Carbon dioxide: properties, production, application. Liquid carbon dioxide (CO2, carbon dioxide, carbon dioxide) What is co2 in biology
DEFINITION
Carbon dioxide(carbon dioxide, carbonic anhydride, carbon dioxide) – carbon monoxide (IV).
Formula – CO 2. Molar mass – 44 g/mol.
Chemical properties of carbon dioxide
Carbon dioxide belongs to the class of acidic oxides, i.e. When interacting with water, it forms an acid called carbonic acid. Carbonic acid is chemically unstable and at the moment of formation it immediately breaks down into its components, i.e. The reaction between carbon dioxide and water is reversible:
CO 2 + H 2 O ↔ CO 2 ×H 2 O(solution) ↔ H 2 CO 3 .
When heated, carbon dioxide breaks down into carbon monoxide and oxygen:
2CO 2 = 2CO + O 2.
Like all acidic oxides, carbon dioxide is characterized by reactions of interaction with basic oxides (formed only by active metals) and bases:
CaO + CO 2 = CaCO 3;
Al 2 O 3 + 3CO 2 = Al 2 (CO 3) 3;
CO 2 + NaOH (dilute) = NaHCO 3;
CO 2 + 2NaOH (conc) = Na 2 CO 3 + H 2 O.
Carbon dioxide does not support combustion; only active metals burn in it:
CO 2 + 2Mg = C + 2MgO (t);
CO 2 + 2Ca = C + 2CaO (t).
Carbon dioxide reacts with simple substances such as hydrogen and carbon:
CO 2 + 4H 2 = CH 4 + 2H 2 O (t, kat = Cu 2 O);
CO 2 + C = 2CO (t).
When carbon dioxide reacts with peroxides of active metals, carbonates are formed and oxygen is released:
2CO 2 + 2Na 2 O 2 = 2Na 2 CO 3 + O 2.
A qualitative reaction to carbon dioxide is the reaction of its interaction with lime water (milk), i.e. with calcium hydroxide, in which a white precipitate is formed - calcium carbonate:
CO 2 + Ca(OH) 2 = CaCO 3 ↓ + H 2 O.
Physical properties of carbon dioxide
Carbon dioxide is a gaseous substance without color or odor. Heavier than air. Thermally stable. When compressed and cooled, it easily transforms into liquid and solid states. Carbon dioxide in a solid aggregate state is called “dry ice” and easily sublimes at room temperature. Carbon dioxide is poorly soluble in water and partially reacts with it. Density – 1.977 g/l.
Production and use of carbon dioxide
There are industrial and laboratory methods for producing carbon dioxide. Thus, in industry it is obtained by burning limestone (1), and in the laboratory by the action of strong acids on carbonic acid salts (2):
CaCO 3 = CaO + CO 2 (t) (1);
CaCO 3 + 2HCl = CaCl 2 + CO 2 + H 2 O (2).
Carbon dioxide is used in the food (carbonating lemonade), chemical (temperature control in the production of synthetic fibers), metallurgical (environmental protection, such as brown gas precipitation) and other industries.
Examples of problem solving
EXAMPLE 1
| Exercise | What volume of carbon dioxide will be released by the action of 200 g of a 10% solution of nitric acid per 90 g of calcium carbonate containing 8% impurities insoluble in acid? |
| Solution | Molar masses of nitric acid and calcium carbonate, calculated using the table of chemical elements by D.I. Mendeleev - 63 and 100 g/mol, respectively. Let us write the equation for the dissolution of limestone in nitric acid: CaCO 3 + 2HNO 3 → Ca(NO 3) 2 + CO 2 + H 2 O. ω(CaCO 3) cl = 100% - ω admixture = 100% - 8% = 92% = 0.92. Then, the mass of pure calcium carbonate is: m(CaCO 3) cl = m limestone × ω(CaCO 3) cl / 100%; m(CaCO 3) cl = 90 × 92 / 100% = 82.8 g. The amount of calcium carbonate substance is equal to: n(CaCO 3) = m(CaCO 3) cl / M(CaCO 3); n(CaCO 3) = 82.8 / 100 = 0.83 mol. The mass of nitric acid in solution will be equal to: m(HNO 3) = m(HNO 3) solution × ω(HNO 3) / 100%; m(HNO 3) = 200 × 10 / 100% = 20 g. The amount of calcium nitric acid is equal to: n(HNO 3) = m(HNO 3) / M(HNO 3); n(HNO 3) = 20 / 63 = 0.32 mol. By comparing the amounts of substances that reacted, we determine that nitric acid is in short supply, therefore, further calculations are made using nitric acid. According to the reaction equation n(HNO 3): n(CO 2) = 2:1, therefore n(CO 2) = 1/2×n(HNO 3) = 0.16 mol. Then, the volume of carbon dioxide will be equal to: V(CO 2) = n(CO 2)×V m; V(CO 2) = 0.16 × 22.4 = 3.58 g. |
| Answer | The volume of carbon dioxide is 3.58 g. |
, carbon dioxide, properties of carbon dioxide, production of carbon dioxide
It is not suitable for supporting life. However, it is this that plants “feed” on, turning it into organic substances. In addition, it is a kind of “blanket” for the Earth. If this gas suddenly disappeared from the atmosphere, the Earth would become much cooler and rain would virtually disappear.
"Blanket of the Earth"
(carbon dioxide, carbon dioxide, CO 2) is formed when two elements combine: carbon and oxygen. It is formed during the combustion of coal or hydrocarbon compounds, during the fermentation of liquids, and also as a product of the respiration of people and animals. It is also found in small quantities in the atmosphere, from where it is assimilated by plants, which, in turn, produce oxygen.
Carbon dioxide is colorless and heavier than air. Freezes at −78.5°C to form snow consisting of carbon dioxide. In aqueous solution it forms carbonic acid, but it is not stable enough to be easily isolated.
Carbon dioxide is the Earth's blanket. It easily transmits ultraviolet rays that heat our planet and reflects infrared rays emitted from its surface into outer space. And if carbon dioxide suddenly disappears from the atmosphere, this will primarily affect the climate. It will become much cooler on Earth, and rain will fall very rarely. It’s not hard to guess where this will ultimately lead.
True, such a catastrophe does not yet threaten us. Quite the contrary. The combustion of organic substances: oil, coal, natural gas, wood - gradually increases the carbon dioxide content in the atmosphere. This means that over time we must expect significant warming and humidification of the earth’s climate. By the way, old-timers believe that it is already noticeably warmer than it was in the days of their youth...
Carbon dioxide is released liquid low temperature, high pressure liquid And gaseous. It is obtained from waste gases from ammonia and alcohol production, as well as from special fuel combustion and other industries. Gaseous carbon dioxide is a colorless and odorless gas at a temperature of 20 ° C and a pressure of 101.3 kPa (760 mm Hg), density - 1.839 kg / m 3. Liquid carbon dioxide is simply a colorless, odorless liquid.
Non-toxic and non-explosive. At concentrations of more than 5% (92 g/m3), carbon dioxide has a harmful effect on human health - it is heavier than air and can accumulate in poorly ventilated areas near the floor. This reduces the volume fraction of oxygen in the air, which can cause oxygen deficiency and suffocation.
Producing carbon dioxide
In industry, carbon dioxide is obtained from furnace gases, from decomposition products of natural carbonates(limestone, dolomite). The mixture of gases is washed with a solution of potassium carbonate, which absorbs carbon dioxide, turning into bicarbonate. When heated, the bicarbonate solution decomposes, releasing carbon dioxide. During industrial production, gas is pumped into cylinders.
In laboratory conditions small amounts are obtained interaction of carbonates and bicarbonates with acids, for example, marble with hydrochloric acid.
"Dry ice" and other beneficial properties of carbon dioxide
Carbon dioxide is used quite widely in everyday practice. For example, sparkling water with the addition of aromatic essences - a wonderful refreshing drink. IN food industry carbon dioxide is also used as a preservative - it is indicated on the packaging under the code E290, and also as a dough leavening agent.
Carbon dioxide fire extinguishers used in fires. Biochemists have found that fertilization... of the air with carbon dioxide a very effective means for increasing the yield of various crops. Perhaps this fertilizer has a single, but significant drawback: it can only be used in greenhouses. At plants that produce carbon dioxide, liquefied gas is packaged in steel cylinders and sent to consumers. If you open the valve, snow comes out with a hiss. What kind of miracle?
Everything is explained simply. The work expended on compressing the gas is significantly less than that required to expand it. And in order to somehow compensate for the resulting deficit, carbon dioxide cools sharply, turning into "dry ice". It is widely used to preserve food and has significant advantages over ordinary ice: firstly, its “cooling capacity” is twice as high per unit weight; secondly, it evaporates without a trace.
Carbon dioxide is used as an active medium in wire welding, since at arc temperature, carbon dioxide decomposes into carbon monoxide CO and oxygen, which, in turn, interacts with the liquid metal, oxidizing it.
Carbon dioxide in cans is used in air guns and as energy source for engines in aircraft modeling.
Carbon dioxide (carbon dioxide, carbon dioxide, CO 2) is formed by the interaction of two elements - oxygen and carbon. Carbon dioxide is formed by the combustion of hydrocarbon compounds or coal, as a result of fermentation of liquids, and also as a product of animal and human respiration. It is found in the atmosphere in small quantities. Plants absorb carbon dioxide from the atmosphere and convert it into organic compounds. When this gas disappears from the atmosphere, there will be virtually no rain on Earth and it will become noticeably cooler.
Properties of carbon dioxide
Carbon dioxide is heavier than air. It freezes at -78 °C. When carbon dioxide freezes, it forms snow. In solution, carbon dioxide forms carbonic acid. Due to certain properties, carbon dioxide is sometimes called the “blanket” of the Earth. It easily passes ultraviolet rays. Infrared rays are emitted from the surface of carbon dioxide into outer space.
Carbon dioxide is released in liquid form at low temperature, liquid form at high pressure, and gaseous form. The gaseous form of carbon dioxide is obtained from waste gases during the production of alcohols, ammonia, and also as a result of fuel combustion. Carbon dioxide gas is a non-toxic and non-explosive gas, odorless and colorless. In liquid form, carbon dioxide is a colorless and odorless liquid. When the content is more than 5%, carbon dioxide accumulates in the floor area in poorly ventilated areas. A decrease in the volume fraction of oxygen in the air can lead to oxygen deficiency and suffocation. Embryologists have found that human and animal cells need about 7% carbon dioxide, and only 2% oxygen. Carbon dioxide is a nervous system tranquilizer and an excellent anesthetic. The gas in the human body is involved in the synthesis of amino acids and has a vasodilating effect. Lack of carbon dioxide in the blood leads to spasm of blood vessels and smooth muscles of all organs, to increased secretion in the nasal passages, bronchi and to the development of polyps and adenoids, to thickening of membranes due to cholesterol deposition.
Production of carbon dioxide
There are several ways to produce carbon dioxide. In industry, carbon dioxide is obtained from dolomite, limestone - products of the decomposition of natural carbonates, as well as from furnace gases. The gas mixture is washed with a solution of potassium carbonate. The mixture absorbs carbon dioxide and turns into bicarbonate. The bicarbonate solution is heated and it decomposes, releasing carbon dioxide. In the industrial production method, carbon dioxide is pumped into cylinders.
In laboratories, the production of carbon dioxide is based on the interaction of bicarbonates and carbonates with acids.
Applications of carbon dioxide
In everyday practice, carbon dioxide is used quite often. In the food industry, carbon dioxide is used as a leavening agent for dough and also as a preservative. It is indicated on the product packaging under the code E290. The properties of carbon dioxide are also used in the production of sparkling water.
Biochemists have found that to increase the yield of various crops, it is very effective to fertilize the air with carbon dioxide. However, this method of fertilization can only be used in greenhouses. In agriculture, gas is used to create artificial rain. When neutralizing an alkaline environment, carbon dioxide replaces potent mineral acids. In vegetable storage facilities, carbon dioxide is used to create a gaseous environment.
In the perfume industry, carbon dioxide is used in the manufacture of perfumes. In medicine, carbon dioxide is used for antiseptic effects during open operations.
When cooled, carbon dioxide turns into “dry ice.” Liquefied carbon dioxide is packaged in cylinders and sent to consumers. Carbon dioxide in the form of “dry ice” is used to preserve food. When heated, such ice evaporates without leaving a residue.
Carbon dioxide is used as an active medium in wire welding. When welding, carbon dioxide decomposes into oxygen and carbon monoxide. Oxygen interacts with the liquid metal and oxidizes it.
In aircraft modeling, carbon dioxide is used as an energy source for engines. Carbon dioxide canisters are used in air guns.
In recent years, the prospects of CO 2 as a refrigerant have increased significantly. Carbon dioxide is one of the few refrigerants for refrigeration systems that is relevant in terms of efficiency and environmental safety. The use of traditional refrigerants is limited by various regulations, and there is a trend towards tightening them all over the world. In this regard, natural refrigerants are increasingly used. We are starting a column dedicated to the use of CO 2 refrigerant in the field of artificial refrigeration.
CO 2 refrigerant belongs to the group of so-called natural refrigerants (ammonia, propane, butane, water, etc.) which has zero ozone depletion potential (ODP=0) and is the reference unit for calculating global warming potential (GWP=1). Each of the natural refrigerants has its own disadvantages, for example, ammonia is toxic, propane is flammable, and water has a limited range of applications. In contrast, CO 2 is not toxic or flammable, although its impact on the environment is not clear. On the one hand, CO 2 is contained in the air around us and is necessary for the flow of life processes. On the other hand, it is believed that a high concentration of carbon dioxide in the air is one of the causes of global warming.
The initiative to return to the use of CO 2 in refrigeration technology comes from the Scandinavian countries, where laws significantly limit the use of HFC and HCFC refrigerants. Ammonia is traditionally used as a refrigerant for industrial installations, but its quantity in the system is limited. This is not a problem for installations operating at high and medium temperatures (up to -15/-25°C), where the amount of ammonia is reduced by using a secondary coolant. For lower temperatures, the use of a secondary coolant is ineffective due to large losses due to temperature differences; in this case, CO 2 is used.
The figure above shows the phase diagram of CO 2. The curved lines that divide the diagram into separate sections define the limiting values of pressure and temperature for various phases: liquid, solid, vapor or supercritical. The points on these curves determine the pressures and corresponding temperatures at which two phases are in equilibrium, for example, solid and vapor, liquid and vapor, solid and liquid.
At atmospheric pressure, CO 2 exists in solid or vapor phases. At this pressure the liquid phase does not exist. At temperatures below –78.4°C, carbon dioxide is in the solid phase (“dry ice”). As the temperature rises, CO 2 sublimates into the vapor phase. At a pressure of 5.2 bar and a temperature of –56.6°C, the refrigerant reaches the so-called triple point. At this point, all three phases exist in an equilibrium state. At a temperature of +31.1°C CO 2 reaches its critical point, where its densities in the liquid and vapor phases are the same (figure above). Consequently, the difference between the two phases disappears and CO 2 exists in a supercritical state.
Carbon dioxide can be used as a refrigerant in various types of refrigeration systems, both subcritical and transcritical. When using CO 2 as a refrigerant, both the triple point and the critical point must be taken into account for all types of refrigeration systems. In the subcritical CO 2 cycle (figure above), the entire range of operating temperatures and pressures lies between the critical and triple points. Single-stage CO 2 refrigeration cycles are similar to other refrigerants, but have some disadvantages, primarily related to temperature and pressure limitations.
Transcritical CO 2 refrigeration systems are currently used in small and commercial refrigeration applications, such as mobile air conditioning systems, small heat pumps and supermarket refrigeration systems. Transcritical systems are practically not used in industrial refrigeration units. The operating pressure in the subcritical cycle is typically in the range of 5.7 to 35 bar with a corresponding temperature of -55 to 0°C. When the evaporator is defrosted with hot gas, the operating pressure increases by approximately 10 bar.
CO 2 is most widely used in cascade systems of industrial refrigeration units. This is due to the fact that the operating pressure range allows the use of standard equipment (compressors, regulators and valves).
There are different types of CO 2 cascade refrigeration systems: direct boiling systems, pump circulation systems, CO 2 systems with a secondary brine circuit, or combinations of these systems.
Carbon dioxide is a colorless gas with a barely perceptible odor, non-toxic, heavier than air. Carbon dioxide is widely distributed in nature. It dissolves in water, forming carbonic acid H 2 CO 3, giving it a sour taste. The air contains about 0.03% carbon dioxide. The density is 1.524 times greater than the density of air and is equal to 0.001976 g/cm 3 (at zero temperature and pressure 101.3 kPa). Ionization potential 14.3V. Chemical formula - CO 2.
In welding production the term is used "carbon dioxide" cm. . In the “Rules for the Design and Safe Operation of Pressure Vessels” the term "carbon dioxide", and in - term "carbon dioxide".
There are many ways to produce carbon dioxide, the main ones are discussed in the article.
The density of carbon dioxide depends on pressure, temperature and the state of aggregation in which it is found. At atmospheric pressure and a temperature of -78.5°C, carbon dioxide, bypassing the liquid state, turns into a white snow-like mass "dry ice".
Under a pressure of 528 kPa and at a temperature of -56.6 ° C, carbon dioxide can be in all three states (the so-called triple point).
Carbon dioxide is thermally stable, dissociating into carbon monoxide only at temperatures above 2000°C.
Carbon dioxide is first gas to be described as a discrete substance. In the seventeenth century, a Flemish chemist Jan Baptist van Helmont (Jan Baptist van Helmont) noticed that after burning coal in a closed vessel, the mass of ash was much less than the mass of the burned coal. He explained this by saying that coal was transformed into an invisible mass, which he called “gas.”
The properties of carbon dioxide were studied much later in 1750. Scottish physicist Joseph Black (Joseph Black).
He discovered that limestone (calcium carbonate CaCO 3), when heated or reacted with acids, releases a gas, which he called “bound air.” It turned out that “bound air” is denser than air and does not support combustion.
CaCO 3 + 2HCl = CO 2 + CaCl 2 + H 2 O
By passing “bound air” i.e. carbon dioxide CO 2 through an aqueous solution of lime Ca(OH) 2 calcium carbonate CaCO 3 is deposited to the bottom. Joseph Black used this experiment to prove that carbon dioxide is released through animal respiration.
CaO + H 2 O = Ca(OH) 2
Ca(OH) 2 + CO 2 = CaCO 3 + H 2 O
Liquid carbon dioxide is a colorless, odorless liquid whose density varies greatly with temperature. It exists at room temperature only at pressures above 5.85 MPa. The density of liquid carbon dioxide is 0.771 g/cm 3 (20°C). At temperatures below +11°C it is heavier than water, and above +11°C it is lighter.
The specific gravity of liquid carbon dioxide varies significantly with temperature, therefore, the amount of carbon dioxide is determined and sold by weight. The solubility of water in liquid carbon dioxide in the temperature range 5.8-22.9°C is not more than 0.05%.
Liquid carbon dioxide turns into gas when heat is supplied to it. Under normal conditions (20°C and 101.3 kPa) When 1 kg of liquid carbon dioxide evaporates, 509 liters of carbon dioxide are formed. When gas is withdrawn too quickly, the pressure in the cylinder decreases and the heat supply is insufficient, the carbon dioxide cools, the rate of its evaporation decreases and when it reaches the “triple point” it turns into dry ice, which clogs the hole in the reduction gear, and further gas extraction stops. When heated, dry ice directly turns into carbon dioxide, bypassing the liquid state. To evaporate dry ice, it is necessary to supply significantly more heat than to evaporate liquid carbon dioxide - therefore, if dry ice has formed in the cylinder, it evaporates slowly.
Liquid carbon dioxide was first produced in 1823. Humphry Davy(Humphry Davy) and Michael Faraday(Michael Faraday).
Solid carbon dioxide "dry ice" resembles snow and ice in appearance. The carbon dioxide content obtained from dry ice briquettes is high - 99.93-99.99%. Moisture content is in the range of 0.06-0.13%. Dry ice, being in the open air, evaporates rapidly, so containers are used for its storage and transportation. Carbon dioxide is produced from dry ice in special evaporators. Solid carbon dioxide (dry ice), supplied in accordance with GOST 12162.
Carbon dioxide is most often used:
- to create a protective environment for metals;
- in the production of carbonated drinks;
- refrigeration, freezing and storage of food products;
- for fire extinguishing systems;
- for cleaning surfaces with dry ice.
The density of carbon dioxide is quite high, which allows the arc reaction space to be protected from contact with air gases and prevents nitriding at relatively low carbon dioxide consumption in the jet. Carbon dioxide is, during the welding process, it interacts with the weld metal and has an oxidizing and also carburizing effect on the metal of the weld pool.
Previously obstacles to the use of carbon dioxide as a protective medium were in the seams. The pores were caused by boiling of the solidifying metal of the weld pool from the release of carbon monoxide (CO) due to its insufficient deoxidation.
At high temperatures, carbon dioxide dissociates to form highly active free, monoatomic oxygen:
Oxidation of the weld metal released free from carbon dioxide during welding is neutralized by the content of an additional amount of alloying elements with a high affinity for oxygen, most often silicon and manganese (in excess of the amount required for alloying the weld metal) or fluxes introduced into the welding zone (welding).
Both carbon dioxide and carbon monoxide are practically insoluble in solid and molten metal. The free active oxidizes the elements present in the weld pool depending on their oxygen affinity and concentration according to the equation:
Me + O = MeO
where Me is a metal (manganese, aluminum, etc.).
In addition, carbon dioxide itself reacts with these elements.
As a result of these reactions, when welding in carbon dioxide, significant burnout of aluminum, titanium and zirconium is observed, and less intense burnout of silicon, manganese, chromium, vanadium, etc.
The oxidation of impurities occurs especially vigorously at . This is due to the fact that when welding with a consumable electrode, the interaction of the molten metal with the gas occurs when a drop remains at the end of the electrode and in the weld pool, and when welding with a non-consumable electrode, it occurs only in the pool. As is known, the interaction of gas with metal in an arc gap occurs much more intensely due to the high temperature and larger contact surface of the metal with the gas.
Due to the chemical activity of carbon dioxide in relation to tungsten, welding in this gas is carried out only with a consumable electrode.
Carbon dioxide is non-toxic and non-explosive. At concentrations of more than 5% (92 g/m3), carbon dioxide has a harmful effect on human health, since it is heavier than air and can accumulate in poorly ventilated areas near the floor. This reduces the volume fraction of oxygen in the air, which can cause oxygen deficiency and suffocation. Premises where welding is carried out using carbon dioxide must be equipped with general supply and exhaust ventilation. The maximum permissible concentration of carbon dioxide in the air of the working area is 9.2 g/m 3 (0.5%).
Carbon dioxide is supplied by . To obtain high-quality seams, gaseous and liquefied carbon dioxide of the highest and first grades is used.
Carbon dioxide is transported and stored in steel cylinders or large-capacity tanks in a liquid state, followed by gasification at the plant, with a centralized supply to welding stations through ramps. A standard one with a water capacity of 40 liters is filled with 25 kg of liquid carbon dioxide, which at normal pressure occupies 67.5% of the volume of the cylinder and produces 12.5 m 3 of carbon dioxide upon evaporation. Air accumulates in the upper part of the cylinder along with carbon dioxide gas. Water, which is heavier than liquid carbon dioxide, collects at the bottom of the cylinder.
To reduce the humidity of carbon dioxide, it is recommended to install the cylinder with the valve down and, after settling for 10...15 minutes, carefully open the valve and release moisture from the cylinder. Before welding, it is necessary to release a small amount of gas from a normally installed cylinder to remove any air trapped in the cylinder. Some of the moisture is retained in carbon dioxide in the form of water vapor, worsening the welding of the seam.
When gas is released from the cylinder, due to the throttling effect and heat absorption during the evaporation of liquid carbon dioxide, the gas cools significantly. With intensive gas extraction, the reducer may become clogged with frozen moisture contained in carbon dioxide, as well as dry ice. To avoid this, when extracting carbon dioxide, a gas heater is installed in front of the reducer. The final removal of moisture after the gearbox is carried out with a special desiccant filled with glass wool and calcium chloride, silica gel, copper sulfate or other moisture absorbers
The carbon dioxide cylinder is painted black, with the words “CARBON ACID” written in yellow letters..
