What a qualitative reaction to carbon dioxide. Teaching aid

A qualitative reaction for the detection of carbon dioxide is the turbidity of lime water:

Ca(OH)2 + CO2 = CaCO3↓ + H2O.

At the beginning of the reaction, a white precipitate is formed, which disappears when CO2 is passed through lime water for a long time, because. insoluble calcium carbonate is converted to soluble bicarbonate:

CaCO3 + H2O + CO2 = Ca(HCO3)2.

Receipt. Carbon dioxide is obtained by thermal decomposition of carbonic acid salts (carbonates), for example, limestone roasting:

CaCO3 = CaO + CO2,

or the action of strong acids on carbonates and bicarbonates:

CaCO3 + 2HCl = CaCl2 + H2O + CO2,

NaHCO3 + HCl = NaCl + H2O + CO2.

Emissions of carbon dioxide, sulfur compounds into the atmosphere as a result of industrial activities, the functioning of energy, metallurgical enterprises lead to the emergence of a greenhouse effect and the associated warming of the climate.

Scientists estimate global warming without action to reduce greenhouse gas emissions will be between 2 and 5 degrees over the next century, which will be unprecedented in the last ten thousand years. Climate warming, an increase in ocean level by 60-80 cm by the end of the next century will lead to an ecological catastrophe of unprecedented scale, which threatens the degradation of the human community.

Carbonic acid and its salts. Carbonic acid is very weak, exists only in aqueous solutions and slightly dissociates into ions. Therefore, aqueous solutions of CO2 have slightly acidic properties. Structural formula of carbonic acid:

As a dibasic, it dissociates in steps: H2CO3H++HCO-3 HCO-3H++CO2-3

When heated, it decomposes into carbon monoxide (IV) and water.

As a dibasic acid, it forms two types of salts: medium salts - carbonates, acidic salts - bicarbonates. They exhibit the general properties of salts. Carbonates and bicarbonates of alkali metals and ammonium are highly soluble in water.

Salts of carbonic acid- the compounds are stable, although the acid itself is unstable. They can be obtained by the interaction of CO2 with base solutions or by exchange reactions:

NaOH+CO2=NaHCO3

KHSO3+KOH=K2CO3+H2O

ВаСl2+Na2CO3=BaCO3+2NaCl

Alkaline earth metal carbonates are sparingly soluble in water. Bicarbonates, on the other hand, are soluble. Bicarbonates are formed from carbonates, carbon monoxide (IV) and water:

CaCO3 + CO2 + H2O \u003d Ca (HCO3) 2

When heated, alkali metal carbonates melt without decomposing, and the remaining carbonates, when heated, easily decompose into the oxide of the corresponding metal and CO2:

CaCO3=CaO+CO2

Bicarbonates, when heated, turn into carbonates:

2NaHCO3=Na2CO3+CO2+Н2О

Alkali metal carbonates in aqueous solutions have a strongly alkaline reaction due to hydrolysis:

Na2CO3+H2O=NaHCO3+NaOH

A qualitative reaction to the C2-3 carbonate ion and HCO-3 bicarbonate is their interaction with stronger acids. The release of carbon monoxide (IV) with a characteristic "boiling" indicates the presence of these ions.

CaCO3 + 2HCl \u003d CaCl2 + CO2 + H2O

Passing the released CO2 through lime water, one can observe the turbidity of the solution due to the formation of calcium carbonate:

Ca(OH)2+CO2=CaCO3+H2O

With a long passage of CO2, the solution becomes transparent again due to

hydrocarbonate formation: CaCO3 + H2O + CO2 = Ca (HCO3) 2

carbon dioxide (carbon dioxide), also called carbonic acid, is the most important component in the composition of carbonated drinks. It determines the taste and biological stability of drinks, gives them sparkling and refreshing properties.

Chemical properties. Chemically, carbon dioxide is inert. Formed with the release of a large amount of heat, it, as a product of the complete oxidation of carbon, is very stable. Carbon dioxide reduction reactions proceed only at high temperatures. So, for example, interacting with potassium at 230 ° C, carbon dioxide is reduced to oxalic acid:

Entering into chemical interaction with water, gas, in an amount of not more than 1% of its content in solution, forms carbonic acid, dissociating into ions H +, HCO 3 -, CO 2 3-. In an aqueous solution, carbon dioxide easily enters into chemical reactions, forming various carbonic salts. Therefore, an aqueous solution of carbon dioxide is highly aggressive towards metals, and also has a destructive effect on concrete.

physical properties. Carbon dioxide is used to saturate drinks, liquefied by compression to high pressure. Depending on temperature and pressure, carbon dioxide can also be in a gaseous or solid state. The temperature and pressure corresponding to a given state of aggregation are shown in the phase equilibrium diagram (Fig. 13).

At a temperature of minus 56.6 ° C and a pressure of 0.52 MN / m 2 (5.28 kg / cm 2), corresponding to the triple point, carbon dioxide can simultaneously be in a gaseous, liquid and solid state. At higher temperatures and pressures, carbon dioxide is in a liquid and gaseous state; at a temperature and pressure that are below these indicators, the gas, directly bypassing the liquid phase, passes into the gaseous state (sublimes). Above the critical temperature of 31.5°C, no amount of pressure can hold carbon dioxide as a liquid.

In the gaseous state, carbon dioxide is colorless, odorless and has a slightly sour taste. At a temperature of 0 ° C and atmospheric pressure, the density of carbon dioxide is 1.9769 kg / l 3; it is 1.529 times heavier than air. At 0°C and atmospheric pressure, 1 kg of gas occupies a volume of 506 liters. The relationship between the volume, temperature and pressure of carbon dioxide is expressed by the equation:

where V is the volume of 1 kg of gas in m 3 / kg; T is the gas temperature in °K; P - gas pressure in N / m 2; R is the gas constant; A is an additional value that takes into account the deviation from the equation of state of an ideal gas;

Liquefied carbon dioxide- a colorless, transparent, easily mobile liquid, resembling alcohol or ether in appearance. The density of a liquid at 0°C is 0.947. At a temperature of 20°C, the liquefied gas is stored at a pressure of 6.37 MN/m 2 (65 kg/cm 2) in steel cylinders. With free flow from the balloon, the liquid evaporates with the absorption of a large amount of heat. When the temperature drops to minus 78.5 ° C, part of the liquid freezes, turning into the so-called dry ice. In terms of hardness, dry ice is close to chalk and has a dull white color. Dry ice evaporates more slowly than liquid, and it directly turns into a gaseous state.

At a temperature of minus 78.9 ° C and a pressure of 1 kg / cm 2 (9.8 MN / m 2), the heat of sublimation of dry ice is 136.89 kcal / kg (573.57 kJ / kg).

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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 in three different ways (the exact ratio of each of these three modes of transport 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 levels in the blood or tissues usually do not stimulate respiration (or rather, the stimulating effect of lack of oxygen on respiration is too weak and “turns on” late, at very low blood oxygen levels, in which a person often is already losing 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 unconsciousness 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, breath, 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.

  Under 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, in equipment repair (for example: cooling one of the mating parts during tight fitting), etc. Carbon dioxide is used to liquefy carbon dioxide and produce dry ice. installation .

  Registration Methods

  Measurement of the partial pressure of carbon dioxide is required in technological processes, in medical applications - the analysis of respiratory mixtures during artificial ventilation of the lungs and in closed life support systems. The analysis of the concentration of CO 2 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.

  Let's imagine the following situation:

  You work in a lab and decide to do an experiment. To do this, you opened the cabinet with reagents and suddenly saw the following picture on one of the shelves. Two jars of reagents had their labels peeled off, which were safely left lying nearby. At the same time, it is no longer possible to determine exactly which jar corresponds to which label, and the external signs of the substances by which they could be distinguished are the same.

  In this case, the problem can be solved using the so-called qualitative reactions.

  Qualitative reactions called such reactions that allow you to distinguish one substance from another, as well as to find out the qualitative composition of unknown substances.

  For example, it is known that the cations of some metals, when their salts are added to the burner flame, color it in a certain color:

  This method can only work if the substances to be distinguished change the color of the flame in different ways, or one of them does not change color at all.

  But, let's say, as luck would have it, the substances you determine do not color the color of the flame, or color it in the same color.

  In these cases, it will be necessary to distinguish substances using other reagents.

  In what case can we distinguish one substance from another with the help of any reagent?

  There are two options:

  • One substance reacts with the added reagent, while the other does not. At the same time, it must be clearly visible that the reaction of one of the starting substances with the added reagent has really passed, that is, some external sign of it is observed - a precipitate has formed, a gas has been released, a color change has occurred, etc.

  For example, it is impossible to distinguish water from a sodium hydroxide solution using hydrochloric acid, despite the fact that alkalis react perfectly with acids:

  NaOH + HCl \u003d NaCl + H 2 O

  This is due to the absence of any external signs of a reaction. A transparent colorless solution of hydrochloric acid, when mixed with a colorless hydroxide solution, forms the same transparent solution:

  But on the other hand, water can be distinguished from an aqueous solution of alkali, for example, using a solution of magnesium chloride - a white precipitate forms in this reaction:

  2NaOH + MgCl 2 = Mg(OH) 2 ↓+ 2NaCl

  2) Substances can also be distinguished from each other if they both react with the added reagent, but do so in different ways.

  For example, a solution of sodium carbonate can be distinguished from a solution of silver nitrate using a solution of hydrochloric acid.

  hydrochloric acid reacts with sodium carbonate to release a colorless, odorless gas - carbon dioxide (CO 2):

  2HCl + Na 2 CO 3 \u003d 2NaCl + H 2 O + CO 2

  and with silver nitrate to form a white cheesy precipitate AgCl

  HCl + AgNO 3 \u003d HNO 3 + AgCl ↓

  The tables below show different options for detecting specific ions:

  Qualitative reactions to cations

  Cation	Reagent	Sign of reaction
  Ba 2+	SO 4 2-	Ba 2+ + SO 4 2- \u003d BaSO 4 ↓
  Cu2+		1) Precipitation of blue color: Cu 2+ + 2OH - \u003d Cu (OH) 2 ↓ 2) Precipitation of black color: Cu 2+ + S 2- \u003d CuS ↓
  Pb 2+	S2-	Precipitation of black color: Pb 2+ + S 2- = PbS↓
  Ag+	Cl-	Precipitation of a white precipitate, insoluble in HNO 3, but soluble in ammonia NH 3 H 2 O: Ag + + Cl − → AgCl↓
  Fe2+	2) Potassium hexacyanoferrate (III) (red blood salt) K 3	1) Precipitation of a white precipitate that turns green in air: Fe 2+ + 2OH - \u003d Fe (OH) 2 ↓ 2) Precipitation of a blue precipitate (turnbull blue): K + + Fe 2+ + 3- = KFe↓
  Fe3+	2) Potassium hexacyanoferrate (II) (yellow blood salt) K 4 3) Rhodanide ion SCN −	1) Precipitation of brown color: Fe 3+ + 3OH - \u003d Fe (OH) 3 ↓ 2) Precipitation of a blue precipitate (Prussian blue): K + + Fe 3+ + 4- = KFe↓ 3) The appearance of intense red (blood red) staining: Fe 3+ + 3SCN - = Fe(SCN) 3
  Al 3+	Alkali (hydroxide amphoteric properties)	Precipitation of a white precipitate of aluminum hydroxide when a small amount of alkali is added: OH - + Al 3+ \u003d Al (OH) 3 and its dissolution upon further addition: Al(OH) 3 + NaOH = Na
  NH4+	OH − , heating	Emission of gas with a pungent odor: NH 4 + + OH - \u003d NH 3 + H 2 O Blue wet litmus paper
  H+ (acid environment)	Indicators: − litmus − methyl orange	Red staining

  Qualitative reactions to anions

  Anion	Impact or reagent	Reaction sign. Reaction equation
  SO 4 2-	Ba 2+	Precipitation of a white precipitate, insoluble in acids: Ba 2+ + SO 4 2- \u003d BaSO 4 ↓
  NO 3 -	1) Add H 2 SO 4 (conc.) and Cu, heat 2) A mixture of H 2 SO 4 + FeSO 4	1) Formation of a blue solution containing Cu 2+ ions, brown gas evolution (NO 2) 2) The appearance of the color of nitroso-iron sulfate (II) 2+. Violet to brown color (brown ring reaction)
  PO 4 3-	Ag+	Precipitation of a light yellow precipitate in a neutral medium: 3Ag + + PO 4 3- = Ag 3 PO 4 ↓
  CrO 4 2-	Ba 2+	Precipitation of a yellow precipitate, insoluble in acetic acid, but soluble in HCl: Ba 2+ + CrO 4 2- = BaCrO 4 ↓
  S2-	Pb 2+	Black precipitation: Pb 2+ + S 2- = PbS↓
  CO 3 2-		1) Precipitation of a white precipitate, soluble in acids: Ca 2+ + CO 3 2- \u003d CaCO 3 ↓ 2) Emission of a colorless gas ("boiling"), causing the lime water to become cloudy: CO 3 2- + 2H + = CO 2 + H 2 O
  CO2	Lime water Ca(OH) 2	Precipitation of a white precipitate and its dissolution upon further passage of CO 2: Ca(OH) 2 + CO 2 = CaCO 3 ↓ + H 2 O CaCO 3 + CO 2 + H 2 O \u003d Ca (HCO 3) 2
  SO 3 2-	H+	SO 2 gas evolution with a characteristic pungent odor (SO 2): 2H + + SO 3 2- \u003d H 2 O + SO 2
  F-	Ca2+	Precipitation of a white precipitate: Ca 2+ + 2F - = CaF 2 ↓
  Cl-	Ag+	Precipitation of a white cheesy precipitate, insoluble in HNO 3 but soluble in NH 3 H 2 O (conc.): Ag + + Cl - = AgCl↓ AgCl + 2(NH 3 H 2 O) =) Did not find an answer to your question? Look at here Two heads and six legs; four walk, and two lie still Self-esteem - what is it: concept, structure, types and levels Cassandra's Path, or Pasta Adventures War on Earth and Underground