Carbon dioxide (carbonic acid gas, carbon dioxide gas, carbon oxide (IV), carbonic anhydride, carbonic acid) – CO2 is a colorless gas with slightly acid flavor.
At standard conditions the density of carbon dioxide is 1.98 kg/m³.
Carbon dioxide does not exist in the liquid state in conditions of standard atmosphere pressure but turns into gas. In the solid state it is known as carbon-dioxide ice. Carbon-dioxide ice is used as a coolant.
In the conditions of increased pressure and normal temperatures, carbon dioxide turns into liquid; it is used for carbon dioxide storage.
According to chemical properties, carbon dioxide refers to acid oxides. In case of dissolving in water, it forms carbonic acid. It reacts with alkalies and forms carbonates and hydrocarbonates.
Carbon dioxide is not toxic, but does not support breathing. High concentration in air causes asphyxia.
Carbon dioxide gas in atmosphere is the main source of carbon for plants. Carbon dioxide gas concentration in the Earth atmosphere is 0.038%.
Carbon dioxide gas easily transmits ultraviolet rays and rays of visible spectrum that come on the Earth from the Sun and heats them. At the same time carbon dioxide gas absorbs infrared rays emitted by the Earth. Carbon dioxide gas is a greenhouse gas.
For industrial purposes, carbon dioxide is produced from furnace gases, products of mineral carbonates decomposition (limestone, dolomite). Gas mixture is washed with potassium carbonate solution which absorbs carbon dioxide gas while passing into hydrocarbonate. During heating, hydrocarbonate solution decomposes, releasing carbonic acid. It is pumped into cylinders in case of industrial production.
In laboratory conditions, small amounts are produced by means of carbonates and hydrocarbonates interaction with acids, e. g. marble with hydrochloric acid.
For purposes of food-processing industry, carbon dioxide is used as a preservative agent and specified on package with code Е290. It is also used as a leavening agent.
Liquid carbon dioxide (liquid food carbon dioxide) is a liquid carbon dioxide storing under high pressure (~ 65-70 atm). Colorless liquid. When liquid carbon dioxide is emitted from cylinder into atmosphere, one part evaporates, and the other – forms carbon dioxide ice.
Carbon dioxide ice is used as a coolant in refrigerators and freezing installations. Sometimes liquid carbon dioxide is used for these purposes as well because it is convenient for transportation through pipes and tubes inside devices.
Cylinders with liquid carbon dioxide are widely used as fire extinguishers. Cylinders with liquid carbon dioxide are widely used for production of soda water and lemonade. Carbon dioxide gas is used as inert media at wire welding. Carbonic acid in cylinders is used for air weapon.