Carbon oxides
In recent years, preference has been given to personality-oriented learning in pedagogical science. The formation of individual personality traits occurs in the process of activity: study, play, work. That's why important factor teaching is the organization of the learning process, the nature of the relationship between the teacher and students and students among themselves. Based on these ideas, I try to build the educational process in a special way. At the same time, each student chooses his own pace of studying the material, has the opportunity to work at a level accessible to him, in a situation of success. In the lesson, it is possible to master and improve not only subject-specific, but also such general educational skills as staging educational goal, choosing means and ways to achieve it, monitoring your achievements, correcting errors. Students learn to work with literature, make notes, diagrams, drawings, work in a group, in pairs, individually, conduct a constructive exchange of opinions, reason logically and draw conclusions.
Conducting such lessons is not easy, but if you succeed, you feel satisfaction. I offer a script for one of my lessons. It was attended by colleagues, administration and a psychologist.
Lesson type. Learning new material.
Goals. Based on motivation and updating the basic knowledge and skills of students, consider the structure, physical and chemical properties, production and use of carbon dioxide and carbon dioxide.
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Equipment and reagents.“Programmed survey” cards, poster diagram, devices for producing gases, glasses, test tubes, fire extinguisher, matches; lime water, sodium oxide, chalk, hydrochloric acid, indicator solutions, H 2 SO 4 (conc.), HCOOH, Fe 2 O 3.
Poster diagram
“Structure of the molecule of carbon monoxide (carbon monoxide (II)) CO”
DURING THE CLASSES
The desks for students in the office are arranged in a circle. The teacher and students have the opportunity to freely move to laboratory tables (1, 2, 3). During the lesson, children sit at study tables (4, 5, 6, 7, ...) with each other as desired (free groups of 4 people).
Teacher. Wise Chinese proverb(written beautifully on the board) reads:
“I hear - I forget,
I see - I remember
I do - I understand.”
Do you agree with the conclusions of the Chinese sages?
What Russian proverbs reflect Chinese wisdom?
Children give examples.
Teacher. Indeed, only by creating can one obtain a valuable product: new substances, devices, machines, as well as intangible values - conclusions, generalizations, conclusions. I invite you today to take part in a study of the properties of two substances. It is known that when undergoing a technical inspection of a car, the driver provides a certificate about the condition of the car’s exhaust gases. What gas concentration is indicated in the certificate?
(O t v e t. SO.)
Student. This gas is poisonous. Getting into the blood, it causes poisoning of the body (“burning”, hence the name of the oxide - carbon monoxide). It is found in car exhaust gases in quantities dangerous to life.(reads a report from a newspaper about a driver who fell asleep in a garage while the engine was running and died of death). The antidote to carbon monoxide poisoning is breathing fresh air and pure oxygen. Another carbon monoxide is carbon dioxide.
Teacher. There is a “Programmed Survey” card on your desks. Familiarize yourself with its contents and, on a blank piece of paper, mark the numbers of those tasks for which you know the answers based on your life experience. Opposite the number of the task-statement, write the formula of carbon monoxide to which this statement relates.
Student consultants (2 people) collect answer sheets and, based on the results of the answers, form new groups for subsequent work.
Programmed survey “Carbon oxides”
1. The molecule of this oxide consists of one carbon atom and one oxygen atom.
2. The bond between atoms in a molecule is polar covalent.
3. A gas that is practically insoluble in water.
4. The molecule of this oxide contains one carbon atom and two oxygen atoms.
5. It has no smell or color.
6. Gas soluble in water.
7. Does not liquefy even at –190 °C ( t kip = –191.5 °C).
8. Acidic oxide.
9. It is easily compressed, at 20 °C under a pressure of 58.5 atm it becomes liquid and hardens into “dry ice”.
10. Not poisonous.
11. Non-salt-forming.
12. Flammable
13. Interacts with water.
14. Interacts with basic oxides.
15. Reacts with metal oxides, reducing free metals from them.
16. Obtained by reacting acids with carbonic acid salts.
17. I.
18. Interacts with alkalis.
19. The source of carbon absorbed by plants in greenhouses and greenhouses leads to increased yield.
20. Used for carbonating water and drinks.
Teacher. Review the contents of the card again. Group the information into 4 blocks:
structure,
Chemical properties,
receiving.
The teacher gives each group of students the opportunity to speak and summarizes the presentations. Then students different groups choose your work plan - the order of studying oxides. For this purpose, they number the blocks of information and justify their choice. The learning order can be as written above, or with any other combination of the four blocks marked.
The teacher draws students' attention to the key points of the topic. Since carbon oxides are gaseous substances, they must be handled with care (safety instructions). The teacher approves the plan for each group and assigns consultants (pre-prepared students).
Demonstration experiments
1. Pouring carbon dioxide from glass to glass.
2. Extinguishing candles in a glass as CO 2 accumulates.
3. Place several small pieces of dry ice into a glass of water. The water will boil and thick white smoke will pour out of it.
CO 2 gas is liquefied already at room temperature under a pressure of 6 MPa. In a liquid state, it is stored and transported in steel cylinders. If you open the valve of such a cylinder, the liquid CO 2 will begin to evaporate, due to which strong cooling occurs and part of the gas turns into a snow-like mass - “dry ice”, which is pressed and used to store ice cream.
4. Demonstration of a chemical foam fire extinguisher (CFO) and explanation of the principle of its operation using a model - a test tube with a stopper and a gas outlet tube.
Information on structure at table No. 1 (instruction cards 1 and 2, structure of CO and CO 2 molecules).
Information about physical properties– at table No. 2 (working with the textbook – Gabrielyan O.S. Chemistry-9. M.: Bustard, 2002, p. 134–135).
Data about receipt and chemical properties – on tables No. 3 and 4 (instruction cards 3 and 4, instructions for practical work, pp. 149–150 of the textbook).
Practical work Place a few pieces of chalk or marble into a test tube and add a little dilute hydrochloric acid. Quickly close the tube with a stopper and a gas outlet tube. Place the end of the tube into another test tube containing 2–3 ml of lime water. Watch for a few minutes as gas bubbles pass through the lime water. Then remove the end of the gas outlet tube from the solution and rinse it in distilled water. Place the tube in another test tube with 2-3 ml of distilled water and pass gas through it. After a few minutes, remove the tube from the solution and add a few drops of blue litmus to the resulting solution. Pour 2-3 ml of dilute sodium hydroxide solution into a test tube and add a few drops of phenolphthalein to it. Then pass gas through the solution. Answer the questions. Questions 1. What happens when chalk or marble is treated with hydrochloric acid? 2. Why, when carbon dioxide is passed through lime water, does the solution first become cloudy, and then the lime dissolve? 3. What happens when carbon(IV) monoxide is passed through distilled water? Write the equations for the corresponding reactions in molecular, ionic, and abbreviated ion forms. Carbonate recognition The four test tubes given to you contain crystalline substances: sodium sulfate, zinc chloride, potassium carbonate, sodium silicate. Determine what substance is in each test tube. Write reaction equations in molecular, ionic, and abbreviated ionic form. |
Homework
The teacher suggests taking the “Programmed Survey” card home and, in preparation for the next lesson, thinking about ways to obtain information. (How did you know that the gas you are studying liquefies, reacts with acid, is poisonous, etc.?)
Independent work students
Practical work groups of children perform with at different speeds. Therefore, games are offered to those who complete the work faster.
Fifth wheel
Four substances can have something in common, but the fifth substance stands out from the series, is superfluous.
1. Carbon, diamond, graphite, carbide, carbine. (Carbide.)
2. Anthracite, peat, coke, oil, glass. (Glass.)
3. Limestone, chalk, marble, malachite, calcite. (Malachite.)
4. Crystalline soda, marble, potash, caustic, malachite. (Caustic.)
5. Phosgene, phosphine, hydrocyanic acid, potassium cyanide, carbon disulfide. (Phosphine.)
6. Sea water, mineral water, distilled water, groundwater, hard water. (Distilled water.)
7. Lime milk, fluff, slaked lime, limestone, lime water. (Limestone.)
8. Li 2 CO 3; (NH 4) 2 CO 3; CaCO 3; K 2 CO 3 , Na 2 CO 3 . (CaCO3.)
Synonyms
Write chemical formulas substances or their names.
1. Halogen -... (Chlorine or bromine.)
2. Magnesite – ... (MgCO 3.)
3. Urea –... ( Urea H 2 NC(O)NH 2 .)
4. Potash - ... (K 2 CO 3.)
5. Dry ice - ... (CO 2.)
6. Hydrogen oxide –... ( Water.)
7. Ammonia -... ( 10% aqueous ammonia solution.)
8. Salts of nitric acid –... ( Nitrates– KNO 3, Ca(NO 3) 2, NaNO 3.)
9. Natural gas – ... ( Methane CH 4.)
Antonyms
Write chemical terms that are opposite in meaning to those proposed.
1. Oxidizing agent –... ( Reducing agent.)
2. Electron donor –… ( Electron acceptor.)
3. Acid properties – ... ( Basic properties.)
4. Dissociation –… ( Association.)
5. Adsorption – ... ( Desorption.)
6. Anode –... ( Cathode.)
7. Anion –… ( Cation.)
8. Metal –... ( Non-metal.)
9. Starting substances –... ( Reaction products.)
Search for patterns
Establish a sign that combines the specified substances and phenomena.
1. Diamond, carbine, graphite – ... ( Allotropic modifications of carbon.)
2. Glass, cement, brick - ... ( Construction Materials.)
3. Breathing, rotting, volcanic eruption - ... ( Processes accompanied by the release of carbon dioxide.)
4. CO, CO 2, CH 4, SiH 4 – ... ( Compounds of group IV elements.)
5. NaHCO 3, CaCO 3, CO 2, H 2 CO 3 – ... ( Oxygen compounds of carbon.)
Physical properties.
Carbon monoxide is a colorless and odorless gas that is slightly soluble in water.
- t pl. 205 °C,
- t kip. 191 °C
- critical temperature =140°C
- critical pressure = 35 atm.
- The solubility of CO in water is about 1:40 by volume.
Chemical properties.
At normal conditions CO is inert; when heated - a reducing agent; non-salt-forming oxide.
1) with oxygen
2C +2 O + O 2 = 2C +4 O 2
2) with metal oxides
C +2 O + CuO = Cu + C +4 O 2
3) with chlorine (in the light)
CO + Cl 2 --hn-> COCl 2 (phosgene)
4) reacts with alkali melts (under pressure)
CO + NaOH = HCOONa (sodium formic acid (sodium formate))
5) forms carbonyls with transition metals
Ni + 4CO =t°= Ni(CO) 4
Fe + 5CO =t°= Fe(CO) 5
Carbon monoxide does not react chemically with water. CO also does not react with alkalis and acids. It is extremely poisonous.
From the chemical side, carbon monoxide is characterized mainly by its tendency to undergo addition reactions and its reducing properties. However, both of these trends usually appear only at elevated temperatures. Under these conditions, CO combines with oxygen, chlorine, sulfur, some metals, etc. At the same time, carbon monoxide, when heated, reduces many oxides to metals, which is very important for metallurgy.
Along with heating, an increase in the chemical activity of CO is often caused by its dissolution. Thus, in solution it is capable of reducing salts of Au, Pt and some other elements to free metals already at ordinary temperatures.
At elevated temperatures And high pressures there is an interaction of CO with water and caustic alkalis: in the first case, HCOOH is formed, and in the second, sodium formic acid. The latter reaction occurs at 120 °C, a pressure of 5 atm and is used technically.
The reduction of palladium chloride in solution is easy according to the general scheme:
PdCl 2 + H 2 O + CO = CO 2 + 2 HCl + Pd
serves as the most commonly used reaction for the discovery of carbon monoxide in a mixture of gases. Even very small amounts of CO are easily detected by the slight coloring of the solution due to the release of finely crushed palladium metal. Quantitative determination of CO is based on the reaction:
5 CO + I 2 O 5 = 5 CO 2 + I 2.
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 mercury salts, KClO 3 - in the presence of OsO 4. In general, in its reducing properties, CO is similar to molecular hydrogen, and its activity under normal conditions is higher than that of the latter. Interestingly, there are bacteria that, through the oxidation of CO, obtain the energy they need for life.
The comparative activity of CO and H2 as reducing agents can be assessed by studying the reversible reaction:
the equilibrium state of which at high temperatures is established quite quickly (especially in the presence of Fe 2 O 3). At 830 °C, the equilibrium mixture contains equal amounts of CO and H 2, i.e., the affinity of both gases for oxygen is the same. Below 830 °C, the stronger reducing agent is CO, above - H2.
The binding of one of the products of the reaction discussed above, in accordance with the law of mass action, shifts its equilibrium. Therefore, by passing a mixture of carbon monoxide and water vapor over calcium oxide, hydrogen can be obtained according to the scheme:
H 2 O + CO + CaO = CaCO 3 + H 2 + 217 kJ.
This reaction occurs already at 500 °C.
In air, CO ignites at about 700 °C and burns with a blue flame to CO 2:
2 CO + O 2 = 2 CO 2 + 564 kJ.
The significant release of heat that accompanies this reaction makes carbon monoxide a valuable gaseous fuel. However, most wide application it is found as a starting product for the synthesis of various organic substances.
The combustion of thick layers of coal in furnaces occurs in three stages:
1) C + O 2 = CO 2;
2) CO 2 + C = 2 CO;
3) 2 CO + O 2 = 2 CO 2.
If the pipe is closed prematurely, a lack of oxygen is created in the furnace, which can cause CO to spread throughout the heated room and lead to poisoning (fumes). It should be noted that the smell of “carbon monoxide” is not caused by CO, but by impurities of some organic substances.
The CO flame can have a temperature of up to 2100 °C. The CO combustion reaction is interesting in that when heated to 700-1000 °C, it proceeds at a noticeable speed only in the presence of traces of water vapor or other hydrogen-containing gases (NH 3, H 2 S, etc.). This is due to the chain nature of the reaction under consideration, which occurs through the intermediate formation of OH radicals according to the following schemes:
H + O 2 = HO + O, then O + CO = CO 2, HO + CO = CO 2 + H, etc.
At very high temperatures The CO combustion reaction becomes noticeably reversible. The CO 2 content in an equilibrium mixture (under a pressure of 1 atm) above 4000 °C can only be negligibly small. The CO molecule itself is so thermally stable that it does not decompose even at 6000 °C. CO molecules have been discovered in the interstellar medium.
When CO acts on metal K at 80 °C, a colorless crystalline, highly explosive compound of the composition K 6 C 6 O 6 is formed. With the elimination of potassium, this substance easily turns into carbon monoxide C 6 O 6 (“triquinone”), which can be considered as a product of CO polymerization. Its structure corresponds to a six-membered cycle formed by carbon atoms, each of which is connected double bond with oxygen atoms.
Interaction of CO with sulfur according to the reaction:
CO + S = COS + 29 kJ
It goes fast only at high temperatures.
The resulting carbon thioxide (O=C=S) is a colorless and odorless gas (mp -139, bp -50 °C).
Carbon (II) monoxide is capable of combining directly with certain metals. As a result, metal carbonyls are formed, which should be considered as complex compounds.
Carbon(II) monoxide also forms complex compounds with some salts. Some of them (OsCl 2 ·3CO, PtCl 2 ·CO, etc.) are stable only in solution. The formation of the latter substance is associated with the absorption of carbon monoxide (II) by a solution of CuCl in strong HCl. Similar compounds are apparently formed in an ammonia solution of CuCl, which is often used to absorb CO in the analysis of gases.
Receipt.
Carbon monoxide is formed when carbon burns in the absence of oxygen. Most often it is obtained as a result of the interaction of carbon dioxide with hot coal:
CO 2 + C + 171 kJ = 2 CO.
This reaction is reversible, and its equilibrium below 400 °C is almost completely shifted to the left, and above 1000 °C - to the right (Fig. 7). However, it is established with noticeable speed only at high temperatures. Therefore, under normal conditions, CO is quite stable.
Rice. 7. Equilibrium CO 2 + C = 2 CO.
The formation of CO from elements follows the equation:
2 C + O 2 = 2 CO + 222 kJ.
It is convenient to obtain small amounts of CO by the decomposition of formic acid:
HCOOH = H 2 O + CO
This reaction occurs easily when HCOOH reacts with hot, strong sulfuric acid. In practice, this preparation is carried out either by the action of conc. sulfuric acid into liquid HCOOH (when heated), or by passing the vapors of the latter over phosphorus hemipentaoxide. The interaction of HCOOH with chlorosulfonic acid according to the scheme:
HCOOH + CISO 3 H = H 2 SO 4 + HCI + CO
It already works at normal temperatures.
A convenient method for laboratory production of CO can be heating with conc. sulfuric acid, oxalic acid or potassium iron sulfide. In the first case, the reaction proceeds according to the following scheme:
H 2 C 2 O 4 = CO + CO 2 + H 2 O.
Along with CO, carbon dioxide is also released, which can be retained by passing gas mixture through a barium hydroxide solution. In the second case, the only gaseous product is carbon monoxide:
K 4 + 6 H 2 SO 4 + 6 H 2 O = 2 K 2 SO 4 + FeSO 4 + 3 (NH 4) 2 SO 4 + 6 CO.
Large quantities CO can be obtained by incomplete combustion coal in special furnaces - gas generators. Conventional (“air”) generator gas contains on average (volume %): CO-25, N2-70, CO 2 -4 and small impurities of other gases. When burned, it produces 3300-4200 kJ per m3. Replacing ordinary air with oxygen leads to a significant increase in CO content (and an increase in the calorific value of the gas).
Even more CO is contained in water gas, consisting (in ideal case) from a mixture of equal volumes of CO and H 2 and giving 11,700 kJ/m 3 upon combustion. This gas is obtained by blowing water vapor through a layer of hot coal, and at about 1000 °C the interaction takes place according to the equation:
H 2 O + C + 130 kJ = CO + H 2.
The reaction of the formation of water gas occurs with the absorption of heat, the coal gradually cools and to maintain it in a hot state, it is necessary to alternate the passage of water vapor with the passage of air (or oxygen) into the gas generator. In this regard, water gas contains approximately CO-44, H 2 -45, CO 2 -5 and N 2 -6%. It is widely used for the synthesis of various organic compounds.
Mixed gas is often obtained. The process of obtaining it boils down to simultaneously blowing air and water vapor through a layer of hot coal, i.e. a combination of both methods described above - Therefore, the composition of the mixed gas is intermediate between generator and water. On average it contains: CO-30, H 2 -15, CO 2 -5 and N 2 -50%. Cubic meter when burned, it produces about 5400 kJ.
Application.
Water and mixed gases (they contain CO) are used as fuel and feedstock chemical industry. They are important, for example, as one of the sources for obtaining a nitrogen-hydrogen mixture for the synthesis of ammonia. When they are passed together with water vapor over a catalyst heated to 500 °C (mainly Fe 2 O 3), a reversible reaction occurs:
H 2 O + CO = CO 2 + H 2 + 42 kJ,
whose balance is strongly shifted to the right.
The resulting carbon dioxide is then removed by washing with water (under pressure), and the remaining CO is removed with an ammonia solution of copper salts. This leaves almost pure nitrogen and hydrogen. Accordingly, by adjusting the relative amounts of generator and water gases, it is possible to obtain N 2 and H 2 in the required volumetric ratio. Before being fed into the synthesis column, the gas mixture is dried and purified from catalyst-poisoning impurities.
CO 2 molecule
The CO molecule is characterized by d(CO) = 113 pm, its dissociation energy is 1070 kJ/mol, which is greater than that of other diatomic molecules. Let's consider electronic structure CO, where the atoms are connected by a double covalent bond and one donor-acceptor bond, with oxygen being the donor and carbon the acceptor.
Effect on the body.
Carbon monoxide is very poisonous. The first signs of acute CO poisoning are headache and dizziness, followed by loss of consciousness. Maximum permissible concentration of CO in the air industrial enterprises considered 0.02 mg/l. The main antidote for CO poisoning is Fresh air. Short-term inhalation of ammonia vapor is also useful.
The extreme toxicity of CO, its lack of color and odor, as well as its very weak absorption activated carbon a regular gas mask make this gas especially dangerous. The issue of protection against it was resolved by the manufacture of special gas masks, the box of which was filled with a mixture of various oxides (mainly MnO 2 and CuO). The effect of this mixture (“hopkalite”) is reduced to the catalytic acceleration of the oxidation reaction of CO to CO 2 by atmospheric oxygen. In practice, hopcalite gas masks are very inconvenient, as they force you to breathe heated air (as a result of an oxidation reaction).
Being in nature.
Carbon monoxide is part of the atmosphere (10-5 vol.%). On average, 0.5% CO contains tobacco smoke and 3% - exhaust gases from internal combustion engines.
CARBON OXIDE (CARBON MONOXIDE). Carbon(II) oxide (carbon monoxide) CO, non-salt-forming carbon monoxide. This means that there is no acid corresponding to this oxide. Carbon monoxide (II) is a colorless and odorless gas that liquefies when atmospheric pressure at a temperature of –191.5o C and solidifies at –205o C. The CO molecule is similar in structure to the N2 molecule: both contain an equal number of electrons (such molecules are called isoelectronic), the atoms in them are connected by a triple bond (two bonds in the CO molecule are formed due to 2p electrons of carbon and oxygen atoms, and the third - according to the donor-acceptor mechanism with the participation of a lone electron pair of oxygen and a free 2p orbital of carbon). As a result, the physical properties of CO and N2 (melting and boiling points, solubility in water, etc.) are very similar.
Carbon oxide (II) is formed during the combustion of carbon-containing compounds with insufficient access to oxygen, as well as when hot coal comes into contact with the product of complete combustion - carbon dioxide: C + CO2 → 2CO. In the laboratory, CO is obtained by dehydration of formic acid by the action of concentrated sulfuric acid on liquid formic acid when heated, or by passing formic acid vapor over P2O5: HCOOH → CO + H2O. CO is obtained by the decomposition of oxalic acid: H2C2O4 → CO + CO2 + H2O. CO can be easily separated from other gases by passing it through an alkali solution.
Under normal conditions, CO, like nitrogen, is chemically quite inert. Only at elevated temperatures does the tendency of CO to undergo oxidation, addition and reduction reactions appear. Thus, at elevated temperatures it reacts with alkalis: CO + NaOH → HCOONa, CO + Ca(OH)2 → CaCO3 + H2. These reactions are used to remove CO from industrial gases.
Carbon monoxide (II) is a high-calorie fuel: combustion is accompanied by the release of significant amount heat (283 kJ per 1 mol CO). Mixtures of CO with air explode when its content ranges from 12 to 74%; Fortunately, in practice such mixtures are extremely rare. In industry, to obtain CO, gasification of solid fuel is carried out. For example, blowing water vapor through a layer of coal heated to 1000oC leads to the formation of water gas: C + H2O → CO + H2, which has a very high calorific value. However, combustion is far from the most profitable use of water gas. From it, for example, it is possible to obtain (in the presence of various catalysts under pressure) a mixture of solid, liquid and gaseous hydrocarbons - a valuable raw material for the chemical industry (Fischer-Tropsch reaction). From the same mixture, enriching it with hydrogen and using the necessary catalysts, you can obtain alcohols, aldehydes, and acids. Special meaning has the synthesis of methanol: CO + 2H2 → CH3OH - the most important raw material for organic synthesis, therefore this reaction is carried out industrially on a large scale.
Reactions in which CO is a reducing agent can be demonstrated by the example of the reduction of iron from ore during the blast furnace process: Fe3O4 + 4CO → 3Fe + 4CO2. The reduction of metal oxides with carbon(II) oxide has great importance in metallurgical processes.
CO molecules are characterized by addition reactions to transition metals and their compounds with the formation of complex compounds - carbonyls. Examples include liquid or solid metal carbonyls Fe(CO)4, Fe(CO)5, Fe2(CO)9, Ni(CO)4, Cr(CO)6, etc. This is very toxic substances, when heated, they again decompose into metal and CO. This way you can obtain powdered metals of high purity. Sometimes metal “smudges” are visible on the burner of a gas stove; this is a consequence of the formation and decay of iron carbonyl. Currently, thousands of different metal carbonyls have been synthesized, containing, in addition to CO, inorganic and organic ligands, for example, PtCl2(CO), K3, Cr(C6H5Cl)(CO)3.
CO is also characterized by a reaction of the compound with chlorine, which in the light occurs already at room temperature with the formation of exclusively poisonous phosgene: CO + Cl2 → COCl2. This reaction is a chain reaction, it follows a radical mechanism with the participation of chlorine atoms and free radicals COCl. Despite its toxicity, phosgene is widely used for the synthesis of many organic compounds.
Carbon monoxide (II) is a strong poison, as it forms strong complexes with metal-containing biologically active molecules; this disrupts tissue respiration. The cells of the central nervous system are especially affected. The binding of CO to Fe(II) atoms in blood hemoglobin prevents the formation of oxyhemogloblin, which carries oxygen from the lungs to the tissues. Even when the air contains 0.1% CO, this gas displaces half of the oxygen from oxyhemoglobin. In the presence of CO, death from suffocation may occur even in the presence large quantity oxygen. Therefore, CO is called carbon monoxide. In a “distressed” person, the brain and nervous system. For salvation it is necessary first of all fresh air, which does not contain CO (or, even better, pure oxygen), while the CO bound to hemoglobin is gradually replaced by O2 molecules and suffocation goes away. Maximum permissible average daily concentration of CO in atmospheric air is 3 mg/m3 (about 3.10–5%), in air working area– 20 mg/m3.
Typically, the CO content in the atmosphere does not exceed 10–5%. This gas enters the air as part of volcanic and swamp gases, with secretions of plankton and other microorganisms. Thus, 220 million tons of CO are released into the atmosphere annually from the surface layers of the ocean. The concentration of CO in coal mines is high. A lot of carbon monoxide is produced when forest fires. The smelting of every million tons of steel is accompanied by the formation of 300–400 tons of CO. In total, the technogenic release of CO into the air reaches 600 million tons per year, more than half of which comes from motor vehicles. If the carburetor is not adjusted, the exhaust gases can contain up to 12% CO! Therefore, most countries have introduced strict standards for the CO content in car exhaust.
The formation of CO always occurs during the combustion of carbon-containing compounds, including wood, with insufficient access to oxygen, as well as when hot coal comes into contact with carbon dioxide: C + CO2 → 2CO. Such processes also occur in village ovens. Therefore, prematurely closing the stove chimney to conserve heat often leads to carbon monoxide poisoning. One should not think that city dwellers who do not heat their stoves are insured against CO poisoning; For example, it is easy for them to get poisoned in a poorly ventilated garage where a car is parked with the engine running. CO is also found in natural gas combustion products in the kitchen. Many aviation accidents in the past were caused by engine wear or poor adjustments, allowing CO to enter the cockpit and poison the crew. The danger is compounded by the fact that CO cannot be detected by smell; in this regard, carbon monoxide is more dangerous than chlorine!
Carbon monoxide (II) is practically not sorbed by active carbon and therefore an ordinary gas mask does not protect against this gas; To absorb it, an additional hopcalite cartridge is required containing a catalyst that “afterburns” CO to CO2 with the help of atmospheric oxygen. More and more passenger cars are now equipped with afterburning catalysts, despite the high cost of these catalysts based on platinum metals.
Physical properties.
Carbon monoxide is a colorless and odorless gas that is slightly soluble in water.
t pl. 205 °C,
t kip. 191 °C
critical temperature =140°C
critical pressure = 35 atm.
The solubility of CO in water is about 1:40 by volume.
Chemical properties.
Under normal conditions, CO is inert; when heated - a reducing agent; non-salt-forming oxide.
1) with oxygen
2C +2 O + O 2 = 2C +4 O 2
2) with metal oxides
C +2 O + CuO = Cu + C +4 O 2
3) with chlorine (in the light)
CO + Cl 2 --hn-> COCl 2 (phosgene)
4) reacts with alkali melts (under pressure)
CO + NaOH = HCOONa (sodium formic acid (sodium formate))
5) forms carbonyls with transition metals
Ni + 4CO =t°= Ni(CO) 4
Fe + 5CO =t°= Fe(CO) 5
Carbon monoxide does not react chemically with water. CO also does not react with alkalis and acids. It is extremely poisonous.
From the chemical side, carbon monoxide is characterized mainly by its tendency to undergo addition reactions and its reducing properties. However, both of these trends usually appear only at elevated temperatures. Under these conditions, CO combines with oxygen, chlorine, sulfur, some metals, etc. At the same time, carbon monoxide, when heated, reduces many oxides to metals, which is very important for metallurgy. Along with heating, an increase in the chemical activity of CO is often caused by its dissolution. Thus, in solution it is capable of reducing salts of Au, Pt and some other elements to free metals already at ordinary temperatures.
At elevated temperatures and high pressures, CO interacts with water and caustic alkalis: in the first case, HCOOH is formed, and in the second, sodium formic acid. The latter reaction occurs at 120 °C, a pressure of 5 atm and is used technically.
The reduction of palladium chloride in solution is easy according to the general scheme:
PdCl 2 + H 2 O + CO = CO 2 + 2 HCl + Pd
serves as the most commonly used reaction for the discovery of carbon monoxide in a mixture of gases. Even very small amounts of CO are easily detected by the slight coloring of the solution due to the release of finely crushed palladium metal. Quantitative determination of CO is based on the reaction:
5 CO + I 2 O 5 = 5 CO 2 + I 2.
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 mercury salts, KClO 3 - in the presence of OsO 4. In general, in its reducing properties, CO is similar to molecular hydrogen, and its activity under normal conditions is higher than that of the latter. Interestingly, there are bacteria that, through the oxidation of CO, obtain the energy they need for life.
The comparative activity of CO and H2 as reducing agents can be assessed by studying the reversible reaction:
H 2 O + CO = CO 2 + H 2 + 42 kJ,
equilibrium state which at high temperatures is established quite quickly (especially in the presence of Fe 2 O 3). At 830 °C, the equilibrium mixture contains equal amounts of CO and H 2, i.e., the affinity of both gases for oxygen is the same. Below 830 °C, the stronger reducing agent is CO, above - H2.
The binding of one of the products of the reaction discussed above, in accordance with the law of mass action, shifts its equilibrium. Therefore, by passing a mixture of carbon monoxide and water vapor over calcium oxide, hydrogen can be obtained according to the scheme:
H 2 O + CO + CaO = CaCO 3 + H 2 + 217 kJ.
This reaction occurs already at 500 °C.
In air, CO ignites at about 700 °C and burns with a blue flame to CO 2:
2 CO + O 2 = 2 CO 2 + 564 kJ.
The significant release of heat that accompanies this reaction makes carbon monoxide a valuable gaseous fuel. However, it is most widely used as a starting product for the synthesis of various organic substances.
The combustion of thick layers of coal in furnaces occurs in three stages:
1) C + O 2 = CO 2; 2) CO 2 + C = 2 CO; 3) 2 CO + O 2 = 2 CO 2.
If the pipe is closed prematurely, a lack of oxygen is created in the furnace, which can cause CO to spread throughout the heated room and lead to poisoning (fumes). It should be noted that the smell of “carbon monoxide” is not caused by CO, but by impurities of some organic substances.
The CO flame can have a temperature of up to 2100 °C. The CO combustion reaction is interesting in that when heated to 700-1000 °C, it proceeds at a noticeable speed only in the presence of traces of water vapor or other hydrogen-containing gases (NH 3, H 2 S, etc.). This is due to the chain nature of the reaction under consideration, which occurs through the intermediate formation of OH radicals according to the following schemes:
H + O 2 = HO + O, then O + CO = CO 2, HO + CO = CO 2 + H, etc.
At very high temperatures, the CO combustion reaction becomes noticeably reversible. The CO 2 content in an equilibrium mixture (under a pressure of 1 atm) above 4000 °C can only be negligibly small. The CO molecule itself is so thermally stable that it does not decompose even at 6000 °C. CO molecules have been discovered in the interstellar medium. When CO acts on metal K at 80 °C, a colorless crystalline, highly explosive compound of the composition K 6 C 6 O 6 is formed. With the elimination of potassium, this substance easily turns into carbon monoxide C 6 O 6 (“triquinone”), which can be considered as a product of CO polymerization. Its structure corresponds to a six-membered cycle formed by carbon atoms, each of which is connected by a double bond to oxygen atoms.
Interaction of CO with sulfur according to the reaction:
CO + S = COS + 29 kJ
It goes fast only at high temperatures. The resulting carbon thioxide (O=C=S) is a colorless and odorless gas (mp -139, bp -50 °C). Carbon (II) monoxide is capable of combining directly with certain metals. As a result, metal carbonyls are formed, which should be considered as complex compounds.
Carbon(II) monoxide also forms complex compounds with some salts. Some of them (OsCl 2 ·3CO, PtCl 2 ·CO, etc.) are stable only in solution. The formation of the latter substance is associated with the absorption of carbon monoxide (II) by a solution of CuCl in strong HCl. Similar compounds are apparently formed in an ammonia solution of CuCl, which is often used to absorb CO in the analysis of gases.
Receipt.
Carbon monoxide is formed when carbon burns in the absence of oxygen. Most often it is obtained as a result of the interaction of carbon dioxide with hot coal:
CO 2 + C + 171 kJ = 2 CO.
This reaction is reversible, and its equilibrium below 400 °C is almost completely shifted to the left, and above 1000 °C - to the right (Fig. 7). However, it is established with noticeable speed only at high temperatures. Therefore, under normal conditions, CO is quite stable.
Rice. 7. Equilibrium CO 2 + C = 2 CO.
The formation of CO from elements follows the equation:
2 C + O 2 = 2 CO + 222 kJ.
It is convenient to obtain small amounts of CO by the decomposition of formic acid: HCOOH = H 2 O + CO
This reaction occurs easily when HCOOH reacts with hot, strong sulfuric acid. In practice, this preparation is carried out either by the action of conc. sulfuric acid into liquid HCOOH (when heated), or by passing the vapors of the latter over phosphorus hemipentaoxide. The interaction of HCOOH with chlorosulfonic acid according to the scheme:
HCOOH + CISO 3 H = H 2 SO 4 + HCI + CO
It already works at normal temperatures.
Convenient method laboratory obtaining CO can serve as heating with conc. sulfuric acid, oxalic acid or potassium iron sulfide. In the first case, the reaction proceeds according to the following scheme: H 2 C 2 O 4 = CO + CO 2 + H 2 O.
Along with CO, carbon dioxide is also released, which can be retained by passing the gas mixture through a solution of barium hydroxide. In the second case, the only gaseous product is carbon monoxide:
K 4 + 6 H 2 SO 4 + 6 H 2 O = 2 K 2 SO 4 + FeSO 4 + 3 (NH 4) 2 SO 4 + 6 CO.
Large quantities of CO can be obtained by incomplete combustion of coal in special furnaces - gas generators. Conventional (“air”) generator gas contains on average (volume %): CO-25, N2-70, CO 2 -4 and small impurities of other gases. When burned, it produces 3300-4200 kJ per m3. Replacing ordinary air with oxygen leads to a significant increase in CO content (and an increase in the calorific value of the gas).
Even more CO is contained in water gas, which consists (in an ideal case) of a mixture of equal volumes of CO and H 2 and produces 11,700 kJ/m 3 upon combustion. This gas is obtained by blowing water vapor through a layer of hot coal, and at about 1000 °C the interaction takes place according to the equation:
H 2 O + C + 130 kJ = CO + H 2.
The reaction of the formation of water gas occurs with the absorption of heat, the coal gradually cools and to maintain it in a hot state, it is necessary to alternate the passage of water vapor with the passage of air (or oxygen) into the gas generator. In this regard, water gas contains approximately CO-44, H 2 -45, CO 2 -5 and N 2 -6%. It is widely used for the synthesis of various organic compounds.
Mixed gas is often obtained. The process of obtaining it boils down to simultaneously blowing air and water vapor through a layer of hot coal, i.e. a combination of both methods described above - Therefore, the composition of the mixed gas is intermediate between generator and water. On average it contains: CO-30, H 2 -15, CO 2 -5 and N 2 -50%. A cubic meter of it produces about 5400 kJ when burned.
Carbon monoxide(II) ), or carbon monoxide, CO was discovered by the English chemist Joseph Priestley in 1799. It is a colorless gas, tasteless and odorless, it is slightly soluble in water (3.5 ml in 100 ml of water at 0 ° C), has low melting temperature (-205 °C) and boiling point (-192 °C).
Carbon monoxide enters the Earth's atmosphere during incomplete combustion of organic substances, during volcanic eruptions, and also as a result of the life activity of some lower plants(algae). Natural level CO in the air is 0.01-0.9 mg/m3. Carbon monoxide is very poisonous. In the human body and higher animals, it actively reacts with
The flame of burning carbon monoxide is a beautiful blue-violet color. It's easy to observe for yourself. To do this you need to light a match. The lower part of the flame is luminous - this color is given to it by hot carbon particles (a product of incomplete combustion of wood). The flame is surrounded by a blue-violet border on top. This burns carbon monoxide generated during the oxidation of wood.
complex iron compound - blood heme (bound to the protein globin), disrupting the functions of oxygen transfer and consumption by tissues. In addition, it enters into an irreversible interaction with some enzymes involved in the energy metabolism of the cell. At a carbon monoxide concentration in the room of 880 mg/m3, death occurs within a few hours, and at 10 g/m3 - almost instantly. The maximum permissible content of carbon monoxide in the air is 20 mg/m3. The first signs of CO poisoning (at a concentration of 6-30 mg/m3) are a decrease in the sensitivity of vision and hearing, headache, and a change in heart rate. If a person has been poisoned by carbon monoxide, he must be taken out into fresh air, given artificial respiration, and in mild cases of poisoning, given strong tea or coffee.
Large amounts of carbon monoxide ( II ) enter the atmosphere as a result of human activity. Thus, on average, a car emits about 530 kg of CO into the air per year. When 1 liter of gasoline is burned in an internal combustion engine, carbon monoxide emissions range from 150 to 800 g. On Russian highways, the average concentration of CO is 6-57 mg/m3, i.e. exceeds the poisoning threshold . Carbon monoxide accumulates in poorly ventilated courtyards in front of houses located near highways, in basements and garages. IN last years organized on highways special items to control the content of carbon monoxide and other products of incomplete combustion of fuel (CO-CH control).
At room temperature, carbon monoxide is quite inert. It does not interact with water and alkali solutions, i.e. it is a non-salt-forming oxide, but when heated it reacts with solid alkalis: CO + KOH = HCOOC (potassium formate, formic acid salt); CO + Ca (OH) 2 = CaCO 3 + H 2. These reactions are used to separate hydrogen from synthesis gas (CO + 3H 2), formed by the interaction of methane with superheated water vapor.
An interesting property of carbon monoxide is its ability to form compounds with transition metals - carbonyls, for example: Ni +4СО ® 70° C Ni (CO ) 4 .
Carbon monoxide(II) ) is an excellent reducing agent. When heated, it is oxidized by air oxygen: 2CO + O 2 = 2CO 2. This reaction can also be carried out at room temperature using a catalyst - platinum or palladium. Such catalysts are installed on cars to reduce CO emissions into the atmosphere.
When CO reacts with chlorine, a very poisonous gas, phosgene, is formed (t kip =7.6 °C): CO+ Cl 2 = COCl 2 . Previously, it was used as a chemical warfare agent, but now it is used in the production of synthetic polyurethane polymers.
Carbon monoxide is used in the smelting of iron and steel to reduce iron from oxides; it is also widely used in organic synthesis. When a mixture of carbon oxide ( II ) with hydrogen, depending on the conditions (temperature, pressure), various products are formed - alcohols, carbonyl compounds, carboxylic acids. The reaction of methanol synthesis is especially important: CO + 2H 2 = CH3OH , which is one of the main products of organic synthesis. Carbon monoxide is used for the synthesis of phos gene, formic acid, as a high-calorie fuel.
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