Physical and chemical properties of oxygen. General characteristics of oxygen and its combustion reaction
DEFINITION
Oxygen- the eighth element of the Periodic Table. Designation - O from the Latin “oxygenium”. Located in the second period, group VIA. Refers to non-metals. The nuclear charge is 8.
Oxygen is the most common element in the earth's crust. In a free state, it is found in the atmospheric air; in a bound form, it is part of water, minerals, rocks and all substances from which the organisms of plants and animals are built. The mass fraction of oxygen in the earth's crust is about 47%.
In its simple form, oxygen is a colorless, odorless gas. It is slightly heavier than air: the mass of 1 liter of oxygen under normal conditions is 1.43 g, and 1 liter of air is 1.293 g. Oxygen dissolves in water, although in small quantities: 100 volumes of water at 0 o C dissolve 4.9, and at 20 o C - 3.1 volumes of oxygen.
Atomic and molecular mass of oxygen
DEFINITION
Relative atomic mass A r is the molar mass of an atom of a substance divided by 1/12 of the molar mass of a carbon-12 atom (12 C).
The relative atomic mass of atomic oxygen is 15.999 amu.
DEFINITION
Relative molecular weight M r is the molar mass of a molecule divided by 1/12 the molar mass of a carbon-12 atom (12 C).
This is a dimensionless quantity. It is known that the oxygen molecule is diatomic - O 2. The relative molecular mass of an oxygen molecule will be equal to:
M r (O 2) = 15.999 × 2 ≈32.
Allotropy and allotropic modifications of oxygen
Oxygen can exist in the form of two allotropic modifications - oxygen O 2 and ozone O 3 (the physical properties of oxygen are described above).
Under normal conditions, ozone is a gas. It can be separated from oxygen by strong cooling; ozone condenses into a blue liquid, boiling at (-111.9 o C).
The solubility of ozone in water is much greater than that of oxygen: 100 volumes of water at 0 o C dissolve 49 volumes of ozone.
The formation of ozone from oxygen can be expressed by the equation:
3O 2 = 2O 3 - 285 kJ.
Isotopes of oxygen
It is known that in nature oxygen can be found in the form of three isotopes 16 O (99.76%), 17 O (0.04%) and 18 O (0.2%). Their mass numbers are 16, 17 and 18, respectively. The nucleus of an atom of the oxygen isotope 16 O contains eight protons and eight neutrons, and the isotopes 17 O and 18 O contain the same number of protons, nine and ten neutrons, respectively.
There are twelve radioactive isotopes of oxygen with mass numbers from 12 to 24, of which the most stable isotope 15 O with a half-life of 120 s.
Oxygen ions
The outer energy level of the oxygen atom has six electrons, which are valence electrons:
1s 2 2s 2 2p 4 .
The structure of the oxygen atom is shown below:
As a result of chemical interaction, oxygen can lose its valence electrons, i.e. be their donor, and turn into positively charged ions or accept electrons from another atom, i.e. be their acceptor and turn into negatively charged ions:
O 0 +2e → O 2- ;
O 0 -1e → O 1+ .
Oxygen molecule and atom
The oxygen molecule consists of two atoms - O 2. Here are some properties characterizing the oxygen atom and molecule:
Examples of problem solving
EXAMPLE 1
Ministry of Education and Science of the Russian Federation
"OXYGEN"
Completed:
Checked:
General characteristics of oxygen.
OXYGEN (lat. Oxygenium), O (read “o”), chemical element with atomic number 8, atomic mass 15.9994. In Mendeleev's periodic table of elements, 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 contains 99.759% by mass), 17 (0.037%) and 18 (0.204%). The radius of a neutral oxygen atom is 0.066 nm. The configuration of the outer electronic 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 (valence II) and, less commonly, –1 (valence I). According to the Pauling scale, the electronegativity of oxygen is 3.5 (the second highest 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; each O2 molecule has 2 unpaired electrons. This fact can be explained by the fact that in the molecule there is one unpaired electron in each of the two antibonding orbitals.
The dissociation energy 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 is found in the form of two modifications O 2 (“ordinary” oxygen) and O 3 (ozone). O 2 is a colorless and odorless gas. Under normal conditions, the density of oxygen gas is 1.42897 kg/m3. 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 there is a modification with a hexagonal lattice and at temperatures below –249.3°C - cubic modification. Other modifications of solid oxygen have been obtained at elevated pressure and low temperatures.
At 20°C, the solubility of O2 gas 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.
The high strength of the chemical bond between the atoms in the O2 molecule leads to the fact that at room temperature oxygen gas is chemically quite inactive. In nature, it slowly undergoes transformation during decay processes. In addition, oxygen at room temperature is able to react with hemoglobin in the blood (more precisely with heme iron II), which ensures the transfer of oxygen from the respiratory organs to other organs.
Oxygen reacts with many substances without heating, for example, with alkali 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 are formed etc.), causes the formation of rust on the surface of steel products. Without heating, oxygen reacts with white phosphorus, with some aldehydes and other organic substances.
When heated, even slightly, the chemical activity of oxygen increases sharply. When ignited, it reacts explosively with hydrogen, methane, other flammable gases, and a large number of simple and complex substances. It is known that when heated in an oxygen atmosphere or in air, many simple and complex substances burn, and various oxides are formed, for example:
S+O 2 = SO 2; C + O 2 = CO 2
4Fe + 3O 2 = 2Fe 2 O 3; 2Cu + O 2 = 2CuO
4NH 3 + 3O 2 = 2N 2 + 6H 2 O; 2H 2 S + 3O 2 = 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 to form water
2H 2 + O 2 = 2H 2 O + 571 kJ
proceeds extremely slowly; According to calculations, the first drops of water should appear in the vessel in about a million years. But when platinum or palladium (playing 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 N2 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:
N2 + O2 = 2NO
The resulting NO then reacts with oxygen to form brown gas (nitrogen dioxide):
2NO + O 2 = 2NO2
Of non-metals, oxygen does not directly interact with halogens under any circumstances, and of metals - with noble metals - silver, gold, platinum, etc.
Binary oxygen compounds in which the oxidation state of oxygen atoms is –2 are called oxides (formerly called 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, 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 may be noted that superoxide formulas are often written as K 2 O 4, Rb 2 O 4, etc.
With the most active nonmetal fluorine, oxygen forms compounds in positive oxidation states. So, in the compound O 2 F 2 the oxidation state of oxygen is +1, and in the compound O 2 F - +2. These compounds do not belong to oxides, but to fluorides. Oxygen fluorides can be synthesized only indirectly, for example, by the action of fluorine F2 on dilute aqueous solutions of KOH.
History of discovery
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 by its nature is not homogeneous, but includes parts, one of which supports combustion and respiration, 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 the air consists of the gas contained in nitrate, as well as inactive gas, which makes up most of the air. The fact that air contains a life-sustaining element was known to many chemists in the 18th century. The Swedish pharmacist and chemist Karl Scheele began studying the composition of air in 1768. For three years, he decomposed saltpeter (KNO 3, NaNO 3) and other substances by heating and obtained “fiery air” that supported respiration 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 gas that supports combustion by heating “burnt mercury” (mercuric oxide HgO). While in Paris, Priestley, who did not know that the gas he obtained was part of the air, reported his discovery to A. Lavoisier and other scientists. By this time, nitrogen had also been 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 “the opposite nature” - nitrogen. Lavoisier called the combustion-supporting gas oxygene - “acid-forming” (from the Greek oxys - sour and gennao - I give birth; hence the 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 oxygen-free, but the name given to Lavoisier’s element 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 different atoms with each other and was used to numerically characterize 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 (in various compounds, mainly silicates) accounts for about 47.4% of the mass of the solid earth's crust. Sea and fresh waters 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 1,500 compounds in the earth's crust.
Receipt:
Currently, oxygen is produced in industry by separating air at low temperatures. First, the air is compressed by a compressor, which heats up the air. The compressed gas is allowed to cool to room temperature and then allowed to expand freely. As it expands, the temperature of the gas drops sharply. Cooled air, the temperature of which is several tens of degrees lower than the ambient temperature, is again compressed to 10-15 MPa. Then the released heat is removed again. After several compression-expansion cycles, the temperature drops below the boiling point of both oxygen and nitrogen. Liquid air is formed, which is then subjected to 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 from the liquid first, and oxygen accumulates in the remainder. Due to slow (fractional) distillation, it is possible to obtain pure oxygen, in which the nitrogen impurity content is less than 0.1 percent by volume.
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
Clarke in the earth's crust is 47% by mass; in the hydrosphere 85.82% by mass; in the atmosphere 20.95% by volume.
The most common element.
Forms of occurrence of 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. Valence = II; oxidation state -2 (except for H 2 O 2, OF 2, O 2 F 2)
Physical properties of O2
Under normal conditions, molecular oxygen O2 is in a gaseous state, has no color, odor or taste, and is slightly soluble in water. When deeply cooled under pressure, it condenses into a pale blue liquid (Tkip - 183°C), which at -219°C turns into blue-blue crystals.
Methods of obtaining
1. Oxygen is formed in nature during 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) electrolysis of water: 2H 2 O → 2H 2 + O 2
3. In the laboratory, the following is obtained by thermal redox decomposition of salts:
a) 2КlO 3 = 3О 2 + 2KCI
b) 2KMnO 4 = O 2 + MnO 2 + K 2 MnO 4
c) 2KNO 3 = O 2 + 2KNO 2
d) 2Cu(NO3)O2 = O2 + 4NO2 + 2CuO
e) 2AgNO 3 = O 2 + 2NO 2 + 2Ag
4. In hermetically sealed rooms and in devices for autonomous breathing, oxygen is obtained by the reaction:
2Na 2 O 2 + 2CO 2 = 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 upon heating, as well as in the presence of catalysts (exceptions are Au, Pt, Hal 2, noble gases). Reactions involving O 2 are in most cases exothermic, often proceeding in combustion mode, sometimes in explosion. As a result of the reactions, compounds are formed in which the oxygen atoms, as a rule, have C.O. -2:
Oxidation of alkali metals
4Li + O 2 = 2Li 2 O lithium oxide
2Na + O 2 = Na 2 O 2 sodium peroxide
K + O 2 = KO 2 potassium superoxide
Oxidation of all metals except Au, Pt
Me + O 2 = Me x O y oxides
Oxidation of non-metals other than halogens and noble gases
N 2 + O 2 = 2NO - Q
S + O 2 = SO 2;
C + O 2 = CO 2;
4P + 5O 2 = 2P 2 O 5
Si + O 2 = SiO 2
Oxidation of hydrogen compounds of nonmetals and metals
4HI + O 2 = 2I 2 + 2H 2 O
2H 2 S + 3O 2 = 2SO 2 + 2H 2 O
4NH 3 + 3O 2 = 2N 2 + 6H 2 O
4NH 3 + 5O 2 = 4NO + 6H 2 O
2PH 3 + 4O 2 = P 2 O 5 + 3H 2 O
SiH 4 + 2O 2 = SiO 2 + 2H 2 O
C x H y + O 2 = CO 2 + H 2 O
MeH x + 3O 2 = Me x O y + H 2 O
Oxidation of lower oxides and hydroxides of polyvalent metals and non-metals
4FeO + O 2 = 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 = 4HNO 3
Oxidation of metal sulfides
4FeS 2 + 11O 2 = 8SO 2 + 2Fe 2 O 3
Oxidation of organic substances
All organic compounds burn, oxidized by atmospheric oxygen.
The oxidation products of various elements included in their molecules are:
In addition to complete oxidation (combustion) reactions, incomplete 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 O3 is a stronger oxidizing agent than O2, since during the reaction its molecules disintegrate to form atomic oxygen.
Pure O 3 is a blue gas, very poisonous.
K + O 3 = KO 3 potassium ozonide, red.
PbS + 2O 3 = PbSO 4 + O 2
2KI + O 3 + H 2 O = I 2 + 2KON + O 2
The latter reaction is used for the qualitative and quantitative determination of ozone.
Oxygen is in the second period of the VIth main group of the outdated short version of the periodic table. According to the new numbering standards, this is the 16th group. The corresponding decision was made by IUPAC in 1988. The formula of oxygen as a simple substance is O 2. Let's consider its main properties, role in nature and economy. Let's start with the characteristics of the entire group of the periodic table, which is headed by oxygen. The element is different from its related chalcogens, and water is different from the hydrogen selenium and tellurium. An explanation for all the distinctive features can be found only by learning about the structure and properties of the atom.
Chalcogens - oxygen-related elements
Atoms with similar properties form one group in the periodic table. Oxygen heads the chalcogen family, but differs from them in a number of properties.
The atomic mass of oxygen, the ancestor of the group, is 16 a. e.m. Chalcogens, when forming compounds with hydrogen and metals, exhibit their usual oxidation state: -2. For example, in the composition of water (H 2 O) the oxidation number of oxygen is -2.
The composition of typical hydrogen compounds of chalcogens corresponds to the general formula: H 2 R. When these substances dissolve, acids are formed. Only the hydrogen compound of oxygen—water—has special properties. Scientists have concluded that this unusual substance is both a very weak acid and a very weak base.
Sulfur, selenium and tellurium have typical positive oxidation states (+4, +6) when combined with oxygen and other highly electronegative (EO) nonmetals. The composition of chalcogen oxides is reflected by the general formulas: RO 2, RO 3. The corresponding acids have the composition: H 2 RO 3, H 2 RO 4.
The elements correspond to simple substances: oxygen, sulfur, selenium, tellurium and polonium. The first three representatives exhibit non-metallic properties. The formula of oxygen is O 2. An allotropic modification of the same element is ozone (O 3). Both modifications are gases. Sulfur and selenium are solid non-metals. Tellurium is a metalloid substance, a conductor of electric current, polonium is a metal.
Oxygen is the most common element
We already know that there is another version of the existence of the same chemical element in the form of a simple substance. This is ozone, a gas that forms a layer at an altitude of about 30 km from the earth's surface, often called the ozone screen. Bound oxygen is included in water molecules, in the composition of many rocks and minerals, and organic compounds.
Structure of the oxygen atom
Mendeleev's periodic table contains complete information about oxygen:
- The serial number of the element is 8.
- Core charge - +8.
- The total number of electrons is 8.
- The electronic formula of oxygen is 1s 2 2s 2 2p 4.
In nature, there are three stable isotopes that have the same serial number in the periodic table, an identical composition of protons and electrons, but a different number of neutrons. Isotopes are designated by the same symbol - O. For comparison, here is a diagram showing the composition of three isotopes of oxygen:
Properties of oxygen - a chemical element
At the 2p sublevel of the atom there are two unpaired electrons, which explains the appearance of oxidation states -2 and +2. Two paired electrons cannot be separated for the oxidation state to increase to +4, as in sulfur and other chalcogens. The reason is the lack of a free sublevel. Therefore, in compounds, the chemical element oxygen does not exhibit a valence and oxidation state equal to the group number in the short version of the periodic table (6). Its usual oxidation number is -2.
Only in compounds with fluorine does oxygen exhibit an uncharacteristic positive oxidation state of +2. The EO value of two strong nonmetals is different: EO (O) = 3.5; EO (F) = 4. As a more electronegative chemical element, fluorine retains its electrons more strongly and attracts valence particles to oxygen atoms. Therefore, in the reaction with fluorine, oxygen is a reducing agent and donates electrons.
Oxygen is a simple substance
During experiments in 1774, the English researcher D. Priestley isolated gas during the decomposition of mercury oxide. Two years earlier, the same substance was obtained in its pure form by K. Scheele. Only a few years later, the French chemist A. Lavoisier established what kind of gas is part of the air and studied its properties. The chemical formula of oxygen is O2. Let us reflect in the composition of the substance the electrons involved in the formation of a nonpolar covalent bond - O::O. Let's replace each bonding electron pair with one line: O=O. This formula for oxygen clearly shows that the atoms in the molecule are bonded between two shared pairs of electrons.
Let's perform simple calculations and determine what the relative molecular mass of oxygen is: Mr(O 2) = Ar(O) x 2 = 16 x 2 = 32. For comparison: Mr(air) = 29. The chemical formula of oxygen differs from by one oxygen atom. This means Mr(O 3) = Ar(O) x 3 = 48. Ozone is 1.5 times heavier than oxygen.
Physical properties
Oxygen is a colorless, tasteless, and odorless gas (at ordinary temperature and pressure equal to atmospheric pressure). The substance is slightly heavier than air; dissolves in water, but in small quantities. The melting point of oxygen is a negative value and is -218.3 °C. The point at which liquid oxygen turns back into gaseous oxygen is its boiling point. For O 2 molecules, the value of this physical quantity reaches -182.96 °C. In liquid and solid states, oxygen acquires a light blue color.
Obtaining oxygen in the laboratory
When oxygen-containing substances, such as potassium permanganate, are heated, a colorless gas is released, which can be collected in a flask or test tube. If you introduce a lit splinter into pure oxygen, it burns more brightly than in air. Two other laboratory methods for producing oxygen are the decomposition of hydrogen peroxide and potassium chlorate (Berthollet salt). Let's consider the diagram of a device that is used for thermal decomposition.
Pour a little Berthollet salt into a test tube or round-bottomed flask and close it with a stopper with a gas outlet tube. Its opposite end should be directed (under water) into the flask turned upside down. The neck should be lowered into a wide glass or crystallizer filled with water. When a test tube containing Berthollet salt is heated, oxygen is released. It enters the flask through the gas outlet tube, displacing water from it. When the flask is filled with gas, it is closed under water with a stopper and turned over. The oxygen obtained in this laboratory experiment can be used to study the chemical properties of a simple substance.
Combustion
If the laboratory burns substances in oxygen, then you need to know and follow fire safety rules. Hydrogen burns instantly in air, and mixed with oxygen in a 2:1 ratio, it is explosive. Combustion of substances in pure oxygen occurs much more intensely than in air. This phenomenon is explained by the composition of the air. Oxygen in the atmosphere makes up a little more than 1/5 of the part (21%). Combustion is the reaction of substances with oxygen, resulting in the formation of various products, mainly oxides of metals and non-metals. Mixtures of O2 with flammable substances are fire hazards; in addition, the resulting compounds can be toxic.
The burning of an ordinary candle (or match) is accompanied by the formation of carbon dioxide. The following experiment can be carried out at home. If you burn a substance under a glass jar or large glass, the combustion will stop as soon as all the oxygen is used up. Nitrogen does not support respiration or combustion. Carbon dioxide, a product of oxidation, no longer reacts with oxygen. Transparent allows you to detect the presence after the candle burns. If combustion products are passed through calcium hydroxide, the solution becomes cloudy. A chemical reaction occurs between lime water and carbon dioxide to produce insoluble calcium carbonate.
Production of oxygen on an industrial scale
The cheapest process, which produces air-free O 2 molecules, does not involve chemical reactions. In industry, say, at metallurgical plants, air is liquefied at low temperature and high pressure. The most important components of the atmosphere, such as nitrogen and oxygen, boil at different temperatures. The air mixture is separated by gradually heating to normal temperature. Nitrogen molecules are released first, then oxygen molecules. The separation method is based on the different physical properties of simple substances. The formula of the simple substance oxygen is the same as it was before cooling and liquefaction of air - O 2.
As a result of some electrolysis reactions, oxygen is also released, which is collected over the corresponding electrode. Industrial and construction enterprises need gas in large volumes. The demand for oxygen is constantly growing, and the chemical industry especially needs it. The resulting gas is stored for industrial and medical purposes in marked steel cylinders. Oxygen containers are painted blue or blue to distinguish them from other liquefied gases - nitrogen, methane, ammonia.
Chemical calculations using the formula and equations of reactions involving O 2 molecules
The numerical value of the molar mass of oxygen coincides with another value - the relative molecular mass. Only in the first case are units of measurement present. Briefly, the formula of the oxygen substance and its molar mass should be written as follows: M(O 2) = 32 g/mol. Under normal conditions, a mole of any gas corresponds to a volume of 22.4 liters. This means that 1 mol O 2 is 22.4 liters of substance, 2 mol O 2 is 44.8 liters. According to the reaction equation between oxygen and hydrogen, you can see that 2 moles of hydrogen and 1 mole of oxygen interact:
If 1 mol of hydrogen is involved in the reaction, then the volume of oxygen will be 0.5 mol. 22.4 l/mol = 11.2 l.
The role of O 2 molecules in nature and human life
Oxygen is consumed by living organisms on Earth and has been involved in the cycle of substances for over 3 billion years. This is the main substance for respiration and metabolism, with its help the decomposition of nutrient molecules occurs and the energy necessary for organisms is synthesized. Oxygen is constantly consumed on Earth, but its reserves are replenished through photosynthesis. The Russian scientist K. Timiryazev believed that thanks to this process, life still exists on our planet.
The role of oxygen in nature and agriculture is great:
- absorbed during respiration by living organisms;
- participates in photosynthesis reactions in plants;
- part of organic molecules;
- the processes of rotting, fermentation, and rusting occur with the participation of oxygen, which acts as an oxidizing agent;
- used to obtain valuable products of organic synthesis.
Liquefied oxygen in cylinders is used for cutting and welding metals at high temperatures. These processes are carried out at machine-building plants, transport and construction enterprises. To carry out work under water, underground, at high altitudes in airless space, people also need O 2 molecules. used in medicine to enrich the composition of the air inhaled by sick people. Gas for medical purposes differs from technical gas in the almost complete absence of foreign impurities and odor.
Oxygen is an ideal oxidizing agent
Oxygen compounds are known with all chemical elements of the periodic table, except for the first representatives of the family of noble gases. Many substances react directly with O atoms, excluding halogens, gold and platinum. Of great importance are phenomena involving oxygen, which are accompanied by the release of light and heat. Such processes are widely used in everyday life and industry. In metallurgy, the interaction of ores with oxygen is called roasting. Pre-crushed ore is mixed with oxygen-enriched air. At high temperatures, metals are reduced from sulfides to simple substances. This is how iron and some non-ferrous metals are obtained. The presence of pure oxygen increases the speed of technological processes in various branches of chemistry, technology and metallurgy.
The emergence of a cheap method for producing oxygen from air by separating it into components at low temperatures stimulated the development of many areas of industrial production. Chemists consider O2 molecules and O atoms to be ideal oxidizing agents. These are natural materials, they are constantly renewed in nature, and do not pollute the environment. In addition, chemical reactions involving oxygen most often result in the synthesis of another natural and safe product - water. The role of O 2 in the neutralization of toxic industrial waste and purification of water from contaminants is great. In addition to oxygen, its allotropic modification, ozone, is used for disinfection. This simple substance has high oxidizing activity. When water is ozonated, pollutants are decomposed. Ozone also has a detrimental effect on pathogenic microflora.
One of the most important elements on our planet is oxygen. The chemical properties of this substance allow it to participate in biological processes, and its increased activity makes oxygen a significant participant in all known chemical reactions. In a free state, this substance is available in the atmosphere. In a bound state, oxygen is part of minerals, rocks, and complex substances that make up various living organisms. The total amount of oxygen on Earth is estimated at 47% of the total mass of our planet.
Oxygen designation
In the periodic table, oxygen occupies the eighth cell of this table. Its international name is oxigenium. In chemical notations it is designated by the Latin letter "O". Atomic oxygen does not occur in the natural environment; its particles combine to form paired gas molecules, the molecular weight of which is 32 g/mol.
Air and oxygen
Air is a mixture of several gases common on Earth. The majority of nitrogen in the air mass is 78.2% by volume and 75.5% by mass. Oxygen ranks only second in volume - 20.9%, and in mass - 23.2%. The third place is assigned to noble gases. The remaining impurities - carbon dioxide, water vapor, dust, etc. - occupy only fractions of a percent in the total air mass.
The entire mass of natural oxygen is a mixture of three isotopes - 16 O, 17 O, 18 O. The percentage of these isotopes in the total mass of oxygen is 99.76%, 0.04% and 0.2%, respectively.
Physical and chemical properties of oxygen
One liter of air under normal conditions weighs 1.293 g. When the temperature drops to -140⁰C, the air becomes a colorless transparent liquid. Despite its low boiling point, air can be kept in a liquid state even at room temperature. To do this, the liquid must be placed in a so-called Dewar flask. Immersion in liquid oxygen radically changes the normal properties of objects.
Oxygen dissolves in water, although in small quantities - sea water contains 3-5% oxygen. But even such a small amount of this gas gave rise to the existence of fish, shellfish and various marine organisms that obtain oxygen from water to maintain their own life support processes.
Structure of the oxygen atom
The described properties of oxygen are primarily explained by the internal structure of this element.
Oxygen belongs to the main subgroup of the sixth group of elements of the periodic table. The outer electron cloud of an element contains six electrons, four of which occupy p orbitals, and the remaining two are located in s orbitals. This internal structure causes large energy expenditures aimed at breaking electronic bonds - it is easier for the oxygen atom to borrow two missing electrons to the outer orbital than to give up its six. Therefore, the covalency of oxygen in most cases is two. Thanks to two free electrons, oxygen easily forms diatomic molecules, which are characterized by high bond strength. Only with applied energy above 498 J/mol do the molecules disintegrate and atomic oxygen is formed. The chemical properties of this element allow it to react with all known substances, excluding helium, neon and argon. The rate of interaction depends on the reaction temperature and the nature of the substance.
Chemical properties of oxygen
Oxygen reacts with various substances to form oxides, and these reactions are characteristic of both metals and non-metals. Compounds of oxygen with metals are called basic oxides - classic examples are magnesium oxide and calcium oxide. The interaction of metal oxides with water leads to the formation of hydroxides, confirming the active chemical properties of oxygen. With non-metals, this substance forms acidic oxides - for example, sulfur trioxide SO 3. When this element reacts with water, sulfuric acid is obtained.
Chemical activity
Oxygen interacts directly with the vast majority of elements. The exceptions are gold, halogens and platinum. The interaction of oxygen with certain substances is significantly accelerated in the presence of catalysts. For example, a mixture of hydrogen and oxygen in the presence of platinum reacts even at room temperature. With a deafening explosion, the mixture turns into ordinary water, an important component of which is oxygen. The chemical properties and high activity of the element explain the release of large amounts of light and heat, which is why chemical reactions with oxygen are often called combustion.
Combustion in pure oxygen occurs much more intensely than in air, although the amount of heat released during the reaction will be approximately the same, but the process proceeds much faster due to the absence of nitrogen, and the combustion temperature becomes higher.
Obtaining oxygen
In 1774, the English scientist D. Priestley isolated an unknown gas from the decomposition reaction of mercury oxide. But the scientist did not connect the released gas with an already known substance that is part of the air. Only a few years later, the great Lavoisier studied the physicochemical properties of oxygen obtained in this reaction and proved its identity with the gas that is part of the air. In the modern world, oxygen is obtained from the air. In laboratories I use industrial oxygen, which is supplied in cylinders at a pressure of about 15 MPa. Pure oxygen can also be obtained in laboratory conditions; the standard method of obtaining it is the thermal decomposition of potassium permanganate, which proceeds according to the formula:
Ozone production
If electricity is passed through oxygen or air, a characteristic odor will appear in the atmosphere, heralding the appearance of a new substance - ozone. Ozone can also be obtained from chemically pure oxygen. The formation of this substance can be expressed by the formula:
This reaction cannot proceed independently; external energy is required for its successful completion. But the reverse conversion of ozone into oxygen occurs spontaneously. The chemical properties of oxygen and ozone differ in many ways. Ozone differs from oxygen in density, melting and boiling points. Under normal conditions, this gas is blue in color and has a characteristic odor. Ozone has greater electrical conductivity and is more soluble in water than oxygen. The chemical properties of ozone are explained by the process of its decomposition - during the decomposition of a molecule of this substance, a diatomic molecule of oxygen is formed plus one free atom of this element, which reacts aggressively with other substances. For example, the reaction between ozone and oxygen is known: 6Ag+O 3 =3Ag 2 O
But ordinary oxygen does not combine with silver even at high temperatures.
In nature, the active decay of ozone is fraught with the formation of so-called ozone holes, which threaten life processes on our planet.
