxygen is constantly replenished with new.
The most important sources of oxygen in nature are carbon dioxide and water. Oxygen enters the atmosphere mainly as a result of the photosynthesis process that occurs in plants, according to the reaction scheme:
CO2 + H2O → C6H12O6 + O2.
Oxygen can also be formed in the upper layers of the Earth's atmosphere: due to the impact solar radiation, water vapor partially decomposes with the formation of oxygen.
Oxygen is consumed during respiration, fuel combustion, oxidation of various substances in living organisms, and oxidation of inorganic substances found in nature. A large amount of oxygen is consumed in technological processes, such as, for example, steel smelting.
The oxygen cycle in nature can be represented as a diagram:
- Oxygen- an element of group VI, the main subgroup, 2 periods of the Periodic System of D.I. Mendeleev
- The element oxygen forms in nature two allotropic modifications: oxygen O2 and ozone O3
- The phenomenon of the existence of a chemical element in the form of several simple substances is called allotropy
- Simple substances are called allotropic modifications
- Oxygen and ozone have different physical properties
- Oxygen- a colorless gas, odorless, tasteless, practically insoluble in water, at a temperature of -183 ° C it condenses into a pale blue liquid. At -218°C crystallizes in the form of blue crystals
- Ozone- a blue gas with a pungent odor. Let's well dissolve in water. At -112°С, it condenses into a violet liquid, crystallizes as dark violet, almost black crystals, at -197°С
- Liquid oxygen, ozone and other gases are stored in Dewar flasks
Oxygen (lat. Oxygenium), O, a chemical element of the VI group of the periodic system of Mendeleev; atomic number 8, atomic mass 15.9994. Under normal conditions, oxygen is a colorless, odorless and tasteless gas. It is difficult to name another element that would play such a role on our planet. important role like oxygen.
Historical reference. The processes of combustion and respiration have long attracted the attention of scientists. The first indications that not all air, but only its "active" part supports combustion, were found in Chinese manuscripts of the 8th century. Much later, Leonardo da Vinci (1452-1519) considered air as a mixture of two gases, only one of which is consumed during combustion and breathing. The final discovery of the two main components of air - nitrogen and oxygen, which made an era in science, occurred only at the end of the 18th century. Oxygen was obtained almost simultaneously by K. Scheele (1769-70) by calcining saltpeter (KNO3, NaNO3), manganese dioxide MnO2 and other substances and J. Priestley (1774) by heating red lead Pb3O4 and mercury oxide HgO. In 1772, D. Rutherford discovered nitrogen. In 1775, A. Lavoisier, having made a quantitative analysis of air, found that it “consists of two (gases) of a different and, so to speak, opposite nature,” that is, of oxygen and nitrogen. Based on broad experimental studies Lavoisier correctly explained combustion and respiration as processes of interaction between substances and oxygen. Since oxygen is a part of acids, Lavoisier called it oxygene, that is, "former of acids" (from the Greek oxys - sour and gennao - I give birth; hence the Russian name "oxygen").
Distribution of oxygen in nature. Oxygen is the most common chemical element on Earth. Bound oxygen makes up about 6/7 of the mass of the Earth's water shell - the hydrosphere (85.82% by mass), almost half of the lithosphere (47% by mass), and only in the atmosphere, where oxygen is in a free state, does it take second place (23 .15% by weight) after nitrogen.
Oxygen also comes first in terms of the number of minerals it forms (1364); Among the minerals containing oxygen, silicates (feldspars, micas, and others), quartz, iron oxides, carbonates, and sulfates predominate. In living organisms, on average, about 70% oxygen; it is part of most of the most important organic compounds (proteins, fats, carbohydrates, etc.) and in the composition of inorganic compounds of the skeleton. The role of free oxygen in biochemical and physiological processes, especially in respiration, is exceptionally important. With the exception of some anaerobic microorganisms, all animals and plants obtain the energy necessary for their life activity due to the biological oxidation of various substances with the help of oxygen.
The entire mass of free Oxygen of the Earth arose and is preserved due to the vital activity of green plants on land and the World Ocean, which release Oxygen in the process of photosynthesis. On earth's surface where photosynthesis proceeds and free oxygen predominates, sharply oxidizing conditions are formed. On the contrary, in magma, as well as deep horizons of underground waters, in the silts of seas and lakes, in swamps, where free oxygen is absent, a reducing environment is formed. Oxidation-reduction processes involving oxygen determine the concentration of many elements and the formation of mineral deposits - coal, oil, sulfur, iron ores, copper, etc. Changes in the oxygen cycle are introduced by economic activity person. In some industrial countries more oxygen is consumed during the combustion of fuel than it is released by plants during photosynthesis. In total, about 9·109 tons of oxygen is annually consumed for fuel combustion in the world.
Isotopes, atom and molecule of oxygen. Oxygen has three stable isotopes: 16O, 17O and 18O, the average content of which is respectively 99.759%, 0.037% and 0.204% of total number oxygen atoms on earth. The sharp predominance of the lightest of them, 16O, in the mixture of isotopes is due to the fact that the nucleus of the 16O atom consists of 8 protons and 8 neutrons. And such nuclei, as follows from the theory atomic nucleus, are particularly stable.
In accordance with the position of Oxygen in the periodic system of elements of Mendeleev, the electrons of the Oxygen atom are located on two shells: 2 - on the inner and 6 - on the outer (configuration 1s22s22p4). Since the outer shell of the oxygen atom is not filled, and the ionization potential and electron affinity are respectively 13.61 and 1.46 eV, the oxygen atom in chemical compounds usually acquires electrons and has a negative effective charge. On the contrary, there are extremely rare compounds in which electrons are detached (more precisely, pulled away) from the oxygen atom (such, for example, F2O, F2O3). Previously, based solely on the position of Oxygen in the periodic system, the oxygen atom in oxides and in most other compounds was assigned a negative charge (-2). However, as experimental data show, the O2 - ion does not exist either in the free state or in compounds, and the negative effective charge of the oxygen atom almost never significantly exceeds unity.
Under normal conditions, the oxygen molecule is diatomic (O2); in a quiet electric discharge, a triatomic O3 molecule, ozone, is also formed; at high pressures, O4 molecules are found in small amounts. Electronic structure O2 is of great theoretical interest. In the ground state, the O2 molecule has two unpaired electrons; the "usual" classical structural formula O=O with two two-electron bonds is inapplicable to it. An exhaustive explanation of this fact is given in the framework of the theory molecular orbitals. The ionization energy of an oxygen molecule (O2 - e > O2+) is 12.2 eV, and the electron affinity (O2 + e > O2-) is 0.94 eV. The dissociation of molecular oxygen into atoms at ordinary temperature is negligible, it becomes noticeable only at 1500°C; at 5000°C the oxygen molecules are almost completely dissociated into atoms.
Physical properties of oxygen. Oxygen is a colorless gas that condenses at -182.9°C and normal pressure to a pale blue liquid, which solidifies at -218.7°C to form blue crystals. The density of gaseous oxygen (at 0°C and normal pressure) is 1.42897 g/l. The critical temperature of oxygen is rather low (Tcrit = -118.84°C), that is, lower than that of Cl2, CO2, SO2, and some other gases; Tcrit = 4.97 MN/m2 (49.71 atm). Thermal conductivity (at 0°C) 23.86 10-3 W/(m K). Molar heat capacity (at 0°C) in j/(mol K) Cp = 28.9, Cv = 20.5, Cp/Cv = 1.403. The dielectric constant of gaseous oxygen is 1.000547 (0°C), liquid 1.491. Viscosity 189 mpoise (0°C). Oxygen is slightly soluble in water: at 20°C and 1 atm, 0.031 m 3 is dissolved in 1 m 3 of water, and at 0° C - 0.049 m 3 of oxygen. Good solid oxygen absorbers are platinum black and activated charcoal.
Chemical properties of oxygen. Oxygen forms chemical compounds with all elements except light inert gases. Being the most active (after fluorine) non-metal, oxygen interacts directly with most elements; the exceptions are heavy inert gases, halogens, gold and platinum; their compounds with oxygen are obtained indirectly. Almost all reactions of oxygen with other substances - oxidation reactions are exothermic, that is, they are accompanied by the release of energy. Oxygen reacts extremely slowly with hydrogen at ordinary temperatures; above 550°C this reaction proceeds with an explosion 2H2 + O2 = 2H2O.
Oxygen reacts very slowly with sulfur, carbon, nitrogen, and phosphorus under normal conditions. With an increase in temperature, the reaction rate increases and at a certain ignition temperature characteristic of each element, combustion begins. The reaction of nitrogen with oxygen due to the special strength of the N2 molecule is endothermic and becomes noticeable only above 1200°C or in an electric discharge: N2 + O2 = 2NO. Oxygen actively oxidizes almost all metals, especially alkali and alkaline earth metals. The activity of the interaction of metal with oxygen depends on many factors - the state of the metal surface, the degree of grinding, the presence of impurities.
In the process of interaction of a substance with oxygen, the role of water is extremely important. For example, even such an active metal as potassium does not react with oxygen completely devoid of moisture, but ignites in oxygen at ordinary temperature in the presence of even negligible amounts of water vapor. It is estimated that up to 10% of all metal produced is lost annually as a result of corrosion.
Oxides of some metals, by adding oxygen, form peroxide compounds containing 2 or more oxygen atoms bonded to each other. Thus, peroxides Na2O2 and BaO2 include peroxide ion O22-, superoxides NaO2 and KO2 - ion O2-, and ozonides NaO3, KO3, RbO3 and CsO3 - ion O3- Oxygen exothermically interacts with many complex substances. So, ammonia burns in oxygen in the absence of catalysts, the reaction proceeds according to the equation: 4NH3 + 3O2 = 2N2 + 6H2O. Oxidation of ammonia with oxygen in the presence of a catalyst gives NO (this process is used to obtain nitric acid). Of particular importance is the combustion of hydrocarbons (natural gas, gasoline, kerosene) - the most important source heat in everyday life and industry, for example CH4 + 2O2 = CO2 + 2H2O. The interaction of hydrocarbons with oxygen underlies many of the most important production processes - such, for example, is the so-called conversion of methane to produce hydrogen: 2CH4 + O2 + 2H2O = 2CO2 + 6H2. Many organic compounds (hydrocarbons with double or triple bonds, aldehydes, phenols, as well as turpentine, drying oils, and others) actively add oxygen. Oxidation of nutrients in cells by oxygen serves as a source of energy for living organisms.
Getting Oxygen. There are 3 main ways to obtain oxygen: chemical, electrolysis (electrolysis of water) and physical (air separation).
The chemical method was invented earlier than others. Oxygen can be obtained, for example, from Bertolet salt KClOz, which decomposes when heated, releasing O2 in an amount of 0.27 m 3 per 1 kg of salt. Barium oxide BaO, when heated to 540°C, first absorbs oxygen from the air, forming BaO2 peroxide, and upon subsequent heating to 870°C, BaO2 decomposes, releasing pure oxygen. It can also be obtained from KMnO4, Ca2PbO4, K2Cr2O7 and other substances by heating and adding catalysts. The chemical method of obtaining oxygen is inefficient and expensive, has no industrial significance and is used only in laboratory practice.
The electrolysis method consists in passing a constant electric current through water, to which a solution of caustic soda NaOH is added to increase its electrical conductivity. In this case, water decomposes into oxygen and hydrogen. Oxygen is collected near the positive electrode of the cell, and hydrogen - near the negative. In this way, oxygen is extracted as a by-product in the production of hydrogen. To obtain 2 m3 of hydrogen and 1 m3 of oxygen, 12-15 kWh of electricity is consumed.
Air separation is the main way to obtain oxygen in modern technology. It is very difficult to carry out the separation of air in a normal gaseous state, therefore, the air is first liquefied, and only then divided into its component parts. This method of obtaining oxygen is called air separation by deep cooling. First, the air is compressed by a compressor, then, after passing through the heat exchangers, it expands in an expander machine or a throttle valve, as a result of which it is cooled to a temperature of 93 K (-180 ° C) and turns into liquid air. Further separation of liquid air, which consists mainly of liquid nitrogen and liquid oxygen, is based on the difference in the boiling points of its components [Boil O2 90.18 K (-182.9°C), N2 Boil 77.36 K (-195.8° WITH)]. With the gradual evaporation of liquid air, nitrogen is first evaporated, and the remaining liquid becomes more and more enriched with oxygen. By repeating this process many times on the distillation plates of the air separation columns, liquid oxygen of the required purity (concentration) is obtained. The USSR manufactures small (several liters) and the world's largest oxygen air separation plants (35,000 m 3 /h of oxygen). These units produce technological Oxygen with a concentration of 95-98.5%, technical Oxygen with a concentration of 99.2-99.9% and purer, medical Oxygen, dispensing products in liquid and gaseous form. The consumption of electrical energy is from 0.41 to 1.6 kWh/m3.
Oxygen can also be obtained by separating air by the method of selective penetration (diffusion) through membrane partitions. Air under high pressure is passed through fluoroplastic, glass or plastic partitions, the structural lattice of which is capable of passing the molecules of some components and retaining others.
Gaseous oxygen is stored and transported in steel cylinders and receivers at a pressure of 15 and 42 MN/m2 (respectively 150 and 420 bar, or 150 and 420 atm), liquid oxygen in metal Dewar vessels or in special tank-tanks. Special pipelines are also used to transport liquid and gaseous oxygen. Oxygen cylinders are painted blue and have a black inscription "oxygen".
The use of oxygen. Technical oxygen is used in the processes of flame treatment of metals, in welding, oxygen cutting, surface hardening, metallization, and others, as well as in aviation, on submarines, and so on. Technological oxygen is used in the chemical industry in the production of artificial liquid fuels, lubricating oils, nitric and sulfuric acids, methanol, ammonia and ammonia fertilizers, metal peroxides and other chemical products. Liquid oxygen is used in blasting, in jet engines, and in laboratory practice as a refrigerant.
Pure oxygen enclosed in cylinders is used for breathing at high altitudes, during space flights, during scuba diving, etc. .P.
Oxygen is widely used in metallurgy to intensify a number of pyrometallurgical processes. Complete or partial replacement of the air entering the metallurgical units with oxygen has changed the chemistry of the processes, their thermal parameters and technical and economic indicators. Oxygen blast made it possible to reduce heat losses with outgoing gases, a significant part of which during air blast was nitrogen. Not taking a significant part in chemical processes, nitrogen slowed down the course of reactions, reducing the concentration of active reagents in the redox medium. When purged with oxygen, fuel consumption is reduced, the quality of the metal is improved, it is possible to obtain new types of products in metallurgical units (for example, slags and gases of an unusual composition for this process, which find special technical applications), etc.
The first experiments on the use of oxygen-enriched blast in blast-furnace production for the smelting of pig iron and ferromanganese were carried out simultaneously in the USSR and Germany in 1932-33. Increased content Oxygen in the blast-furnace blast is accompanied by a large reduction in the consumption of the latter, while the content of carbon monoxide in the blast-furnace gas increases and its calorific value increases. Oxygen enrichment of the blast makes it possible to increase the productivity of the blast furnace, and in combination with gaseous and liquid fuel supplied to the hearth, it leads to a reduction in coke consumption. In this case, for each additional percentage of Oxygen in the blast, the productivity increases by about 2.5%, and the coke consumption decreases by 1%.
Oxygen in open-hearth production in the USSR was first used to intensify fuel combustion (on an industrial scale, oxygen was first used for this purpose at the Sickle and Hammer and Krasnoye Sormovo plants in 1932-33). In 1933 they began to blow oxygen directly into the liquid bath in order to oxidize impurities during the finishing period. With an increase in the intensity of melt blowing by 1 m 3 /t per 1 hour, the productivity of the furnace increases by 5-10%, fuel consumption is reduced by 4-5%. However, blowing increases the loss of metal. At an oxygen consumption of up to 10 m 3 /t for 1 hour, the yield of steel decreases slightly (up to 1%). Oxygen is becoming more and more widespread in open-hearth production. So, if in 1965 with the use of oxygen in open-hearth furnaces 52.1% of steel was smelted, then in 1970 it was already 71%.
Experiments on the use of oxygen in electric steel-smelting furnaces in the USSR began in 1946 at the Elektrostal plant. The introduction of oxygen blast made it possible to increase the productivity of furnaces by 25-30%, reduce the specific power consumption by 20-30%, improve the quality of steel, and reduce the consumption of electrodes and some scarce alloying additives. The supply of oxygen to electric furnaces proved to be especially effective in the production of stainless steels with a low carbon content, the smelting of which is very difficult due to the carburizing effect of the electrodes. The share of electric steel produced in the USSR using oxygen grew continuously and in 1970 amounted to 74.6% of the total steel production.
In cupola melting, oxygen-enriched blast is mainly used for high overheating of cast iron, which is necessary in the production of high-quality, in particular high-alloy, castings (silicon, chromium, etc.). Depending on the degree of oxygen enrichment of the cupola blast, fuel consumption is reduced by 30-50%, the sulfur content in the metal is reduced by 30-40%, the productivity of the cupola is increased by 80-100%, and the temperature of cast iron produced from it increases significantly (up to 1500 ° C). .
Oxygen in non-ferrous metallurgy became widespread somewhat later than in ferrous metallurgy. Oxygen-enriched blast is used in the converting of matte, in the processes of slag sublimation, walezation, agglomeration, and in the reflective melting of copper concentrates. In lead, copper and nickel production, oxygen blast intensified the processes of mine smelting, made it possible to reduce coke consumption by 10-20%, increase penetration by 15-20% and reduce the amount of fluxes in some cases by 2-3 times. Oxygen enrichment of the air blast up to 30% during the roasting of zinc sulfide concentrates increased the productivity of the process by 70% and reduced the volume of exhaust gases by 30%.
oxygen element isotope property
