Lesson 18. Physical and chemical properties of oxygen

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In lesson 18 “ Physical and chemical properties of oxygen ” from the course “ Chemistry for Dummies ” we will find out what physical and chemical properties oxygen has and learn about combustion reactions.

Like any chemical substance, oxygen has its own set of physical and chemical properties by which it can be distinguished from other substances.

Physical properties

According to its physical properties, the simple substance oxygen is a non-metal. Under normal conditions, it is in a gaseous aggregate state. Oxygen is colorless, odorless and tasteless. Mass of oxygen with a volume of 1 dm3 at N. u. equal to approximately 1.43 g.

At temperatures below −183 °C, oxygen turns into a blue liquid, and at −219 °C this liquid turns into a solid. This means that the boiling point of oxygen is: t boiling = −183 °C, and the melting point is: t melting = −219 °C. Oxygen is poorly soluble in water.

General characteristics of elements of group 6 of the main subgroup

From O to Po (from top to bottom in the periodic table)

Increases

atomic radius,
metallic, basic, reducing properties,

Decreases

electronegativity,
ionization energy,
electron affinity.

The electronic configurations of these elements are similar; they all contain 6 electrons in the ns2np4 outer layer:

O – 2s2 2p4;

S – 3s23p4;

Se – 4s2 4p4;

Te – 5s2 5p4;

Po – 6s2 6p4

Electronic structure of oxygen and sulfur

Chemical properties

Oxygen is a chemically active substance. It is capable of reacting with many other substances, but most of these reactions require a temperature higher than room temperature. When heated, oxygen reacts with non-metals and metals.

If a glass flask is filled with oxygen and a spoonful of burning sulfur is added to it, the sulfur flares up to form a bright flame and burns quickly (Fig. 80).

The chemical reaction occurring in this case can be described by the following equation:

As a result of the reaction, a substance SO2 is formed, which is called sulfur dioxide. Sulfur dioxide has a pungent odor that you smell when you light a regular match. This suggests that the match head contains sulfur, which, when burned, produces sulfur dioxide.

Ignited red phosphorus in a flask with oxygen flares up even brighter and quickly burns, forming thick white smoke (Fig. 81).

In this case, a chemical reaction occurs:

White smoke is made up of small particulate matter from the reaction product, P2O5.

If you add a glowing ember, consisting mainly of carbon, to a flask with oxygen, it also flares up and burns with a bright flame (Fig. 82).

The ongoing chemical reaction can be represented by the following equation:

The product of the reaction is CO2, or carbon dioxide, which you are already familiar with. You can prove the formation of carbon dioxide by adding a little lime water to the flask. Cloudiness indicates the presence of CO2 in the flask.

The combustion of ember can be used to distinguish oxygen from other gases. If you add a glowing coal to a vessel (flask, test tube) with gas and it flares up, this indicates the presence of oxygen in the vessel.

In addition to non-metals, many metals also react with oxygen. Let us introduce a red-hot steel wire, consisting mainly of iron, into a flask with oxygen. The wire begins to glow brightly and scatter hot sparks in different directions, as if a sparkler is burning (Fig. 83).

In this case, the following chemical reaction occurs:

As a result of the reaction, the substance Fe3O4 (iron scale) is formed. The formula unit of this substance contains three iron atoms, one of which has valency II, and the other two atoms have valency III. Therefore, the formula of this substance can be represented as FeO * Fe2O3.

Note: The reaction of iron with oxygen is used to cut steel products. To do this, a certain area of the part is first heated using an oxygen-gas burner. Then a stream of pure oxygen is directed to the heated area, for which the valve for the supply of flammable gas to the burner is closed. Iron heated to a high temperature enters into a chemical reaction with oxygen and turns into scale. This way you can cut very thick iron parts.

In metallurgy, for cutting and welding metals

Oxygen is used in metallurgy to produce steel. Also, in many metallurgical units, for more efficient combustion of fuel, instead of air in the burners, an oxygen-air mixture is used, i.e. enrich the air with oxygen.

Rice. 1. Steel production

Oxygen in cylinders is widely used for flame cutting and welding of metals. Combustible acetylene gas, burning in a stream of oxygen, allows you to get temperatures above 3000°C! This is approximately twice the melting point of iron.

2. Fuel oxidizer

Oxygen doesn't burn

Surprisingly, this is the honest truth. Oxygen promotes the combustion of other elements, but does not burn itself. And it’s good, because if this were not so, one burning match would be enough to burn all the oxygen in the atmosphere of our planet.

Oxygen is highly soluble

It dissolves in water almost twice as much as nitrogen. If this element had the same solubility as nitrogen, there would be much less oxygen in the seas, lakes and rivers, which would make life much more difficult for a huge number of living organisms.

Oxygen weight

This gas is responsible for almost two-thirds of the weight of most living organisms, mainly because living things are made up of a large amount of water, and 88.9% of the weight of water is oxygen.

Unstable gas

Oxygen (O) is unstable in the atmosphere of our planet and disappears regularly, so its supply must be constantly replenished by photosynthesis. Without vegetation and algae, our atmosphere would contain almost no O.

By the way, speaking of algae, green seaweed provides approximately 70% of the oxygen produced on Earth through photosynthesis, with the remaining 30% produced by the remaining green plants.

Alien life

If we discover any other planets with oxygen-rich atmospheres, we can be almost certain that these planets harbor life. Significant amounts of O are observed only where it can be supplied by living organisms.

Earth's crust

Just five chemical elements make up more than 90% of the weight of the earth's crust. Almost half of this weight is oxygen. Silicon, aluminum, iron and calcium are the remaining elements.

Cold

The world's oceans contain a lot of oxygen dissolved in the water, which supports life. The polar oceans, being the coldest, contain more dissolved oxygen and therefore support a huge number of living organisms.

Ozone

Ozone (O3) is an allotropic form of oxygen that reacts better than regular oxygen. Ozone is released in nature during large electrical emissions (storms and thunderstorms with lightning) or ultraviolet radiation in the upper layers of the Earth's atmosphere. Ozone acts as a protective layer that protects us from the harmful effects of ultraviolet rays. Ozone is sometimes used instead of chlorine in drinking water treatment.

Water

Water (H2O) is the most widely known oxygen-containing molecule. Other known molecules are oxides, such as iron oxide, or rust (Fe2O3), carbon dioxide (CO2), aluminum oxide (Al2O3) and quartz (SiO2).

Combustion reactions

What is common to the reactions we have considered is that they produce a lot of light and heat. Many substances interact with each other in exactly this way.

The reactions of the simple substances sulfur, phosphorus, carbon and iron with oxygen discussed above are combustion reactions .

Combustion reactions are chemical reactions that occur with the release of large amounts of heat and light.

In addition to simple substances, many complex substances, such as methane CH4, also burn in oxygen. When methane burns, carbon dioxide and water are formed:

As a result of this reaction, a lot of heat is released. This is why many homes are supplied with natural gas, the main component of which is methane. The heat released when methane burns is used for cooking and other purposes.

Note: Some chemical reactions occur very quickly. Such reactions are called explosive or simply explosions. For example, the interaction of oxygen with hydrogen can occur in the form of an explosion.

Combustion can occur not only in oxygen, but also in other gases. You will learn about these processes as you further study chemistry.

Sulfur

Methods for obtaining sulfur

Industrial method

Extraction of native sulfur from its deposits or volcanoes
Production of sulfur from sulfur ore using steam-water, filtration, thermal, centrifugal and extraction methods.
Processing of natural gases containing H2S and their oxidation with a lack of O2.

Laboratory method

Interaction of SO2 and H2S in aqueous solution:

SO2 + 2H2S = 3S↓ + 2H2O

Incomplete oxidation of hydrogen sulfide:

2H2S + SO2 → 3S + 2H 2 O

Physical properties of sulfur

Sulfur is a hard, brittle, yellow substance. It is not wetted by water and practically insoluble in it. It has several allotropic modifications. See allotropic modifications of sulfur.

Storage and precautions

Liquid oxygen does not ignite or explode on its own, it is not toxic to humans and is not harmful to the environment. However, the active reaction in chemical processes, as well as the cryogenic effect, make it not an entirely safe substance.

When working with it, you need to keep lubricants, combustible and flammable materials away, and always use gloves and protective clothing. Oxygen at very low temperatures easily damages the skin and can lead to frostbite, injury and death of living cells. If the fluid covers a significant part of the body, it can even end in death.

Technical and medical liquid oxygen is stored in Dewar vessels, which are made primarily of steel or aluminum. These are cylindrical containers with double walls, between the walls of which there is a vacuum cavity, as well as thermal insulation materials. They work on the principle of thermoses, keeping liquids inside well.

Obtaining oxygen

One of the production methods is refractive distillation of air, but such oxygen contains about 3% inert gases (mainly argon). Another option is rectification of liquid air. This process can be briefly described as follows:

air is compressed at a pressure of 100−200 atm;
heated and then cooled in special ammonia refrigerators;
the cooled mixture is passed through a throttle, upon exiting which the pressure drops sharply.

As gases expand, the temperature drops and the air liquefies. This operation is repeated many times to increase the yield of the final product.

Liquefied air is a mixture of gases (mainly nitrogen and oxygen, the rest are less than 1%). Due to the difference in boiling temperatures (for N2 it is -195.8°C, oxygen boils at -183°C), nitrogen is distilled from liquid air, and then O2.

The oxygen obtained by this method contains nitrogen impurities, so it is subjected to additional purification.

It can be obtained in the laboratory in several ways. The main ones:

Decomposition of Berthollet salt. The reaction occurs at elevated temperatures and in the presence of a catalyst, which is manganese dioxide: 2KClO3 → 2KCl + 3O2.
The process of decomposition of potassium permanganate when heated: 2KMnO4 → K2MnO4 + MnO2 + O2.
Isolated from alkali metal nitrates: 2NaNO3 → 2NaNO2 + O2.
During the decomposition of mercury oxide: 2HgO → 2Hg + O2.

Another synthesis method is the electrolysis of water in the presence of alkali metal hydroxides, for example, KOH. These substances are added to increase electrical conductivity.

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Health effects

Oxygen is essential to all life forms as it is a constituent of DNA and almost all other biologically important compounds. In the lungs, this element is absorbed by the iron atom in the center of hemoglobin in the blood and is thus transported to where it is needed.

Every person needs this element to breathe, but, as with many things, too much of it is harmful. If a person is exposed to large amounts of O2 for a long time, lung damage can occur. Inhaling 50-100% oxygen at normal pressure over an extended period causes lung damage. People who work with frequent or potentially high exposure to pure elements should undergo pulmonary function tests before starting work and upon completion.

Application and industrial significance

Due to its properties, oxygen is widely used in technology. In the presence of this element, oxidative processes occur much more intensely than in plain air. This increases the flame temperature. Therefore, O2 is actively used to intensify oxidation in the chemical and metallurgical industries (smelting iron and steel, roasting sulfide ores, cutting metals, etc.).

Mixtures of liquid oxygen with flammable substances (carbon, sulfur, sawdust) called oxyliquits are used as an explosive in the mining and mining industry (during mining and blasting operations). Pure O2 is used in medicine (in the treatment of bronchial asthma, gastrointestinal tract - preparing special cocktails, etc.), in oxygen devices when working underground and under water, at high altitudes. It is also indispensable in the process of producing rocket fuel (oxidizer).