Chemical element oxygen in nature. Oxygen, its general characteristics

§8 Elements VI And the groups.

Oxygen, sulfur, selenium, tellurium, polonium.

General information about elements Group VI A:

Group VI A elements (except polonium) are called chalcogenides. The outer electronic level of these elements contains six valence electrons (ns 2 np 4), so in the normal state they exhibit a valence of 2, and in an excited state -4 or 6 (except for oxygen). The oxygen atom differs from the atoms of other elements of the subgroup in the absence of a d-sublevel in the outer electronic layer, which causes large energy costs for the “pairing” of its electrons, which is not compensated by the energy of the formation of new covalent bonds. Therefore, the covalency of oxygen is two. However, in some cases, an oxygen atom having lone electron pairs can act as an electron donor and form additional covalent bonds through a donor-acceptor mechanism.

The electronegativity of these elements gradually decreases in the order O-S-Se-Te-Po. Oxidation state from -2,+2,+4,+6. The radius of the atom increases, which weakens the non-metallic properties of the elements.

Elements of this subgroup form compounds of the form H 2 R (H 2 O, H 2 S, H 2 Se, H 2 Te, H 2 Po) with hydrogen. These compounds dissolve in water and form acids. Acid properties increase in the direction H 2 O → H 2 S → H 2 Se → H 2 Te → H 2 Po. S, Se and Te form compounds like RO 2 and RO 3 with oxygen. From these oxides acids like H 2 RO 3 and H 2 RO 4 are formed. As the atomic number increases, the strength of the acids decreases. All of them have oxidizing properties. Acids like H 2 RO 3 also exhibit reducing properties.

Oxygen

Natural compounds and preparations: Oxygen is the most common element in the earth's crust. In a free state, it is found in atmospheric air (21%); in bound form it is part of water (88.9%), minerals, rocks and all substances from which the organisms of plants and animals are built. Atmospheric air is a mixture of many gases, the main part of which is nitrogen and oxygen, and a small amount of noble gases, carbon dioxide and water vapor. Carbon dioxide is formed in nature during the combustion of wood, coal and other types of fuel, animal respiration, and decay. In some places around the world, CO 2 is released into the air due to volcanic activity, as well as from underground sources.

Natural oxygen consists of three stable isotopes: 8 16 O (99.75%), 8 17 O (0.04), 8 18 O (0.20). The isotopes 8 14 O, 8 15 O, and 8 19 O were also obtained artificially.

Oxygen was first obtained in pure form by K.V. Scheele in 1772, and then in 1774 by D.Yu. Priestley, who isolated it from HgO. However, Priestley did not know that the gas he obtained was part of the air. Only a few years later, Lavoisier, who studied the properties of this gas in detail, established that it is the main part of air.

In the laboratory, oxygen is obtained using the following methods:

E electrolysis of water. To increase the electrical conductivity of water, an alkali solution (usually 30% KOH) or alkali metal sulfates is added to it:

In general form: 2H 2 O → 2H 2 + O 2

At the cathode: 4H 2 O+4e¯→ 2H 2 +4OH¯

At the anode: 4OH−4е→2H 2 O+O 2

- Decomposition of oxygen-containing compounds:

Thermal decomposition of Berthollet salt under the action of a MnO 2 catalyst.

KClO 3 →2KCl+3O 2

Thermal decomposition of potassium permanganate

KMnO 4 →K 2 MnO 4 +MnO 2 +O 2.

Thermal decomposition of alkali metal nitrates:

2KNO 3 →2KNO 2 +O 2.

Decomposition of peroxides:

2H 2 O 2 →2H 2 O+O 2.

2BaO 2 →2BaO+O 2.

Thermal decomposition of mercury (II) oxide:

2HgO→2HgO+O 2.

Interaction of alkali metal peroxides with carbon monoxide (IV):

2Na 2 O 2 +2CO 2 →2Na 2 CO 3 +O 2.

Thermal decomposition of bleach in the presence of a catalyst - cobalt salts:

2Ca(OCl)Cl →2CaCl 2 +O 2.

Oxidation of hydrogen peroxide with potassium permanganate in an acidic environment:

2KMnO 4 +H 2 SO 4 +5H 2 O 2 →K 2 SO 4 +2Mn SO 4 +8H 2 O+5O 2.

In industry: Currently, in industry, oxygen is obtained by fractional distillation of liquid air. When liquid air is slightly heated, nitrogen is first separated from it (t bp (N 2) = -196ºC), then oxygen is released (t bp (O 2) = -183ºC).

The oxygen obtained by this method contains nitrogen impurities. Therefore, to obtain pure oxygen, the resulting mixture is distilled again and ultimately produces 99.5% oxygen. In addition, some oxygen is obtained by electrolysis of water. The electrolyte is a 30% KOH solution.

Oxygen is usually stored in blue cylinders at a pressure of 15 MPa.

Physicochemical characteristics: Oxygen is a colorless, odorless, tasteless gas, slightly heavier than air, slightly soluble in water. Oxygen at a pressure of 0.1 MPa and a temperature of -183ºС turns into a liquid state, and freezes at -219ºС. In liquid and solid states it is attracted by a magnet.

According to the valence bond method, the structure of the oxygen molecule, represented by the diagram -:Ö::Ö: , does not explain the greater strength of a molecule that has paramagnetic properties, that is, unpaired electrons in the normal state.

As a result of the bond between the electrons of two atoms, one common electron pair is formed, after which the unpaired electron in each atom forms a mutual bond with the unshared pair of another atom and a three-electron bond is formed between them. In an excited state, the oxygen molecule exhibits diamagnetic properties, which correspond to the structure according to the scheme: Ö = Ö: ,

An oxygen atom lacks two electrons to fill an electron level. Therefore, oxygen in chemical reactions can easily add two electrons and exhibit an oxidation state of -2. Oxygen only in compounds with the more electronegative element fluorine exhibits the oxidation state +1 and +2: O 2 F 2, OF 2.

Oxygen is a strong oxidizing agent. It does not interact only with heavy inert gases (Kr, Xe, He, Rn), with gold and platinum. Oxides of these elements are formed in other ways. Oxygen enters into combustion and oxidation reactions with both simple and complex substances. When non-metals interact with oxygen, acidic or salt-forming oxides are formed, and when metals interact, amphoteric or mixed oxides are formed. Thus, oxygen reacts with phosphorus at a temperature of ~ 60 ° C,

4P+5O 2 → 2P 2 O 5

With metals - oxides of the corresponding metals

4Al + 3O 2 → 2Al 2 O 3

3Fe + 2O 2 → Fe 3 O 4

When alkali metals are heated in dry air, only lithium forms Li 2 O oxide, and the rest are peroxides and superoxides:

2Na+O 2 →Na 2 O 2 K+O 2 →KO 2

Oxygen reacts with hydrogen at 300 °C:

2H 2 + O 2 = 2H 2 O.

When interacting with fluorine, it exhibits restorative properties:

O 2 + F 2 = F 2 O 2 (in electrical discharge),

with sulfur - at a temperature of about 250 °C:

S + O 2 = SO 2.

Oxygen reacts with graphite at 700 °C

C + O 2 = CO 2.

The interaction of oxygen with nitrogen begins only at 1200°C or in an electrical discharge.

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 (valency 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 (the corresponding oxides like Li 2 O, CaO, etc., peroxides like Na 2 O2, BaO 2, etc., and superoxides like 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.

Oxygen formsperoxides with oxidation state −1.
— For example, peroxides are produced by the combustion of alkali metals in oxygen:
2Na + O 2 → Na 2 O 2

— Some oxides absorb oxygen:
2BaO + O 2 → 2BaO 2

— According to the principles of combustion developed by A. N. Bach and K. O. Engler, oxidation occurs in two stages with the formation of an intermediate peroxide compound. This intermediate compound can be isolated, for example, when a flame of burning hydrogen is cooled with ice, hydrogen peroxide is formed along with water:
H 2 + O 2 → H 2 O 2

Superoxides have an oxidation state of −1/2, that is, one electron per two oxygen atoms (O 2 - ion). Obtained by reacting peroxides with oxygen at elevated pressures and temperatures:
Na 2 O 2 + O 2 → 2NaO 2

Ozonides contain the O 3 - ion with an oxidation state of −1/3. Obtained by the action of ozone on alkali metal hydroxides:
KOH(tv) + O 3 → KO 3 + KOH + O 2

And he dioxygenyl O 2 + has an oxidation state of +1/2. Obtained by the reaction:
PtF 6 + O 2 → O 2 PtF 6

Oxygen fluorides
Oxygen difluoride, OF 2 oxidation state +2, is obtained by passing fluorine through an alkali solution:
2F 2 + 2NaOH → OF 2 + 2NaF + H 2 O

Oxygen monofluoride (Dioxydifluoride), O 2 F 2, unstable, oxidation state +1. It is obtained from a mixture of fluorine and oxygen in a glow discharge at a temperature of −196 °C.

By passing a glow discharge through a mixture of fluorine and oxygen at a certain pressure and temperature, mixtures of higher oxygen fluorides O 3 F 2, O 4 F 2, O 5 F 2 and O 6 F 2 are obtained.
Oxygen supports the processes of respiration, combustion, and decay. In its free form, the element exists in two allotropic modifications: O 2 and O 3 (ozone).

Application of oxygen

The widespread industrial use of oxygen began in the middle of the 20th century, after the invention of turboexpanders - devices for liquefying and separating liquid air.

In metallurgy

The converter method of steel production involves the use of oxygen.

Welding and cutting of metals

Oxygen in cylinders is widely used for flame cutting and welding of metals.

Rocket fuel

Liquid oxygen, hydrogen peroxide, nitric acid and other oxygen-rich compounds are used as oxidizers for rocket fuel. A mixture of liquid oxygen and liquid ozone is one of the most powerful oxidizers of rocket fuel (the specific impulse of the hydrogen-ozone mixture exceeds the specific impulse for the hydrogen-fluorine and hydrogen-oxygen fluoride pairs).

In medicine

Oxygen is used to enrich respiratory gas mixtures for breathing problems, for the treatment of asthma, in the form of oxygen cocktails, oxygen pillows, etc.

In the food industry

In the food industry, oxygen is registered as a food additive E948, as propellant and packaging gas.

Biological role of oxygen

Living things breathe oxygen from the air. Oxygen is widely used in medicine. In case of cardiovascular diseases, to improve metabolic processes, oxygen foam (“oxygen cocktail”) is injected into the stomach. Subcutaneous administration of oxygen is used for trophic ulcers, elephantiasis, gangrene and other serious diseases. Artificial ozone enrichment is used to disinfect and deodorize air and purify drinking water. The radioactive isotope of oxygen 15 O is used to study blood flow speed and pulmonary ventilation.

Toxic oxygen derivatives

Some oxygen derivatives (so-called reactive oxygen species), such as singlet oxygen, hydrogen peroxide, superoxide, ozone and hydroxyl radical, are highly toxic. They are formed during the process of activation or partial reduction of oxygen. Superoxide (superoxide radical), hydrogen peroxide and hydroxyl radical can form in cells and tissues of humans and animals and cause oxidative stress.

Isotopes of oxygen

Oxygen has three stable isotopes: 16 O, 17 O and 18 O, the average content of which is, respectively, 99.759%, 0.037% and 0.204% of the total number of oxygen atoms on Earth. The sharp predominance of the lightest of them, 16 O, in the mixture of isotopes is due to the fact that the nucleus of the 16 O atom consists of 8 protons and 8 neutrons. And such nuclei, as follows from the theory of the structure of the atomic nucleus, are particularly stable.

There are radioactive isotopes 11 O, 13 O, 14 O (half-life 74 sec), 15 O (T 1/2 = 2.1 min), 19 O (T 1/2 = 29.4 sec), 20 O (contradictory half-life data from 10 minutes to 150 years).

Additional Information

Oxygen compounds
Liquid oxygen
Ozone

Oxygen, Oxygenium, O (8)
The discovery of oxygen (Oxygen, French Oxygene, German Sauerstoff) marked the beginning of the modern period in the development of chemistry. It has been known since ancient times that combustion requires air, but for many centuries the combustion process remained unclear. Only in the 17th century. Mayow and Boyle independently expressed the idea that the air contains some substance that supports combustion, but this completely rational hypothesis was not developed at that time, since the idea of ​​combustion as a process of combining a burning body with a certain component of the air seemed at that time contradicting such an obvious act as the fact that during combustion the decomposition of the burning body into elementary components takes place. It was on this basis that at the turn of the 17th century. The phlogiston theory arose, created by Becher and Stahl. With the advent of the chemical-analytical period in the development of chemistry (the second half of the 18th century) and the emergence of “pneumatic chemistry” - one of the main branches of the chemical-analytical direction - combustion, as well as respiration, again attracted the attention of researchers. The discovery of various gases and the establishment of their important role in chemical processes was one of the main incentives for the systematic studies of combustion processes undertaken by Lavoisier. Oxygen was discovered in the early 70s of the 18th century.

The first report of this discovery was made by Priestley at a meeting of the Royal Society of England in 1775. Priestley, by heating red mercury oxide with a large burning glass, obtained a gas in which the candle burned more brightly than in ordinary air, and the smoldering splinter flared up. Priestley determined some of the properties of the new gas and called it daphlogisticated air. However, two years earlier than Priestley (1772), Scheele also obtained oxygen by the decomposition of mercuric oxide and other methods. Scheele called this gas fire air (Feuerluft). Scheele was able to report his discovery only in 1777.

In 1775, Lavoisier spoke before the Paris Academy of Sciences with the message that he had succeeded in obtaining “the purest part of the air that surrounds us,” and described the properties of this part of the air. At first, Lavoisier called this “air” empyrean, vital (Air empireal, Air vital) the basis of vital air (Base de l'air vital). The almost simultaneous discovery of oxygen by several scientists in different countries gave rise to disputes about priority. Priestley was especially persistent in recognizing himself as a discoverer In essence, these disputes have not ended yet. A detailed study of the properties of oxygen and its role in the processes of combustion and the formation of oxides led Lavoisier to the incorrect conclusion that this gas is an acid-forming principle. In 1779, Lavoisier, in accordance with this conclusion. introduced a new name for oxygen - the acid-forming principle (principe acidifiant ou principe oxygine). Lavoisier derived the word oxygine appearing in this complex name from the Greek - acid and “I produce”.

Chemistry lesson 8th grade

Subject: Oxygen, its general characteristics. Being in nature. Production of oxygen and its physical properties.

The purpose of the lesson: continue the formation of the concepts of “chemical element”, “simple substance”, “chemical reaction”. Develop ideas about methods for producing oxygen in the laboratory. Introduce the concept of a catalyst, physical properties, characterize the element according to the table D.I. Mendeleev. Improve your interactive whiteboard skills.

Basic Concepts. Catalysts.

Planned learning outcomes

Subject. Be able to distinguish between the concepts of “chemical element” and “simple substance” using oxygen as an example. Be able to characterize the physical properties and methods of collecting oxygen.

Metasubject. Develop the ability to work according to a plan, formulate, argue, organize educational cooperation and joint activities with the teacher and peers.

Personal. To form a responsible attitude towards learning, readiness for self-education.

Main types of student activities. Describe a chemical element according to the proposed plan. Describe the chemical reactions observed in the demonstration experiment. Participate in a joint discussion of the results. Draw conclusions from the results of experiments.

Demonstrations. Obtaining oxygen from hydrogen peroxide.

During the classes

Learning new material.

1. Frontal conversation:

What gas supports respiration and combustion?

What information about oxygen do you already know from natural history and botany courses?

What substances contain oxygen? (water, sand, rocks, minerals, proteins, fats, carbohydrates).

General characteristics of the chemical element oxygen:

Chemical sign (O).

Relative atomic mass (16).

Valence (II).

Chemical formula of a simple substance (O2).

Relative molecular weight of a simple substance (32).

Characterize element No. 8 based on its position in the periodic table of chemical elements D.I. Mendeleev. (serial number – 8, atomic mass – 16, IV – group number, period number – 2).

Being in nature.

Oxygen is the most abundant chemical element in the earth's crust (49%). Air contains 21% oxygen gas. Oxygen is an important part of organic compounds that are of great importance for living organisms.

Physical properties: oxygen is a colorless gas, tasteless and odorless, slightly soluble in water (in 100 volumes of water – 3.1 volumes of oxygen). Oxygen is slightly heavier than air (Mr (O2) = 2x16 = 32, p air = 29).

2. Experiments on oxygen production.

Obtained in the laboratory.

Oxygen gas was first obtained in 1774. scientist Joseph Priestley. When mercury(II) oxide was calcined, Priestley obtained “air”:

The scientist decided to study the effect of the resulting gas on a candle flame: under the influence of this gas, the candle flame became dazzlingly bright, and the iron wire burned in the stream of the resulting gas. Mice placed in a vessel with this gas breathed easily; the scientist himself tried to inhale this gas and noted that it was easy to breathe.

In the school laboratory we will obtain this gas from hydrogen peroxide. To observe the physical properties of oxygen, we repeat the rules safety precautions.

We place a little manganese (IV) oxide MnO2 into a test tube with a solution of hydrogen peroxide, a violent reaction begins with the release of oxygen. We confirm the release of oxygen with a smoldering splinter (it flares up and burns). At the end of the reaction, manganese (IV) oxide settles to the bottom and can be used again. Consequently, manganese (IV) oxide accelerates the decomposition reaction of hydrogen peroxide, but is not consumed.

Definition:

Substances that accelerate chemical reactions, but are not consumed and are not part of the reaction products, are called catalysts.

2H2O2 MnO2 2H2O+O2

In the school laboratory, oxygen is obtained in another way:

By heating potassium permanganate

2КМnO4=К2MnO4+MnO2+О2

Manganese (IV) oxide accelerates another oxygen production reaction - the decomposition reaction when heating potassium chlorate KClO3 (Berthollet salt): 2КlO3 MnO2 2Кl+3О2

3. Working with the textbook:

Us. 75 read about the use of catalysts in industry.

In Fig. 25 and fig. 26 shows methods for collecting oxygen. What physical properties are known to you based on the methods of collecting oxygen by air displacement? (oxygen is heavier than air: 32 29), by water displacement method? (oxygen is slightly soluble in water). How to properly assemble a device for collecting oxygen using the air displacement method? (Fig. 25) Answer: the test tube for collecting oxygen should be positioned bottom down. How can you detect or prove the presence of oxygen in a vessel? (by the flash of a smoldering splinter).

With. 75 read the textbook article “getting into industry.” What physical property of oxygen is this method of its production based on? (liquid oxygen has a higher boiling point than liquid nitrogen, so the nitrogen will evaporate and the oxygen will remain).

II.Consolidation of knowledge and skills.

What substances are called catalysts?

With. 76 test tasks.

Work in pairs. Choose two correct answers:

Chemical element oxygen:

1. colorless gas

2. has serial number 8 (+)

3. part of the air

4. is part of water (+)

5. slightly heavier than air.

4. Simple substance oxygen:

1. has an atomic mass of 16

2. part of water

3. supports breathing and combustion (+)

4. formed during the decomposition of hydrogen peroxide (+).

5. Fill out the table:

Calculate the mass fraction of the chemical element oxygen in sulfur oxide (VI). SO3

W= (nхAr):Mr x 100%

W (O)= (3x16): 80x100%=60%

How to recognize which flask contains carbon dioxide and oxygen? (with the help of a smoldering splinter: in oxygen it flashes brightly, in carbon dioxide it goes out).

DEFINITION

Oxygen– element of the second period VIA group of the Periodic Table of Chemical Elements D.I. Mendeleev, with atomic number 8. Symbol - O.

Atomic mass – 16 amu. The oxygen molecule is diatomic and has the formula – O 2

Oxygen belongs to the family of p-elements. The electronic configuration of the oxygen atom is 1s 2 2s 2 2p 4. In its compounds, oxygen can exhibit several oxidation states: “-2”, “-1” (in peroxides), “+2” (F 2 O). Oxygen is characterized by the manifestation of the phenomenon of allotropy - existence in the form of several simple substances - allotropic modifications. Allotropic modifications of oxygen are oxygen O 2 and ozone O 3 .

Chemical properties of oxygen

Oxygen is a strong oxidizing agent because To complete the outer electron level, it only needs 2 electrons, and it easily adds them. In terms of chemical activity, oxygen is second only to fluorine. Oxygen forms compounds with all elements except helium, neon and argon. Oxygen directly reacts with halogens, silver, gold and platinum (their compounds are obtained indirectly). Almost all reactions involving oxygen are exothermic. A characteristic feature of many reactions of a compound with oxygen is the release of large amounts of heat and light. Such processes are called combustion.

Interaction of oxygen with metals. With alkali metals (except lithium), oxygen forms peroxides or superoxides, with the rest - oxides. For example:

4Li + O 2 = 2Li 2 O;

2Na + O 2 = Na 2 O 2;

K + O 2 = KO 2 ;

2Ca + O 2 = 2CaO;

4Al + 3O 2 = 2Al 2 O 3;

2Cu + O 2 = 2CuO;

3Fe + 2O 2 = Fe 3 O 4.

Interaction of oxygen with nonmetals. The interaction of oxygen with non-metals occurs when heated; all reactions are exothermic, with the exception of interaction with nitrogen (the reaction is endothermic, occurs at 3000C in an electric arc, in nature - during a lightning discharge). For example:

4P + 5O 2 = 2P 2 O 5 ;

C + O 2 = CO 2;

2H 2 + O 2 = 2H 2 O;

N 2 + O 2 ↔ 2NO – Q.

Interaction with complex inorganic substances. When complex substances burn in excess oxygen, oxides of the corresponding elements are formed:

2H 2 S + 3O 2 = 2SO 2 + 2H 2 O (t);

4NH 3 + 3O 2 = 2N 2 + 6H 2 O (t);

4NH 3 + 5O 2 = 4NO + 6H 2 O (t, kat);

2PH 3 + 4O 2 = 2H 3 PO 4 (t);

SiH 4 + 2O 2 = SiO 2 + 2H 2 O;

4FeS 2 +11O 2 = 2Fe 2 O 3 +8 SO 2 (t).

Oxygen is capable of oxidizing oxides and hydroxides to compounds with a higher oxidation state:

2CO + O 2 = 2CO 2 (t);

2SO 2 + O 2 = 2SO 3 (t, V 2 O 5);

2NO + O 2 = 2NO 2;

4FeO + O 2 = 2Fe 2 O 3 (t).

Interaction with complex organic substances. Almost all organic substances burn, oxidized by atmospheric oxygen to carbon dioxide and water:

CH 4 + 2O 2 = CO 2 +H 2 O.

In addition to combustion reactions (complete oxidation), incomplete or catalytic oxidation reactions are also possible; in this case, the reaction products can be alcohols, aldehydes, ketones, carboxylic acids and other substances:

The oxidation of carbohydrates, proteins and fats serves as a source of energy in a living organism.

Physical properties of oxygen

Oxygen is the most abundant element on earth (47% by mass). The oxygen content in air is 21% by volume. Oxygen is a component of water, minerals, and organic substances. Plant and animal tissues contain 50-85% oxygen in the form of various compounds.

In its free state, oxygen is a colorless, tasteless, and odorless gas, poorly soluble in water (3 liters of oxygen dissolve in 100 liters of water at 20C. Liquid oxygen is blue in color and has paramagnetic properties (it is drawn into a magnetic field).

Obtaining oxygen

There are industrial and laboratory methods for producing oxygen. Thus, in industry, oxygen is obtained by distillation of liquid air, and the main laboratory methods for producing oxygen include reactions of thermal decomposition of complex substances:

2KMnO 4 = K 2 MnO 4 + MnO 2 + O 2

4K 2 Cr 2 O 7 = 4K 2 CrO 4 + 2Cr 2 O 3 +3 O 2

2KNO 3 = 2KNO 2 + O 2

2KClO 3 = 2KCl +3 O 2

Examples of problem solving

EXAMPLE 1