Interaction of dichloroethane with oxygen 9 gaseous state. Chemical and physical properties, use and production of oxygen

Lecture "Oxygen - a chemical element and a simple substance »

Lecture plan:

1. Oxygen is a chemical element:

c) The prevalence of a chemical element in nature

2. Oxygen is a simple substance

a) Obtaining oxygen

b) Chemical properties of oxygen

c) The oxygen cycle in nature

d) The use of oxygen

"Dum spiro spero "(While I breathe, I hope ...), - says Latin

Breathing is synonymous with life, and the source of life on Earth is oxygen.

Emphasizing the importance of oxygen for terrestrial processes, Jacob Berzelius said: “Oxygen is the substance around which the terrestrial chemistry revolves.”

The material of this lecture summarizes previously acquired knowledge on the topic "Oxygen".

1. Oxygen is a chemical element

a) Characteristics of the chemical element - oxygen according to its position in the PSCE

Oxygen - an element of the main subgroup of the sixth group, the second period of the periodic system of chemical elements of D. I. Mendeleev, with atomic serial number 8. It is indicated by the symbol O(lat.Oxygenium). The relative atomic mass of the chemical element oxygen is 16, i.e. Ar(O)=16.

b) Valence possibilities of the oxygen atom

In compounds, oxygen is usually divalent (in oxides), valency VI does not exist. It occurs in free form in the form of two simple substances: O 2 (“ordinary” oxygen) and O 3 (ozone). About 2 - colorless and odorless gas, with a relative molecular weight =32. O 3 - a colorless gas with a pungent odor, with a relative molecular weight = 48.

Attention! H 2 O 2 ( hydrogen peroxide) - O (valence II)

CO (carbon monoxide) - O (valence III)

c) The prevalence of the chemical element oxygen in nature

Oxygen is the most common element on Earth, its share (as part of various compounds, mainly silicates), accounts for about 49% of the mass of the solid earth's crust. Marine and fresh waters contain a huge amount of bound oxygen - 85.5% (by mass), in the atmosphere the content of free oxygen is 21% by volume and 23% 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 20%, in terms of mass fraction - about 65%.

2. Oxygen is a simple substance

a) Obtaining oxygen

Obtaining in the laboratory

1) Decomposition of potassium permanganate (potassium permanganate):

2KMnO 4 t˚C \u003d K 2 MnO 4 +MnO 2 +O 2

2) Decomposition of hydrogen peroxide:

2H 2 O 2 MnO2 \u003d 2H 2 O + O 2

3) Decomposition of Berthollet salt:

2KClO 3 t˚C, MnO2 \u003d 2KCl + 3O 2

Receipt in industry

1) Water electrolysis

2 H 2 O el. current \u003d 2 H 2 + O 2

2) Out of thin air

AIR pressure, -183˚ C = O 2 (blue liquid)

At present, in industry, oxygen is obtained from the air. In laboratories, small amounts of oxygen can be obtained by heating potassium permanganate (potassium permanganate) KMnO 4 . Oxygen is slightly soluble in water and heavier than air, so it can be obtained in two ways:

Plan:

Discovery history

Origin of name

Being in nature

Receipt

Physical properties

Chemical properties

Application

The biological role of oxygen

Toxic oxygen derivatives

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), and therefore 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).

1. 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 found 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.

1. 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.

1. 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%.

Oxygen (lat. Oxygenium), O, a chemical element of the VI group of the periodic system of Mendeleev; atomic number 8, atomic mass 15.9994. Under normal conditions, oxygen is a colorless, odorless and tasteless gas. It is difficult to name another element that would play such an important role on our planet as oxygen.

History reference. The processes of combustion and respiration have long attracted the attention of scientists. The first indications that not all air, but only its "active" part supports combustion, were found in Chinese manuscripts of the 8th century. Much later, Leonardo da Vinci (1452-1519) considered air as a mixture of two gases, only one of which is consumed during combustion and breathing. The final discovery of the two main components of air - nitrogen and oxygen, which made an era in science, occurred only at the end of the 18th century. Oxygen was obtained almost simultaneously by K. Scheele (1769-70) by calcining saltpeter (KNO3, NaNO3), manganese dioxide MnO2 and other substances and J. Priestley (1774) by heating red lead Pb3O4 and mercury oxide HgO. In 1772, D. Rutherford discovered nitrogen. In 1775, A. Lavoisier, having made a quantitative analysis of air, found that it “consists of two (gases) of a different and, so to speak, opposite nature,” that is, of oxygen and nitrogen. On the basis of extensive experimental research, Lavoisier correctly explained combustion and respiration as processes of the interaction of substances with oxygen. Since oxygen is a part of acids, Lavoisier called it oxygene, that is, "former of acids" (from the Greek oxys - sour and gennao - I give birth; hence the Russian name "oxygen").

Distribution of oxygen in nature. Oxygen is the most common chemical element on Earth. Bound oxygen makes up about 6/7 of the mass of the Earth's water shell - the hydrosphere (85.82% by mass), almost half of the lithosphere (47% by mass), and only in the atmosphere, where oxygen is in a free state, does it take second place (23 .15% by weight) after nitrogen.

Oxygen also comes first in terms of the number of minerals it forms (1364); Among the minerals containing oxygen, silicates (feldspars, micas, and others), quartz, iron oxides, carbonates, and sulfates predominate. In living organisms, on average, about 70% oxygen; it is part of most of the most important organic compounds (proteins, fats, carbohydrates, etc.) and in the composition of inorganic compounds of the skeleton. The role of free oxygen in biochemical and physiological processes, especially in respiration, is exceptionally important. With the exception of some anaerobic microorganisms, all animals and plants obtain the energy necessary for their life activity due to the biological oxidation of various substances with the help of oxygen.

The entire mass of free Oxygen of the Earth arose and is preserved due to the vital activity of green plants on land and the World Ocean, which release Oxygen in the process of photosynthesis. On the earth's surface, where photosynthesis proceeds and free oxygen predominates, sharply oxidizing conditions are formed. On the contrary, in magma, as well as deep horizons of underground waters, in the silts of seas and lakes, in swamps, where free oxygen is absent, a reducing environment is formed. Oxidation-reduction processes involving oxygen determine the concentration of many elements and the formation of mineral deposits - coal, oil, sulfur, iron ores, copper, etc. Human economic activity also introduces changes in the oxygen cycle. In some industrialized countries, the combustion of fuel consumes more oxygen than plants produce during photosynthesis. In total, about 9·109 tons of oxygen is consumed annually for fuel combustion in the world.

Isotopes, atom and molecule of oxygen. Oxygen has three stable isotopes: 16O, 17O and 18O, 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, 16O, in the mixture of isotopes is due to the fact that the nucleus of the 16O atom consists of 8 protons and 8 neutrons. And such nuclei, as follows from the theory of the atomic nucleus, have a special stability.

In accordance with the position of Oxygen in the periodic system of elements of Mendeleev, the electrons of the Oxygen atom are located on two shells: 2 - on the inner and 6 - on the outer (configuration 1s22s22p4). Since the outer shell of the oxygen atom is not filled, and the ionization potential and electron affinity are respectively 13.61 and 1.46 eV, the oxygen atom in chemical compounds usually acquires electrons and has a negative effective charge. On the contrary, there are extremely rare compounds in which electrons are detached (more precisely, pulled away) from the oxygen atom (such, for example, F2O, F2O3). Previously, based solely on the position of Oxygen in the periodic system, the oxygen atom in oxides and in most other compounds was assigned a negative charge (-2). However, as experimental data show, the O2 - ion does not exist either in the free state or in compounds, and the negative effective charge of the oxygen atom practically never significantly exceeds unity.

Under normal conditions, the oxygen molecule is diatomic (O2); in a quiet electric discharge, a triatomic O3 molecule, ozone, is also formed; at high pressures, O4 molecules are found in small amounts. The electronic structure of O2 is of great theoretical interest. In the ground state, the O2 molecule has two unpaired electrons; the "usual" classical structural formula O=O with two two-electron bonds is inapplicable to it. An exhaustive explanation of this fact is given within the framework of the theory of molecular orbitals. The ionization energy of an oxygen molecule (O2 - e > O2+) is 12.2 eV, and the electron affinity (O2 + e > O2-) is 0.94 eV. The dissociation of molecular oxygen into atoms at ordinary temperature is negligible, it becomes noticeable only at 1500°C; at 5000°C the oxygen molecules are almost completely dissociated into atoms.

Physical properties of oxygen. Oxygen is a colorless gas that condenses at -182.9°C and normal pressure to a pale blue liquid, which solidifies at -218.7°C to form blue crystals. The density of gaseous oxygen (at 0°C and normal pressure) is 1.42897 g/l. The critical temperature of oxygen is quite low (Tcrit = -118.84°C), that is, lower than that of Cl2, CO2, SO2, and some other gases; Tcrit = 4.97 MN/m2 (49.71 atm). Thermal conductivity (at 0°C) 23.86 10-3 W/(m K). Molar heat capacity (at 0°C) in j/(mol K) Cp = 28.9, Cv = 20.5, Cp/Cv = 1.403. The dielectric constant of gaseous oxygen is 1.000547 (0°C), liquid 1.491. Viscosity 189 mpoise (0°C). Oxygen is slightly soluble in water: at 20°C and 1 atm, 0.031 m 3 is dissolved in 1 m 3 of water, and at 0° C - 0.049 m 3 of oxygen. Good solid oxygen absorbers are platinum black and active charcoal.

Chemical properties of oxygen. Oxygen forms chemical compounds with all elements except light inert gases. Being the most active (after fluorine) non-metal, oxygen interacts directly with most elements; the exceptions are heavy inert gases, halogens, gold and platinum; their compounds with oxygen are obtained indirectly. Almost all reactions of oxygen with other substances - oxidation reactions are exothermic, that is, they are accompanied by the release of energy. Oxygen reacts extremely slowly with hydrogen at ordinary temperatures; above 550°C this reaction proceeds with an explosion 2H2 + O2 = 2H2O.

Oxygen reacts very slowly with sulfur, carbon, nitrogen, and phosphorus under normal conditions. With an increase in temperature, the reaction rate increases and at a certain ignition temperature characteristic of each element, combustion begins. The reaction of nitrogen with oxygen due to the special strength of the N2 molecule is endothermic and becomes noticeable only above 1200°C or in an electric discharge: N2 + O2 = 2NO. Oxygen actively oxidizes almost all metals, especially alkali and alkaline earth metals. The activity of the interaction of metal with oxygen depends on many factors - the state of the metal surface, the degree of grinding, the presence of impurities.

In the process of interaction of a substance with oxygen, the role of water is extremely important. For example, even such an active metal as potassium does not react with oxygen completely devoid of moisture, but ignites in oxygen at ordinary temperature in the presence of even negligible amounts of water vapor. It is estimated that up to 10% of all metal produced is lost annually as a result of corrosion.

Oxides of some metals, by adding oxygen, form peroxide compounds containing 2 or more oxygen atoms bonded to each other. Thus, peroxides Na2O2 and BaO2 include peroxide ion O22-, superoxides NaO2 and KO2 - ion O2-, and ozonides NaO3, KO3, RbO3 and CsO3 - ion O3- Oxygen exothermically interacts with many complex substances. So, ammonia burns in oxygen in the absence of catalysts, the reaction proceeds according to the equation: 4NH3 + 3O2 = 2N2 + 6H2O. Oxidation of ammonia with oxygen in the presence of a catalyst gives NO (this process is used in the production of nitric acid). Of particular importance is the combustion of hydrocarbons (natural gas, gasoline, kerosene) - the most important source of heat in everyday life and industry, for example CH4 + 2O2 = CO2 + 2H2O. The interaction of hydrocarbons with oxygen underlies many of the most important production processes - such, for example, is the so-called conversion of methane, carried out to produce hydrogen: 2CH4 + O2 + 2H2O = 2CO2 + 6H2. Many organic compounds (hydrocarbons with double or triple bonds, aldehydes, phenols, as well as turpentine, drying oils, and others) actively add oxygen. Oxidation of nutrients in cells by oxygen serves as a source of energy for living organisms.

Getting Oxygen. There are 3 main ways to obtain oxygen: chemical, electrolysis (electrolysis of water) and physical (air separation).

The chemical method was invented earlier than others. Oxygen can be obtained, for example, from Bertolet salt KClOz, which decomposes when heated, releasing O2 in an amount of 0.27 m 3 per 1 kg of salt. Barium oxide BaO, when heated to 540°C, first absorbs oxygen from the air, forming BaO2 peroxide, and upon subsequent heating to 870°C, BaO2 decomposes, releasing pure oxygen. It can also be obtained from KMnO4, Ca2PbO4, K2Cr2O7 and other substances by heating and adding catalysts. The chemical method of obtaining oxygen is inefficient and expensive, has no industrial significance and is used only in laboratory practice.

The electrolysis method consists in passing a direct electric current through water, to which a solution of caustic soda NaOH is added to increase its electrical conductivity. In this case, water decomposes into oxygen and hydrogen. Oxygen is collected near the positive electrode of the cell, and hydrogen - near the negative. In this way, oxygen is extracted as a by-product in the production of hydrogen. To obtain 2 m3 of hydrogen and 1 m3 of oxygen, 12-15 kWh of electricity is consumed.

Air separation is the main way to obtain oxygen in modern technology. It is very difficult to carry out the separation of air in a normal gaseous state, therefore, the air is first liquefied, and only then divided into its component parts. This method of obtaining oxygen is called air separation by deep cooling. First, the air is compressed by a compressor, then, after passing through the heat exchangers, it expands in an expander machine or a throttle valve, as a result of which it is cooled to a temperature of 93 K (-180 ° C) and turns into liquid air. Further separation of liquid air, which consists mainly of liquid nitrogen and liquid oxygen, is based on the difference in the boiling points of its components [Boil O2 90.18 K (-182.9°C), N2 Boil 77.36 K (-195.8° FROM)]. With the gradual evaporation of liquid air, nitrogen is first evaporated, and the remaining liquid becomes more and more enriched with oxygen. By repeating this process many times on the distillation plates of the air separation columns, liquid oxygen of the required purity (concentration) is obtained. The USSR manufactures small (several liters) and the world's largest oxygen air separation plants (35,000 m 3 /h of oxygen). These units produce technological Oxygen with a concentration of 95-98.5%, technical Oxygen with a concentration of 99.2-99.9% and purer, medical Oxygen, dispensing products in liquid and gaseous form. The consumption of electrical energy is from 0.41 to 1.6 kWh/m3.

Oxygen can also be obtained by separating air by the method of selective penetration (diffusion) through membrane partitions. Air under high pressure is passed through fluoroplastic, glass or plastic partitions, the structural lattice of which is capable of passing the molecules of some components and retaining others.

Gaseous oxygen is stored and transported in steel cylinders and receivers at a pressure of 15 and 42 MN/m2 (respectively 150 and 420 bar, or 150 and 420 atm), liquid oxygen in metal Dewar vessels or in special tank-tanks. Special pipelines are also used to transport liquid and gaseous oxygen. Oxygen cylinders are painted blue and have a black inscription "oxygen".

The use of oxygen. Technical oxygen is used in the processes of flame treatment of metals, in welding, oxygen cutting, surface hardening, metallization, and others, as well as in aviation, on submarines, and so on. Technological oxygen is used in the chemical industry in the production of artificial liquid fuels, lubricating oils, nitric and sulfuric acids, methanol, ammonia and ammonia fertilizers, metal peroxides and other chemical products. Liquid oxygen is used in blasting, in jet engines, and in laboratory practice as a refrigerant.

Pure oxygen enclosed in cylinders is used for breathing at high altitudes, during space flights, during scuba diving, and others. In medicine, oxygen is given for inhalation by seriously ill patients, is used to prepare oxygen, water and air (in oxygen tents) baths, for intramuscular injection, etc. .P.

Oxygen is widely used in metallurgy to intensify a number of pyrometallurgical processes. Complete or partial replacement of the air entering the metallurgical units with oxygen has changed the chemistry of the processes, their thermal parameters and technical and economic indicators. Oxygen blast made it possible to reduce heat losses with outgoing gases, a significant part of which during air blast was nitrogen. Not taking a significant part in chemical processes, nitrogen slowed down the course of reactions, reducing the concentration of active reagents in the redox medium. When purged with oxygen, fuel consumption is reduced, the quality of the metal is improved, it is possible to obtain new types of products in metallurgical units (for example, slags and gases of an unusual composition for this process, which find special technical applications), etc.

The first experiments on the use of oxygen-enriched blast in blast-furnace production for the smelting of pig iron and ferromanganese were carried out simultaneously in the USSR and Germany in 1932-33. The increased oxygen content in the blast furnace is accompanied by a large reduction in the consumption of the latter, while the content of carbon monoxide in the blast furnace gas increases and its calorific value increases. Oxygen enrichment of the blast makes it possible to increase the productivity of the blast furnace, and in combination with gaseous and liquid fuel supplied to the hearth, it leads to a reduction in coke consumption. In this case, for each additional percentage of Oxygen in the blast, the productivity increases by about 2.5%, and the coke consumption decreases by 1%.

Oxygen in open-hearth production in the USSR was first used to intensify fuel combustion (on an industrial scale, oxygen was first used for this purpose at the Sickle and Hammer and Krasnoye Sormovo plants in 1932-33). In 1933 they began to blow oxygen directly into the liquid bath in order to oxidize impurities during the finishing period. With an increase in the intensity of melt blowing by 1 m 3 /t per 1 hour, the productivity of the furnace increases by 5-10%, fuel consumption is reduced by 4-5%. However, blowing increases the loss of metal. At an oxygen consumption of up to 10 m 3 /t for 1 hour, the yield of steel decreases slightly (up to 1%). Oxygen is becoming more and more widespread in open-hearth production. So, if in 1965 with the use of oxygen in open-hearth furnaces 52.1% of steel was smelted, then in 1970 it was already 71%.

Experiments on the use of oxygen in electric steel-smelting furnaces in the USSR began in 1946 at the Elektrostal plant. The introduction of oxygen blast made it possible to increase the productivity of furnaces by 25-30%, reduce the specific power consumption by 20-30%, improve the quality of steel, reduce the consumption of electrodes and some scarce alloying additives. The supply of oxygen to electric furnaces proved to be especially effective in the production of stainless steels with a low carbon content, the smelting of which is very difficult due to the carburizing effect of the electrodes. The share of electric steel produced in the USSR using oxygen grew continuously and in 1970 amounted to 74.6% of the total steel production.

In cupola melting, oxygen-enriched blast is used mainly for high overheating of cast iron, which is necessary in the production of high-quality, in particular high-alloy, castings (silicon, chromium, etc.). Depending on the degree of oxygen enrichment of the cupola blast, fuel consumption is reduced by 30-50%, the sulfur content in the metal is reduced by 30-40%, the productivity of the cupola is increased by 80-100%, and the temperature of cast iron produced from it increases significantly (up to 1500 ° C). .

Oxygen in non-ferrous metallurgy became widespread somewhat later than in ferrous metallurgy. Oxygen-enriched blast is used in the converting of matte, in the processes of slag sublimation, waltzing, agglomeration, and in the reflective melting of copper concentrates. In the lead, copper and nickel production, oxygen blast intensified the processes of mine smelting, made it possible to reduce coke consumption by 10-20%, increase penetration by 15-20% and reduce the amount of fluxes in some cases by 2-3 times. Oxygen enrichment of the air blast up to 30% during the roasting of zinc sulfide concentrates increased the productivity of the process by 70% and reduced the volume of exhaust gases by 30%.

oxygen element isotope property

The structure of the outer shell: 1 s 2 2s 2 2p 4, which suggests that it is easier for oxygen to attach 2 electrons to itself before filling the outer level than to give it away. Therefore, oxygen is an oxidizing agent.

Isotopes of oxygen.

There are 3 stable forms oxygen: 16 Oh, 17 Oh and 18 Oh, the average content of which is respectively 99.759%, 0.037% and 0.204% of the total number of atoms.

The most frequently occurring 16 O, since it is the lightest (consists of 8 protons and 8 electrons), which makes it very stable.

Physical properties of oxygen.

Methods for obtaining oxygen.

There are 4 ways to get oxygen:

1. Water electrolysis.

2. Industrial method: distillation of the air mixture (oxygen, as a heavier element, remains in the mixture, and nitrogen evaporates)

3. Laboratory methods for the decomposition of oxides, peroxides, salts:

2KMnO 4 \u003d K 2 MnO 4 + MnO 2 + O 2,

2BaO 2 \u003d 2BaO + O 2,

2KNO 3 \u003d 2KNO 2 + O 2.

4. From peroxides (used in space for regeneration O2 from carbon dioxide)

2 K2O 2 + 2CO2 = 2K2CO3+O 2.

Chemical properties of oxygen.

Reacts with metals already at room temperature:

2Ca + O 2 \u003d 2CaO,

2Mg + O 2 \u003d 2MgO,

With non-metals (when heated):

S + O 2 \u003d SO 2 (T=250°С),

C + O 2 = CO 2 (T=700°C),

O2 interacts with complex compounds:

2NO + O 2 \u003d 2NO 2,

2H 2 S + O 2 \u003d 2S + 2H 2 O,

Finding oxygen in nature.

Oxygen is the most common chemical element. Bound oxygen makes up about 6/7 of the mass of the Earth's water shell - the hydrosphere (85.82% by mass), almost half of the lithosphere (47% by mass), and only in the atmosphere, where oxygen is in a free state, does it take second place (23 .15% by weight) after nitrogen.

Oxygen forms a large number of minerals: silicates, quartz, iron oxides, carbonates, sulfates, nitrates. It is part of the cells of living organisms, participates in the processes of respiration, diffusion, blood flow, in the reaction of oxidation and reduction.

Oxygen is the main component of photosynthesis.

Oxygen is in the second period of the VI-th main group of the outdated short version of the periodic table. According to the new numbering standards, this is the 16th group. The corresponding decision was made by IUPAC in 1988. The formula for oxygen as a simple substance is O 2 . Consider its main properties, role in nature and economy. Let's start with the characteristics of the entire group headed by oxygen. The element is different from its related chalcogens, and water is different from the hydrogen selenium and tellurium. An explanation of all the distinctive features can be found only by learning about the structure and properties of the atom.

Chalcogens are elements related to oxygen.

Atoms with similar properties form one group in the periodic system. Oxygen heads the chalcogen family, but differs from them in a number of properties.

The atomic mass of oxygen, the ancestor of the group, is 16 amu. m. Chalcogens in the formation of compounds with hydrogen and metals show their usual oxidation state: -2. For example, in the composition of water (H 2 O), the oxidation number of oxygen is -2.

The composition of typical hydrogen compounds of chalcogens corresponds to the general formula: H 2 R. When these substances are dissolved, acids are formed. Only the hydrogen compound of oxygen - water - has special properties. According to scientists, this unusual substance is both a very weak acid and a very weak base.

Sulfur, selenium and tellurium have typical positive oxidation states (+4, +6) in compounds with oxygen and other high electronegativity (EO) non-metals. The composition of chalcogen oxides reflect the general formulas: RO 2 , RO 3 . The corresponding acids have the composition: H 2 RO 3 , H 2 RO 4 .

Elements correspond to simple substances: oxygen, sulfur, selenium, tellurium and polonium. The first three representatives exhibit non-metallic properties. The formula of oxygen is O 2. An allotropic modification of the same element is ozone (O 3). Both modifications are gases. Sulfur and selenium are solid non-metals. Tellurium is a metalloid substance, a conductor of electric current, polonium is a metal.

Oxygen is the most common element

We already know that there is another kind of existence of the same chemical element in the form of a simple substance. This is ozone, a gas that forms a layer at a height of about 30 km from the earth's surface, often called the ozone layer. Bound oxygen is included in water molecules, in the composition of many rocks and minerals, organic compounds.

The structure of the oxygen atom

The periodic table of Mendeleev contains complete information about oxygen:

1. The ordinal number of the element is 8.
2. Core charge - +8.
3. The total number of electrons is 8.
4. The electronic formula of oxygen is 1s 2 2s 2 2p 4 .

In nature, there are three stable isotopes that have the same serial number in the periodic table, the identical composition of protons and electrons, but a different number of neutrons. Isotopes are designated by the same symbol - O. For comparison, we present a diagram reflecting the composition of three oxygen isotopes:

Properties of oxygen - a chemical element

There are two unpaired electrons on the 2p sublevel of the atom, which explains the appearance of the oxidation states -2 and +2. The two paired electrons cannot be separated to increase the oxidation state to +4, as with sulfur and other chalcogens. The reason is the absence of a free sublevel. Therefore, in compounds, the chemical element oxygen does not show valency and oxidation state equal to the group number in the short version of the periodic system (6). Its usual oxidation number is -2.

Only in compounds with fluorine does oxygen exhibit a positive oxidation state of +2, which is uncharacteristic for it. The EO value of two strong non-metals is different: EO(O) = 3.5; EO (F) = 4. As a more electronegative chemical element, fluorine holds its electrons more strongly and attracts valence particles to oxygen atoms. Therefore, in the reaction with fluorine, oxygen is a reducing agent, it donates electrons.

Oxygen is a simple substance

The English researcher D. Priestley in 1774, during the experiments, released gas during the decomposition of mercury oxide. Two years earlier, K. Scheele obtained the same substance in its pure form. Only a few years later, the French chemist A. Lavoisier established what kind of gas is part of the air, studied the properties. The chemical formula of oxygen is O 2 . Let us reflect in the record of the composition of the substance the electrons involved in the formation of a nonpolar covalent bond - O::O. Let's replace each bonding electron pair with one line: O=O. This oxygen formula clearly shows that the atoms in the molecule are connected between two common pairs of electrons.

Let's perform simple calculations and determine what the relative molecular weight of oxygen is: Mr (O 2) \u003d Ar (O) x 2 \u003d 16 x 2 \u003d 32. For comparison: Mr (air) \u003d 29. The chemical formula of oxygen differs from one an oxygen atom. This means that Mr (O 3) \u003d Ar (O) x 3 \u003d 48. Ozone is 1.5 times heavier than oxygen.

Physical properties

Oxygen is a colorless, tasteless and odorless gas (at normal temperature and atmospheric pressure). The substance is slightly heavier than air; soluble in water, but in small quantities. The melting point of oxygen is negative and is -218.3 °C. The point at which liquid oxygen turns back into gaseous oxygen is its boiling point. For O 2 molecules, the value of this physical quantity reaches -182.96 ° C. In the liquid and solid state, oxygen acquires a light blue color.

Obtaining oxygen in the laboratory

When heated, oxygen-containing substances, such as potassium permanganate, a colorless gas is released, which can be collected in a flask or test tube. If you bring a lighted torch into pure oxygen, it burns more brightly than in air. Two other laboratory methods for obtaining oxygen are the decomposition of hydrogen peroxide and potassium chlorate (berthollet salt). Consider the scheme of the device, which is used for thermal decomposition.

In a test tube or a round-bottom flask, pour a little berthollet salt, close with a stopper with a gas outlet tube. Its opposite end should be directed (under water) to the flask turned upside down. The neck should be lowered into a wide glass or crystallizer filled with water. When a test tube with Berthollet salt is heated, oxygen is released. Through the gas outlet tube, it enters the flask, displacing water from it. When the flask is filled with gas, it is closed under water with a cork and turned over. The oxygen obtained in this laboratory experiment can be used to study the chemical properties of a simple substance.

Combustion

If the laboratory is burning substances in oxygen, then you need to know and follow the fire rules. Hydrogen burns instantly in air, and mixed with oxygen in a ratio of 2:1, it is explosive. The combustion of substances in pure oxygen is much more intense than in air. This phenomenon is explained by the composition of the air. Oxygen in the atmosphere is slightly more than 1/5 of the part (21%). Combustion is the reaction of substances with oxygen, as a result of which various products are formed, mainly oxides of metals and non-metals. Mixtures of O 2 with combustible substances are flammable, in addition, the resulting compounds can be toxic.

The burning of an ordinary candle (or match) is accompanied by the formation of carbon dioxide. The following experience can be done at home. If you burn a substance under a glass jar or a large glass, then the combustion will stop as soon as all the oxygen is used up. Nitrogen does not support respiration and combustion. Carbon dioxide, a product of oxidation, no longer reacts with oxygen. Transparent allows you to detect the presence after the burning of the candle. If the combustion products are passed through calcium hydroxide, the solution becomes cloudy. A chemical reaction occurs between lime water and carbon dioxide, resulting in insoluble calcium carbonate.

Production of oxygen on an industrial scale

The cheapest process, which results in air-free O 2 molecules, does not involve chemical reactions. In industry, say, in metallurgical plants, air is liquefied at low temperature and high pressure. The most important components of the atmosphere, such as nitrogen and oxygen, boil at different temperatures. Separate the air mixture while gradually heating to normal temperature. First, nitrogen molecules are released, then oxygen. The separation method is based on different physical properties of simple substances. The formula of a simple substance of oxygen is the same as it was before cooling and liquefying air - O 2.

As a result of some electrolysis reactions, oxygen is also released, it is collected over the corresponding electrode. Gas is needed by industrial and construction enterprises in large volumes. The demand for oxygen is constantly growing, especially in the chemical industry. The resulting gas is stored for industrial and medical purposes in steel cylinders provided with markings. Tanks with oxygen are painted blue or blue to distinguish them from other liquefied gases - nitrogen, methane, ammonia.

Chemical calculations according to the formula and equations of reactions involving O 2 molecules

The numerical value of the molar mass of oxygen coincides with another value - the relative molecular weight. Only in the first case there are units of measure. Briefly, the formula for the substance of oxygen and its molar mass should be written as follows: M (O 2) \u003d 32 g / mol. Under normal conditions, a mole of any gas corresponds to a volume of 22.4 liters. This means that 1 mol O 2 is 22.4 liters of a substance, 2 mol O 2 is 44.8 liters. According to the reaction equation between oxygen and hydrogen, it can be seen that 2 moles of hydrogen and 1 mole of oxygen interact:

If 1 mol of hydrogen is involved in the reaction, then the volume of oxygen will be 0.5 mol. 22.4 l / mol \u003d 11.2 l.

The role of O 2 molecules in nature and human life

Oxygen is consumed by living organisms on Earth and has been involved in the cycle of matter for over 3 billion years. This is the main substance for respiration and metabolism, with its help the decomposition of nutrient molecules occurs, the energy necessary for organisms is synthesized. Oxygen is constantly consumed on Earth, but its reserves are replenished through photosynthesis. The Russian scientist K. Timiryazev believed that thanks to this process, life still exists on our planet.

The role of oxygen in nature and economy is great:

• absorbed in the process of respiration by living organisms;
• participates in photosynthesis reactions in plants;
• is part of organic molecules;
• the processes of decay, fermentation, rusting proceed with the participation of oxygen, which acts as an oxidizing agent;
• used to obtain valuable products of organic synthesis.

Liquefied oxygen in cylinders is used for cutting and welding metals at high temperatures. These processes are carried out at machine-building plants, at transport and construction enterprises. To carry out work under water, underground, at high altitude in a vacuum, people also need O 2 molecules. are used in medicine to enrich the composition of the air inhaled by sick people. Gas for medical purposes differs from technical gas in the almost complete absence of impurities and odor.

Oxygen is the ideal oxidizing agent

Oxygen compounds are known with all the chemical elements of the periodic table, except for the first representatives of the noble gas family. Many substances directly react with O atoms, except for halogens, gold and platinum. Of great importance are the phenomena involving oxygen, which are accompanied by the release of light and heat. Such processes are widely used in everyday life and industry. In metallurgy, the interaction of ores with oxygen is called roasting. The pre-crushed ore is mixed with oxygen enriched air. At high temperatures, metals are reduced from sulfides to simple substances. This is how iron and some non-ferrous metals are obtained. The presence of pure oxygen increases the speed of technological processes in various branches of chemistry, technology and metallurgy.

The emergence of a cheap method of obtaining oxygen from air by separation into components at low temperatures stimulated the development of many areas of industrial production. Chemists consider O 2 molecules and O atoms to be ideal oxidizing agents. These are natural materials, they are constantly renewed in nature, do not pollute the environment. In addition, chemical reactions involving oxygen most often end in the synthesis of another natural and safe product - water. The role of O 2 in the neutralization of toxic industrial wastes, purification of water from pollution is great. In addition to oxygen, its allotropic modification, ozone, is used for disinfection. This simple substance has a high oxidizing activity. When water is ozonized, pollutants are decomposed. Ozone also has a detrimental effect on pathogenic microflora.