In Lesson 17 " Obtaining oxygen» from the course « Chemistry for dummies» find out how oxygen is obtained in the laboratory; learn what a catalyst is and how plants affect the production of oxygen on our planet.
The most important substance for humans and other living organisms that is part of the air is oxygen. Large quantities of oxygen are used in industry, so it is important to know how to get it.
In a chemical laboratory, oxygen can be obtained by heating some complex substances, which include oxygen atoms. Among these substances is the substance KMnO 4, which is available in your home first aid kit called "potassium permanganate".
You are familiar with the simplest devices for obtaining gases. If a little KMnO 4 powder is placed in one of these devices and heated, oxygen will be released (Fig. 76):
Oxygen can also be obtained by decomposition of hydrogen peroxide H 2 O 2 . To do this, a very small amount of a special substance should be added to a test tube with H 2 O 2 - catalyst- and close the test tube with a stopper with a gas outlet tube (Fig. 77).
For this reaction, the catalyst is a substance whose formula is MnO 2. The following chemical reaction takes place:
Note that there is no catalyst formula on either the left or right side of the equation. Its formula is usually written in the reaction equation over the equal sign. Why is a catalyst added? The process of decomposition of H 2 O 2 under room conditions proceeds very slowly. Therefore, it takes a long time to obtain appreciable amounts of oxygen. However, this reaction can be drastically accelerated by the addition of a catalyst.
Catalyst A substance that speeds up a chemical reaction but is not itself consumed in it.
Precisely because the catalyst is not consumed in the reaction, we do not write down its formula in any of the parts of the reaction equation.
Another way to obtain oxygen is the decomposition of water under the action of a direct electric current. This process is called electrolysis water. You can get oxygen in the device, schematically shown in Figure 78.
The following chemical reaction takes place:
Oxygen in nature
A huge amount of gaseous oxygen is contained in the atmosphere, dissolved in the waters of the seas and oceans. Oxygen is essential for all living organisms to breathe. Without oxygen, it would be impossible to obtain energy by burning various types of fuel. Approximately 2% of atmospheric oxygen is consumed annually for these needs.
Where does oxygen come from on Earth, and why does its amount remain approximately constant despite such consumption? The only source of oxygen on our planet is green plants, which produce it under the action of sunlight through the process of photosynthesis. This is a very complex process with many steps. As a result of photosynthesis in the green parts of plants, carbon dioxide and water are converted into glucose C 6 H 12 O 6 and oxygen. Total
the equation of reactions occurring in the process of photosynthesis can be represented as follows:
It has been established that about one tenth (11%) of the oxygen produced by green plants is provided by terrestrial plants, and the remaining nine tenths (89%) is provided by aquatic plants.
Obtaining oxygen and nitrogen from the air
Huge reserves of oxygen in the atmosphere make it possible to obtain and use it in various industries. Under industrial conditions, oxygen, nitrogen and some other gases (argon, neon) are obtained from the air.
To do this, the air is first converted into a liquid (Fig. 79) by cooling to such a low temperature at which all its components pass into a liquid state of aggregation.
Then this liquid is slowly heated, as a result of which, at different temperatures, the substances contained in the air are sequentially boiled away (i.e., transition to a gaseous state). By collecting gases boiling off at different temperatures, nitrogen, oxygen and other substances are obtained separately.
Lesson summary:
- Under laboratory conditions, oxygen is obtained by the decomposition of some complex substances, which include oxygen atoms.
- A catalyst is a substance that speeds up a chemical reaction without being consumed.
- The source of oxygen on our planet is green plants in which the process of photosynthesis takes place.
- In industry, oxygen is obtained from the air.
I hope lesson 17 " Obtaining oxygen' was clear and informative. If you have any questions, write them in the comments.
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 appropriate 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.
We will strengthen the test tube of refractory glass on a tripod and add 5 g of powdered nitrate (potassium nitrate KNO 3 or sodium nitrate NaNO 3) to it. Let us place a cup made of refractory material filled with sand under the test tube, since in this experiment the glass often melts and a hot mass flows out. Therefore, when heating, we will keep the burner on the side. When we heat the saltpeter strongly, it will melt and oxygen will be released from it (we will detect this with the help of a smoldering torch - it will ignite in a test tube). In this case, potassium nitrate will turn into KNO2 nitrite. Then, with crucible tongs or tweezers, we throw a piece of cutting sulfur into the melt (never hold your face over the test tube).
Sulfur will ignite and burn with the release of a large amount of heat. The experiment should be carried out with open windows (because of the resulting sulfur oxides). The resulting sodium nitrite will be saved for subsequent experiments.
The process proceeds as follows (through heating):
2KNO 3 → 2KNO 2 + O 2
You can get oxygen in other ways.
Potassium permanganate KMnO 4 (potassium salt of manganese acid) gives off oxygen when heated and turns into manganese (IV) oxide:
4KMnO 4 → 4Mn 2 + 2K 2 O + 3O 2
or 4KMnO 4 → MnO 2 + K 2 MnO 4 + O 2
From 10 g of potassium permanganate, you can get about a liter of oxygen, so two grams is enough to fill five test tubes of normal size with oxygen. Potassium permanganate can be purchased at any pharmacy if it is not available in the home first aid kit.
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. The crystals crack and break, and often a certain amount of dusty permanganate is entrained along with the gas. The water in the pneumatic bath and the outlet pipe will turn red in this case. After the end of the experiment, we clean the bath and the tube with a solution of sodium thiosulfate (hyposulfite) - a photo-fixer, which we slightly acidify with dilute hydrochloric acid.
In large quantities, oxygen can also be obtained from hydrogen peroxide (peroxide) H 2 O 2 . We will buy a three percent solution in a pharmacy - a disinfectant or a preparation for treating wounds. Hydrogen peroxide is not very stable. Already when standing in air, it decomposes into oxygen and water:
2H 2 O 2 → 2H 2 O + O 2
Decomposition can be significantly accelerated by adding a little manganese dioxide MnO 2 (pyrolusite), activated carbon, metal powder, blood (coagulated or fresh), saliva to the peroxide. These substances act as catalysts.
We can be convinced of this if we place about 1 ml of hydrogen peroxide with one of the above substances in a small test tube, and we establish the presence of evolving oxygen using a test with a splinter. If an equal amount of animal blood is added to 5 ml of a 3% 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.
Then we will test the catalytic effect of a 10% solution of copper (II) sulfate with the addition of potassium hydroxide (caustic potash), a solution of iron sulfate (P), a solution of iron (III) chloride (with and without the addition of iron powder), sodium carbonate, chloride sodium and organic substances (milk, sugar, crushed leaves of green plants, etc.). Now we have seen from experience that various substances catalytically accelerate the decomposition of hydrogen peroxide.
Catalysts increase the rate of a chemical reaction without being consumed. Ultimately, they reduce the activation energy needed to excite the reaction. But there are also substances that act in the opposite way. They are called negative catalysts, anti-catalysts, stabilizers or inhibitors. For example, phosphoric acid prevents the decomposition of hydrogen peroxide. Therefore, a commercial hydrogen peroxide solution is usually stabilized with phosphoric or uric acid.
Catalysts are essential for many chemical-technological processes. But even in wildlife, so-called biocatalysts (enzymes, enzymes, hormones) are involved in many processes. Since catalysts are not consumed in reactions, they can act even in small quantities. One gram of rennet is enough to coagulate 400-800 kg of milk protein.
Of particular importance for the operation of catalysts is their surface area. To increase the surface, porous, cracked substances with a developed inner surface are used, compact substances or metals are sprayed onto so-called carriers. For example, 100 g of a supported platinum catalyst contains only about 200 mg of platinum; 1 g of compact nickel has a surface area of 0.8 cm 2 and 1 g of nickel powder has 10 mg. This corresponds to a ratio of 1: 100,000; 1 g of active alumina has a surface area of 200 to 300 m2, for 1 g of active carbon this value is even 1000 m2. In some catalyst installations - several million marks. Thus, an 18 m high gasoline contact furnace in Belen contains 9-10 tons of catalyst.
Plan:
Discovery history
Origin of name
Being in nature
Receipt
Physical properties
Chemical properties
Application
10. Isotopes
Oxygen
Oxygen- an element of the 16th group (according to the outdated classification - the main subgroup of group VI), the second period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 8. It is designated by the symbol O (lat. Oxygenium). Oxygen is a reactive non-metal and is the lightest element of the chalcogen group. simple substance oxygen(CAS number: 7782-44-7) under normal conditions - a colorless, tasteless and odorless gas, the molecule of which consists of two oxygen atoms (formula O 2), in connection with which it is also called dioxygen. Liquid oxygen has a light blue, and the solid is light blue crystals.
There are other allotropic forms of oxygen, for example, ozone (CAS number: 10028-15-6) - under normal conditions, a blue gas with a specific odor, the molecule of which consists of three oxygen atoms (formula O 3).
Discovery history
It is officially believed that oxygen was discovered by the English chemist Joseph Priestley on August 1, 1774 by decomposing mercury oxide in a hermetically sealed vessel (Priestley directed the sun's rays at this compound using a powerful lens).
However, Priestley did not initially realize that he had discovered a new simple substance, he believed that he isolated one of the constituent parts of air (and called this gas "dephlogisticated air"). Priestley reported his discovery to the outstanding French chemist Antoine Lavoisier. In 1775, A. Lavoisier established that oxygen is an integral part of air, acids and is contained in many substances.
A few years earlier (in 1771), the Swedish chemist Carl Scheele had obtained oxygen. He calcined saltpeter with sulfuric acid and then decomposed the resulting nitric oxide. Scheele called this gas "fiery air" and described his discovery in a book published in 1777 (precisely because the book was published later than Priestley announced his discovery, the latter is considered the discoverer of oxygen). Scheele also reported his experience to Lavoisier.
An important stage that contributed to the discovery of oxygen was the work of the French chemist Pierre Bayen, who published work on the oxidation of mercury and the subsequent decomposition of its oxide.
Finally, A. Lavoisier finally figured out the nature of the resulting gas, using information from Priestley and Scheele. His work was of great importance, because thanks to it, the phlogiston theory that dominated at that time and hindered the development of chemistry was overthrown. Lavoisier conducted an experiment on the combustion of various substances and refuted the theory of phlogiston by publishing the results on the weight of the burned elements. The weight of the ash exceeded the initial weight of the element, which gave Lavoisier the right to assert that during combustion a chemical reaction (oxidation) of the substance occurs, in connection with this, the mass of the original substance increases, which refutes the theory of phlogiston.
Thus, the credit for the discovery of oxygen is actually shared by Priestley, Scheele, and Lavoisier.
Origin of name
The word oxygen (at the beginning of the 19th century it was still called "acid"), its appearance in the Russian language is to some extent due to M.V. Lomonosov, who introduced, along with other neologisms, the word "acid"; thus the word "oxygen", in turn, was a tracing-paper of the term "oxygen" (French oxygène), proposed by A. Lavoisier (from other Greek ὀξύς - "sour" and γεννάω - "I give birth"), which translates as “generating acid”, which is associated with its original meaning - “acid”, which previously meant substances called oxides according to modern international nomenclature.
Being in nature
Oxygen is the most common element on Earth; its share (as part of various compounds, mainly silicates) accounts for about 47.4% of the mass of the solid earth's crust. 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 and 23.12% by mass. More than 1500 compounds of the earth's crust contain oxygen in their composition.
Oxygen is a constituent of many organic substances and is present in all living cells. In terms of the number of atoms in living cells, it is about 25%, in terms of mass fraction - about 65%.
Receipt
At present, in industry, oxygen is obtained from the air. The main industrial method for obtaining oxygen is cryogenic distillation. Oxygen plants based on membrane technology are also well known and successfully used in industry.
In laboratories, industrial oxygen is used, supplied in steel cylinders under a pressure of about 15 MPa.
Small amounts of oxygen can be obtained by heating potassium permanganate KMnO 4:
The reaction of the catalytic decomposition of hydrogen peroxide H 2 O 2 in the presence of manganese (IV) oxide is also used:
Oxygen can be obtained by catalytic decomposition of potassium chlorate (bertolet salt) KClO 3:
Laboratory methods for obtaining oxygen include the method of electrolysis of aqueous solutions of alkalis, as well as the decomposition of mercury (II) oxide (at t = 100 ° C):
On submarines, it is usually obtained by the reaction of sodium peroxide and carbon dioxide exhaled by a person:
Physical properties
In the oceans, the content of dissolved O 2 is greater in cold water, and less in warm water.
Under normal conditions, oxygen is a colorless, tasteless and odorless gas.
1 liter of it has a mass of 1.429 g. It is slightly heavier than air. Slightly soluble in water (4.9 ml/100 g at 0°C, 2.09 ml/100 g at 50°C) and alcohol (2.78 ml/100 g at 25°C). It dissolves well in molten silver (22 volumes of O 2 in 1 volume of Ag at 961 ° C). Interatomic distance - 0.12074 nm. It is paramagnetic.
When gaseous oxygen is heated, its reversible dissociation into atoms occurs: at 2000 °C - 0.03%, at 2600 °C - 1%, 4000 °C - 59%, 6000 °C - 99.5%.
Liquid oxygen (boiling point −182.98 °C) is a pale blue liquid.
O 2 phase diagram
Solid oxygen (melting point −218.35°C) - blue crystals. Six crystalline phases are known, of which three exist at a pressure of 1 atm.:
α-O 2 - exists at temperatures below 23.65 K; bright blue crystals belong to the monoclinic system, cell parameters a=5.403 Å, b=3.429 Å, c=5.086 Å; β=132.53°.
β-O 2 - exists in the temperature range from 23.65 to 43.65 K; pale blue crystals (with increasing pressure, the color turns into pink) have a rhombohedral lattice, cell parameters a=4.21 Å, α=46.25°.
γ-O 2 - exists at temperatures from 43.65 to 54.21 K; pale blue crystals have cubic symmetry, lattice period a=6.83 Å.
Three more phases are formed at high pressures:
δ-O 2 temperature range 20-240 K and pressure 6-8 GPa, orange crystals;
ε-O 4 pressure from 10 to 96 GPa, crystal color from dark red to black, monoclinic system;
ζ-O n pressure more than 96 GPa, metallic state with a characteristic metallic luster, at low temperatures passes into a superconducting state.
Chemical properties
A strong oxidizing agent, interacts with almost all elements, forming oxides. The oxidation state is −2. As a rule, the oxidation reaction proceeds with the release of heat and accelerates with increasing temperature (see Combustion). An example of reactions occurring at room temperature:
Oxidizes compounds that contain elements with a non-maximum oxidation state:
Oxidizes most organic compounds:
Under certain conditions, it is possible to carry out a mild oxidation of an organic compound:
Oxygen reacts directly (under normal conditions, when heated and/or in the presence of catalysts) with all simple substances, except for Au and inert gases (He, Ne, Ar, Kr, Xe, Rn); reactions with halogens occur under the influence of an electric discharge or ultraviolet radiation. Oxides of gold and heavy inert gases (Xe, Rn) were obtained indirectly. In all two-element compounds of oxygen with other elements, oxygen plays the role of an oxidizing agent, except for compounds with fluorine
Oxygen forms peroxides with the oxidation state of the oxygen atom formally equal to −1.
For example, peroxides are obtained by burning alkali metals in oxygen:
Some oxides absorb oxygen:
According to the combustion theory 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, along with water, hydrogen peroxide is formed:
In superoxides, oxygen formally has an oxidation state of −½, that is, one electron per two oxygen atoms (the O − 2 ion). Obtained by the interaction of peroxides with oxygen at elevated pressure and temperature:
Potassium K, rubidium Rb and cesium Cs react with oxygen to form superoxides:
In the dioxygenyl ion O 2 +, oxygen formally has an oxidation state of +½. Get by reaction:
Oxygen fluorides
Oxygen difluoride, OF 2 oxygen oxidation state +2, is obtained by passing fluorine through an alkali solution:
Oxygen monofluoride (Dioxydifluoride), O 2 F 2 , is unstable, oxygen oxidation state is +1. Obtained from a mixture of fluorine and oxygen in a glow discharge at a temperature of −196 ° C:
Passing a glow discharge through a mixture of fluorine with 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.
Quantum mechanical calculations predict the stable existence of the OF 3 + trifluorohydroxonium ion. If this ion really exists, then the oxidation state of oxygen in it will be +4.
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). As established in 1899 by Pierre Curie and Maria Sklodowska-Curie, under the influence of ionizing radiation, O 2 turns into O 3.
Application
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.
ATmetallurgy
The converter method of steel production or matte processing is associated with the use of oxygen. In many metallurgical units, for more efficient combustion of fuel, an oxygen-air mixture is used in burners instead of air.
Welding and cutting of metals
Oxygen in blue 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 an oxidizing agent for rocket fuel. A mixture of liquid oxygen and liquid ozone is one of the most powerful rocket fuel oxidizers (the specific impulse of a hydrogen-ozone mixture exceeds the specific impulse for a hydrogen-fluorine and hydrogen-oxygen fluoride pair).
ATmedicine
Medical oxygen is stored in blue high-pressure metal gas cylinders (for compressed or liquefied gases) of various capacities from 1.2 to 10.0 liters under pressure up to 15 MPa (150 atm) and is used to enrich respiratory gas mixtures in anesthesia equipment, with respiratory failure, for relief of an attack of bronchial asthma, elimination of hypoxia of any origin, with decompression sickness, for the treatment of pathology of the gastrointestinal tract in the form of oxygen cocktails. For individual use, medical oxygen from cylinders is filled with special rubberized containers - oxygen pillows. To supply oxygen or an oxygen-air mixture simultaneously to one or two victims in the field or in a hospital, oxygen inhalers of various models and modifications are used. The advantage of an oxygen inhaler is the presence of a condenser-humidifier of the gas mixture, which uses the moisture of the exhaled air. To calculate the amount of oxygen remaining in the cylinder in liters, the pressure in the cylinder in atmospheres (according to the pressure gauge of the reducer) is usually multiplied by the cylinder capacity in liters. For example, in a cylinder with a capacity of 2 liters, the pressure gauge shows an oxygen pressure of 100 atm. The volume of oxygen in this case is 100 × 2 = 200 liters.
ATFood Industry
In the food industry, oxygen is registered as food additive E948, as a propellant and packaging gas.
ATchemical industry
In the chemical industry, oxygen is used as an oxidizing agent in numerous syntheses, for example, the oxidation of hydrocarbons to oxygen-containing compounds (alcohols, aldehydes, acids), ammonia to nitrogen oxides in the production of nitric acid. Due to the high temperatures developed during oxidation, the latter are often carried out in the combustion mode.
ATagriculture
In greenhouses, for the manufacture of oxygen cocktails, for weight gain in animals, for enriching the aquatic environment with oxygen in fish farming.
The biological role of oxygen
Emergency supply of oxygen in a bomb shelter
Most living things (aerobes) breathe oxygen in the air. Oxygen is widely used in medicine. In 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 the air and purify drinking water. The radioactive isotope of oxygen 15 O is used to study the rate of blood flow, pulmonary ventilation.
Toxic oxygen derivatives
Some oxygen derivatives (so-called reactive oxygen species), such as singlet oxygen, hydrogen peroxide, superoxide, ozone, and the hydroxyl radical, are highly toxic products. They are formed in the process of activation or partial reduction of oxygen. Superoxide (superoxide radical), hydrogen peroxide and hydroxyl radical can be formed in the cells and tissues of the human and animal body and cause oxidative stress.
isotopes
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 (double magic nucleus with filled neutron and proton shells). And such nuclei, as follows from the theory of the structure of the atomic nucleus, have a special stability.
Radioactive oxygen isotopes with mass numbers from 12 O to 24 O are also known. All radioactive oxygen isotopes have a short half-life, the longest-lived of them is 15 O with a half-life of ~120 s. The shortest-lived 12 O isotope has a half-life of 5.8·10 −22 s.
Hello. You have already read my articles on the Tutoronline.ru blog. Today I will tell you about oxygen and how to get it. I remind you that if you have questions for me, you can write them in the comments to the article. If you need any help in chemistry, sign up for my classes in the schedule. 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
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 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
site, with full or partial copying of the material, a link to the source is required.
