Chemical formula of the air we breathe. What is air: science for adults

Air is a mixture of gases that surrounds the Earth and forms its atmosphere. Air is invisible and tasteless and usually odorless. Air has weight, it can be expanded or compressed, and under extreme low temperatures can be turned into a liquid or even a solid. We call air in motion wind. It has enough power to turn mill blades and move ships across the sea.

The composition of air is quite complex, although its main components are nitrogen - about 78% and oxygen - about 21%. Air also contains argon, carbon dioxide, water vapor, neon, helium, methane, krypton and ozone.

Oxygen in the air is vital for all earthly animals and plants. Through respiration, animals and plants obtain oxygen and use it to obtain energy from food and release carbon dioxide. Carbon dioxide is used by plants for photosynthesis, during which plants obtain energy and release oxygen.

Carbon dioxide makes up only 0.03% of air volume. It is formed not only during combustion, but also during combustion and decomposition of organic substances.

Air also contains water in gaseous form. The percentage of water in the air is called humidity. Humidity may vary depending on altitude and temperature.

The Air also typically contains many small particulate matter, such as volcanic dust, pollen, mold and algae spores, bacteria, soot and dust. Dust particles, for example, can be seen in illuminated sun rays room. Scattering sunlight results in the color of the Sun during sunrise and sunset.

Air has density and pressure. At sea level, the density of the atmosphere is approximately 1.3 kg/m3. The atmospheric pressure at sea level is 101.3 kPa. This pressure is "one atmosphere" - a unit of pressure measured in, for example, car tires. As altitude increases, pressure decreases. At an altitude of 6 km, the air pressure is already 2 times less (about 50 kPa). Air pressure is measured using a special device - a barometer.

Compressed air has long been used in various fields, for example, for the operation of jackhammers, jacks, winches, molding machines, riveting devices, medical instruments. Compressed air is also used in sandblasting machines for cleaning parts, as well as drilling glass, metal and concrete. Back in the late 1950s, the first hovercraft was manufactured, which moves along a layer of created compressed air.

It cannot be touched and cannot be seen, but the main thing we owe to him is life. Of course, this is the air that was not occupied last place in the folklore of every nation. How the people of antiquity imagined it, and what it really is - I will write about this below.

Gases that make up air

Natural mixture of gases called air. Its necessity and importance for living things can hardly be underestimated - it plays an important role in oxidative processes, which are accompanied by the release of energy necessary for all living things. Through experiments, scientists were able to determine its exact composition, but the main thing that needs to be understood is it is not a homogeneous substance, but gas mixture . About 99% of the composition is a mixture of oxygen and nitrogen, and in general air forms the atmosphere of our planet. So, the mixture consists of the following gases:

• methane;
• krypton;
• helium;
• xenon;
• hydrogen;
• neon;
• carbon dioxide;
• oxygen;
• nitrogen;
• argon.

It should be noted that composition is not constant and may vary significantly from one area to another. For example, big cities characterized by a high content of carbon dioxide. In the mountains it will be observed decreased oxygen levels, since this gas is heavier than nitrogen, and as it rises its density will decrease. Science says the composition may differ depending on the different parts planets from 1% to 4% for each gas.

Except percentage gases, air is characterized by the following parameters:

• humidity;
• temperature;
• pressure.

The air is constantly in motion, forming vertical flows. Horizontal - winds, depend on certain natural conditions, so they may have different characteristics speed, force and direction.

Air in folklore

Legends of every people endow the air with certain “living” qualities. As a rule, the spirits of this element were elusive and invisible creatures. According to legends, they inhabited mountain tops or clouds, and differed in their predisposition to humans. They were the ones who were thought to be created snowflakes and collected clouds in the clouds, flying across the sky on the winds.

The Egyptians counted the air symbol of life, and the Indians believed that Brahma's exhalation is life, and inhalation, accordingly, means death. As for the Slavs, air (wind) occupied almost a central place in the legends of this people. He could hear and sometimes even fulfill small requests. However, he was not always kind, sometimes siding with the forces of evil. in the form of an evil and unpredictable wanderer.

The air of the hot, sunny south and the harsh, cold north contains the same amount of oxygen.

One liter of air always contains 210 cubic centimeters of oxygen, which is 21 percent by volume.

The most nitrogen in the air is contained in 780 cubic centimeters per liter, or 78 percent by volume. There is also a small amount of inert gases in the air. These gases are called inert because they almost do not combine with other elements.

Of the inert gases in the air, argon is the most abundant - there are about 9 cubic centimeters per liter. Neon is found in much smaller quantities in the air: there is 0.02 cubic centimeter in a liter of air. There is even less helium - only 0.005 cubic centimeters. Krypton is 5 times less than helium - 0.001 cubic centimeter, and xenon is very small - 0.00008 cubic centimeter.

The air also contains gaseous chemical compounds, for example, carbon dioxide or carbon dioxide (CO 2). The amount of carbon dioxide in the air ranges from 0.3 to 0.4 cubic centimeters per liter. The content of water vapor in the air is also variable. There are fewer of them in dry and hot weather, and more in rainy weather.

The composition of air can also be expressed as a percentage by weight. Knowing the weight of 1 liter of air and the specific gravity of each gas included in its composition, it is easy to move from volumetric values ​​to weight ones. Nitrogen in the air contains about 75.5, oxygen - 23.1, argon - 1.3 and carbon dioxide (carbon dioxide) -0.04 weight percent.

The difference between weight and volume percentages is due to the different specific gravities of nitrogen, oxygen, argon and carbon dioxide.

Oxygen, for example, easily oxidizes copper at high temperatures. Therefore, if you pass air through a tube filled with hot copper filings, when it leaves the tube it will not contain oxygen. You can also remove oxygen from the air with phosphorus. During combustion, phosphorus greedily combines with oxygen, forming phosphorus anhydride (P 2 O 5).

The composition of air was determined in 1775 by Lavoisier.

While heating a small amount of metallic mercury in a glass retort, Lavoisier brought the narrow end of the retort under a glass bell, which was tipped into a vessel filled with mercury. This experiment lasted twelve days. The mercury in the retort, heated almost to a boil, became more and more covered with red oxide. At the same time, the level of mercury in the overturned cap began to rise noticeably above the level of mercury in the vessel in which the cap was located. The mercury in the retort, oxidizing, took more and more oxygen from the air, the pressure in the retort and the bell dropped, and instead of the consumed oxygen, mercury was sucked into the bell.

When all the oxygen was consumed and the oxidation of mercury stopped, the absorption of mercury into the bell also stopped. The volume of mercury in the bell was measured. It turned out that it constituted V 5 part of the total volume of the bell and retort.

The gas remaining in the bell and retort did not support combustion or life. This part of the air, which occupied almost 4/6 of the volume, was called nitrogen.

More accurate experiments in late XVIII century, it was found that air contains 21 percent oxygen and 79 percent nitrogen by volume.

And only in late XIX century, it became known that air contains argon, helium and other inert gases.

On the blog pages we talk a lot about a variety of chemicals and mixtures, but we have not yet had a story about one of the most important complex substances - air. Let's fix this and talk about air. In the first article: a little history of the study of air, its chemical composition and basic facts about him.

A little history of air exploration

Currently, air is understood as a mixture of gases that form the atmosphere of our planet. But it was not always so: for a long time scientists thought that air was a simple substance, an integral substance. And although many scientists have hypothesized about complex composition air, things did not go further than guesses until the 18th century. In addition, air was given philosophical significance. IN Ancient Greece air was considered one of the fundamental cosmic elements, along with earth, fire, earth and water, forming all things. Aristotle attributed air to the sublunar light elements, personifying humidity and heat. Nietzsche in his works wrote about air as a symbol of freedom, as the highest and most subtle form of matter, for which there are no barriers.

In the 17th century, it was proven that air is a material entity, a substance whose properties, such as density and weight, can be measured.

In the 18th century, scientists conducted reactions of air with various substances in sealed chemical vessels. Thus, it was found that approximately a fifth of the air volume is absorbed, and the remaining part of combustion and respiration is not supported. As a result, it was concluded that air is a complex substance, consisting of two components, one of which, oxygen, supports combustion, and the second, nitrogen, “spoiled air,” does not support combustion and respiration. This is how oxygen was discovered. A little later received in pure form nitrogen. And only at the very end of the 19th century, argon, helium, krypton, xenon, radon and neon, also found in air, were discovered.

Chemical composition

Air is made up of a mixture of about twenty-seven different gases. About 99% is a mixture of oxygen and nitrogen. The remaining percentage includes water vapor, carbon dioxide, methane, hydrogen, ozone, inert gases (argon, xenon, neon, helium, krypton) and others. For example, hydrogen sulfide, carbon monoxide, iodine, nitrogen oxides, and ammonia can often be found in the air.

It is believed that clean air under normal conditions contains 78.1% nitrogen and 20.93% oxygen. However, depending on geographical location and altitude above sea level, the air composition may vary.

There is also such a thing as polluted air, that is, air whose composition differs from natural atmospheric air due to the presence of pollutants. These substances are:
. of natural origin (volcanic gases and dust, sea salt, smoke and gases from natural fires, plant pollen, dust from soil erosion, etc.).
. anthropogenic origin - resulting from industrial and domestic human activities (emissions of carbon, sulfur, nitrogen compounds; coal and other dust from mining and industrial enterprises; agricultural waste, industrial and domestic landfills, emergency oil spills and other hazardous environment substances; gas exhausts Vehicle and so on.).

Properties

Clean atmospheric air is colorless and odorless; it is invisible, although it can be felt. The physical parameters of air are determined by the following characteristics:

Mass;
. temperature;
. density;
. atmospheric pressure;
. humidity;
. heat capacity;
. thermal conductivity;
. viscosity.

Most air parameters depend on its temperature, so there are many tables of air parameters for different temperatures. Air temperature is measured using a meteorological thermometer, and humidity is measured using a hygrometer.

Air exhibits oxidizing properties (due to great content oxygen), supports combustion and respiration; conducts heat poorly and dissolves well in water. Its density decreases as temperature increases, and its viscosity increases.

In the following article you will learn about several interesting facts about air and its use.

The lower layers of the atmosphere consist of a mixture of gases called air , in which liquid and solid particles are suspended. The total mass of the latter is insignificant in comparison with the entire mass of the atmosphere.

Atmospheric air is a mixture of gases, the main of which are nitrogen N2, oxygen O2, argon Ar, carbon dioxide CO2 and water vapor. Air without water vapor is called dry air. At the earth's surface, dry air is 99% nitrogen (78% by volume or 76% by mass) and oxygen (21% by volume or 23% by mass). The remaining 1% is almost entirely argon. Only 0.08% remains for carbon dioxide CO2. Numerous other gases are part of the air in thousandths, millionths and even smaller fractions of a percent. These are krypton, xenon, neon, helium, hydrogen, ozone, iodine, radon, methane, ammonia, hydrogen peroxide, nitrous oxide, etc. Composition of dry atmospheric air near the Earth's surface is given in Table. 1.

Table 1

Composition of dry atmospheric air near the Earth's surface

The percentage composition of dry air near the earth's surface is very constant and almost the same everywhere. Only the carbon dioxide content can change significantly. As a result of the processes of breathing and combustion, its volumetric content in the air of closed, poorly ventilated rooms, as well as industrial centers, can increase several times - up to 0.1-0.2%. The percentage of nitrogen and oxygen changes quite slightly.

The real atmosphere contains three important variable components - water vapor, ozone and carbon dioxide. The content of water vapor in the air varies within significant limits, unlike other components air: near the earth's surface it fluctuates between hundredths of a percent and several percent (from 0.2% in polar latitudes to 2.5% at the equator, and in some cases fluctuates from almost zero to 4%). This is explained by the fact that, under the conditions existing in the atmosphere, water vapor can transform into liquid and solid states and, conversely, can enter the atmosphere again due to evaporation from the earth’s surface.

Water vapor continuously enters the atmosphere through evaporation from water surfaces, from moist soil and through transpiration of plants, in different places and in different time it comes in varying quantities. It spreads upward from the earth's surface, and is transported by air currents from one place on the earth to another.

A saturation state may occur in the atmosphere. In this state, water vapor is contained in the air in the amount that is maximum possible at a given temperature. Water vapor is called saturating(or saturated), and the air containing it saturated.

The saturation state is usually reached when the air temperature decreases. When this state is reached, then with a further decrease in temperature, part of the water vapor becomes excess and condenses, turns into a liquid or solid state. Water droplets and ice crystals of clouds and fogs appear in the air. Clouds may evaporate again; in other cases, cloud droplets and crystals, becoming larger, can fall onto the earth's surface in the form of precipitation. As a result of all this, the content of water vapor in each part of the atmosphere is constantly changing.

With water vapor in the air and its transitions from gaseous state connected into liquid and solid critical processes weather and climate features. The presence of water vapor in the atmosphere significantly affects the thermal conditions of the atmosphere and the earth's surface. Water vapor strongly absorbs long-wave infrared radiation emitted by the earth's surface. In turn, it itself emits infrared radiation, most of which goes to the earth's surface. This reduces the nighttime cooling of the earth's surface and thus also the lower air layers.

The evaporation of water from the earth's surface takes large quantities heat, and when water vapor condenses in the atmosphere, this heat is transferred to the air. Clouds resulting from condensation reflect and absorb solar radiation on its way to the earth's surface. Precipitation from clouds is an essential element of weather and climate. Finally, the presence of water vapor in the atmosphere is important for physiological processes.

Water vapor, like any gas, has elasticity (pressure). Water vapor pressure e is proportional to its density (content per unit volume) and its absolute temperature. It is expressed in the same units as air pressure, i.e. either in millimeters of mercury, either in millibars

The pressure of water vapor at saturation is called saturation elasticity. This the maximum pressure of water vapor possible at a given temperature. For example, at a temperature of 0° the saturation elasticity is 6.1 mb . For every 10° temperature increase, the saturation elasticity approximately doubles.

If the air contains less water vapor than is needed to saturate it at a given temperature, you can determine how close the air is to the saturation state. To do this, calculate relative humidity. This is the name given to the ratio of actual elasticity e water vapor in the air to saturation elasticity E at the same temperature, expressed as a percentage, i.e.

For example, at a temperature of 20° the saturation pressure is 23.4 mb. If the actual vapor pressure in the air is 11.7 mb, then the relative humidity is

The elasticity of water vapor at the earth's surface varies from hundredths of a millibar (at very low temperatures in winter in Antarctica and Yakutia) to more than 35 mb (at the equator). The warmer the air, the more water vapor it can contain without saturation and, therefore, the greater the water vapor pressure in it.

Relative air humidity can take on all values ​​- from zero for completely dry air ( e= 0) to 100% for saturation condition (e = E).