When cutting metal, it is carried out by a high-temperature gas flame obtained by burning a combustible gas or liquid vapor mixed with commercially pure oxygen.

Oxygen is the most abundant element on earth found in the form of chemical compounds with various substances: in the earth - up to 50% by mass, in combination with hydrogen in water - about 86% by mass and in air - up to 21% by volume and 23% by mass.

Oxygen under normal conditions (temperature 20 ° C, pressure 0.1 MPa) is a colorless, non-combustible gas, slightly heavier than air, odorless, but actively supporting combustion. At normal atmospheric pressure and a temperature of 0 ° C, the mass of 1 m 3 of oxygen is 1.43 kg, and at a temperature of 20 ° C and normal atmospheric pressure - 1.33 kg.

Oxygen has a high reactivity, forming compounds with all chemical elements, except (argon, helium, xenon, krypton and neon). The reactions of the compound with oxygen proceed with the release of a large amount of heat, that is, they are exothermic in nature.

When compressed gaseous oxygen comes into contact with organic substances, oils, fats, coal dust, combustible plastics, they can spontaneously ignite as a result of heat release during rapid oxygen compression, friction and impact of solid particles on metal, as well as electrostatic spark discharge. Therefore, when using oxygen, care must be taken to ensure that it does not come into contact with flammable and combustible substances.

All oxygen equipment, oxygen lines and cylinders must be thoroughly degreased. it is capable of forming explosive mixtures with combustible gases or liquid combustible vapors over a wide range, which can also lead to explosions in the presence of an open flame or even a spark.

The noted features of oxygen should always be kept in mind when using it in flame treatment processes.

Atmospheric air is mainly a mechanical mixture of three gases with the following volume content: nitrogen - 78.08%, oxygen - 20.95%, argon - 0.94%, the rest is carbon dioxide, nitrous oxide, etc. Oxygen is obtained by separating air on oxygen and by the method of deep cooling (liquefaction), along with the separation of argon, the use of which is continuously increasing at. Nitrogen is used as a shielding gas when welding copper.

Oxygen can be obtained chemically or by electrolysis of water. Chemical methods unproductive and uneconomical. At water electrolysis direct current oxygen is obtained as a by-product in the production of pure hydrogen.

Oxygen is produced in industry from atmospheric air by deep cooling and rectification. In installations for the production of oxygen and nitrogen from air, the latter is cleaned of harmful impurities, compressed in a compressor to the corresponding pressure of the refrigeration cycle of 0.6-20 MPa and cooled in heat exchangers to a liquefaction temperature, the difference in the temperatures of oxygen and nitrogen liquefaction is 13 ° C, which enough for their complete separation in the liquid phase.

Liquid pure oxygen accumulates in the air separation apparatus, evaporates and collects in a gas holder, from where it is pumped into cylinders by a compressor at a pressure of up to 20 MPa.

Technical oxygen is also transported through the pipeline. The pressure of oxygen transported through the pipeline must be agreed between the manufacturer and the consumer. Oxygen is delivered to the place in oxygen cylinders, and in liquid form - in special vessels with good thermal insulation.

To convert liquid oxygen into gas, gasifiers or pumps with liquid oxygen evaporators are used. At normal atmospheric pressure and a temperature of 20 ° C, 1 dm 3 of liquid oxygen during evaporation gives 860 dm 3 of gaseous oxygen. Therefore, it is advisable to deliver oxygen to the welding site in a liquid state, since this reduces the tare weight by 10 times, which saves metal for the manufacture of cylinders, and reduces the cost of transportation and storage of cylinders.

For welding and cutting according to -78 technical oxygen is produced in three grades:

• 1st - purity not less than 99.7%
• 2nd - not less than 99.5%
• 3rd - not less than 99.2% by volume

The purity of oxygen is of great importance for oxyfuel cutting. The less gas impurities it contains, the higher the cutting speed, cleaner and less oxygen consumption.

Hello .. Today I will tell you about oxygen and how to get it. I remind you, if you have questions for me, you can write them in the comments to the article. If you need any help with chemistry, . I will be glad to help you.

Oxygen is distributed in nature in the form of isotopes 16 O, 17 O, 18 O, which have the following percentage on Earth - 99.76%, 0.048%, 0.192%, respectively.

In the free state, oxygen is in the form of three allotropic modifications : atomic oxygen - O o, dioxygen - O 2 and ozone - O 3. Moreover, atomic oxygen can be obtained as follows:

KClO 3 \u003d KCl + 3O 0

KNO 3 = KNO 2 + O 0

Oxygen is part of more than 1400 different minerals and organic substances, in the atmosphere its content is 21% by volume. The human body contains up to 65% oxygen. Oxygen is a colorless and odorless gas, slightly soluble in water (3 volumes of oxygen dissolve in 100 volumes of water at 20 ° C).

In the laboratory, oxygen is obtained by moderate heating of certain substances:

1) When decomposing manganese compounds (+7) and (+4):

2KMnO 4 → K 2 MnO 4 + MnO 2 + O 2
permanganate manganate
potassium potassium

2MnO 2 → 2MnO + O 2

2) When perchlorates are decomposed:

2KClO 4 → KClO 2 + KCl + 3O 2
perchlorate
potassium

3) When decomposing berthollet salt (potassium chlorate).
In this case, atomic oxygen is formed:

2KClO 3 → 2KCl + 6O 0
chlorate
potassium

4) When the salts of hypochlorous acid decompose in the light- hypochlorites:

2NaClO → 2NaCl + O 2

Ca(ClO) 2 → CaCl 2 + O 2

5) When heating nitrates.
This produces atomic oxygen. Depending on what position the nitrate metal occupies in the activity series, various reaction products are formed:

2NaNO 3 → 2NaNO 2 + O 2

Ca(NO 3) 2 → CaO + 2NO 2 + O 2

2AgNO 3 → 2 Ag + 2NO 2 + O 2

6) When decomposing peroxides:

2H 2 O 2 ↔ 2H 2 O + O 2

7) When heating oxides of inactive metals:

2Ag 2 O ↔ 4Ag + O 2

This process is relevant in everyday life. The fact is that dishes made of copper or silver, having a natural layer of an oxide film, form active oxygen when heated, which is an antibacterial effect. The dissolution of salts of inactive metals, especially nitrates, also leads to the formation of oxygen. For example, the overall process of dissolving silver nitrate can be represented in stages:

AgNO 3 + H 2 O → AgOH + HNO 3

2AgOH → Ag 2 O + O 2

2Ag 2 O → 4Ag + O 2

or in summary form:

4AgNO 3 + 2H 2 O → 4Ag + 4HNO 3 + 7O 2

8) When heating chromium salts of the highest oxidation state:

4K 2 Cr 2 O 7 → 4K 2 CrO 4 + 2Cr 2 O 3 + 3 O 2
bichromate chromate
potassium potassium

In industry, oxygen is obtained:

1) Electrolytic decomposition of water:

2H 2 O → 2H 2 + O 2

2) Interaction of carbon dioxide with peroxides:

CO 2 + K 2 O 2 → K 2 CO 3 + O 2

This method is an indispensable technical solution to the problem of breathing in isolated systems: submarines, mines, spacecraft.

3) When ozone interacts with reducing agents:

O 3 + 2KJ + H 2 O → J 2 + 2KOH + O 2

Of particular importance is the production of oxygen in the process of photosynthesis. occurring in plants. All life on Earth depends fundamentally on this process. Photosynthesis is a complex multi-step process. The beginning gives him light. Photosynthesis itself consists of two phases: light and dark. In the light phase, the pigment chlorophyll contained in the leaves of plants forms the so-called “light-absorbing” complex, which takes electrons from water, and thereby splits it into hydrogen ions and oxygen:

2H 2 O \u003d 4e + 4H + O 2

The accumulated protons contribute to the synthesis of ATP:

ADP + F = ATP

In the dark phase, carbon dioxide and water are converted into glucose. And oxygen is released as a by-product:

6CO 2 + 6H 2 O \u003d C 6 H 12 O 6 + O 2

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Question number 2 How is oxygen obtained in the laboratory and in industry? Write the equations for the corresponding reactions. How do these methods differ from each other?

Answer:

In the laboratory, oxygen can be obtained in the following ways:

1) Decomposition of hydrogen peroxide in the presence of a catalyst (manganese oxide

2) Decomposition of Berthollet salt (potassium chlorate):

3) Decomposition of potassium permanganate:

In industry, oxygen is obtained from air, which contains about 20% by volume. Air is liquefied under pressure and with strong cooling. Oxygen and nitrogen (the second main component of air) have different boiling points. Therefore, they can be separated by distillation: nitrogen has a lower boiling point than oxygen, so nitrogen evaporates before oxygen.

Differences between industrial and laboratory methods for producing oxygen:

1) All laboratory methods for obtaining oxygen are chemical, that is, in this case, some substances are converted into others. The process of obtaining oxygen from the air is a physical process, since the transformation of some substances into others does not occur.

2) Oxygen can be obtained from the air in much larger quantities.

Air is an inexhaustible source of oxygen. To obtain oxygen from it, this gas must be separated from nitrogen and other gases. An industrial method for producing oxygen is based on this idea. It is implemented using special, rather bulky equipment. First, the air is strongly cooled until it turns into a liquid. Then the temperature of the liquefied air is gradually increased. Nitrogen gas is the first to be released from it (the boiling point of liquid nitrogen is -196 ° C), and the liquid is enriched with oxygen.

Obtaining oxygen in the laboratory. Laboratory methods for obtaining oxygen are based on chemical reactions.

J. Priestley obtained this gas from a compound whose name is mercury (II) oxide. The scientist used a glass lens to focus sunlight on matter.

In a modern version, this experience is shown in Figure 54. When heated, mercury (||) oxide (yellow powder) turns into mercury and oxygen. Mercury is released in a gaseous state and condenses on the walls of the test tube in the form of silvery droplets. Oxygen is collected over water in the second test tube.

Now the Priestley method is not used because mercury vapor is toxic. Oxygen is produced by other reactions similar to the one discussed. They usually occur when heated.

Reactions in which several other substances are formed from one substance are called decomposition reactions.

To obtain oxygen in the laboratory, the following oxygen-containing compounds are used:

Potassium permanganate KMnO4 (common name potassium permanganate; the substance is a common disinfectant)

Potassium chlorate, KClO3

A small amount of catalyst - manganese (IV) oxide MnO2 - is added to potassium chlorate so that the decomposition of the compound occurs with the release of oxygen1.

Molecular structure of chalcogen hydrides H2E can be analyzed using the molecular orbital (MO) method. As an example, consider the scheme of molecular orbitals of a water molecule (Fig. 3)

For construction (For details, see G. Gray "Electrons and chemical bond", M., publishing house "Mir", 1967, pp. 155-62 and G. L. Miessier, D. A. Tarr, "Inorganic Chemistry", Prantice Hall Int. Inc. ., 1991, p.153-57) of the MO scheme of the H2O molecule, the origin of coordinates is compatible with the oxygen atom, and the hydrogen atoms are located in the xz plane (Fig. 3). The overlap of the 2s- and 2p-AO of oxygen with the 1s-AO of hydrogen is shown in Fig. 4. Hydrogen and oxygen AOs, which have the same symmetry and similar energies, take part in the formation of the MO. However, the contribution of AO to the formation of MOs is different, which is reflected in different values ​​of the coefficients in the corresponding linear combinations of AOs. Interaction (overlapping) of 1s-AO of hydrogen, 2s- and 2pz-AO of oxygen leads to the formation of 2a1-bonding and 4a1-loosening MO.

>> Obtaining oxygen

Obtaining oxygen

This paragraph is about:

> about the discovery of oxygen;
> on the production of oxygen in industry and laboratories;
> about decomposition reactions.

Discovery of oxygen.

J. Priestley obtained this gas from a compound whose name is mercury (II) oxide. The scientist used a glass lens to focus sunlight on matter.

In a modern version, this experience is shown in Figure 54. When heated, mercury (||) oxide (yellow powder) turns into mercury and oxygen. Mercury is released in a gaseous state and condenses on the walls of the test tube in the form of silvery droplets. Oxygen is collected over water in the second test tube.

Now the Priestley method is not used because mercury vapor is toxic. Oxygen is produced by other reactions similar to the one discussed. They usually occur when heated.

Reactions in which several other substances are formed from one substance are called decomposition reactions.

To obtain oxygen in the laboratory, the following oxygen-containing compounds are used:

Potassium permanganate KMnO 4 (common name potassium permanganate; substance is a common disinfectant)

Potassium chlorate KClO3

A small amount of catalyst - manganese (IV) oxide MnO 2 - is added to potassium chlorate so that the decomposition of the compound occurs with the release of oxygen 1 .

Laboratory experiment No. 8

Obtaining oxygen by decomposition of hydrogen peroxide H 2 O 2

Pour 2 ml of a hydrogen peroxide solution (the traditional name for this substance is hydrogen peroxide) into a test tube. Light a long splinter and extinguish it (as you do with a match), so that it barely smolders.
Pour a little catalyst - black powder of manganese (IV) oxide into a test tube with a hydrogen oxide solution. Observe vigorous evolution of gas. Use a smoldering splinter to verify that this gas is oxygen.

Write an equation for the decomposition of hydrogen peroxide, the product of which is water.

In the laboratory, oxygen can also be obtained by decomposition of sodium nitrate NaNO 3 or potassium nitrate KNO 3 2 . When heated, compounds first melt and then decompose:

1 When the compound is heated without a catalyst, another reaction occurs

2 These substances are used as fertilizers. Their common name is saltpeter.

Scheme 7. Laboratory methods for obtaining oxygen

Turn reaction schemes into chemical equations.

Information on how oxygen is obtained in the laboratory is collected in Scheme 7.

Oxygen together with hydrogen are products of the decomposition of water under the action of an electric current:

In nature, oxygen is produced by photosynthesis in the green leaves of plants. A simplified diagram of this process is as follows:

findings

Oxygen was discovered at the end of the 18th century. several scientists .

Oxygen is obtained in industry from the air, and in the laboratory - with the help of decomposition reactions of certain oxygen-containing compounds. During a decomposition reaction, two or more substances are formed from one substance.

129. How is oxygen obtained in industry? Why is potassium permanganate or hydrogen peroxide not used for this?

130. What reactions are called decomposition reactions?

131. Turn the following reaction schemes into chemical equations:

132. What is a catalyst? How can it affect the course of chemical reactions? (Also refer to § 15 for your answer.)

133. Figure 55 shows the moment of decomposition of a white solid that has the formula Cd(NO3)2. Look at the picture carefully and describe everything that happens during the reaction. Why does a smoldering splinter flare up? Write the appropriate chemical equation.

134. The mass fraction of Oxygen in the residue after heating potassium nitrate KNO 3 was 40%. Has this compound completely decomposed?

Rice. 55. Decomposition of a substance when heated

Popel P. P., Kriklya L. S., Chemistry: Pdruch. for 7 cells. zahalnosvit. navch. zakl. - K .: Exhibition Center "Academy", 2008. - 136 p.: il.

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