What is the qualitative reaction to carbon dioxide. Physical and chemical properties of carbon dioxide

Carbon dioxide, carbon monoxide, carbon dioxide - all these are names for one substance known to us as carbon dioxide. So what properties does this gas have, and what are its areas of application?

Carbon dioxide and its physical properties

Carbon dioxide consists of carbon and oxygen. The formula for carbon dioxide looks like this – CO₂. In nature, it is formed during the combustion or decay of organic substances. The gas content in the air and mineral springs is also quite high. In addition, humans and animals also emit carbon dioxide when they exhale.

Rice. 1. Carbon dioxide molecule.

Carbon dioxide is a completely colorless gas and cannot be seen. It also has no smell. However, with high concentrations, a person may develop hypercapnia, that is, suffocation. Lack of carbon dioxide can also cause health problems. As a result of a lack of this gas, the opposite condition to suffocation can develop - hypocapnia.

If you place carbon dioxide in low temperature conditions, then at -72 degrees it crystallizes and becomes like snow. Therefore, carbon dioxide in a solid state is called “dry snow”.

Rice. 2. Dry snow – carbon dioxide.

Carbon dioxide is 1.5 times denser than air. Its density is 1.98 kg/m³. The chemical bond in the carbon dioxide molecule is polar covalent. It is polar due to the fact that oxygen has a higher electronegativity value.

An important concept in the study of substances is molecular and molar mass. The molar mass of carbon dioxide is 44. This number is formed from the sum of the relative atomic masses of the atoms that make up the molecule. The values ​​of relative atomic masses are taken from the table of D.I. Mendeleev and are rounded to whole numbers. Accordingly, the molar mass of CO₂ = 12+2*16.

To calculate the mass fractions of elements in carbon dioxide, it is necessary to follow the formula for calculating the mass fractions of each chemical element in a substance.

n– number of atoms or molecules.
A r– relative atomic mass of a chemical element.
Mr– relative molecular mass of the substance.
Let's calculate the relative molecular mass of carbon dioxide.

Mr(CO₂) = 14 + 16 * 2 = 44 w(C) = 1 * 12 / 44 = 0.27 or 27% Since the formula of carbon dioxide includes two oxygen atoms, then n = 2 w(O) = 2 * 16 / 44 = 0.73 or 73%

Answer: w(C) = 0.27 or 27%; w(O) = 0.73 or 73%

Chemical and biological properties of carbon dioxide

Carbon dioxide has acidic properties because it is an acidic oxide, and when dissolved in water it forms carbonic acid:

CO₂+H₂O=H₂CO₃

Reacts with alkalis, resulting in the formation of carbonates and bicarbonates. This gas does not burn. Only certain active metals, such as magnesium, burn in it.

When heated, carbon dioxide breaks down into carbon monoxide and oxygen:

2CO₃=2CO+O₃.

Like other acidic oxides, this gas easily reacts with other oxides:

СaO+Co₃=CaCO₃.

Carbon dioxide is part of all organic substances. The circulation of this gas in nature is carried out with the help of producers, consumers and decomposers. In the process of life, a person produces approximately 1 kg of carbon dioxide per day. When we inhale, we receive oxygen, but at this moment carbon dioxide is formed in the alveoli. At this moment, an exchange occurs: oxygen enters the blood, and carbon dioxide comes out.

Carbon dioxide is produced during the production of alcohol. This gas is also a by-product in the production of nitrogen, oxygen and argon. The use of carbon dioxide is necessary in the food industry, where carbon dioxide acts as a preservative, and carbon dioxide in liquid form is found in fire extinguishers.

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 breaks down into its components, i.e. The reaction between carbon dioxide and 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 = 2CO + O 2.

Like all acidic oxides, carbon dioxide is characterized by reactions of interaction with basic oxides (formed only by active metals) and bases:

CaO + CO 2 = CaCO 3;

Al 2 O 3 + 3CO 2 = Al 2 (CO 3) 3;

CO 2 + NaOH (dilute) = NaHCO 3;

CO 2 + 2NaOH (conc) = Na 2 CO 3 + H 2 O.

Carbon dioxide does not support combustion; only active metals burn in it:

CO 2 + 2Mg = C + 2MgO (t);

CO 2 + 2Ca = C + 2CaO (t).

Carbon dioxide reacts with simple substances such as hydrogen and carbon:

CO 2 + 4H 2 = CH 4 + 2H 2 O (t, kat = Cu 2 O);

CO 2 + C = 2CO (t).

When carbon dioxide reacts with peroxides of active metals, carbonates are formed and oxygen is released:

2CO 2 + 2Na 2 O 2 = 2Na 2 CO 3 + O 2.

A qualitative reaction to carbon dioxide is the reaction of its interaction with lime water (milk), i.e. with calcium hydroxide, in which a white precipitate is formed - calcium carbonate:

CO 2 + Ca(OH) 2 = CaCO 3 ↓ + H 2 O.

Physical properties of carbon dioxide

Carbon dioxide is a gaseous substance without color or odor. Heavier than air. Thermally stable. When compressed and cooled, it easily transforms into liquid and solid states. Carbon dioxide in a solid aggregate state is called “dry ice” and easily sublimes at room temperature. Carbon dioxide is poorly soluble in water and partially reacts with it. Density – 1.977 g/l.

Production and use of carbon dioxide

There are industrial and laboratory methods for producing carbon dioxide. Thus, in industry it is obtained by burning limestone (1), and in the laboratory by the action of strong acids on carbonic acid salts (2):

CaCO 3 = CaO + CO 2 (t) (1);

CaCO 3 + 2HCl = CaCl 2 + CO 2 + H 2 O (2).

Carbon dioxide is used in the food (carbonating lemonade), chemical (temperature control in the production of synthetic fibers), metallurgical (environmental protection, such as brown gas precipitation) and other industries.

Examples of problem solving

EXAMPLE 1

A qualitative reaction for detecting 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 turns into soluble bicarbonate:

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

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

CaCO3 = CaO + CO2,

or by the action of strong acids on carbonates and bicarbonates:

CaCO3 + 2HCl = CaCl2 + H2O + CO2,

NaHCO3 + HCl = NaCl + H2O + CO2.

Carbon emissions, sulfur compounds into the atmosphere as a result of industrial activity, the functioning of energy and metallurgical enterprises lead to the occurrence of the greenhouse effect and associated climate warming.

Scientists estimate that global warming without measures to reduce greenhouse gas emissions will range from 2 to 5 degrees over the next century, which will be an unprecedented phenomenon in the last ten thousand years. Climate warming and an increase in sea level by 60-80 cm by the end of the next century will lead to an environmental disaster 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 stepwise: 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, acid salts - bicarbonates. They exhibit the general properties of salts. Carbonates and bicarbonates of alkali metals and ammonium are highly soluble in water.

Carbonic acid salts- the compounds are stable, although the acid itself is unstable. They can be obtained by reacting CO2 with solutions of bases or by exchange reactions:

NaOH+CO2=NaHCO3

KHCO3+KOH=K2CO3+H2O

BaCl2+Na2CO3=BaCO3+2NaCl

Carbonates of alkaline earth metals are slightly soluble in water. Hydrocarbonates, on the other hand, are soluble. Hydrocarbonates are formed from carbonates, carbon monoxide (IV) and water:

CaCO3+CO2+H2O=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

When heated, hydrocarbonates turn into carbonates:

2NaHCO3=Na2CO3+CO2+H2O

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

Na2CO3+H2O=NaHCO3+NaOH

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

CaCO3+2HCl=CaCl2+CO2+H2O

By passing the released CO2 through lime water, you can observe the solution becoming cloudy due to the formation of calcium carbonate:

Ca(OH)2+CO2=CaCO3+H2O

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

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

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 k = 2. According to the Gibbs phase rule, the number of degrees of freedom of the system will be equal to

C = 2 + 2 – 2 = 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 Le Chatelier's principle, an increase in temperature shifts the equilibrium of the reaction in the direction of the formation of additional amount of CO.

When reaction (2.1) occurs, 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:

1. 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 the formation of CO 2.
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, we can assume with sufficient accuracy that the change in the volume of interacting substances is determined only by the number of moles of gaseous substances on the right and left sides of the reaction equation.

The equilibrium constant of reaction (2.1) is determined from the expression

If we take graphite as the standard state when determining the activity of carbon, then a C = 1

The numerical value of the equilibrium constant of reaction (2.1) can be determined from the equation

Data on the effect of temperature on the value of the reaction equilibrium constant 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 is clear that at a temperature of about 1000K (700 o C) the equilibrium constant of the reaction is close to unity. This means that in the region of moderate temperatures, reaction (2.1) is almost completely reversible. At high temperatures the reaction proceeds irreversibly towards the formation of CO, 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 volume 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 the air or blast enriched with oxygen. At the same time, another component appears in the system - nitrogen. The introduction of nitrogen into the gas mixture affects the ratio of the equilibrium concentrations of CO and CO 2 in a similar way to a decrease in pressure.

From equation (2.6) it is clear that the composition of the equilibrium gas mixture is a function of temperature and pressure. Therefore, the solution to equation (2.6) is graphically interpreted using a surface in three-dimensional space in coordinates T, Ptot and (%CO). The perception of such dependence is difficult. It is much more convenient to depict it in the form of a dependence of the composition of an equilibrium mixture of gases on one of the variables, with the second of the system parameters being constant. As an example, Figure 2.1 shows data on the effect of temperature on the composition of the equilibrium gas mixture at Ptot = 10 5 Pa.

Given the known initial composition of the gas mixture, one can judge the direction of reaction (2.1) 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, points above the equilibrium curve characterize systems whose approach to the state of thermodynamic equilibrium proceeds through the reaction

Similarly, it can be shown that points below the equilibrium curve characterize systems that approach the equilibrium state by reaction

Let's imagine this situation:

You are working in a laboratory and have decided to conduct 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 and safely remained 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 These are reactions that make it possible to distinguish one substance from another, as well as to find out the qualitative composition of unknown substances.

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

This method can only work if the substances being distinguished change the color of the flame differently, or one of them does not change color at all.

But, let’s say, as luck would have it, the substances being determined do not color the flame, or color it 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 using any reagent?

There are two options:

• One substance reacts with the added reagent, but the second does not. In this case, it must be clearly visible that the reaction of one of the starting substances with the added reagent actually took place, that is, some external sign of it is observed - a precipitate formed, a gas was released, a color change occurred, etc.

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

NaOH + HCl = NaCl + H2O

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

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

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, you can distinguish a sodium carbonate solution from a silver nitrate solution using a hydrochloric acid solution.

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

2HCl + Na 2 CO 3 = 2NaCl + H 2 O + CO 2

and with silver nitrate to form a white cheesy precipitate AgCl

HCl + AgNO 3 = HNO 3 + AgCl↓

The tables below present various options for detecting specific ions:

Qualitative reactions to cations

Qualitative reactions to anions

Anion	Impact or reagent	Sign of reaction. Reaction equation
SO 4 2-	Ba 2+	Precipitation of a white precipitate, insoluble in acids: Ba 2+ + SO 4 2- = BaSO 4 ↓
NO 3 −	1) Add H 2 SO 4 (conc.) and Cu, heat 2) Mixture of H 2 SO 4 + FeSO 4	1) Formation of a blue solution containing Cu 2+ ions, release of brown gas (NO 2) 2) The appearance of color of nitroso-iron (II) sulfate 2+. Color ranges from violet to brown (brown ring reaction)
PO 4 3-	Ag+	Precipitation of a light yellow precipitate in a neutral environment: 3Ag + + PO 4 3- = Ag 3 PO 4 ↓
CrO 4 2-	Ba 2+	Formation of a yellow precipitate, insoluble in acetic acid, but soluble in HCl: Ba 2+ + CrO 4 2- = BaCrO 4 ↓
S 2-	Pb 2+	Black precipitate: Pb 2+ + S 2- = PbS↓
CO 3 2-		1) Precipitation of a white precipitate, soluble in acids: Ca 2+ + CO 3 2- = CaCO 3 ↓ 2) The release of colorless gas (“boiling”), causing cloudiness of lime water: CO 3 2- + 2H + = CO 2 + H 2 O
CO2	Lime water Ca(OH) 2	Precipitation of a white precipitate and its dissolution with further passage of CO 2: Ca(OH) 2 + CO 2 = CaCO 3 ↓ + H 2 O CaCO 3 + CO 2 + H 2 O = Ca(HCO 3) 2
SO 3 2-	H+	Emission of SO 2 gas with a characteristic pungent odor (SO 2): 2H + + SO 3 2- = H 2 O + SO 2
F −	Ca2+	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) = ) Latest materials in the section: