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.
For obtaining oxygen, you will need substances that are rich in it. These are peroxides, nitrates, chlorates. We will use those that can be obtained without much difficulty.
There are several ways to obtain oxygen at home; let’s look at them in order.
The simplest and most accessible way to obtain oxygen is to use potassium permanganate (or the more correct name is potassium permanganate). Everyone knows that potassium permanganate is an excellent antiseptic and is used as a disinfectant. If you don’t have it, you can buy it at the pharmacy.
Let's do this. Pour some potassium permanganate into the test tube, close it with a test tube with a hole, and install a gas outlet tube in the hole (oxygen will flow through it). Place the other end of the tube in another test tube (it should be placed upside down, since the released oxygen is lighter than air and will rise upward. We close the second test tube with the same stopper.
As a result, we should have two test tubes connected to each other by a gas outlet tube through plugs. In one (uninverted) test tube there is potassium permanganate. We will heat a test tube with potassium permanganate. The dark purple cherry color of the potassium permanganate crystals will disappear and turn into dark green potassium manganate crystals.
The reaction proceeds like this:
2KMnO 4 → MnO 2 + K 2 MnO 4 +O 2
So from 10 grams of potassium permanganate you can get almost 1 liter of oxygen. After a couple of minutes, you can remove the flask with potassium permanganate from the flame. We received oxygen in an inverted test tube. We can check it out. To do this, carefully disconnect the second tube (with oxygen) from the gas outlet tube, covering the hole with your finger. Now, if you bring a weakly burning match into a flask with oxygen, it will flare up brightly!
Obtaining oxygen it is also possible using sodium or potassium nitrate (the corresponding sodium and potassium salts of nitric acid).
(Potassium and sodium nitrates - also known as nitrates - are sold in fertilizer stores).
So, to obtain oxygen from saltpeter, take a test tube made of refractory glass on a stand, place saltpeter powder there (5 grams will be enough). You will need to place a ceramic cup with sand under the test tube, since the glass can melt from the temperature and flow. Consequently, the burner will need to be held slightly to the side, and the test tube with saltpeter – at an angle.
When nitrate is heated strongly, it begins to melt, releasing oxygen. The reaction goes like this:
2KNO 3 → 2KNO 2 +O 2
The resulting substance is potassium nitrite (or sodium nitrite, depending on what kind of saltpeter is used) - a salt of nitrous acid.
Another way obtaining oxygen– use hydrogen peroxide. Peroxide and hydroperite are all the same substance. Hydrogen peroxide is sold in tablets and in the form of solutions (3%, 5%, 10%), which can be purchased at the pharmacy.
Unlike previous substances, saltpeter or potassium permanganate, hydrogen peroxide is an unstable substance. Already in the presence of light, it begins to break down into oxygen and water. Therefore, in pharmacies, peroxide is sold in dark glass bottles.
In addition, catalysts such as manganese oxide, activated carbon, steel powder (fine shavings) and even saliva contribute to the rapid decomposition of hydrogen peroxide into water and oxygen. Therefore, there is no need to heat hydrogen peroxide, a catalyst is enough!
Oxygen is a gas without taste, smell or color. In terms of content in the atmosphere, it ranks second after nitrogen. Oxygen is a strong oxidizing agent and a reactive non-metal. This gas was discovered simultaneously by several scientists in the 18th century. The Swedish chemist Scheele was the first to extract oxygen in 1772. The study of oxygen was carried out by the French chemist Lavoisier, who gave it the name “oxygène”. A smoldering splinter helps identify oxygen: upon contact with gas, it flashes brightly.
Oxygen value
This gas is involved in combustion processes. Oxygen is produced by green plants, in the leaves of which the process of photosynthesis occurs, which enriches the atmosphere with this vital gas.
How to get oxygen? Gas is extracted from the air industrially, and the air is purified and liquefied. Our planet has huge reserves of water, the component of which is oxygen. This means that gas can be produced by decomposing water. This can be done at home.
How to get oxygen from water
To conduct the experiment you will need the following tools and materials:
Power supply;
Plastic glasses (2 pieces);
Electrodes (2 pieces);
Galvanic bath.
Let's look at the process itself. Pour water into the galvanic bath to more than half the volume, then add 2 ml of caustic soda or dilute sulfuric acid - this will increase the electrical conductivity of the water.
We make holes in the bottom of plastic glasses and stretch electrodes - carbon plates - through them. It is necessary to insulate the air gap between the glass and the plate. We place the glasses in the bath so that the electrodes are in the water and the glasses are upside down. There should be very little air between the surface of the water and the bottom of the glass.
We solder a metal wire to each electrode and connect it to a power source. The electrode connected to the negative pole is called the cathode, and the electrode connected to the positive pole is called the anode.
Electric current passes through water - electrolysis of water occurs.
Electrolysis of water
A chemical reaction occurs during which two gases are formed. Hydrogen collects inside the glass with the cathode, and oxygen collects in the glass with the anode. The formation of gases in glasses with electrodes is determined by air bubbles rising from the water. Through the tube we remove oxygen from the glass into another container.
Safety regulations
Conducting a chemical experiment to obtain oxygen from water is possible only if safety regulations are observed. Gases obtained during the electrolysis of water must not be mixed. The resulting hydrogen is explosive, so it should not come into contact with air. You can find out what experiments with gases are safe to conduct at home.
How to produce oxygen in a laboratory way
Method one: pour potassium permanganate into a test tube, put the test tube on the fire. Potassium permanganate heats up and oxygen is released. We catch gas with a pneumatic bath. Result: 1 liter of oxygen is released from 10 g of potassium permanganate.
Stephen Hales Pneumatic Bath
Method two: pour 5 g of nitrate into a test tube, close the test tube with a fireproof stopper with a glass tube. We fix the test tube on the table using a tripod, and place a bath of sand under it to avoid excessive heating. Turn on the gas burner and direct the fire to the test tube with saltpeter. The substance melts and oxygen is released. We collect gas through a glass tube into a balloon placed on it.
Method three: pour potassium chlorate into a test tube and place the test tube on the fire of a gas burner, having previously closed it with a fireproof stopper with a glass tube. Berthollet salt releases oxygen when heated. We collect gas through a tube by placing a balloon on it.
Method four: We fix the glass test tube on the table using a tripod, pour hydrogen peroxide into the test tube. On contact with air, the unstable compound decomposes into oxygen and water. To speed up the oxygen release reaction, add activated carbon to the test tube. We close the test tube with a fireproof stopper with a glass tube, put a balloon on the tube and collect oxygen.
Hello.. Today I will tell you about oxygen and how to obtain it. Let me 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, . 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 percentages on Earth - 99.76%, 0.048%, 0.192%, respectively.
In the free state, oxygen exists 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 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 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. During the 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
blog.site, when copying material in full or in part, a link to the original source is required.
>> 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.
Lesson content lesson notes and supporting frame lesson presentation interactive technologies accelerator teaching methods Practice tests, testing online tasks and exercises homework workshops and trainings questions for class discussions Illustrations video and audio materials photographs, pictures, graphs, tables, diagrams, comics, parables, sayings, crosswords, anecdotes, jokes, quotes Add-ons abstracts cheat sheets tips for the curious articles (MAN) literature basic and additional dictionary of terms Improving textbooks and lessons correcting errors in the textbook, replacing outdated knowledge with new ones Only for teachers calendar plans training programs methodological recommendations