Carbon dioxide

Carbon monoxide, a molecule of which consists of one C atom and two O atoms (that is, the degree of carbon oxidation in it is +4) is called carbon dioxide (other names: carbon dioxide, carbonic anhydride, carbon dioxide). This substance is customarily written down by the molecular formula of CO2. Its molar mass is 44.01 g / mol. In appearance, under normal conditions, carbonic anhydride is a colorless gas. At low concentrations it has no odor, at higher concentrations it acquires a sharp, sour smell.

For this chemical, three aggregate states are possible, which are characterized by different density values:

• Solid (dry ice); At a pressure of 1 atm. And a temperature of -78.5 ° C - 1562 kg / m³;
• Liquid (carbonic acid); At a pressure of 56 atm. And temperature +20 ° C - 770 kg / m³;
• Gaseous; At a pressure of 1 atm. And temperature 0 ° С - 1,977 kg / m³.

The melting point of carbon dioxide is -78 ° C, the boiling point is -57 ° C. The substance dissolves in water: at 25 ° C and a pressure of 100 kPa, its solubility is 1.45 g / l.

Carbon dioxide is a natural chemical compound in which a molecule of oxygen atoms with a carbon atom are linked by a covalent bond. The carbon dioxide molecule is linear and centrosymmetric. Both bonds between carbon and two oxygen atoms are equivalent (in fact, they are double). The molecule is symmetric about its center, so it has no electric dipole moment.

Carbon dioxide was one of the first gaseous chemical compounds that ceased to be identified with air. In the seventeenth century, the Flemish chemist Jan Baptista van Helmont noticed that when he burned coal in a closed vessel, the mass of the resulting ash is much less than that of ordinary charcoal. The properties of carbon dioxide were studied more thoroughly in 1750 by Scottish physician Joseph Black.

Carbon dioxide at standard pressure and temperature is in the Earth's atmosphere in an amount of about 0.04% volumetric. Within the carbon cycle, known as photosynthesis, carbon dioxide is absorbed by plants, algae, cyanobacteria. As a result, water and carbohydrates are formed, but this process occurs only under the influence of light. Carbon dioxide is also formed by burning coal or hydrocarbons, fermenting liquids and exhaling air by humans and animals. In addition, it is thrown out of volcanoes, hot springs, geysers.

In the atmosphere of the Earth, carbon dioxide plays an important role (it absorbs and emits radiation in the thermal infrared range). Also this chemical compound is one of the main sources of reducing the pH of the ocean: dissolving in water, it forms a weak carbonic acid: CO2 + H2O ↔ H2CO3, unable to completely dissociate into ions.

Carbon dioxide does not support combustion and breathing. The lit beam in its atmosphere goes out. Animals and humans at a high concentration of CO2 suffocate. At 3% concentration in the air, breathing quickens, at 10% there is a loss of consciousness and rapid death, and a 20% content causes instant paralysis.

Carbon dioxide is an anhydride of carbonic acid, so it is characterized by the properties of an acid oxide. Under laboratory conditions, it is obtained by the interaction of chalk with hydrochloric acid in the Kipp apparatus: CaCO3 + 2HCl → CaCl2 + CO2 + H2O. In industry, it is produced by the thermal decomposition of limestone or chalk (less often magnesite or dolomite): CaCO3 → CaO + CO2. The production of carbon dioxide is a by-product of the low-temperature separation of air into nitrogen and oxygen. Nowadays, special generators are produced for obtaining carbon dioxide from the air. Such generators are used to supply CO2 to greenhouses in order to create a favorable environment for plants.

Carbon dioxide has a wide application in chemical industries. It is used for the production of soda, for the synthesis of organic acids, for the production of non-alcoholic beverages. Dry ice is used as a refrigerant, for example, in winemaking. The carbon dioxide atmosphere is created to prevent rotting food products, the same grapes after harvesting and before the production of wine.

The production of carbon dioxide or liquefied carbon dioxide is carried out to fill them with carbon dioxide fire extinguishers, which are used to extinguish fires. However, they can not extinguish a person, since a significant portion of the liquid CO2 jet evaporates, while the temperature drops sharply (which can cause frostbite) and CO2 turns into dry ice. Carbon dioxide is usually extinguished by flammable liquids and electrical wiring. The mechanism is to stop the access of oxygen from the air to the source of ignition.