Question No. 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 extreme 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 producing oxygen are chemical, that is, the transformation of some substances into others occurs. The process of obtaining oxygen from air is a physical process, since the transformation of some substances into others does not occur.
2) Oxygen can be obtained from air in much larger quantities.
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 producing oxygen from various compounds 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. The general equation looks like this:
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 because carbon dioxide is absorbed along with the release of oxygen.
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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>> Obtaining oxygen
Obtaining oxygen
This paragraph talks about:
> about the discovery of oxygen;
> about obtaining oxygen in industry and laboratories;
> about decomposition reactions.
Discovery of oxygen.
J. Priestley obtained this gas from a compound called mercury(II) oxide. The scientist used a glass lens with which he focused sunlight on the substance.
In a modern version, this experiment is depicted 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 drops. Oxygen is collected above the water in the second test tube.
Priestley's method is no longer used because mercury vapor is toxic. Oxygen is produced using other reactions similar to the one discussed. They usually occur when heated.
Reactions in which several others 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 KClO 3 (trivial name - Berthollet's salt, in honor of the French chemist of the late 18th - early 19th centuries C.-L. Berthollet)
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
Oxygen production by decomposition of hydrogen peroxide H 2 O 2
Pour 2 ml of hydrogen peroxide solution into a test tube (the traditional name for this substance is hydrogen peroxide). Light a long splinter and extinguish it (as you do with a match) so that it barely smolders.
Pour a little catalyst - black powder manganese (IV) oxide - into a test tube with a solution of hydrogen oxide. Observe the rapid release of gas. Use a smoldering splinter to verify that the gas is oxygen.
Write an equation for the decomposition reaction of hydrogen peroxide, the reaction product of which is water.
In the laboratory, oxygen can also be obtained by decomposing sodium nitrate NaNO 3 or potassium nitrate KNO 3 2. When heated, compounds first melt and then decompose:
1 When a compound is heated without a catalyst, a different reaction occurs
2 These substances are used as fertilizers. Their common name is saltpeter.
Scheme 7. Laboratory methods for producing oxygen
Convert reaction diagrams into chemical equations.
Information on how oxygen is produced in the laboratory is collected in Scheme 7.
Oxygen together with hydrogen are products of the decomposition of water under the influence of electric current:
In nature, oxygen is produced through photosynthesis in the green leaves of plants. A simplified diagram of this process is as follows:
conclusions
Oxygen was discovered at the end of the 18th century. several scientists .
Oxygen is obtained in industry from the air, and in the laboratory through 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 don't they use potassium permanganate or hydrogen peroxide for this?
130. What reactions are called decomposition reactions?
131. Convert the following reaction schemes into chemical equations:
132. What is a catalyst? How can it influence the course of chemical reactions? (For your answer, also use the material in § 15.)
133. Figure 55 shows the moment of decomposition of a white solid, which has the formula Cd(NO3)2. Look carefully at the drawing 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., Kryklya L. S., Chemistry: Pidruch. for 7th grade zagalnosvit. navch. closing - K.: VC "Academy", 2008. - 136 p.: ill.
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History of discovery
Origin of name
Being in nature
Receipt
Physical properties
Chemical properties
Application
Biological role of oxygen
Toxic oxygen derivatives
10. Isotopes
Oxygen
Oxygen- 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. Denoted by the symbol O (lat. Oxygenium). Oxygen is a chemically active non-metal and is the lightest element from the group of chalcogens. Simple substance oxygen(CAS number: 7782-44-7) under normal conditions is a colorless, tasteless and odorless gas, the molecule of which consists of two oxygen atoms (formula O 2), and therefore it is also called dioxygen. Liquid oxygen has a light blue color, and solid crystals are light blue in color.
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).
History of discovery
It is officially believed that oxygen was discovered by the English chemist Joseph Priestley on August 1, 1774 by decomposing mercuric oxide in a hermetically sealed vessel (Priestley directed sunlight at this compound using a powerful lens).
However, Priestley initially did not realize that he had discovered a new simple substance; he believed that he had 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 a component of air, acids and is found in many substances.
A few years earlier (in 1771), oxygen was obtained by the Swedish chemist Karl Scheele. He calcined saltpeter with sulfuric acid and then decomposed the resulting nitric oxide. Scheele called this gas “fire 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 step that contributed to the discovery of oxygen was the work of the French chemist Pierre Bayen, who published works 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 enormous importance because thanks to it, the phlogiston theory, which was dominant at that time and hampered the development of chemistry, was overthrown. Lavoisier conducted experiments on the combustion of various substances and disproved the theory of phlogiston, publishing results on the weight of the burned elements. The weight of the ash exceeded the original weight of the element, which gave Lavoisier the right to claim that during combustion a chemical reaction (oxidation) of the substance occurs, and therefore the mass of the original substance increases, which refutes the theory of phlogiston.
Thus, the credit for the discovery of oxygen is actually shared between Priestley, Scheele and Lavoisier.
origin of name
The word oxygen (also called “acid solution” at the beginning of the 19th century) owes its appearance in the Russian language to some extent to M.V. Lomonosov, who introduced the word “acid”, along with other neologisms; Thus, the word “oxygen”, in turn, was a tracing of the term “oxygen” (French oxygène), proposed by A. Lavoisier (from ancient Greek ὀξύς - “sour” and γεννάω - “giving birth”), which is translated 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 (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 and 23.12% by mass. More than 1,500 compounds in the earth's crust contain oxygen.
Oxygen is part 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%, and in terms of mass fraction - about 65%.
When cutting metal, it is carried out with a high-temperature gas flame obtained by burning flammable gas or liquid vapor mixed with technically pure oxygen.
Oxygen is the most abundant element on earth, found in the form of chemical compounds with various substances: in the ground - up to 50% by weight, in combination with hydrogen in water - about 86% by weight and in the air - up to 21% by volume and 23% by weight.
Oxygen under normal conditions (temperature 20°C, pressure 0.1 MPa) is a colorless, non-flammable 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 high chemical activity, forming compounds with all chemical elements except (argon, helium, xenon, krypton and neon). Reactions of the compound with oxygen occur with the release of a large amount of heat, i.e. they are exothermic in nature.
When compressed gaseous oxygen comes into contact with organic substances, oils, fats, coal dust, flammable plastics, they may spontaneously ignite as a result of the release of heat during rapid compression of oxygen, friction and impact of solid particles on metal, as well as an electrostatic spark discharge. Therefore, when using oxygen, care must be taken to ensure that it does not come into contact with flammable or combustible substances.
All oxygen equipment, oxygen lines and cylinders must be thoroughly degreased. capable of forming explosive mixtures with flammable gases or liquid flammable 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 gas-flame processing 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 to oxygen and by the method of deep cooling (liquefaction), along with the separation of argon, the use of which is continuously increasing. Nitrogen is used as a shielding gas when welding copper.
Oxygen can be obtained chemically or by electrolysis of water. Chemical methods inefficient and uneconomical. At electrolysis of water With direct current, oxygen is produced 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 obtaining oxygen and nitrogen from air, the latter is cleaned of harmful impurities, compressed in a compressor to the appropriate refrigeration cycle pressure of 0.6-20 MPa and cooled in heat exchangers to the liquefaction temperature, the difference in the liquefaction temperatures of oxygen and nitrogen is 13 ° C, which sufficient for their complete separation in the liquid phase.
Liquid pure oxygen accumulates in an air separation apparatus, evaporates and collects in a gas tank, from where it is pumped into cylinders by a compressor under a pressure of up to 20 MPa.
Technical oxygen is also transported via pipeline. The pressure of oxygen transported through the pipeline must be agreed upon between the manufacturer and the consumer. Oxygen is delivered to the site 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 upon 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 weight of the container by 10 times, which saves metal for the manufacture of cylinders and reduces the cost of transporting and storing cylinders.
For welding and cutting According to -78, technical oxygen is produced in three grades:
- 1st - purity of at least 99.7%
- 2nd - no less than 99.5%
- 3rd - no less than 99.2% by volume
Oxygen purity is of great importance for oxyfuel cutting. The less gas impurities it contains, the higher the cutting speed, cleaner and less oxygen consumption.