Carbon monoxide has a molecular structure. Carefully! Carbon monoxide in the house! Normal human physiology
Carbon forms two extremely stable oxides (CO and CO 2), three much less stable oxides (C 3 O 2, C 5 O 2 and C 12 O 9), a number of unstable or poorly studied oxides (C 2 O, C 2 O 3 etc.) and non-stoichiometric graphite oxide. Among the listed oxides, CO and CO 2 play a special role.
DEFINITION
Carbon monoxide Under normal conditions, a flammable gas is colorless and odorless.
It is quite toxic due to its ability to form a complex with hemoglobin, which is approximately 300 times more stable than the oxygen-hemoglobin complex.
DEFINITION
Carbon dioxide under normal conditions, it is a colorless gas, approximately 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.
Direct oxidation of carbon with a lack of oxygen or air leads to the formation of CO; with a sufficient amount of them, CO 2 is formed. Some properties of these oxides are presented in table. 1.
Table 1. Physical properties of carbon oxides.
Production of carbon monoxide
Pure CO can be obtained in the laboratory by dehydrating formic acid (HCOOH) with concentrated sulfuric acid at ~140 °C:
HCOOH = CO + H2O.
In small quantities, carbon dioxide can be easily obtained by the action of acids on carbonates:
CaCO 3 + 2HCl = CaCl 2 + H 2 O + CO 2.
On an industrial scale, CO 2 is produced mainly as a by-product in the process of ammonia synthesis:
CH 4 + 2H 2 O = CO 2 + 4H 2;
CO + H 2 O = CO 2 + H 2.
Large quantities of carbon dioxide are produced by burning limestone:
CaCO 3 = CaO + CO 2.
Chemical properties of carbon monoxide
Carbon monoxide is chemically reactive at high temperatures. It proves to be a strong reducing agent. Reacts with oxygen, chlorine, sulfur, ammonia, alkalis, metals.
CO + NaOH = Na(HCOO) (t = 120 - 130 o C, p);
CO + H 2 = CH 4 + H 2 O (t = 150 - 200 o C, cat. Ni);
CO + 2H 2 = CH 3 OH (t = 250 - 300 o C, cat. CuO/Cr 2 O 3);
2CO + O 2 = 2CO 2 (cat. MnO 2 /CuO);
CO + Cl 2 = CCl 2 O(t = 125 - 150 o C, kat. C);
4CO + Ni = (t = 50 - 100 o C);
5CO + Fe = (t = 100 - 200 o C, p).
Carbon dioxide exhibits acidic properties: it reacts with alkalis and ammonia hydrate. Reduced by active metals, hydrogen, carbon.
CO 2 + NaOH dilute = NaHCO 3 ;
CO 2 + 2NaOH conc = Na 2 CO 3 + H 2 O;
CO 2 + Ba(OH) 2 = BaCO 3 + H 2 O;
CO 2 + BaCO 3 + H 2 O = Ba(HCO 3) 2;
CO 2 + NH 3 ×H 2 O = NH 4 HCO 3;
CO 2 + 4H 2 = CH 4 + 2H 2 O (t = 200 o C, cat. Cu 2 O);
CO 2 + C = 2CO (t > 1000 o C);
CO 2 + 2Mg = C + 2MgO;
2CO 2 + 5Ca = CaC 2 + 4CaO (t = 500 o C);
2CO 2 + 2Na 2 O 2 = 2Na 2 CO 3 + O 2.
Applications of carbon monoxide
Carbon monoxide is widely used as a fuel in the form of generator gas or water gas and is also formed when many metals are separated from their oxides by reduction with coal. Producer gas is produced by passing air through hot coal. It contains about 25% CO, 4% CO2 and 70% N2 with traces of H2 and CH4 62.
The use of carbon dioxide is most often due to its physical properties. It is used as a cooling agent, for carbonating drinks, in the production of lightweight (foamed) plastics, and also as a gas for creating an inert atmosphere.
Examples of problem solving
EXAMPLE 1
EXAMPLE 2
| Exercise | Determine how many times carbon monoxide (IV)CO 2 is heavier than air. |
| Solution | The ratio of the mass of a given gas to the mass of another gas taken in the same volume, at the same temperature and the same pressure is called the relative density of the first gas to the second. This value shows how many times the first gas is heavier or lighter than the second gas. The relative molecular weight of air is taken to be 29 (taking into account the content of nitrogen, oxygen and other gases in the air). It should be noted that the concept of “relative molecular mass of air” is used conditionally, since air is a mixture of gases. D air (CO 2) = M r (CO 2) / M r (air); D air (CO 2) = 44 / 29 = 1.517. M r (CO 2) = A r (C) + 2×A r (O) = 12 + 2× 16 = 12 + 32 = 44. |
| Answer | Carbon monoxide (IV)CO 2 is 1.517 times heavier than air. |
Has a triple bond. Since these molecules are similar in structure, their properties are also similar - very low melting and boiling points, close values of standard entropies, etc.
Within the framework of the valence bond method, the structure of the CO molecule can be described by the formula: C≡O:, and the third bond is formed according to the donor-acceptor mechanism, where carbon is the donor of the electron pair, and oxygen is the acceptor.
According to the molecular orbital method, the electronic configuration of an unexcited CO molecule is σ 2 O σ 2 z π 4 x, y σ 2 C. Triple bond formed σ -connection formed due to σ z electron pair, and the electrons are doubly degenerate level π x, y correspond to two σ - connections. Electrons in the nonbonding σ C orbitals and σ O orbitals correspond to two electron pairs, one of which is localized at the atom, the other at the atom.
Due to the presence of a triple bond, the CO molecule is very strong (dissociation energy 1069 kJ/mol, or 256 kcal/mol, which is greater than that of any other diatomic molecules) and has a small internuclear distance (d C≡O = 0.1128 nm or 1. 13Å).
The molecule is weakly polarized, the electric moment of its dipole μ = 0.04·10 -29 C m (direction of the dipole moment C - →O +). Ionization potential 14.0 V, force coupling constant k = 18.6.
History of discovery
Carbon monoxide was first produced by French chemist Jacques de Lassonne by heating zinc oxide with coal, but was initially mistaken for hydrogen because it burned with a blue flame. The fact that this gas contains carbon and oxygen was discovered by the English chemist William Cruickshank. Carbon monoxide in the Earth's atmosphere was first discovered by the Belgian scientist M. Migeotte in 1949 by the presence of a main vibrational-rotational band in the IR spectrum of the Sun.
Carbon monoxide in the Earth's atmosphere
There are natural and anthropogenic sources of entry. Under natural conditions, on the Earth's surface, CO is formed during incomplete anaerobic decomposition of organic compounds and during the combustion of biomass, mainly during forest and steppe fires. Carbon monoxide is formed in soil both biologically (released by living organisms) and non-biologically. The release of carbon monoxide due to phenolic compounds common in soils, containing OCH 3 or OH groups in ortho- or para-positions relative to the first hydroxyl group, has been experimentally proven.
The overall balance between the production of non-biological CO and its oxidation by microorganisms depends on specific environmental conditions, primarily on the purpose. For example, carbon monoxide is released directly into the atmosphere from arid soils, thus creating local maximums in the concentration of this gas.
In the atmosphere, CO is the product of chains of reactions involving methane and other hydrocarbons (primarily isoprene).
The main anthropogenic source of CO is currently exhaust gases from internal combustion engines. Carbon monoxide is formed when hydrocarbon fuels are burned in internal combustion engines at insufficient temperatures or poor air supply settings (not enough oxygen to oxidize CO into CO 2). In the past, a significant portion of the anthropogenic input of CO into the atmosphere was provided by illuminating gas used for indoor lighting. It roughly corresponded in composition, that is, it contained up to 45% carbon monoxide. Currently, in the public utilities sector, this gas is replaced by much less toxic natural gas (lower representatives of the homologous series - propane, etc.)
CO input from natural and anthropogenic sources is approximately the same.
Carbon monoxide in the atmosphere is in rapid circulation: its average residence time is about 0.1 year, being oxidized by hydroxyl to carbon dioxide.
Receipt
Industrial method
2C + O 2 → 2CO (thermal effect of this reaction is 22 kJ),
2. or when restoring with hot coal:
CO 2 + C ↔ 2CO (ΔH=172 kJ, ΔS=176 J/K).
This reaction often occurs in a stove fire when the stove damper is closed too early (before the coals have completely burned out). The carbon monoxide formed in this case, due to its toxicity, causes physiological disorders (“fumes”) and even death (see below), hence one of the trivial names - “carbon monoxide”. A picture of the reactions occurring in the furnace is shown in the diagram.
The reduction reaction of carbon dioxide is reversible; the effect of temperature on the equilibrium state of this reaction is shown in the graph. The flow of a reaction to the right is ensured by the entropy factor, and to the left by the enthalpy factor. At temperatures below 400°C the equilibrium is almost completely shifted to the left, and at temperatures above 1000°C to the right (towards the formation of CO). At low temperatures, the rate of this reaction is very low, so carbon monoxide is quite stable under normal conditions. This equilibrium has a special name Boudoir balance.
3. Mixtures of carbon monoxide with other substances are obtained by passing air, water vapor, etc. through a layer of hot coke, coal or brown coal, etc. (see,).
Laboratory method
Physiological effect, toxicity
Carbon monoxide is very dangerous because it does not cause and even... Signs of poisoning include headache, dizziness and loss of consciousness. The toxic effect of carbon monoxide is based on the fact that it binds to the blood more strongly than oxygen (this forms carboxyhemoglobin), thus blocking the processes of oxygen transport and cellular respiration. carbon monoxide in the air of industrial enterprises is 0.02 mg/l.
TLV (limit limit concentration, USA): 25 ppm; 29 mg/m 3 (as TWA - US shift average) (ACGIH 1994-1995). MAC (maximum permissible concentration, USA): 30 ppm; 33 mg/m3; Pregnancy: B (harmful effect likely even at MAK level) (1993)
Carbon Monoxide Protection
Properties
Carbon monoxide is a colorless, tasteless and odorless gas. The so-called “carbon monoxide smell” is actually the smell of organic impurities.
| Molecular mass | 28,01 |
| Melting temperature | −205°C |
| Boiling temperature | −191.5°C |
| Solubility | Extremely slightly soluble in (2.3 ml CO/100 ml H 2 O at 20°C) |
| Density ρ | 0.00125 g/cm 3 (at 0°C) |
| Standard enthalpy of formation ΔH | −110.52 kJ/mol (g) (at 298 K) |
| Standard Gibbs energy of formation ΔG | −137.14 kJ/mol (g) (at 298 K) |
| Standard entropy of formation S | 197.54 J/mol K (g) (at 298 K) |
| Standard molar C p | 29.11 J/mol K (g) (at 298 K) |
| Melting enthalpy ΔH pl | 0.838 kJ/mol |
| Enthalpy of boiling ΔH boil | 6.04 kJ/mol |
| t crit | −140.23°C |
| P crit | 3.499 MPa |
| ρ crit | 0.301 g/cm 3 |
The main types of chemical reactions in which carbon monoxide participates are addition reactions and in which it exhibits reducing properties.
At room temperatures, CO is inactive, its chemical activity increases significantly when heated and in solutions (for example, in solutions it reduces salts and others to metals already at room temperature. When heated, it also reduces other metals, for example CO + CuO → Cu + CO 2 This is widely used in pyrometallurgy. The reaction of CO in solution with palladium chloride is the basis for the qualitative detection of CO, see below).
The oxidation of CO in solution often occurs at a noticeable rate only in the presence of a catalyst. When selecting the latter, the main role is played by the nature of the oxidizing agent. Thus, CO oxidizes most quickly in the presence of finely crushed silver, - in the presence of salts, - in the presence of OsO 4. In general, CO is similar in its reducing properties to molecular hydrogen.
Below 830°C the stronger reducing agent is CO, above it is hydrogen. Therefore, the reaction equilibrium is:
H 2 O + CO ↔ CO 2 + H 2 + 42 kJ
up to 830°C is shifted to the right, above 830°C to the left.
Interestingly, there are bacteria that, through the oxidation of CO, obtain the energy they need for life.
Carbon monoxide burns with a blue flame (reaction temperature 700°C) in air:
CO + 1 / 2 O 2 → 2CO 2 ΔG° 298 = −257 kJ, ΔS° 298 = −86 J/K
The combustion temperature of CO can reach 2100°C; it is a chain combustion, with small amounts of hydrogen-containing compounds (water, etc.) serving as initiators.
Due to such a good calorific value, CO is a component of various technical gas mixtures (see, for example), used, among other things, for heating.
Carbon monoxide reacts with . The reaction with the greatest practical application is
Carbon monoxide– CO (carbon monoxide) is a deadly and insidious poison that binds much stronger than life-giving oxygen. It is a colorless, poisonous gas (under normal conditions) without taste or odor. Chemical formula – CO. Death occurs when carbon monoxide combines with 80% of hemoglobin. Carbon monoxide is contained (up to 12%) in car exhaust gases.
The main types of chemical reactions in which carbon monoxide is involved are addition reactions and redox reactions, in which it exhibits reducing properties.
At room temperatures, carbon monoxide is inactive; its chemical activity increases significantly when heated and in solutions. Thus, in solutions it reduces salts of Au, Pt, Pd and others to metals already at room temperature. When heated, it also reduces other metals, for example CO + CuO = Cu + CO 2. It is widely used in pyrometallurgy. The method for qualitative detection of carbon monoxide is based on the reaction of CO in solution with palladium chloride.
It is interesting that there are animals capable of obtaining the energy they need for life through the oxidation of CO.
As already noted, carbon monoxide is very dangerous. Signs of poisoning: headache and dizziness; there is tinnitus, shortness of breath, palpitations, flickering before the eyes, redness of the face, general weakness, nausea, and sometimes vomiting; in severe cases, convulsions, loss of consciousness, coma.
There have been cases when some imprudent drivers spent the night in the winter in a car that was parked in a garage, the doors of which were closed. To sleep warmly, they turned on the engine and it idled. As a rule, carbon monoxide accumulated in the garage and such careless people died. The author of one book rightly noted that “starting the engine in a small garage with the door closed is suicide.”
The toxic effect of CO is due to the formation of carboxyhemoglobin - a much stronger carbonyl complex with hemoglobin, compared to the complex of hemoglobin with oxygen. Thus, the processes of oxygen transport and cellular respiration are blocked. Concentrations in the air of more than 0.1% lead to death within one hour.
The combination of carbon monoxide with hemoglobin is reversible. The victim should be taken out into fresh air. For mild poisoning, hyperventilation of the lungs with oxygen is sufficient.
There are natural and anthropogenic sources of carbon monoxide entering the Earth's atmosphere. CO input from natural and anthropogenic sources is approximately the same. Under natural conditions, on the surface of the Earth, carbon monoxide is formed during incomplete anaerobic decomposition of organic compounds and during the combustion of biomass, mainly during forest and steppe fires.
The main anthropogenic source of CO is currently exhaust gases from internal combustion engines.
Everyone who has had to deal with the operation of heating systems - stoves, boilers, boilers, water heaters, designed for household fuel in any form - knows how dangerous carbon monoxide is for humans. It is quite difficult to neutralize it in the gas state; there are no effective home methods to combat carbon monoxide, so most protective measures are aimed at preventing and timely detection of carbon monoxide in the air.
Properties of a toxic substance
There is nothing unusual in the nature and properties of carbon monoxide. Essentially, it is a product of partial oxidation of coal or coal-containing fuels. The formula of carbon monoxide is simple and straightforward - CO, in chemical terms - carbon monoxide. One carbon atom is connected to an oxygen atom. The nature of the combustion processes of organic fuel is such that carbon monoxide is an integral part of any flame.
When heated in the firebox, coals, related fuels, peat, and firewood are gasified into carbon monoxide, and only then are burned with an influx of air. If carbon dioxide has leaked from the combustion chamber into the room, it will remain in a stable state until the moment when the carbon flow is removed from the room by ventilation or accumulates, filling the entire space, from floor to ceiling. In the latter case, only an electronic carbon monoxide sensor can save the situation, responding to the slightest increase in the concentration of toxic fumes in the atmosphere of the room.
What you need to know about carbon monoxide:
- Under standard conditions, the density of carbon monoxide is 1.25 kg/m3, which is very close to the specific gravity of air 1.25 kg/m3. Hot and even warm monoxide easily rises to the ceiling, and as it cools, it settles and mixes with air;
- Carbon monoxide is tasteless, colorless and odorless, even in high concentrations;
- To start the formation of carbon monoxide, it is enough to heat the metal in contact with carbon to a temperature of 400-500 o C;
- The gas is capable of burning in air, releasing a large amount of heat, approximately 111 kJ/mol.
Not only is inhalation of carbon monoxide dangerous, the gas-air mixture can explode when the volume concentration reaches from 12.5% to 74%. In this sense, the gas mixture is similar to household methane, but much more dangerous than network gas.
Methane is lighter than air and less toxic when inhaled; in addition, thanks to the addition of a special additive - mercaptan - to the gas flow, its presence in the room can be easily detected by smell. If the kitchen is slightly gassed, you can enter the room and ventilate it without any health consequences.
With carbon monoxide everything is more complicated. The close relationship between CO and air prevents the effective removal of the toxic gas cloud. As it cools, the gas cloud will gradually settle in the floor area. If a carbon monoxide detector is triggered, or a leak of combustion products is detected from a stove or solid fuel boiler, it is necessary to immediately take measures for ventilation, otherwise children and pets will be the first to suffer.
This property of a carbon monoxide cloud was previously widely used to fight rodents and cockroaches, but the effectiveness of a gas attack is significantly lower than modern means, and the risk of poisoning is disproportionately higher.
For your information! A CO gas cloud, in the absence of ventilation, can retain its properties unchanged for a long time.
If there is a suspicion of carbon monoxide accumulation in basements, utility rooms, boiler rooms, cellars, the first step is to ensure maximum ventilation with a gas exchange rate of 3-4 units per hour.
Conditions for the appearance of fumes in the room
Carbon monoxide can be produced using dozens of chemical reactions, but this requires specific reagents and conditions for their interaction. The risk of gas poisoning in this way is practically zero. The main reasons for the appearance of carbon monoxide in a boiler room or kitchen area remain two factors:
- Poor draft and partial flow of combustion products from the combustion source into the kitchen area;
- Improper operation of boiler, gas and furnace equipment;
- Fires and local fires of plastic, wiring, polymer coatings and materials;
- Waste gases from sewer lines.
The source of carbon monoxide can be secondary combustion of ash, loose soot deposits in chimneys, soot and resin embedded in the brickwork of fireplace mantels and soot extinguishers.
Most often, the source of gas CO is smoldering coals that burn out in the firebox when the valve is closed. Especially a lot of gas is released during the thermal decomposition of firewood in the absence of air; approximately half of the gas cloud is occupied by carbon monoxide. Therefore, any experiments with smoking meat and fish using the haze obtained from smoldering shavings should be carried out only in the open air.
A small amount of carbon monoxide may also appear during cooking. For example, anyone who has encountered the installation of gas heating boilers with a closed firebox in the kitchen knows how carbon monoxide sensors react to fried potatoes or any food cooked in boiling oil.
The insidious nature of carbon monoxide
The main danger of carbon monoxide is that it is impossible to sense and sense its presence in the atmosphere of a room until the gas enters the respiratory system with the air and dissolves in the blood.
The consequences of inhaling CO depend on the concentration of the gas in the air and the length of stay in the room:
- Headache, malaise and the development of a drowsy state begin when the volumetric gas content in the air is 0.009-0.011%. A physically healthy person can withstand up to three hours of exposure to a polluted atmosphere;
- Nausea, severe muscle pain, convulsions, fainting, loss of orientation may develop at a concentration of 0.065-0.07%. The time spent in the room until the onset of inevitable consequences is only 1.5-2 hours;
- When the concentration of carbon monoxide is above 0.5%, even a few seconds of staying in a gas-polluted space means death.
Even if a person safely got out of a room with a high concentration of carbon monoxide on his own, he will still need medical attention and the use of antidotes, since the consequences of poisoning the circulatory system and impaired blood circulation in the brain will still appear, only a little later.
Carbon monoxide molecules are well absorbed by water and saline solutions. Therefore, ordinary towels and napkins moistened with any available water are often used as the first available means of protection. This allows you to stop carbon monoxide from entering your body for a few minutes until you can leave the room.
This property of carbon monoxide is often abused by some owners of heating equipment that has built-in CO sensors. When a sensitive sensor is triggered, instead of ventilating the room, the device is often simply covered with a wet towel. As a result, after a dozen such manipulations, the carbon monoxide sensor fails, and the risk of poisoning increases by an order of magnitude.
Technical carbon monoxide detection systems
In fact, today there is only one way to successfully combat carbon monoxide, using special electronic devices and sensors that record excess CO concentrations in the room. You can, of course, do something simpler, for example, install powerful ventilation, as those who like to relax by a real brick fireplace do. But in such a solution there is a certain risk of carbon monoxide poisoning when changing the direction of draft in the pipe, and besides, living under a strong draft is also not very good for health.
Carbon monoxide sensor device
The problem of controlling the carbon monoxide content in the atmosphere of residential and utility rooms today is as pressing as the presence of a fire or security alarm.
In specialized heating and gas equipment stores, you can purchase several options for gas content monitoring devices:
- Chemical alarms;
- Infrared scanners;
- Solid state sensors.
The sensitive sensor of the device is usually equipped with an electronic board that provides power, calibration and conversion of the signal into an understandable form of indication. This could be simply green and red LEDs on a panel, a sound siren, digital information to issue a signal to a computer network, or a control pulse for an automatic valve that shuts off the supply of domestic gas to the heating boiler.
It is clear that the use of sensors with a controlled shut-off valve is a necessary measure, but often heating equipment manufacturers deliberately build in “foolproofing” to avoid all sorts of manipulations with the safety of gas equipment.
Chemical and solid state control instruments
The cheapest and most accessible version of the sensor with a chemical indicator is made in the form of a mesh flask, easily permeable to air. Inside the flask there are two electrodes separated by a porous partition impregnated with an alkali solution. The appearance of carbon monoxide leads to carbonization of the electrolyte, the conductivity of the sensor drops sharply, which is immediately read by the electronics as an alarm signal. After installation, the device is in an inactive state and does not operate until there are traces of carbon monoxide in the air that exceed the permissible concentration.
Solid-state sensors use two-layer bags of tin dioxide and ruthenium instead of an alkali-impregnated piece of asbestos. The appearance of gas in the air causes a breakdown between the contacts of the sensor device and automatically triggers an alarm.
Scanners and electronic guards
Infrared sensors operating on the principle of scanning the surrounding air. The built-in infrared sensor perceives the glow of the laser LED, and a trigger device is activated based on a change in the intensity of absorption of thermal radiation by the gas.
CO absorbs the thermal part of the spectrum very well, so such devices operate in watchman or scanner mode. The scanning result can be displayed in the form of a two-color signal or an indication of the amount of carbon monoxide in the air on a digital or linear scale.
Which sensor is better
To correctly select a carbon monoxide sensor, it is necessary to take into account the operating mode and the nature of the room in which the sensor device is to be installed. For example, chemical sensors, considered obsolete, work great in boiler rooms and utility rooms. An inexpensive carbon monoxide detection device can be installed in your home or workshop. In the kitchen, the mesh quickly becomes covered with dust and grease deposits, which sharply reduces the sensitivity of the chemical cone.
Solid state carbon monoxide sensors work equally well in all conditions, but they require a powerful external power source to operate. The cost of the device is higher than the price of chemical sensor systems.
Infrared sensors are the most common today. They are actively used to complete security systems for residential individual heating boilers. At the same time, the sensitivity of the control system practically does not change over time due to dust or air temperature. Moreover, such systems, as a rule, have built-in testing and calibration mechanisms, which allows you to periodically check their performance.
Installation of carbon monoxide monitoring devices
Carbon monoxide sensors must be installed and maintained exclusively by qualified personnel. Periodically, instruments are subject to inspection, calibration, maintenance and replacement.
The sensor must be installed at a distance from the gas source of 1 to 4 m; the housing or remote sensors are mounted at a height of 150 cm above floor level and must be calibrated according to the upper and lower sensitivity thresholds.
The service life of residential carbon monoxide detectors is 5 years.
Conclusion
The fight against the formation of carbon monoxide requires care and a responsible attitude towards the installed equipment. Any experiments with sensors, especially semiconductor ones, sharply reduce the sensitivity of the device, which ultimately leads to an increase in the carbon monoxide content in the atmosphere of the kitchen and the entire apartment, slowly poisoning all its inhabitants. The problem of carbon monoxide monitoring is so serious that it is possible that the use of sensors in the future may be made mandatory for all categories of individual heating.
Carbon monoxide (carbon monoxide, carbon monoxide, carbon monoxide) is a colorless poisonous gas (under normal conditions) without taste or smell. Chemical formula - CO. Lower and upper concentration limits of flame propagation: from 12.5 to 74% (by volume).
Molecule structure
The CO molecule has a triple bond, just like the nitrogen molecule N2. Since these molecules are similar in structure (isoelectronic, diatomic, have a similar molar mass), their properties are also similar - very low melting and boiling points, similar standard entropies, etc.
Due to the presence of a triple bond, the CO molecule is very strong (dissociation energy 1069 kJ/mol, or 256 kcal/mol, which is greater than that of any other diatomic molecules) and has a small internuclear distance (d C≡O = 0.1128 nm or 1. 13Å).
The molecule is weakly polarized, the electric moment of its dipole is μ = 0.04·10 −29 C m. Numerous studies have shown that the negative charge in the CO molecule is concentrated on the carbon atom C − ←O + (the direction of the dipole moment in the molecule is opposite to that previously assumed). Ionization potential 14.0 V, force coupling constant k = 18.6.
Properties
Carbon (II) monoxide is a colorless, tasteless and odorless gas. Flammable The so-called “carbon monoxide smell” is actually the smell of organic impurities.
The main types of chemical reactions in which carbon(II) monoxide is involved are addition reactions and redox reactions, in which it exhibits reducing properties.
At room temperatures, CO is inactive; its chemical activity increases significantly when heated and in solutions (thus, in solutions it reduces salts, , and others to metals already at room temperature. When heated, it also reduces other metals, for example CO + CuO → Cu + CO 2. It is widely used in pyrometallurgy. The reaction of CO in solution with palladium chloride is the basis for the qualitative detection of CO, see below).
The oxidation of CO in solution often occurs at a noticeable rate only in the presence of a catalyst. When selecting the latter, the main role is played by the nature of the oxidizing agent. Thus, KMnO 4 oxidizes CO most quickly in the presence of finely crushed silver, K 2 Cr 2 O 7 - in the presence of salts, KClO 3 - in the presence of OsO 4. In general, CO is similar in its reducing properties to molecular hydrogen.
Below 830 °C the stronger reducing agent is CO, above - hydrogen. Therefore, the reaction equilibrium is:
up to 830 °C is shifted to the right, above 830 °C to the left.
Interestingly, there are bacteria that, through the oxidation of CO, obtain the energy they need for life.
Carbon monoxide (II) burns with a blue flame (reaction temperature 700 °C) in air:
ΔG° 298 = −257 kJ, ΔS° 298 = −86 J/KThe combustion temperature of CO can reach 2100 °C; it is a chain combustion, with small amounts of hydrogen-containing compounds (water, ammonia, hydrogen sulfide, etc.) serving as initiators.
Due to such a good calorific value, CO is a component of various technical gas mixtures (see, for example, generator gas), used, among other things, for heating.
halogens. The reaction with chlorine has received the greatest practical application:
The reaction is exothermic, its thermal effect is 113 kJ, and in the presence of a catalyst (activated carbon) it occurs at room temperature. As a result of the reaction, phosgene is formed, a substance that is widely used in various branches of chemistry (and also as a chemical warfare agent). By similar reactions, COF 2 (carbonyl fluoride) and COBr 2 (carbonyl bromide) can be obtained. Carbonyl iodide was not obtained. The exothermicity of reactions quickly decreases from F to I (for reactions with F 2 the thermal effect is 481 kJ, with Br 2 - 4 kJ). It is also possible to obtain mixed derivatives, for example COFCl (for more details, see halogen derivatives of carbonic acid).
By reacting CO with F 2 , in addition to carbonyl fluoride, one can obtain a peroxide compound (FCO) 2 O 2 . Its characteristics: melting point −42 °C, boiling point +16 °C, has a characteristic odor (similar to the smell of ozone), when heated above 200 °C, decomposes explosively (reaction products CO 2, O 2 and COF 2), in acidic medium reacts with potassium iodide according to the equation:
Carbon(II) monoxide reacts with chalcogens. With sulfur it forms carbon sulfide COS, the reaction occurs when heated, according to the equation:
ΔG° 298 = −229 kJ, ΔS° 298 = −134 J/KSimilar carbon selenoxide COSe and carbon telluroxide COTe were also obtained.
Restores SO 2:
With transition metals it forms very volatile, flammable and toxic compounds - Carbonyls, such as Cr(CO) 6, Ni(CO) 4, Mn 2 CO 10, Co 2 (CO) 9, etc.
Carbon (II) monoxide is slightly soluble in water, but does not react with it. It also does not react with solutions of alkalis and acids. However, it reacts with alkali melts to form the corresponding formates:
The reaction of carbon monoxide (II) with potassium metal in an ammonia solution is interesting. This produces the explosive compound potassium dioxodicarbonate:
The toxic effect of carbon monoxide (II) is due to the formation of carboxyhemoglobin - a much stronger carbonyl complex with hemoglobin, in comparison with the complex of hemoglobin with oxygen (oxyhemoglobin), thus blocking the processes of oxygen transport and cellular respiration. Concentrations in the air of more than 0.1% lead to death within one hour.
History of discovery
Carbon(II) monoxide was first prepared by French chemist Jacques de Lassonne by heating zinc oxide with coal, but was initially mistaken for hydrogen because it burned with a blue flame.
The fact that this gas contains carbon and oxygen was discovered by the English chemist William Cruickshank. Carbon (II) monoxide outside the Earth's atmosphere was first discovered by the Belgian scientist M. Migeotte in 1949 from the presence of a main vibrational-rotational band in the IR spectrum of the Sun.
Receipt
Industrial method
- Formed during the combustion of carbon or carbon-based compounds (for example, gasoline) under conditions of lack of oxygen:
- or when reducing carbon dioxide with hot coal:
This reaction occurs during a stove fire when the stove damper is closed too early (before the coals have completely burned out). The resulting carbon monoxide (II), due to its toxicity, causes physiological disorders (“fumes”) and even death (see below), hence one of the trivial names - “carbon monoxide”.
The reduction reaction of carbon dioxide is reversible; the effect of temperature on the equilibrium state of this reaction is shown in the graph. The flow of a reaction to the right is ensured by the entropy factor, and to the left by the enthalpy factor. At temperatures below 400 °C the equilibrium is almost completely shifted to the left, and at temperatures above 1000 °C to the right (towards the formation of CO). At low temperatures, the rate of this reaction is very low, so carbon (II) monoxide is quite stable under normal conditions. This equilibrium has a special name Boudoir balance.
- Mixtures of carbon monoxide (II) with other substances are obtained by passing air, water vapor, etc. through a layer of hot coke, coal or brown coal, etc. (see generator gas, water gas, mixed gas, synthesis gas ).
Laboratory method
- Decomposition of liquid formic acid under the action of hot concentrated sulfuric acid, or passing formic acid over phosphorus oxide P 2 O 5. Reaction scheme:
- Heating a mixture of oxalic and concentrated sulfuric acids. The reaction proceeds according to the equation:
- Heating a mixture of potassium hexacyanoferrate (II) with concentrated sulfuric acid. The reaction proceeds according to the equation:
Determination of carbon monoxide (II)
The presence of CO can be qualitatively determined by the darkening of solutions of palladium chloride (or paper soaked in this solution). Darkening is associated with the release of fine metal palladium according to the following scheme:
This reaction is very sensitive. Standard solution: 1 gram of palladium chloride per liter of water.
Quantitative determination of carbon monoxide (II) is based on the iodometric reaction:
Application
- Carbon (II) monoxide is an intermediate reagent used in reactions with hydrogen in critical industrial processes to produce organic alcohols and straight hydrocarbons.
- Carbon monoxide (II) is used to process animal meat and fish, giving them a bright red color and the appearance of freshness without changing the taste (en: Clear smoke or en: Tasteless smoke technology). The permissible CO concentration is 200 mg/kg of meat.
- Carbon monoxide from engine exhaust was used by the Nazis during World War II for the mass killing of people by poisoning.
Carbon (II) monoxide in the Earth's atmosphere
There are natural and anthropogenic sources of entry into