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 a pressure of 101.3 kPa). Ionization potential 14.3V. The chemical formula is CO 2 .
In welding production, the term is used "carbon dioxide" cm. . The "Rules for the Design and Safe Operation of Pressure Vessels" adopted 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 the pressure, temperature and state of aggregation in which it is located. 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, dissociates into carbon monoxide and 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 the fact that coal is 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 \u003d CO 2 + CaCl 2 + H 2 O
Passing "bound air" i.e. carbon dioxide CO 2 through an aqueous solution of lime Ca (OH) 2 calcium carbonate CaCO 3 is deposited on the bottom. Joseph Black used this experience to prove that carbon dioxide is released as a result of animal respiration.
CaO + H 2 O \u003d 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 a pressure of more than 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, so the amount of carbon dioxide is determined and sold by weight. The solubility of water in liquid carbon dioxide in the temperature range of 5.8-22.9°C is not more than 0.05%.
Liquid carbon dioxide turns into a gas when heat is applied 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. With excessively rapid gas extraction, a decrease in pressure in the cylinder and insufficient heat supply, carbon dioxide cools, its evaporation rate decreases, and when the “triple point” is reached, 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. Much more heat is required to vaporize dry ice than to vaporize liquid carbon dioxide - so if dry ice has formed in a cylinder, it evaporates slowly.
Liquid carbon dioxide was first obtained in 1823. Humphrey Davy(Humphry Davy) and Michael Faraday(Michael Faraday).
Solid carbon dioxide is "dry ice", similar in appearance to snow and ice. The content of carbon dioxide obtained from dry ice briquettes is high - 99.93-99.99%. Moisture content in the range of 0.06-0.13%. Dry ice, being in the open air, evaporates intensively, therefore, 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 the most commonly used:
- to create a protective environment for metals;
- in the production of carbonated drinks;
- cooling, freezing and food storage;
- for fire extinguishing systems;
- for cleaning surfaces with dry ice.
The density of carbon dioxide is quite high, which makes it possible to protect the reaction space of the arc from contact with air gases and prevents nitriding at relatively low carbon dioxide flow rates in the jet. Carbon dioxide is, during the welding process, it interacts with the weld metal and has an oxidizing and carburizing effect on the metal of the weld pool.
Previously an obstacle to the use of carbon dioxide as a protective medium were at the seams. The pores were caused by boiling of the hardening 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, monatomic oxygen:
Oxidation of the weld metal released during welding from carbon dioxide free 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 to alloy 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. Free active oxidizes the elements present in the weld pool, depending on their affinity for oxygen 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, a significant burnout of aluminum, titanium and zirconium is observed, and less intense - 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 molten metal with gas occurs when the drop is at the end of the electrode and in the weld pool, and when welding with a non-consumable electrode, only in the bath. As is known, the interaction of gas with metal in the arc gap is much more intense due to the high temperature and the larger contact surface of the metal with the gas.
Due to the chemical activity of carbon dioxide with respect 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/m 3 ) carbon dioxide has a harmful effect on human health, as it is heavier than air and can accumulate in poorly ventilated rooms near the floor. This reduces the volume fraction of oxygen in the air, which can cause the phenomenon of oxygen deficiency and suffocation. Premises where welding is carried out using carbon dioxide must be equipped with general-exchange supply and exhaust ventilation. The maximum allowable 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 are 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 of welding stations through ramps. 25 kg of liquid carbon dioxide is poured into a standard one with a water capacity of 40 liters, which at normal pressure occupies 67.5% of the volume of the cylinder and gives 12.5 m 3 of carbon dioxide upon evaporation. Air accumulates in the upper part of the cylinder along with gaseous carbon dioxide. Water, being 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 in order to remove air trapped in the cylinder. Part of the moisture is retained in carbon dioxide in the form of water vapor, worsening when welding a seam.
When the gas is released from the cylinder, due to the effect of throttling and absorption of heat during the evaporation of liquid carbon dioxide, the gas is significantly cooled. With intensive gas extraction, the reducer can be blocked by frozen moisture contained in carbon dioxide, as well as dry ice. To avoid this, when taking carbon dioxide, a gas heater is installed in front of the reducer. The final removal of moisture after the reducer is carried out with a special desiccant filled with glass wool and calcium chloride, silica helium, copper sulphate or other moisture absorbers.
The carbon dioxide cylinder is painted black, with the inscription in yellow letters "CARBON DIOXIDE".
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 decomposes into components, i.e. The reaction of the interaction of carbon dioxide with 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 \u003d 2CO + O 2.
As with all acidic oxides, carbon dioxide is characterized by reactions of interaction with basic oxides (formed only by active metals) and bases:
CaO + CO 2 \u003d CaCO 3;
Al 2 O 3 + 3CO 2 \u003d Al 2 (CO 3) 3;
CO 2 + NaOH (dilute) = NaHCO 3 ;
CO 2 + 2NaOH (conc) \u003d Na 2 CO 3 + H 2 O.
Carbon dioxide does not support combustion; only active metals burn in it:
CO 2 + 2Mg \u003d C + 2MgO (t);
CO 2 + 2Ca \u003d C + 2CaO (t).
Carbon dioxide enters into reactions with simple substances such as hydrogen and carbon:
CO 2 + 4H 2 \u003d CH 4 + 2H 2 O (t, kat \u003d Cu 2 O);
CO 2 + C \u003d 2CO (t).
When carbon dioxide interacts with peroxides of active metals, carbonates are formed and oxygen is released:
2CO 2 + 2Na 2 O 2 \u003d 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 \u003d CaCO 3 ↓ + H 2 O.
Physical properties of carbon dioxide
Carbon dioxide is a colorless and odorless gaseous substance. Heavier than air. Thermally stable. When compressed and cooled, it easily transforms into liquid and solid states. Carbon dioxide in a solid state of aggregation is called "dry ice" and easily sublimates at room temperature. Carbon dioxide is poorly soluble in water and partially reacts with it. Density - 1.977 g / l.
Obtaining and using carbon dioxide
Allocate industrial and laboratory methods for producing carbon dioxide. So, in industry it is obtained by roasting limestone (1), and in the laboratory - by the action of strong acids on carbonic acid salts (2):
CaCO 3 \u003d CaO + CO 2 (t) (1);
CaCO 3 + 2HCl \u003d CaCl 2 + CO 2 + H 2 O (2).
Carbon dioxide is used in food (carbonation of lemonade), chemical (temperature control in the production of synthetic fibers), metallurgical (protection environment, for example, brown gas deposition) and other industries.
Examples of problem solving
EXAMPLE 1
| Exercise | What volume of carbon dioxide will be released under the action of 200 g of a 10% solution of nitric acid on 90 g of calcium carbonate containing 8% impurities insoluble in acid? |
| Decision | The molar masses of nitric acid and calcium carbonate, calculated using the table of chemical elements of D.I. Mendeleev - 63 and 100 g/mol, respectively. We 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 \u003d 100% - ω admixture \u003d 100% - 8% \u003d 92% \u003d 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 \u003d 90 × 92 / 100% \u003d 82.8 g. The amount of calcium carbonate substance is: n (CaCO 3) \u003d m (CaCO 3) cl / M (CaCO 3); n (CaCO 3) \u003d 82.8 / 100 \u003d 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) \u003d 200 × 10 / 100% \u003d 20 g. The amount of calcium nitric acid substance is: n(HNO 3) = m(HNO 3) / M(HNO 3); n (HNO 3) \u003d 20/63 \u003d 0.32 mol. Comparing the amounts of substances that have entered into the reaction, we determine that nitric acid is in short supply, therefore, we make further calculations for nitric acid. According to the reaction equation n (HNO 3): n (CO 2) \u003d 2: 1, therefore n (CO 2) \u003d 1 / 2 × n (HNO 3) \u003d 0.16 mol. Then, the volume of carbon dioxide will be equal to: V(CO 2) = n(CO 2)×V m ; V(CO 2) \u003d 0.16 × 22.4 \u003d 3.58 g. |
| Answer | The volume of carbon dioxide is 3.58 g. |
Carbon dioxide, having universal properties, is used in industry, medicine, and agriculture. Today, CO2 is a fertilizer in agriculture, a medical instrument, a temperature regulator and a source of new energy.
The production of carbon dioxide in industry is methodologically diverse. It is found in flue waste released into the atmosphere by thermal power plants and power plants, it is obtained during the fermentation of alcohol and acts as a reaction product with natural carbonates.
The carbon dioxide production industry is wide. The gas can be absorbed in several ways from a single source. In all cases, this is a step-by-step process of cleaning from impurities (to achieve the requirements of GOST) and achieving the desired consistency, state of aggregation.
Production of gaseous carbon dioxide
Gaseous CO2 is recovered from industrial (petroleum) fumes by adsorption of monoethanolamine (commercially beneficial) and potassium carbonate (rarely). The principle of collecting carbon particles is the same for both substances. They are sent through the pipeline to the waste and collect carbon dioxide. After collection, the gases saturated with carbon dioxide are sent for purification.
In special containers, the reaction takes place at elevated temperature or low pressure. In the process, pure carbon dioxide and decomposition products (ammonia and others) are released.
Carbon Dioxide Plant
Schematically, the process looks like this:
- Exhaust smoke is mixed with adsorbents (gaseous potassium carbonate or monoethanolamine);
- The gases that have accumulated carbon dioxide in themselves enter a special gas holder for purification;
- In a reaction with high temperature or low pressure, carbon dioxide is separated from the adsorbent.
Chemical industry:
- Participates in the synthesis of artificial chemicals;
- Regulates temperature in reactions;
- Neutralizes alkalis;
- Purifies tissues of animals and plants;
- Can be reduced to methane.
Metallurgy:
- Deposition of exhaust smoke;
- Regulates the direction of water flow during the removal of mines;
- Some lasers use CO2 as an energy source (neon).
Paper production:
- Regulates the pH in wood pulp or pulp;
- Strengthens production machines in power.
Dry ice plays a special role in industrial and related industries. It is applied as:
- Cooling source in freezers during transportation;
- Cooling during solidification of alloys;
- Dry ice cleaning of equipment (cryoblasting).
Fish frozen in dry ice.
Application in other fields of activity
Man also uses carbon dioxide in other areas of activity and in everyday life. The availability of dioxide causes its wide distribution, and its properties are in demand even among ordinary people.
Where else is carbon dioxide used?
- When welding. Protects metal from heating and oxidation by flowing around an electric arc.
- In agriculture. Carbon dioxide coupled with sunlight is the perfect way to fertilize any crop. Spraying gas in a greenhouse or greenhouse increases the yield by 2-3 times;
- In medicine, it is used to create an atmosphere close to the real one during artificial operations on organs. It is used as a stimulant to restore the patient's breathing and when introducing him into anesthesia;
- Pharmaceutics. Creates an ideal environment for the synthesis of chemistry and low-temperature water transportation;
- Devices and equipment. Cools equipment and units indiscriminately into modules, acts as an abrasive cleaning element;
- Environment protection. Regulates the rate of hydrogen in the drains;
- Food industry. Used as a preservative and baking powder. It is added to drinks, making them carbonated;
- To create pressure in pneumatic weapons.
The use of carbon dioxide is especially in demand in fire extinguishing systems. It is filled into carbon dioxide gas fire extinguishers and, when ignited, allows you to isolate the fire from the oxygen source. Combustion cannot continue for a long time without air supply, and gasification with carbon dioxide will not allow it to penetrate to the fire.
Obtained in small quantities from alcoholic fermentation, it is used as a way to carbonate drinks. It also keeps flour, dried fruits, peanuts free from insects without affecting the quality and speed of their spoilage.
Carbon dioxide is a first-class environment for growing flowers, feeding vegetables and underwater plants. It accelerates photosynthesis and improves metabolic processes in plant cells. The main thing is that it has an affordable price even for ordinary people.
Carbon dioxide can also be used in cryodestruction, as a freezing. It burns the surface of warts and moles with cold, causing them to fall off, but not leave scars from the scalpel and stitches.
Conclusion
Carbon dioxide is a simple and widespread substance throughout the planet, which plays a practical function in key industries. Industry, medicine, the food industry and even simple human life cannot do without it.
More recently, CO2 has been used as the basis for the production of a fuel source (methanol). The method is gaining popularity as a renewable geothermal energy source that can increase electricity production and.
DEFINITION
Carbon dioxide (carbon dioxide) under normal conditions, it is a colorless gas, about 1.5 times heavier than air, due to which it can be poured, like a liquid, from one vessel to another.
The mass of 1 liter of CO 2 under normal conditions is 1.98 g. The solubility of carbon dioxide in water is low: 1 volume of water at 20 o C dissolves 0.88 volumes of CO 2 , and at 0 o C - 1.7 volumes.
Under a pressure of about 0.6 MPa, carbon dioxide turns into a liquid at room temperature. Liquid carbon dioxide is stored in steel cylinders. When it is quickly poured out of the cylinder, so much heat is absorbed due to evaporation that CO 2 turns into a solid white snow-like mass, which, without melting, sublimes at -78.5 o C.
A solution of CO 2 in water has a sour taste and has a slightly acidic reaction due to the presence in the solution of small amounts of carbonic acid H 2 CO 3 formed as a result of a reversible reaction:
CO 2 + H 2 O↔H 2 CO 3.
Some properties of carbon dioxide are presented in the table below:
Getting carbon dioxide
Carbon dioxide is produced in small quantities by the action of acids on carbonates:
CaCO 3 + 2HCl \u003d CaCl 2 + H 2 O + CO 2.
On an industrial scale, CO 2 is produced mainly as a by-product in the ammonia synthesis process:
CH 4 + 2H 2 O \u003d CO 2 + 4H 2;
CO + H 2 O \u003d CO 2 + H 2.
In addition, large amounts of carbon dioxide are obtained during the burning of limestone:
CaCO 3 \u003d CaO + CO 2.
Chemical properties of carbon dioxide
Carbon dioxide exhibits acidic properties: it reacts with alkalis, ammonia hydrate. It is restored by active metals, hydrogen, carbon.
CO 2 + NaOH dilute = NaHCO 3 ;
CO 2 + 2NaOH conc \u003d Na 2 CO 3 + H 2 O;
CO 2 + Ba(OH) 2 = BaCO 3 + H 2 O;
CO 2 + BaCO 3 + H 2 O \u003d Ba (HCO 3) 2;
CO 2 + NH 3 × H 2 O \u003d NH 4 HCO 3;
CO 2 + 4H 2 \u003d CH 4 + 2H 2 O (t \u003d 200 o C, kat. Cu 2 O);
CO 2 + C \u003d 2CO (t\u003e 1000 o C);
CO 2 + 2Mg \u003d C + 2MgO;
2CO 2 + 5Ca = CaC 2 + 4CaO (t = 500 o C);
2CO 2 + 2Na 2 O 2 \u003d 2Na 2 CO 3 + O 2.
Application of carbon dioxide
Carbon dioxide is used in the production of soda by the ammonia-chloride method, for the synthesis of urea, for the production of carbonic acid salts, as well as for carbonation of fruit and mineral waters and other drinks.
Solid carbon dioxide called "dry ice" is used to cool perishable foods, to make and preserve ice cream, and in many other applications where low temperatures are required.
Examples of problem solving
EXAMPLE 1
EXAMPLE 2
| Exercise | What volume and what mass of carbon dioxide will be released during the thermal decomposition of calcium carbonate weighing 45.4 g? |
| Decision | We write the equation for the thermal decomposition of calcium carbonate: CaCO 3 \u003d CaO + CO 2. Find the amount of calcium carbonate substance: n (CaCO 3) \u003d m (CaCO 3) / M (CaCO 3); M (CaCO 3) \u003d Ar (Ca) + Ar (C) + 3 × Ar (O) \u003d 40 + 12 + 3 × 16 \u003d 100 g / mol; n (CaCO 3) \u003d 45.4 / 100 \u003d 0.454 mol. According to the reaction equation n (CaCO 3) : n (CO 2) = 1: 1, therefore n (CaCO 3) \u003d n (CO 2) \u003d 0.454 mol. Calculate the mass and volume of carbon dioxide released: V (CO 2) \u003d V m × n (CO 2) \u003d 22.4 × 0.454 \u003d 10.2 l; m(CO 2) = n(CO 2)× M(CO 2); M (CO 2) \u003d Ar (C) + 2 × Ar (O) \u003d 12 + 2 × 16 \u003d 44 g / mol; m(CO 2) \u003d 0.454 × 44 \u003d 20 g. |
| Answer | The mass of carbon dioxide is 20 g, the volume is 10.2 liters. |
Other names: carbon dioxide, carbon dioxide, carbon monoxide (IV), carbonic anhydride.
Carbon dioxide is an inorganic compound with chemical formula CO2; colorless and odorless gas.
Physical properties
Chemical properties and preparation methods
cleaning
Purification of CO 2 stored in steel cylinders. Sales CO 2 in steel cylinders may contain the following impurities: water vapor, O 2 , N 2, less often traces of H 2 S and SO 2. In most cases, commercial CO 2 is of sufficient purity to carry out chemical reactions. Only for higher requirements (for example, in physical research) commercial CO 2 should be subjected to additional purification. To do this, the gas is passed through a saturated solution of CuSO 4 , then through a solution of KHCO 3 and finally through a fractionator, which is part of an industrial plant for producing pure H 2 S . For CO 2 fractionation, four vertical washers, eight U-tubes for deep cooling and two freeze traps are used. Before the last freezer there is also a branch to the mercury manometer. CO 2 passes through the first four U-tubes for deep cooling (kept at the specified temperature) and freezes at 8. When 8 is full, open the valve 9, solder at point 10 and create a high vacuum in this part of the apparatus. After that, the remaining four 11-shaped tubes are cooled to -78 ° C (dry ice + 4-acetone), liquid air cooling is removed from 5, the first gas stream is pumped out, and then it is already immersed in a vessel for condensation 11 into liquid air. The middle fraction is collected in 11, and the remainder in 8. The fraction of 11 is sublimated twice more and the gas purity is controlled by determining the vapor pressure at different temperatures. The gas is stored in 25-liter glass flasks, which are degassed by many hours of heating in high vacuum at 350 °C.Fig.1. Installation for the production of hydrogen sulfide.
Dry ice
"Dry ice" - solid carbon dioxide, under normal conditions (atmospheric pressure and room temperature) passing into a vapor state, bypassing the liquid phase. In appearance, it resembles ice (hence the name).The sublimation temperature at normal pressure is -78.5˚ C. Technical "dry ice" has a density of about 1560 kg / m 3, absorbs about 590 kJ / kg (140 kcal / kg) of heat during sublimation. Produced in carbon dioxide plants.
List of used literature
- Volkov, A.I., Zharsky, I.M. Big chemical reference book / A.I. Volkov, I.M. Zharsky. - Mn.: modern school, 2005. - 608 with ISBN 985-6751-04-7.
- Hoffman W., Rüdorf W., Haas A., Schenk P. W., Huber F., Schmeiser M., Baudler M., Becher H.-J., Dönges E., Schmidbaur H., Erlich P., Seifert H. I Guide to inorganic synthesis: In 6 volumes. T.3. Per. with. German / Ed. G. Brouwer. - M.: Mir, 1985. - 392 p., ill. [with. 682]