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

In the free state, oxygen is found 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 = KCl + 3O 0

KNO 3 = KNO 2 + O 0

Oxygen is part of more than 1,400 different minerals and organic substances; in the atmosphere its content is 21% by volume. And 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 o C).

In the laboratory, oxygen is obtained by moderately heating 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 decomposing perchlorates:

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

3) During the decomposition of berthollet salt (potassium chlorate).
In this case, atomic oxygen is formed:

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

4) During the decomposition of hypochlorous acid salts in the light- hypochlorites:

2NaClO → 2NaCl + O 2

Ca(ClO) 2 → CaCl 2 + O 2

5) When heating nitrates.
In this case, atomic oxygen is formed. Depending on the position of the nitrate metal in the activity series, various reaction products are formed:

2NaNO 3 → 2NaNO 2 + O 2

Ca(NO 3) 2 → CaO + 2NO 2 + O 2

2AgNO3 → 2Ag + 2NO2 + O2

6) During the decomposition of peroxides:

2H 2 O 2 ↔ 2H 2 O + O 2

7) When heating oxides of inactive metals:

2Аg 2 O ↔ 4Аg + O 2

This process is relevant in everyday life. The fact is that dishes made of copper or silver, having a natural layer of 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 highest degree oxidation:

4K 2 Cr 2 O 7 → 4K 2 CrO 4 + 2Cr 2 O 3 + 3 O 2
dichromate 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 during the process of photosynthesis. occurring in plants. All life on Earth fundamentally depends on this process. Photosynthesis is a complex multi-step process. Light gives it its beginning. Photosynthesis itself consists of two phases: light and dark. IN light phase the chlorophyll pigment contained in plant leaves forms a so-called “light-absorbing” complex,” which takes electrons from water, and thereby splits it into hydrogen ions and oxygen:

2H 2 O = 4e + 4H + O 2

Accumulated protons contribute to the synthesis of ATP:

ADP + P = ATP

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

6CO 2 + 6H 2 O = C 6 H 12 O 6 + O 2

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Today, the issue of ecology comes to the fore. But a healthy ecology is impossible without oxygen. It is this that is the main building block for maintaining life on the planet. In addition, oxygen is often involved in many chemical reactions. Let's consider, how to get oxygen in a chemical laboratory.

To obtain oxygen, we strengthen a test tube made of refractory glass on a stand and add 5 g of powder (potassium nitrate KNO 3 or sodium nitrate NaNO 3) into it. Let's place a cup made of refractory material filled with sand under the test tube, since during this experiment the hot mass often melts and flows out. Therefore, we will keep the burner on the side when heating. When we heat up the saltpeter very much, it will melt and oxygen will be released from it (we will detect this with the help of a smoldering splinter - it will ignite in a test tube). In this case, potassium nitrate will turn into nitrite KNO 2. Then use crucible tongs or tweezers to throw a piece of cuttings into the melt (never hold your face above the test tube). The sulfur will ignite and burn, releasing large quantity heat. The experiment should be carried out with open windows(due to the resulting sulfur oxides).

The process proceeds as follows (heating):

2KNO 3 → 2KNO 2 + O 2

Oxygen can also be obtained by other methods. Potassium permanganate KMnO 4 gives up oxygen when heated and is converted into manganese oxide (4):

2KMnO 4 → MnO 2 + K 2 MnO 4 + O 2.

From 10 g of potassium permanganate you can get about a liter of oxygen, which means two grams is enough to fill five normal-sized test tubes with oxygen.

We heat a certain amount of potassium permanganate in a refractory test tube and catch the released oxygen in the test tubes using a pneumatic bath. When the crystals crack, they are destroyed, and often a certain amount of dusty permanganate is entrained along with the gas. In this case, the water in the pneumatic bath and the outlet pipe will turn red.

Oxygen can also be obtained in large quantities from hydrogen peroxide (peroxide) H 2 O 2 . Hydrogen peroxide is not very stable. Already when standing in air, it decomposes into oxygen and:

2H 2 O 2 → 2H 2 O + O 2

You can get oxygen much faster if you add a little manganese dioxide MnO 2, active carbon, metal powder, blood (coagulated or fresh), and saliva to the peroxide. These substances act as catalysts.

We can verify this if we place approximately 1 ml of hydrogen peroxide with one of the named substances in a small test tube, and determine the presence of released oxygen using a splinter test. If an equal amount of animal blood is added to 5 ml of a three percent hydrogen peroxide solution in a beaker, the mixture will foam strongly, the foam will harden and swell as a result of the release of oxygen bubbles.

Catalysts increase the rate of reaction chemical process and at the same time they themselves are not consumed. They ultimately reduce the activation energy required to initiate a reaction. But there are also substances that act in the opposite way. They are called negative catalysts or inhibitors. For example, phosphoric acid prevents the decomposition of hydrogen peroxide. Therefore, commercial hydrogen peroxide solution is usually stabilized with phosphoric or uric acid. In living nature, so-called biocatalysts (enzymes, hormones) participate in many processes.

Oxygen O has atomic number 8, located in the main subgroup (subgroup a) VI group, in the second period. In oxygen atoms, valence electrons are located on the 2nd energy level, having only s- And p-orbitals. This excludes the possibility of transition of O atoms to an excited state, therefore oxygen in all compounds exhibits a constant valency equal to II. Having high electronegativity, oxygen atoms in compounds are always negatively charged (c.d. = -2 or -1). An exception is the fluorides OF 2 and O 2 F 2 .

For oxygen, the oxidation states are known -2, -1, +1, +2

General characteristics of the element

Oxygen is the most common element on Earth, accounting for slightly less than half, 49% of the total mass earth's crust. Natural oxygen consists of 3 stable isotopes 16 O, 17 O and 18 O (16 O predominates). Oxygen is part of the atmosphere (20.9% by volume, 23.2 by mass), in the composition of water and more than 1,400 minerals: silica, silicates and aluminosilicates, marbles, basalts, hematite and other minerals and rocks. Oxygen makes up 50-85% of the mass of tissues of plants and animals, as it is contained in proteins, fats and carbohydrates that make up living organisms. The role of oxygen for respiration and oxidation processes is well known.

Oxygen is relatively slightly soluble in water - 5 volumes in 100 volumes of water. However, if all the oxygen dissolved in water passed into the atmosphere, it would occupy a huge volume - 10 million km 3 (n.s.). This is equal to approximately 1% of all oxygen in the atmosphere. The formation of an oxygen atmosphere on earth is due to the processes of photosynthesis.

It was discovered by the Swede K. Scheele (1771 – 1772) and the Englishman J. Priestley (1774). The first used heating of nitrate, the second – mercury oxide (+2). The name was given by A. Lavoisier (“oxygenium” - “giving birth to acids”).

In its free form, it exists in two allotropic modifications - “ordinary” oxygen O 2 and ozone O 3 .

The structure of the ozone molecule

3O 2 = 2O 3 – 285 kJ
Ozone in the stratosphere forms a thin layer that absorbs most of the biologically harmful ultraviolet radiation.
During storage, ozone spontaneously turns into oxygen. Chemically, oxygen O2 is less active than ozone. The electronegativity of oxygen is 3.5.

Physical properties of oxygen

O 2 – colorless, odorless and tasteless gas, m.p. –218.7 °C, bp. –182.96 °C, paramagnetic.

Liquid O 2 blue, solid – of blue color. O 2 is soluble in water (better than nitrogen and hydrogen).

Obtaining oxygen

1. Industrial method - distillation of liquid air and electrolysis of water:

2H 2 O → 2H 2 + O 2

2. In the laboratory oxygen is obtained:
1. Electrolysis of alkaline aqueous solutions or aqueous solutions of oxygen-containing salts (Na 2 SO 4, etc.)

2. Thermal decomposition of potassium permanganate KMnO 4:
2KMnO 4 = K 2 MnO4 + MnO 2 + O 2,

Berthollet salt KClO 3:
2KClO 3 = 2KCl + 3O 2 (MnO 2 catalyst)

Manganese oxide (+4) MnO 2:
4MnO 2 = 2Mn 2 O 3 + O 2 (700 o C),

3MnO 2 = 2Mn 3 O 4 + O 2 (1000 o C),

Barium peroxide BaO 2:
2BaO2 = 2BaO + O2

3. Decomposition of hydrogen peroxide:
2H 2 O 2 = H 2 O + O 2 (MnO 2 catalyst)

4. Decomposition of nitrates:
2KNO 3 → 2KNO 2 + O 2

On spaceships and submarines, oxygen is obtained from a mixture of K 2 O 2 and K 2 O 4:
2K 2 O 4 + 2H 2 O = 4KOH +3O 2
4KOH + 2CO 2 = 2K 2 CO 3 + 2H 2 O

Total:
2K 2 O 4 + 2CO 2 = 2K 2 CO 3 + 3O 2

When K 2 O 2 is used, the overall reaction looks like this:
2K 2 O 2 + 2CO 2 = 2K 2 CO 3 + O 2

If you mix K 2 O 2 and K 2 O 4 in equal molar (i.e. equimolar) quantities, then one mole of O 2 will be released per 1 mole of absorbed CO 2.

Chemical properties of oxygen

Oxygen supports combustion. Combustion - b a rapid process of oxidation of a substance, accompanied by the release of a large amount of heat and light. To prove that the bottle contains oxygen and not some other gas, you need to lower a smoldering splinter into the bottle. In oxygen, a smoldering splinter flashes brightly. The combustion of various substances in air is a redox process in which oxygen is the oxidizing agent. Oxidizing agents are substances that “take” electrons from reducing substances. Good oxidizing properties oxygen can be easily explained by the structure of its outer electron shell.

The valence shell of oxygen is located at the 2nd level - relatively close to the core. Therefore, the nucleus strongly attracts electrons to itself. On the valence shell of oxygen 2s 2 2p 4 there are 6 electrons. Consequently, the octet is missing two electrons, which oxygen tends to accept from the electron shells of other elements, reacting with them as an oxidizing agent.

Oxygen has the second (after fluorine) electronegativity on the Pauling scale. Therefore, in the vast majority of its compounds with other elements, oxygen has negative degree of oxidation. The only stronger oxidizing agent than oxygen is its neighbor in the period, fluorine. Therefore, compounds of oxygen with fluorine are the only ones where oxygen has a positive oxidation state.

So, oxygen is the second most powerful oxidizing agent among all the elements of the Periodic Table. Most of its most important chemical properties are associated with this.
All elements react with oxygen except Au, Pt, He, Ne and Ar; in all reactions (except for the interaction with fluorine), oxygen is an oxidizing agent.

Oxygen easily reacts with alkali and alkaline earth metals:

4Li + O 2 → 2Li 2 O,

2K + O 2 → K 2 O 2,

2Ca + O 2 → 2CaO,

2Na + O 2 → Na 2 O 2,

2K + 2O 2 → K 2 O 4

Fine iron powder (the so-called pyrophoric iron) spontaneously ignites in air, forming Fe 2 O 3, and steel wire burns in oxygen if it is heated in advance:

3 Fe + 2O 2 → Fe 3 O 4

2Mg + O 2 → 2MgO

2Cu + O 2 → 2CuO

Oxygen reacts with non-metals (sulfur, graphite, hydrogen, phosphorus, etc.) when heated:

S + O 2 → SO 2,

C + O 2 → CO 2,

2H 2 + O 2 → H 2 O,

4P + 5O 2 → 2P 2 O 5,

Si + O 2 → SiO 2, etc.

Almost all reactions involving oxygen O2 are exothermic, with rare exceptions, for example:

N2+O2 → 2NO–Q

This reaction occurs at temperatures above 1200 o C or in an electrical discharge.

Oxygen is capable of oxidizing complex substances, for example:

2H 2 S + 3O 2 → 2SO 2 + 2H 2 O (excess oxygen),

2H 2 S + O 2 → 2S + 2H 2 O (lack of oxygen),

4NH 3 + 3O 2 → 2N 2 + 6H 2 O (without catalyst),

4NH 3 + 5O 2 → 4NO + 6H 2 O (in the presence of a Pt catalyst),

CH 4 (methane) + 2O 2 → CO 2 + 2H 2 O,

4FeS 2 (pyrite) + 11O 2 → 2Fe 2 O 3 + 8SO 2.

Compounds containing the dioxygenyl cation O 2 + are known, for example, O 2 + - (the successful synthesis of this compound prompted N. Bartlett to try to obtain compounds of inert gases).

Ozone

Ozone is chemically more active than oxygen O2. Thus, ozone oxidizes iodide - I ions - in a Kl solution:

O 3 + 2Kl + H 2 O = I 2 + O 2 + 2KOH

Ozone is highly toxic, its toxic properties are stronger than, for example, hydrogen sulfide. However, in nature, ozone contained in high layers atmosphere, acts as a protector of all life on Earth from the destructive ultraviolet radiation of the sun. The thin ozone layer absorbs this radiation and it does not reach the Earth's surface. There are significant fluctuations in the thickness and extent of this layer over time (the so-called ozone hole); the reasons for such fluctuations have not yet been clarified.

Application of Oxygen O 2: to intensify the processes of producing cast iron and steel, in the smelting of non-ferrous metals, as an oxidizer in various chemical industries, for life support on submarines, as an oxidizer for rocket fuel (liquid oxygen), in medicine, in welding and cutting metals.

Application of ozone O 3: for disinfection of drinking water, Wastewater, air, for bleaching fabrics.

Four “chalcogen” elements (i.e., “giving birth to copper”) lead the main subgroup of group VI (according to new classification- 16th group) of the periodic table. In addition to sulfur, tellurium and selenium, these also include oxygen. Let's take a closer look at the properties of this element, the most common on Earth, as well as the use and production of oxygen.

Element prevalence

In bound form, oxygen enters chemical composition water - his percentage makes up about 89%, as well as in the composition of the cells of all living beings - plants and animals.

In the air, oxygen is in a free state in the form of O2, occupying a fifth of its composition, and in the form of ozone - O3.

Physical properties

Oxygen O2 is a gas that is colorless, tasteless and odorless. Slightly soluble in water. The boiling point is 183 degrees below zero Celsius. In liquid form, oxygen is blue, and in solid form it forms blue crystals. The melting point of oxygen crystals is 218.7 degrees below zero Celsius.

Chemical properties

When heated, this element reacts with many simple substances, both metals and non-metals, forming so-called oxides - compounds of elements with oxygen. in which elements enter with oxygen is called oxidation.

For example,

4Na + O2= 2Na2O

2. Through the decomposition of hydrogen peroxide when it is heated in the presence of manganese oxide, which acts as a catalyst.

3. Through the decomposition of potassium permanganate.

Oxygen is produced in industry in the following ways:

1. For technical purposes, oxygen is obtained from air, in which its usual content is about 20%, i.e. fifth part. To do this, the air is first burned, producing a mixture containing about 54% liquid oxygen, 44% liquid nitrogen and 2% liquid argon. These gases are then separated using a distillation process, using the relatively small range between the boiling points of liquid oxygen and liquid nitrogen - minus 183 and minus 198.5 degrees, respectively. It turns out that nitrogen evaporates earlier than oxygen.

Modern equipment ensures the production of oxygen of any degree of purity. Nitrogen, which is obtained by separating liquid air, is used as a raw material in the synthesis of its derivatives.

2. Also produces very pure oxygen. This method has become widespread in countries with rich resources and cheap electricity.

Application of oxygen

Oxygen is the most important element in the life of our entire planet. This gas, which is contained in the atmosphere, is consumed in the process by animals and people.

Obtaining oxygen is very important for such areas of human activity as medicine, welding and cutting of metals, blasting, aviation (for human breathing and for engine operation), and metallurgy.

In progress economic activity human oxygen is consumed in large quantities - for example, when burning various types fuels: natural gas, methane, coal, wood. In all these processes, it is formed. At the same time, nature has provided for the process of natural binding of this compound using photosynthesis, which takes place in green plants under the influence sunlight. As a result of this process, glucose is formed, which the plant then uses to build its tissues.

Oxygen appeared in the earth's atmosphere with the emergence of green plants and photosynthetic bacteria. Thanks to oxygen, aerobic organisms carry out respiration or oxidation. It is important to obtain oxygen in industry - it is used in metallurgy, medicine, aviation, national economy and other industries.

Properties

Oxygen is the eighth element of the periodic table. It is a gas that supports combustion and oxidizes substances.

Rice. 1. Oxygen in the periodic table.

Oxygen was officially discovered in 1774. English chemist Joseph Priestley isolated the element from mercuric oxide:

2HgO → 2Hg + O 2 .

However, Priestley did not know that oxygen is part of air. The properties and presence of oxygen in the atmosphere were later determined by Priestley’s colleague, the French chemist Antoine Lavoisier.

General characteristics of oxygen:

• colorless gas;
• has no smell or taste;
• heavier than air;
• the molecule consists of two oxygen atoms (O 2);
• in a liquid state it has a pale blue color;
• poorly soluble in water;
• is a strong oxidizing agent.

Rice. 2. Liquid oxygen.

The presence of oxygen can be easily checked by lowering a smoldering splinter into a vessel containing gas. In the presence of oxygen, the torch bursts into flames.

How do you get it?

There are several known methods for obtaining oxygen from various connections in industrial and laboratory conditions. In industry, oxygen is obtained from air by liquefying it under pressure and at a temperature of -183°C. Liquid air is subjected to evaporation, i.e. gradually heat up. At -196°C, nitrogen begins to evaporate, and oxygen remains liquid.

In the laboratory, oxygen is formed from salts, hydrogen peroxide and as a result of electrolysis. The decomposition of salts occurs when heated. For example, potassium chlorate or bertholite salt is heated to 500°C, and potassium permanganate or potassium permanganate is heated to 240°C:

• 2KClO 3 → 2KCl + 3O 2;
• 2KMnO 4 → K 2 MnO 4 + MnO 2 + O 2 .

Rice. 3. Heating Berthollet salt.

You can also get oxygen by heating nitrate or potassium nitrate:

2KNO 3 → 2KNO 2 + O 2 .

When decomposing hydrogen peroxide, manganese (IV) oxide - MnO 2, carbon or iron powder is used as a catalyst. General equation as follows:

2H 2 O 2 → 2H 2 O + O 2.

A sodium hydroxide solution undergoes electrolysis. As a result, water and oxygen are formed:

4NaOH → (electrolysis) 4Na + 2H 2 O + O 2.

Oxygen is also isolated from water using electrolysis, decomposing it into hydrogen and oxygen:

2H 2 O → 2H 2 + O 2.

On nuclear submarines, oxygen was obtained from sodium peroxide - 2Na 2 O 2 + 2CO 2 → 2Na 2 CO 3 + O 2. The method is interesting in that, along with the release of oxygen, carbon dioxide is absorbed.

How to use

Collection and recognition are necessary to release pure oxygen, which is used in industry to oxidize substances, as well as to maintain breathing in space, under water, and in smoky rooms (oxygen is necessary for firefighters). In medicine, oxygen cylinders help patients with breathing difficulties breathe. Oxygen is also used to treat respiratory diseases.

Oxygen is used to burn fuels - coal, oil, natural gas. Oxygen is widely used in metallurgy and mechanical engineering, for example, for melting, cutting and welding metal.

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