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 reacts 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 precipitate forms white color- 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, precipitation brown gas) 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 | Molar masses of nitric acid and calcium carbonate calculated using the table chemical elements DI. 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. |
Before considering Chemical properties carbon dioxide, let's find out some characteristics of this compound.
General information
It is the most important component of carbonated water. It is he who gives the drinks freshness, sparkling. This compound is an acidic, salt-forming oxide. carbon dioxide is 44 g/mol. This gas is heavier than air, therefore it accumulates in the lower part of the room. This compound is poorly soluble in water.
Chemical properties
Consider the chemical properties of carbon dioxide briefly. When interacting with water, a weak carbonic acid is formed. Almost immediately after formation, it dissociates into hydrogen cations and carbonate or bicarbonate anions. The resulting compound interacts with active metals, oxides, and also with alkalis.
What are the main chemical properties of carbon dioxide? The reaction equations confirm the acidic nature of this compound. (4) capable of forming carbonates with basic oxides.
Physical properties
Under normal conditions, this compound is in a gaseous state. When the pressure is increased, it can be converted to a liquid state. This gas is colorless, odorless, and has a slight sour taste. Liquefied carbon dioxide is a colorless, transparent, highly mobile acid, similar in its external parameters to ether or alcohol.
Relative molecular mass carbon dioxide is 44 g/mol. This is almost 1.5 times more than air.
In the case of a decrease in temperature to -78.5 degrees Celsius, the formation occurs. It is similar in hardness to chalk. When this substance evaporates, gaseous carbon monoxide is formed (4).
Qualitative reaction
Considering the chemical properties of carbon dioxide, it is necessary to highlight its qualitative reaction. When this chemical reacts with lime water, a cloudy precipitate of calcium carbonate is formed.
Cavendish was able to discover such characteristic physical properties carbon monoxide (4) as solubility in water, and high specific gravity.
Lavoisier was carried out during which he tried to isolate pure metal from lead oxide.
The chemical properties of carbon dioxide revealed as a result of such studies became a confirmation of the reducing properties of this compound. Lavoisier, when calcining lead oxide with carbon monoxide (4), managed to obtain a metal. In order to make sure that the second substance is carbon monoxide (4), he passed lime water through the gas.
All the chemical properties of carbon dioxide confirm the acidic nature of this compound. In the earth's atmosphere, this compound is contained in sufficient quantities. With the systematic growth of this compound in the earth's atmosphere, serious climate change (global warming) is possible.
It is carbon dioxide that plays an important role in wildlife, because this Chemical substance takes an active part in the metabolism of living cells. Exactly this chemical compound is the result of a variety of oxidative processes associated with the respiration of living organisms.
Carbon dioxide contained in the earth's atmosphere is the main source of carbon for living plants. In the process of photosynthesis (in the light), the process of photosynthesis occurs, which is accompanied by the formation of glucose, the release of oxygen into the atmosphere.
Carbon dioxide is non-toxic and does not support respiration. With an increased concentration of this substance in the atmosphere, a person experiences a delay in breathing, severe headaches appear. In living organisms, carbon dioxide is of great physiological importance, for example, it is necessary for the regulation of vascular tone.
Features of obtaining
On an industrial scale, carbon dioxide can be isolated from the flue gas. In addition, CO2 is a by-product of the decomposition of dolomite, limestone. Modern installations for the production of carbon dioxide involve the use of an aqueous solution of ethanamine, which adsorbs the gas contained in the flue gas.
In the laboratory, carbon dioxide is released when carbonates or bicarbonates react with acids.
Application of carbon dioxide
The acid oxide used in industry as a baking powder or preservative. On the product packaging, this compound is indicated in the form of E290. In liquid form, carbon dioxide is used in fire extinguishers to extinguish fires. Carbon monoxide (4) is used to make carbonated water and lemonade drinks.
The interaction of carbon with carbon dioxide proceeds according to the reaction
The system under consideration consists of two phases, solid carbon and gas (f = 2). Three interacting substances are interconnected by one reaction equation, therefore, the number of independent components is k = 2. According to the Gibbs phase rule, the number of degrees of freedom of the system will be equal to
C \u003d 2 + 2 - 2 \u003d 2.
This means that the equilibrium concentrations of CO and CO 2 are functions of temperature and pressure.
Reaction (2.1) is endothermic. Therefore, according to the principle of Le Chatelier, an increase in temperature shifts the equilibrium of the reaction in the direction of the formation of an additional amount of CO.
During the course of reaction (2.1), 1 mol of CO 2 is consumed, which under normal conditions has a volume of 22400 cm 3, and 1 mol of solid carbon with a volume of 5.5 cm 3. As a result of the reaction, 2 moles of CO are formed, the volume of which under normal conditions is 44800 cm 3.
From the above data on the change in the volume of reagents during reaction (2.1), it follows:
- The transformation under consideration is accompanied by an increase in the volume of interacting substances. Therefore, in accordance with Le Chatelier's principle, an increase in pressure will promote the reaction in the direction of formation of CO 2 .
- The change in the volume of the solid phase is negligible compared to the change in the volume of the gas. Therefore, for heterogeneous reactions involving gaseous substances with sufficient accuracy, we can assume that the change in the volume of interacting substances is determined only by the number of moles of gaseous substances in the right and left parts of the reaction equation.
The equilibrium constant of the reaction (2.1) is determined from the expression
If graphite is taken as the standard state in determining the activity of carbon, then a C = 1
Numerical value the equilibrium constants of reaction (2.1) can be determined from the equation
Data on the effect of temperature on the value of the equilibrium constant of the reaction are given in Table 2.1.
Table 2.1– Values of the equilibrium constant of reaction (2.1) at different temperatures
From the given data it can be seen that at a temperature of about 1000K (700 o C) the equilibrium constant of the reaction is close to unity. This means that reaction (2.1) is almost completely reversible at moderate temperatures. At high temperatures, the reaction proceeds irreversibly in the direction of CO formation, and at low temperatures in the opposite direction.
If the gas phase consists only of CO and CO 2 , by expressing the partial pressures of the interacting substances in terms of their volumetric concentrations, equation (2.4) can be reduced to the form
In industrial conditions, CO and CO 2 are obtained as a result of the interaction of carbon with oxygen in air or blast enriched with oxygen. At the same time, another component, nitrogen, appears in the system. The introduction of nitrogen into the gas mixture affects the ratio of the equilibrium concentrations of CO and CO 2 similarly to a decrease in pressure.
Equation (2.6) shows that the composition of the equilibrium gas mixture is a function of temperature and pressure. Therefore, the solution of equation (2.6) is graphically interpreted using the surface in three-dimensional space in the coordinates T, Ptot and (% CO). The perception of such dependence is difficult. It is much more convenient to represent it as a dependence of the composition of an equilibrium mixture of gases on one of the variables, while the second of the system parameters is constant. As an example, Figure 2.1 shows data on the effect of temperature on the composition of an equilibrium gas mixture at Ptot = 10 5 Pa.
With a known initial composition of the gas mixture, the direction of reaction (2.1) can be judged using the equation
If the pressure in the system remains unchanged, relation (2.7) can be reduced to the form
Figure 2.1- Dependence of the equilibrium composition of the gas phase for the reaction C + CO 2 = 2CO on temperature at P CO + P CO 2 = 10 5 Pa.
For a gas mixture whose composition corresponds to point a in Figure 2.1, . Wherein
and G > 0. Thus, the points above the equilibrium curve characterize systems whose approach to the state of thermodynamic equilibrium proceeds by the reaction
Similarly, it can be shown that the points below the equilibrium curve characterize systems that approach the equilibrium state by the reaction
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Carbon monoxide (IV) does not support combustion. Only some active metals burn in it:
2 M g + C O 2 → 2 M g O + C (\displaystyle (\mathsf (2Mg+CO_(2)\rightarrow 2MgO+C)))Interaction with active metal oxide:
C a O + C O 2 → C a C O 3 (\displaystyle (\mathsf (CaO+CO_(2)\rightarrow CaCO_(3))))When dissolved in water, it forms carbonic acid:
C O 2 + H 2 O ⇄ H 2 C O 3 (\displaystyle (\mathsf (CO_(2)+H_(2)O\rightleftarrows H_(2)CO_(3))))Reacts with alkalis to form carbonates and bicarbonates:
C a (O H) 2 + C O 2 → C a C O 3 ↓ + H 2 O (\displaystyle (\mathsf (Ca(OH)_(2)+CO_(2)\rightarrow CaCO_(3)\downarrow +H_( 2)O)))(qualitative reaction to carbon dioxide) K O H + C O 2 → K H C O 3 (\displaystyle (\mathsf (KOH+CO_(2)\rightarrow KHCO_(3))))Biological
The human body emits approximately 1 kg of carbon dioxide per day.
This carbon dioxide is transported from the tissues, where it is formed as one of the end products of metabolism, through the venous system and is then excreted in the exhaled air through the lungs. Thus, the content of carbon dioxide in the blood is high in the venous system, and decreases in the capillary network of the lungs, and low in the arterial blood. The content of carbon dioxide in a blood sample is often expressed in terms of partial pressure, that is, the pressure that carbon dioxide contained in a given amount of carbon dioxide would have if only carbon dioxide occupied the entire volume of the blood sample.
Carbon dioxide (CO 2) is transported in the blood by three different ways(the exact ratio of each of these three ways transportation depends on whether the blood is arterial or venous).
Hemoglobin, the main oxygen-transporting protein of red blood cells, is capable of transporting both oxygen and carbon dioxide. However, carbon dioxide binds to hemoglobin at a different site than oxygen. It binds to the N-terminal ends of the globin chains, not to the heme. However, due to allosteric effects, which lead to a change in the configuration of the hemoglobin molecule upon binding, the binding of carbon dioxide reduces the ability of oxygen to bind to it, at a given partial pressure of oxygen, and vice versa - the binding of oxygen to hemoglobin reduces the ability of carbon dioxide to bind to it, at a given partial pressure of carbon dioxide. In addition, the ability of hemoglobin to preferentially bind to oxygen or carbon dioxide also depends on the pH of the medium. These features are very important for the successful capture and transport of oxygen from the lungs to the tissues and its successful release in the tissues, as well as for the successful capture and transport of carbon dioxide from the tissues to the lungs and its release there.
Carbon dioxide is one of the most important mediators of blood flow autoregulation. It is a powerful vasodilator. Accordingly, if the level of carbon dioxide in the tissue or in the blood rises (for example, due to intensive metabolism - caused, say, by exercise, inflammation, tissue damage, or due to obstruction of blood flow, tissue ischemia), then the capillaries dilate, which leads to an increase in blood flow and respectively, to an increase in the delivery of oxygen to the tissues and the transport of accumulated carbon dioxide from the tissues. In addition, carbon dioxide in certain concentrations(increased, but not yet reaching toxic values) has a positive inotropic and chronotropic effect on the myocardium and increases its sensitivity to adrenaline, which leads to an increase in the strength and frequency of heart contractions, cardiac output and, as a result, stroke and minute blood volume. It also contributes to the correction of tissue hypoxia and hypercapnia (elevated levels of carbon dioxide).
Bicarbonate ions are very important for regulating blood pH and maintaining normal acid-base balance. The respiratory rate affects the amount of carbon dioxide in the blood. Weak or slow breathing causes respiratory acidosis, while rapid and excessively deep breathing leads to hyperventilation and the development of respiratory alkalosis.
In addition, carbon dioxide is also important in the regulation of respiration. Although our body requires oxygen for metabolism, low oxygen in the blood or tissues usually does not stimulate respiration (or rather, the stimulating effect of lack of oxygen on respiration is too weak and “turns on” late, with very low levels oxygen in the blood, at which a person often already loses consciousness). Normally, respiration is stimulated by an increase in the level of carbon dioxide in the blood. The respiratory center is much more sensitive to an increase in carbon dioxide than to a lack of oxygen. As a consequence, breathing highly rarefied air (with a low partial pressure of oxygen) or a gas mixture containing no oxygen at all (for example, 100% nitrogen or 100% nitrous oxide) can quickly lead to loss of consciousness without causing a feeling of lack of air (because the level of carbon dioxide does not rise in the blood, because nothing prevents its exhalation). This is especially dangerous for pilots of military aircraft flying at high altitudes (in the event of an emergency depressurization of the cockpit, pilots can quickly lose consciousness). This feature of the breathing regulation system is also the reason why on airplanes flight attendants instruct passengers in the event of a depressurization of the aircraft cabin to first put on an oxygen mask themselves before trying to help someone else - by doing this, the helper risks quickly losing consciousness himself, and even without feeling any discomfort and need for oxygen until the last moment.
The human respiratory center tries to maintain a partial pressure of carbon dioxide in the arterial blood no higher than 40 mm Hg. With conscious hyperventilation, the content of carbon dioxide in the arterial blood can decrease to 10-20 mmHg, while the oxygen content in the blood will practically not change or increase slightly, and the need to take another breath will decrease as a result of a decrease in the stimulating effect of carbon dioxide on the activity of the respiratory center. This is the reason why after a period of conscious hyperventilation it is easier to hold the breath for a long time than without prior hyperventilation. Such conscious hyperventilation followed by breath-holding can result in loss of consciousness before the person feels the need to breathe. In a safe environment, such a loss of consciousness does not threaten anything special (having lost consciousness, a person will lose control over himself, stop holding his breath and take a breath, breathing, and with it the supply of oxygen to the brain will be restored, and then consciousness will be restored). However, in other situations, such as before diving, this can be dangerous (loss of consciousness and the need to breathe will come at a depth, and in the absence of conscious control, water will enter the airways, which can lead to drowning). That is why hyperventilation before diving is dangerous and not recommended.
Receipt
In industrial quantities, carbon dioxide is emitted from flue gases, or as a by-product of chemical processes, for example, during the decomposition of natural carbonates (limestone, dolomite) or in the production of alcohol (alcoholic fermentation). The mixture of gases obtained is washed with a solution of potassium carbonate, which absorb carbon dioxide, turning into hydrocarbonate. A solution of bicarbonate, when heated or under reduced pressure, decomposes, releasing carbon dioxide. In modern installations for the production of carbon dioxide, instead of bicarbonate, an aqueous solution of monoethanolamine is more often used, which, under certain conditions, is able to absorb CO₂ contained in the flue gas, and give it away when heated; thus separating the finished product from other substances.
Carbon dioxide is also produced in air separation plants as a by-product of obtaining pure oxygen, nitrogen and argon.
AT laboratory conditions small amounts are obtained by reacting carbonates and bicarbonates with acids, such as marble, chalk or soda with hydrochloric acid, using, for example, a Kipp apparatus. Using the reaction of sulfuric acid with chalk or marble results in the formation of slightly soluble calcium sulfate, which interferes with the reaction and is removed by a significant excess of acid.
For the preparation of drinks, the reaction of baking soda with citric acid or with sour lemon juice can be used. It was in this form that the first carbonated drinks appeared. Pharmacists were engaged in their manufacture and sale.
Application
In the food industry, carbon dioxide is used as a preservative and baking powder, indicated on the packaging with the code E290.
A device for supplying carbon dioxide to an aquarium may include a gas tank. The simplest and most common method for producing carbon dioxide is based on the design for making the alcoholic drink mash. During fermentation, the carbon dioxide released may well provide top dressing for aquarium plants.
Carbon dioxide is used to carbonate lemonade and sparkling water. Carbon dioxide is also used as a protective medium in wire welding, but at high temperatures it decomposes with the release of oxygen. The released oxygen oxidizes the metal. In this regard, it is necessary to introduce deoxidizers into the welding wire, such as manganese and silicon. Another consequence of the influence of oxygen, also associated with oxidation, is a sharp decrease in surface tension, which leads, among other things, to more intense metal spatter than when welding in an inert atmosphere.
Storing carbon dioxide in a steel cylinder in a liquefied state is more profitable than in the form of a gas. Carbon dioxide has a relatively low critical temperature of +31°C. About 30 kg of liquefied carbon dioxide is poured into a standard 40-liter cylinder, and at room temperature there will be a liquid phase in the cylinder, and the pressure will be approximately 6 MPa (60 kgf / cm²). If the temperature is above +31°C, then carbon dioxide will go into a supercritical state with a pressure above 7.36 MPa. The standard operating pressure for a typical 40 liter cylinder is 15 MPa (150 kgf/cm²), however, it must safely withstand pressures 1.5 times higher, i.e. 22.5 MPa - thus, work with such cylinders can be considered quite safe.
Solid carbon dioxide - "dry ice" - is used as a refrigerant in laboratory research, in retail trade, when repairing equipment (for example: cooling one of the mating parts during an interference fit), etc. Carbon dioxide plants are used to liquefy carbon dioxide and produce dry ice.
Registration Methods
Measurement of the partial pressure of carbon dioxide is required in technological processes, in medical applications- analysis of respiratory mixtures during artificial ventilation of the lungs and in closed life support systems. The analysis of CO 2 concentration in the atmosphere is used for environmental and scientific research, to study the greenhouse effect. Carbon dioxide is recorded using gas analyzers based on the principle of infrared spectroscopy and other gas measuring systems. A medical gas analyzer for recording the content of carbon dioxide in exhaled air is called a capnograph. To measure low concentrations of CO 2 (as well as ) in process gases or in atmospheric air, a gas chromatographic method with a methanator and registration on a flame ionization detector can be used.
carbon dioxide in nature
Annual fluctuations in the concentration of atmospheric carbon dioxide on the planet are determined mainly by the vegetation of the middle (40-70 °) latitudes of the Northern Hemisphere.
A large amount of carbon dioxide is dissolved in the ocean.
Carbon dioxide makes up a significant part of the atmospheres of some planets in the solar system: Venus, Mars.
Toxicity
Carbon dioxide is non-toxic, but due to the effect of its elevated concentrations in the air on air-breathing living organisms, it is classified as an asphyxiant gas. (English) Russian. Slight increases in concentration up to 2-4% indoors lead to the development of drowsiness and weakness in people. Dangerous concentrations are considered levels of about 7-10%, at which suffocation develops, manifesting itself in headache, dizziness, hearing loss and loss of consciousness (symptoms similar to those of altitude sickness), depending on the concentration, over a period of several minutes up to one hour. When air with high concentrations of the gas is inhaled, death occurs very quickly by asphyxiation.
Although, in fact, even a concentration of 5-7% CO 2 is not lethal, already at a concentration of 0.1% (such a carbon dioxide content is observed in the air of megacities), people begin to feel weak, drowsy. This shows that even at high oxygen levels, a high concentration of CO 2 has a strong effect on well-being.
Inhalation of air with an increased concentration of this gas does not lead to long-term health problems, and after the victim is removed from the polluted atmosphere, full recovery of health quickly occurs.
Carbon
The element carbon 6 C is in the 2nd period, in the main subgroup of group IV of PS.
Valence possibilities carbon are due to the structure of the outer electron layer of its atom in the ground and in the excited states:
Being in the ground state, a carbon atom can form two covalent bonds by the exchange mechanism and one donor-acceptor bond, using a free orbital. However, in most compounds, carbon atoms are in an excited state and exhibit valency IV.
The most characteristic oxidation states of carbon are: in compounds with more electronegative elements +4 (rarely +2); in compounds with less electronegative elements -4.
Being in nature
Carbon content in earth's crust 0.48% by weight. Free carbon is in the form of diamond and graphite. The bulk of carbon is found in the form of natural carbonates, as well as in fossil fuels: peat, coal, oil, natural gas (a mixture of methane and its closest homologues). In the atmosphere and hydrosphere, carbon is in the form of carbon dioxide CO 2 (0.046% by mass in air).
CaCO 3 - limestone, chalk, marble, Icelandic spar
CaCO 3 ∙MgCO 3 - dolomite
SiC - carborundum
CuCO 3 ∙Cu(OH) 2 - malachite
Physical properties
Diamond has an atomic crystal lattice, a tetrahedral arrangement of atoms in space ( bond angle equal to 109 °), very hard, refractory, dielectric, colorless, transparent, poorly conducts heat.
Graphite has an atomic crystal lattice, its atoms are arranged in layers along the vertices of regular hexagons (bond angle 120°), dark gray, opaque, with a metallic sheen, soft, oily to the touch, conducts heat and electricity, like diamond, has very high melting points (3700°C) and boiling points (4500°C). The carbon-carbon bond length in diamond (0.537 nm) is longer than in graphite (0.142 nm). The density of diamond is greater than that of graphite.
Carbine – linear polymer, consists of chains of two types: –C≡C–C≡C– or =C=C=C=C=, valence angle is 180°, black powder, semiconductor.
Fullerenes – crystalline substances black with a metallic sheen, consist of hollow spherical molecules (has a molecular structure) of the composition C 60, C 70, etc. The carbon atoms on the surface of the molecules are interconnected in regular pentagons and hexagons.
Diamond Graphite Fullerenes
Chemical properties
Carbon is inactive, in the cold it reacts only with fluorine; chemical activity is manifested at high temperatures.
Oxides of carbon
Carbon forms non-salt-forming oxide CO and Salt-forming oxide CO 2 .
Carbon monoxide (II) CO, carbon monoxide, carbon monoxide- colorless and odorless gas, slightly soluble in water, poisonous. The bond in the molecule is triple, very strong. For carbon monoxide characterized by reducing properties in reactions with simple and complex substances.
CuO + CO \u003d Cu + CO 2
Fe 2 O 3 + 3CO \u003d 2FeO + 3CO 3
2CO + O 2 \u003d 2CO 2
CO + Cl 2 = COCl 2
CO + H 2 O \u003d H 2 + CO 2
Carbon monoxide (II) reacts with H 2 , NaOH and methanol:
CO + 2H 2 = CH 3 OH
CO + NaOH = HCOONa
CO + CH 3 OH = CH 3 COOH
Getting carbon monoxide
1) In industry (in gas generators):
C + O 2 = CO 2 + 402 kJ, then CO 2 + C = 2CO - 175 kJ
C + H 2 O \u003d CO + H 2 - Q,
2) In the laboratory- thermal decomposition of formic or oxalic acid in the presence of H 2 SO4 (conc.):
HCOOH → H2O + CO
H 2 C 2 O 4 → CO + CO 2 + H2O
Carbon monoxide (IV) CO 2 , carbon dioxide, carbon dioxide- a colorless, odorless and tasteless gas, soluble in water, causes asphyxiation in large quantities, turns into a white solid mass under pressure - "dry ice", which is used to cool perishable products.
The CO 2 molecule is non-polar, has a linear structure O=C=O.
Receipt
1. Thermal decomposition of salts of carbonic acid (carbonates). Calcination of limestone - in industry:
CaCO 3 → CaO + CO 2
2. The action of strong acids on carbonates and bicarbonates - in the laboratory:
CaCO 3 (marble) + 2HCl → CaCl 2 + H 2 O + CO 2
NaHCO 3 + HCl → NaCl + H 2 O + CO 2
Collection methods
air displacement
3. Combustion of carbonaceous substances:
CH 4 + 2O 2 → 2H 2 O + CO 2
4. With slow oxidation in biochemical processes (respiration, decay, fermentation)
Chemical properties
1) With water gives unstable carbonic acid:
CO 2 + H 2 O ↔ H 2 CO 3
2) Reacts with basic oxides and bases, forming salts of carbonic acid
Na 2 O + CO 2 → Na 2 CO 3
2NaOH + CO 2 → Na 2 CO 3 + H 2 O
NaOH + CO 2 (excess) → NaHCO 3
3) At elevated temperatures, it can exhibit oxidizing properties - oxidizes metals
CO 2 + 2Mg → 2MgO + C
4) Reacts with peroxides and superoxides:
2Na 2 O 2 + 2CO 2 \u003d 2Na 2 CO 3 + O 2
4KO 2 + 2CO 2 \u003d 2K 2 CO 3 + 2O 2
Qualitative reaction for carbon dioxide
Turbidity of lime water Ca (OH) 2 due to the formation of a white precipitate - an insoluble salt CaCO 3:
Ca(OH) 2 + CO 2 → CaCO 3 ↓+ H 2 O
Carbonic acid
H 2 CO 3 exists only in solutions, unstable, weak, dibasic, dissociates in steps, forms medium (carbonates) and acidic (hydrocarbonates) salts, a solution of CO 2 in water turns litmus not red, but pink.
Chemical properties
1) with active metals
H 2 CO 3 + Ca \u003d CaCO 3 + H 2
2) with basic oxides
H 2 CO 3 + CaO \u003d CaCO 3 + H 2 O
3) with bases
H 2 CO 3 (ex) + NaOH \u003d NaHCO 3 + H 2 O
H 2 CO 3 + 2NaOH \u003d Na 2 CO 3 + 2H 2 O
4) Very fragile acid - decomposes
H 2 CO 3 \u003d H 2 O + CO 2
Salts of carbonic acid are obtained using CO 2:
CO 2 + 2NaOH \u003d Na 2 CO 3 + H 2 O
CO 2 + KOH = KHCO 3
or according to the exchange reaction:
K 2 CO 3 + BaCl 2 \u003d 2KCl + BaCO 3
When interacting with aqueous solution with CO 2 carbonates are converted into bicarbonates:
Na 2 CO 3 + CO 2 + H 2 O \u003d 2NaHCO 3
CaCO 3 + CO 2 + H 2 O \u003d Ca (HCO 3) 2
On the contrary, when heated (or under the action of alkalis), bicarbonates turn into bicarbonates:
2NaHCO 3 \u003d Na 2 CO 3 + CO 2 + H 2 O
KHCO 3 + KOH \u003d K 2 CO 3 + H 2 O
Carbonates alkali metals(except lithium) are resistant to heating, carbonates of other metals decompose when heated:
MgCO \u003d MgO + CO 2
Ammonium salts of carbonic acid are especially easily decomposed:
(NH 4) 2 CO 3 \u003d 2NH 3 + CO 2 + H 2 O
NH 4 HCO 3 \u003d NH 3 + CO 2 + H 2 O
Application
Carbon used to obtain soot, coke, metals from ores, lubricants, in medicine, as a gas absorber, for the manufacture of drill tips (diamond).
Na 2 CO 3 ∙10H 2 O - crystalline soda (soda ash); used to produce soap, glass, dyes, sodium compounds;
NaHCO 3 - baking soda; used in the food industry;
CaCO 3 is used in construction to produce CO 2 , CaO;
K 2 CO 3 - potash; used to produce glass, soap, fertilizers;
CO - as a reducing agent, fuel;
CO 2 - for food storage, water carbonation, production of soda, sugar.
