Carbon monoxide, the 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 usually written in the molecular formula CO2. Its molar mass is 44.01 g / mol. In appearance, under normal conditions, carbonic anhydride is a colorless gas. At low concentrations, it is odorless, at higher concentrations it acquires a sharp, sour smell.
Three aggregate states are possible for this chemical substance, which are characterized by different density values:
- hard (dry ice); at a pressure of 1 atm. and temperature -78.5 ° - 1562 kg / m³;
- liquid (carbon dioxide); at a pressure of 56 atm. and temperature +20 ° - 770 kg / m³;
- gaseous; at a pressure of 1 atm. and temperature 0 ° - 1.977 kg / m³.
The melting point of carbon dioxide is -78 ° C, the boiling point is -57 ° C. The substance is soluble 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 the molecule of which oxygen atoms are bonded to a carbon atom by a covalent bond. The carbon dioxide molecule is linear and centrosymmetric. Both bonds between carbon and two oxygen atoms are equivalent (essentially double). The molecule is symmetric about its center, therefore, it does not have any electric dipole moment.
Carbon dioxide was one of the first gaseous chemical compounds that were no longer identified with air. In the seventeenth century, the Flemish chemist Jan Baptista van Helmont noticed that when he burns coal in a closed vessel, the mass of ash obtained 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 atmosphere of the Earth in an amount of about 0.04% by volume. Within the carbon cycle, known as photosynthesis, carbon dioxide is absorbed by plants, algae, and cyanobacteria. As a result, water and carbohydrates are formed, but this process occurs only under the influence of light. Carbon dioxide is also produced during the combustion of coal or hydrocarbons, during the fermentation of liquids, and during the expiration of air by humans and animals. In addition, it is thrown from volcanoes, hot springs, geysers.
In the Earth’s atmosphere, carbon dioxide plays an important role (absorbs and emits radiation in the thermal infrared range). This chemical compound is also one of the main sources of lowering the pH of the ocean: dissolving in water, it forms a weak carbonic acid: CO2 + H2O ↔ H2CO3, which is unable to completely dissociate into ions.
Carbon dioxide does not support combustion and respiration. A lit torch in its atmosphere goes out. Animals and humans suffocate when CO2 is high. At a 3% concentration in the air, breathing quickens, at 10% a loss of consciousness and rapid death occurs, and a 20% concentration causes instant paralysis.
Carbon dioxide is carbonic anhydride, therefore, it is characterized by the properties of 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 thermal decomposition of limestone or chalk (less often magnesite or dolomite): CaCO3 → CaO + CO2. The production of carbon dioxide is a byproduct of the low-temperature separation of air into nitrogen and oxygen. Nowadays, special generators for producing carbon dioxide from air are produced. Such generators are used to supply CO2 to greenhouses in order to create a favorable environment for plants.
Carbon dioxide is widely used in chemical industries. It is used to produce soda, for the synthesis of organic acids, for the manufacture of soft drinks. Dry ice is used as a refrigerant, for example, in winemaking. A carbon dioxide atmosphere is created to prevent rotting of food products of the same grape after its collection and before the start of wine production.
The production of carbon dioxide or liquefied carbon dioxide is carried out to fill it with carbon dioxide fire extinguishers, which are used to extinguish fires. However, they should not put out a person, as a significant part of a stream of liquid CO2 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 consists in the cessation of access of air oxygen to the source of ignition.