Molar volume. Amount of substance, mole. Molar mass. What have we learned

The amount of substance. Molar mass. Molar volume of gas. Avogadro's law
From the physics course, we know about such physical quantities as mass, volume and density. It is easy to characterize substances using these quantities. For example, we go to the store and buy 1 kg of sugar or a liter bottle of mineral water. But it turns out that these values ​​are not enough if it is necessary to consider the substance from the point of view of the number of particles. How many sugar molecules are there in 1 kg of sugar? How many water molecules are in a liter bottle? And in one drop? The answer to this question can be obtained if you know about another physical quantity, which is called the amount of matter. It is difficult to calculate the exact number of molecules, but if you count not in pieces, but in portions, then the task is simplified. For example, we never buy matches by the piece in a store, but having bought one portion of matches - boxes, we know that there are 100 pieces. And we do not buy napkins by the piece either, but having bought a pack of napkins, that is, a portion, we will know exactly how many pieces of napkins we bought.
The amount of a substance is a portion of a substance with a certain number of structural particles. The amount of a substance is usually denoted by the Greek letter ν [nu]. In the SI system, the unit for measuring the amount of a substance is called the mole. One mole of a substance contains the same number of structural particles as atoms are contained in 12 g of carbon, namely 6 * 1023 particles. This amount is constant and is called "Avogadro's constant". The amount of a substance can be defined as the ratio of the number of structural particles to the number of particles in one mole of the substance.
For example, the amount of a substance that corresponds to 3 * 1023 iron atoms can be easily calculated using this formula.
By transforming the original formula, it is easy to determine the number of structural particles by the known amount of substance: N = v * NA
This constant received its name in honor of Amedeo Avogadro, who in 1811 made an assumption, which was then experimentally confirmed and now bears the name of Avogadro's Law. Avogadro's law: "equal volumes of different gases under the same conditions (temperature and pressure) contain the same number of molecules."
It follows from Avogadro's law that under the same conditions, the masses of gases containing the same number of structural particles will occupy the same volume. At a pressure of 1 atmosphere and a temperature of 0 degrees Celsius, 1 mole of any gas occupies a volume of 22.4 liters. This volume is called molar volume. And conditions are normal conditions. The molar volume is denoted Vm, shows the volume of gas in the amount of 1 mol. Under normal conditions, it is constant.
Under normal conditions, the amount of a substance is the ratio of volume to molar volume.
Using this formula, you can determine the volume of a substance if its amount is known: V = ν * Vm
The mass of a substance in the amount of 1 mol is called molar mass, denoted by the letter M. Molar mass is numerically equal to the relative molecular mass. The unit of measure for molar mass is g / mol.
Knowing the mass of a substance, it is easy to determine the amount of a substance.

Let's find the amount of the substance 5.6 g of iron.
To find the mass of a substance by a known amount, we transform the formula: m = ν * M
Reference material
The amount of substance ν [nu] is a physical quantity that characterizes the number of structural units of the same type (any particles that make up a substance - atoms, molecules, ions, etc.) contained in a substance. The unit for measuring the amount of a substance in the International System of Units (SI) is mol.
A mole is a unit of measure for the amount of a substance. One mole of a substance contains as many structural particles as there are atoms in 12 g of carbon.
Molar mass (M) is the mass of a substance in the amount of one mole. The unit of measurement is g / mol.
Normal conditions (n.o.) - physical conditions determined by a pressure of 101325 Pa (normal atmosphere) and a temperature of 273.15 K (0 ° C).
Molar volume (Vm) - the volume of one mole of a substance. Unit of measurement l / mol; at n.u. Vm = 22.4 l / mol
Avogadro's law - equal volumes of different gases under the same conditions (temperature and pressure) contain the same number of molecules.
Avogadro's constant (NA) shows the number of structural particles in a substance in the amount of one mole.

Before solving problems, you should learn the formulas and rules for how to find the volume of gas. Remember Avogadro's law. And the gas volume itself can be calculated using several formulas, choosing the appropriate one from them. When choosing the required formula, environmental conditions, in particular temperature and pressure, are of great importance.

Avogadro's law

It says that at the same pressure and the same temperature, in the same volumes of different gases, the same number of molecules will be contained. The number of gas molecules contained in one mole is Avogadro's number. It follows from this law that: 1 Kmole (kilomole) of an ideal gas, and any, at the same pressure and temperature (760 mm Hg and t = 0 * C) always occupies one volume = 22.4136 m3.

How to determine the volume of gas

• The formula V = n * Vm is most often found in problems. Here the volume of gas in liters is V, Vm is the molar volume of gas (l / mol), which under normal conditions = 22.4 l / mol, and n is the amount of substance in moles. When there is no amount of matter under the conditions, but there is a mass of matter, then we do this: n = m / M. Here M is g / mol (molar mass of a substance), and the mass of a substance in grams is m. In the periodic table, it is written under each element, as its atomic mass. Let's add all the masses and get the desired one.
• So how to calculate the gas volume. Here's the problem: dissolve 10 g of aluminum in hydrochloric acid. Question: how much hydrogen can be released during n. at.? The reaction equation looks like this: 2Al + 6HCl (ex) = 2AlCl3 + 3H2. At the very beginning, we find aluminum (amount), which has reacted according to the formula: n (Al) = m (Al) / M (Al). We take the mass of aluminum (molar) from the periodic table M (Al) = 27g / mol. Substitute: n (Al) = 10/27 = 0.37 mol. It can be seen from the chemical equation that 3 moles of hydrogen were formed by dissolving 2 moles of aluminum. It is necessary to calculate how much hydrogen will be released from 0.4 mol of aluminum: n (H2) = 3 * 0.37 / 2 = 0.56 mol. Let's substitute the data into the formula and find the volume of this gas. V = n * Vm = 0.56 * 22.4 = 12.54 liters.

The mass of 1 mol of a substance is called molar. And what is the volume of 1 mole of a substance called? Obviously, this is also called the molar volume.

What is the molar volume of water? When we measured out 1 mole of water, we did not weigh 18 g of water on a scale - this is inconvenient. We used measuring dishes: a cylinder or a beaker, because we knew that the density of water is 1 g / ml. Therefore, the molar volume of water is 18 ml / mol. For liquids and solids, the molar volume depends on their density (Fig. 52, a). Gases are a different matter (Fig. 52, b).

Rice. 52.
Molar volumes (n.a.):
a - liquids and solids; b - gaseous substances

If we take 1 mole of hydrogen H 2 (2 g), 1 mole of oxygen O 2 (32 g), 1 mole of ozone O 3 (48 g), 1 mole of carbon dioxide CO 2 (44 g) and even 1 mole of water vapor H 2 O (18 g) under the same conditions, for example, normal (in chemistry it is customary to call the temperature 0 ° C and the pressure 760 mm Hg, or 101.3 kPa), it turns out that 1 mol any of the gases will occupy the same volume, equal to 22.4 liters, and contain the same number of molecules - 6 × 10 23.

And if you take 44.8 liters of gas, then how much of its substance will be taken? Of course, 2 mol, since the given volume is twice the molar volume. Hence:

where V is the gas volume. From here

Molar volume is a physical quantity equal to the ratio of the volume of a substance to the amount of a substance.

The molar volume of gaseous substances is expressed in l / mol. Vm - 22.4 l / mol. The volume of one kilomole is called kilomolar and is measured in m 3 / kmol (Vm = 22.4 m 3 / kmol). Accordingly, the millimolar volume is 22.4 ml / mmol.

Problem 1. Find the mass of 33.6 m 3 of ammonia NH 3 (n. At.).

Problem 2. Find the mass and volume (n.v.) that 18 × 10 20 molecules of hydrogen sulfide H 2 S have.

When solving the problem, let us pay attention to the number of molecules 18 × 10 20. Since 10 20 is 1000 times less than 10 23, it is obvious that calculations should be carried out using mmol, ml / mmol and mg / mmol.

Key words and phrases

1. Molar, millimolar and kilomolar volumes of gases.
2. The molar volume of gases (under normal conditions) is 22.4 l / mol.
3. Normal conditions.

Work with computer

1. Please refer to the electronic attachment. Study the lesson material and complete the proposed tasks.
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Questions and tasks

1. Find the mass and number of molecules at n. at. for: a) 11.2 liters of oxygen; b) 5.6 m 3 nitrogen; c) 22.4 ml of chlorine.
2. Find the volume that is at n. at. will take: a) 3 g of hydrogen; b) 96 kg of ozone; c) 12 × 10 20 nitrogen molecules.
3. Find the density (mass of 1 liter) of argon, chlorine, oxygen and ozone at n. at. How many molecules of each substance will be contained in 1 liter under the same conditions?
4. Calculate the mass of 5 l (n. At.): A) oxygen; b) ozone; c) carbon dioxide CO 2.
5. Indicate which is heavier: a) 5 liters of sulfur dioxide (SO 2) or 5 liters of carbon dioxide (CO 2); b) 2 liters of carbon dioxide (CO 2) or 3 liters of carbon monoxide (CO).

The molar volume of a gas is equal to the ratio of the volume of the gas to the amount of the substance of this gas, i.e.

V m = V (X) / n (X),

where V m - molar volume of gas - constant for any gas under the given conditions;

V (X) - gas volume X;

n (X) is the amount of substance in gas X.

The molar volume of gases under normal conditions (normal pressure p n = 101 325 Pa ≈ 101.3 kPa and temperature T n = 273.15 K ≈ 273 K) is V m = 22.4 l / mol.

The laws of ideal gases

In calculations related to gases, it is often necessary to move from given conditions to normal conditions, or vice versa. In this case, it is convenient to use the formula following from the combined gas law of Boyle-Mariotte and Gay-Lussac:

pV / T = p n V n / T n

Where p is the pressure; V is the volume; T is the temperature on the Kelvin scale; the subscript "n" indicates normal conditions.

Volume fraction

The composition of gas mixtures is often expressed using the volume fraction - the ratio of the volume of a given component to the total volume of the system, i.e.

φ (X) = V (X) / V

where φ (X) is the volume fraction of the X component;

V (X) is the volume of the X component;

V is the volume of the system.

The volume fraction is a dimensionless quantity, it is expressed in fractions of a unit or as a percentage.

Example 1. What volume will ammonia weighing 51 g take at a temperature of 20 ° C and a pressure of 250 kPa?

Example 2. Determine the volume that will take under normal conditions a gas mixture containing hydrogen, weighing 1.4 g and nitrogen, weighing 5.6 g.

Volumetric relationship law

How to solve the problem using the "Law of Volumetric Relations"?

The law of volumetric ratios: the volumes of gases involved in the reaction are related to each other as small whole numbers equal to the coefficients in the reaction equation.

The coefficients in the reaction equations show the number of volumes of reacting and formed gaseous substances.

Example. Calculate the volume of air required to burn 112 liters of acetylene.

1. We compose the reaction equation:

2. Based on the law of volumetric ratios, we calculate the volume of oxygen:

112/2 = X / 5, whence X = 112 5/2 = 280 liters

3. Determine the volume of air:

V (air) = V (O 2) / φ (O 2)

V (air) = 280 / 0.2 = 1400 liters.

Target:
To acquaint students with the concepts of "amount of substance", "molar mass" to give an idea of ​​the Avogadro constant. Show the relationship between the amount of matter, the number of particles and Avogadro's constant, as well as the relationship between molar mass, mass and amount of matter. To teach how to make calculations.

1) What is the amount of a substance?
2) What is a mole?
3) How many structural units are there in 1 mole?
4) What quantities can be used to determine the amount of a substance?
5) What is molar mass, with which it numerically coincides?
6) What is molar volume?

The amount of a substance is a physical quantity that means a certain number of structural elements (molecules, atoms, ions). It is designated n (en) is measured in the international system of units (Cu) mol
Avogadro's number - shows the number of particles in 1 mol of a substance Denoted NA is measured in mol-1 has a numerical value of 6.02 * 10 ^ 23
The molar mass of a substance is numerically equal to its relative molecular mass. Molar mass is a physical quantity that shows the mass in 1 mole of a substance. It is denoted M is measured in g / mol M = m / n
Molar volume is a physical quantity that shows the volume that any gas occupies with the amount of a substance 1 mol. Vm is denoted in l / mol. Vm = V / n. Vm = 22.4 l / mol
Mole is the AMOUNT of SUBSTANCE equal to 6.02. 10 23 structural units of a given substance - molecules (if the substance consists of molecules), atoms (if it is an atomic substance), ions (if the substance is an ionic compound).
1 mol (1 M) water = 6 . 10 23 molecules Н 2 О,

1 mole (1 M) iron = 6 . 10 23 Fe atoms,

1 mol (1 M) chlorine = 6 . 10 23 molecules of Cl 2,

1 mol (1 M) chlorine ions Cl - = 6 . 10 23 Cl ions -.

1 mol (1 M) electrons e - = 6 . 10 23 electrons e -.

Tasks:
1) How many moles of oxygen are there in 128 g of oxygen?

2) With lightning discharges in the atmosphere, the following reaction occurs: N 2 + O 2 ® NO 2. Equalize your reaction. How many moles of oxygen is required for the complete conversion of 1 mole of nitrogen to NO 2? How many grams of oxygen will it be? How many grams of NO 2 are formed?

3) 180 g of water was poured into a glass. How many water molecules are there in a glass? How many moles of H 2 O are these?

4) 4 g of hydrogen and 64 g of oxygen were mixed. The mixture was blown up. How many grams of water did you get? How many grams of oxygen are left unused?

Homework: paragraph 15, exercise. 1-3.5

Molar volume of gaseous substances.
Target: educational - to systematize the knowledge of students about the concepts of the amount of substance, Avogadro's number, molar mass, on their basis to form an idea of ​​the molar volume of gaseous substances; to reveal the essence of Avogadro's law and its practical application;

developing - to form the ability for adequate self-control and self-esteem; develop the ability to think logically, put forward hypotheses, draw reasoned conclusions.

During the classes:
1. Organizational moment.
2.Announcement of the topic and objectives of the lesson.

3. Updating basic knowledge
4.Solving problems

Avogadro's law- this is one of the most important laws of chemistry (formulated by Amadeo Avogadro in 1811), stating that "in equal volumes of different gases, which are taken at the same pressure and temperature, contain the same number of molecules."

Molar volume of gases- the volume of gas containing 1 mole of particles of this gas.

Normal conditions- temperature 0 С (273 K) and pressure 1 atm (760 mm Hg or 101 325 Pa).

Answer the questions:

1. What is called an atom? (An atom is the smallest chemically indivisible part of a chemical element, which is the carrier of its properties).

2. What is a mole? (A mole is the amount of a substance, which is equal to 6.02.10 ^ 23 structural units of this substance - molecules, atoms, ions. This is the amount of a substance containing as many particles as there are atoms in 12 g of carbon).

3. How is the amount of a substance measured? (In a mole).

4. How is the mass of a substance measured? (The mass of a substance is measured in grams).

5. What is molar mass and how is it measured? (Molar mass is the mass of 1 mol of a substance. It is measured in g / mol).

Consequences of Avogadro's law.

Two consequences follow from Avogadro's law:

1. One mole of any gas occupies the same volume under the same conditions. In particular, under normal conditions, i.e. at 0 ° C (273K) and 101.3 kPa, the volume of 1 mole of gas is 22.4 liters. This volume is called the molar volume of the gas Vm. It is possible to recalculate this value for other temperature and pressure using the Mendeleev-Clapeyron equation (Figure 3).

The molar volume of a gas under normal conditions is a fundamental physical constant widely used in chemical calculations. It allows you to use the volume of the gas instead of its mass. The value of the molar volume of gas at normal conditions. is the coefficient of proportionality between the Avogadro and Loschmidt constants

2. The molar mass of the first gas is equal to the product of the molar mass of the second gas by the relative density of the second of the first gas. This position was of great importance for the development of chemistry, since it made it possible to determine the partial weight of bodies that are capable of passing into a vaporous or gaseous state. Consequently, the ratio of the mass of a certain volume of one gas to the mass of the same volume of another gas taken under the same conditions is called the density of the first gas for the second

1. Fill in the blanks:

Molar volume is a physical quantity that shows ....................., denoted by .................. .., measured in .......................

2. Write down the formula according to the rule.

The volume of a gaseous substance (V) is equal to the product of the molar volume

(Vm) for the amount of substance (n) ..............................

3. Using the material of task 3, deduce formulas for calculation:

a) the volume of the gaseous substance.

b) molar volume.

Homework: paragraph 16, exercise. 1-5

Solving problems for calculating the amount of matter, mass and volume.

Generalization and systematization of knowledge on the topic "Simple substances"
Target: to generalize and systematize the knowledge of students about the main classes of compounds
Progress:

1) Organizational moment

2) Generalization of the studied material:

a) Oral questioning on the topic of the lesson

b) Fulfillment of task 1 (finding oxides, bases, acids, salts among the given substances)

c) Fulfillment of task 2 (drawing up formulas of oxides, bases, acids, salts)

3. Fastening (independent work)

5. Homework

2)
a)
- What two groups can be divided into substances?

What substances are called simple?

What are the two groups of simple substances?

What substances are called complex?

What complex substances are known?

What substances are called oxides?

What substances are called bases?

What substances are called acids?

What substances are called salts?

b)
Write out separately oxides, bases, acids, salts:

KOH, SO 2, HCI, BaCI 2, P 2 O 5,

NaOH, CaCO 3, H 2 SO 4, HNO 3,

MgO, Ca (OH) 2, Li 3 PO 4

Name them.

v)
Draw up the formulas of oxides corresponding to bases and acids:

Potassium hydroxide-potassium oxide

Iron (III) hydroxide - iron (III) oxide

Phosphoric acid-phosphorus (V) oxide

Sulfuric acid - sulfur (VI) oxide

Formulate the barium nitrate salt; by ion charges, oxidation states of elements, write down

formulas of the corresponding hydroxides, oxides, simple substances.

1. The oxidation state of sulfur is +4 in the compound:

2. The substance belongs to oxides:

3. Formula of sulfurous acid:

4. The base is a substance:

5. Salt K 2 CO 3 is called:

1- potassium silicate

2- potassium carbonate

3- potassium carbide

4- calcium carbonate

6. In a solution of what substance the litmus will change its color to red:

2- in alkali

3- in acid

Homework: Review paragraphs 13-16

Examination work No. 2
"Simple substances"

Oxidation state: binary compounds

Purpose: to teach how to draw up molecular formulas of substances consisting of two elements according to the oxidation state. continue strengthening the skill of determining the oxidation state of an element by the formula.
1. The oxidation state (s. O.) Is the conditional charge of atoms of a chemical element in a complex substance, calculated on the basis of the assumption that it consists of simple ions.

You should know!

1) In connections with. O. hydrogen = +1, except for hydrides.
2) In connections with. O. oxygen = -2, except for peroxides and fluorides
3) The oxidation state of metals is always positive.

For metals of the main subgroups of the first three groups with. O. constant:
Group IA metals - p. O. = +1,
Group IIA metals - p. O. = +2,
Group IIIA metals - p. O. = +3.
4) For free atoms and simple substances p. O. = 0.
5) Total s. O. all elements in the compound = 0.

2. The way names are formed two-element (binary) compounds.

3.

Tasks:
Make formulas of substances by name.

How many molecules are there in 48 g of sulfur (IV) oxide?

The oxidation state of manganese in the K2MnO4 compound is:

Chlorine exhibits the maximum oxidation state in a compound, the formula of which is:

Homework: paragraph 17, exercise. 2,5,6

Oxides. Volatile hydrogen compounds.
Target: formation of knowledge among students about the most important classes of binary compounds - oxides and volatile hydrogen compounds.

Questions:
- What substances are called binary?
- What is called the oxidation state?
- What oxidation state will the elements have if they donate electrons?
- What oxidation state will the elements have if they accept electrons?
- How to determine how many electrons will give or receive elements?
- What is the oxidation state of single atoms or molecules?
- What will the compounds be called if sulfur is in second place in the formula?
- What will the compounds be called if chlorine is in second place in the formula?
- What will the compounds be called if hydrogen is in second place in the formula?
- What will the compounds be called if nitrogen is in second place in the formula?
- What will the compounds be called if oxygen is in second place in the formula?
Learning a new topic:
- What do these formulas have in common?
- What will be the name of such substances?

SiO 2, H 2 O, CO 2, AI 2 O 3, Fe 2 O 3, Fe 3 O 4, CO.
Oxides- a class of inorganic compounds widespread in nature. Oxides include such well-known compounds as:

Sand (silicon dioxide SiO2 with a small amount of impurities);

Water (hydrogen oxide H2O);

Carbon dioxide (carbon dioxide CO2 IV);

Carbon monoxide (CO II carbon monoxide);

Clay (aluminum oxide AI2O3 with a small amount of other compounds);

Most ferrous metal ores contain oxides, for example, red iron ore - Fe2O3 and magnetic iron ore - Fe3O4.

Volatile hydrogen compounds- the most practically important group of compounds with hydrogen. These include substances commonly found in nature or used in industry, such as water, methane and other hydrocarbons, ammonia, hydrogen sulfide, and hydrogen halides. Many of the volatile hydrogen compounds are found in the form of solutions in soil waters, in living organisms, as well as in gases formed during biochemical and geochemical processes; therefore, their biochemical and geochemical role is very important.
Depending on the chemical properties, a distinction is made between:

Salt-forming oxides:

o basic oxides (for example, sodium oxide Na2O, copper (II) oxide CuO): metal oxides, the oxidation state of which is I-II;

o acid oxides (for example, sulfur oxide (VI) SO3, nitrogen oxide (IV) NO2): metal oxides with the oxidation state V-VII and nonmetal oxides;

o amphoteric oxides (for example, zinc oxide ZnO, aluminum oxide Al2O3): metal oxides with oxidation states III-IV and exceptions (ZnO, BeO, SnO, PbO);

Non-salt-forming oxides: carbon monoxide (II) CO, nitrogen oxide (I) N2O, nitrogen oxide (II) NO, silicon oxide (II) SiO.

Homework: paragraph 18, exercises 1, 4, 5

Foundations.
Target:
to acquaint students with the composition, classification and representatives of the class of grounds

continue the formation of knowledge about ions on the example of complex hydroxide ions

continue the formation of knowledge about the oxidation state of elements, chemical bonds in substances;

to give an idea of ​​the qualitative reactions and indicators;

develop skills in handling chemical utensils and reagents;

to form a respectful attitude towards their health.

In addition to binary compounds, there are complex substances, for example, bases, which consist of three elements: metal, oxygen and hydrogen.
Hydrogen and oxygen are included in them in the form of OH - hydroxo group. Consequently, the OH- hydroxo group is an ion, but not a simple one like Na + or Cl-, but a complex OH- - hydroxide ion.

Foundations are complex substances consisting of metal ions and one or more hydroxide ions associated with them.
If the charge of the metal ion is 1+, then, of course, one hydroxo group OH- is associated with the metal ion, if 2+, then two, etc. Therefore, the composition of the base can be written by the general formula: M (OH) n, where M is the metal , m is the number of OH groups and at the same time the charge of the ion (oxidation state) of the metal.

Base names are composed of the word hydroxide and the name of the metal. For example, Na0H is sodium hydroxide. Ca (0H) 2 - calcium hydroxide.
If the metal exhibits a variable oxidation state, then its value, as well as for binary compounds, is indicated with a Roman numeral in brackets and pronounced at the end of the base name, for example: CuOH - copper (I) hydroxide, read "copper hydroxide one"; Cr (OH), - copper (II) hydroxide, reads "copper hydroxide two".

In relation to water, the bases are divided into two groups: soluble NaOH, Ca (OH) 2, K0H, Ba (OH)? and insoluble Cr (OH) 7, Re (OH) 2. Soluble bases are also called alkalis. You can find out whether a base is soluble or insoluble in water using the table "Solubility of bases, acids and salts in water".

Sodium hydroxide NaOH- a solid white substance, hygroscopic and therefore diffuse in air; dissolves well in water, while generating heat. A solution of sodium hydroxide in water is soapy to the touch and very corrosive. It is corrosive to leather, textiles, paper and other materials. For this property, sodium hydroxide is called caustic soda. Sodium hydroxide and its solutions must be handled with care, fearing that they do not get on clothes, shoes, and even more so on hands and face. On the skin from this substance, wounds that do not heal for a long time are formed. NaOH is used in soap making, leather and pharmaceutical industries.

Potassium hydroxide KOH- also a solid white substance, readily soluble in water, with the release of a large amount of heat. Potassium hydroxide solution, like sodium hydroxide solution, is soapy to the touch and very caustic. Therefore, potassium hydroxide is otherwise called caustic potassium. It is used as an additive in the production of soap, refractory glass.

Calcium hydroxide Ca (OH) 2 or slaked lime, is a loose white powder, slightly soluble in water (in the solubility table against the Ca (OH) formula, there is the letter M, which means a slightly soluble substance). It is obtained by the interaction of CaO quicklime with water. This process is called quenching. Calcium hydroxide is used in construction for masonry and plastering of walls, for whitewashing trees, for obtaining bleach, which is a disinfectant.

The clear calcium hydroxide solution is called lime water. When CO2 is passed through lime water, it becomes cloudy. This experience serves to recognize carbon dioxide.

The reactions that recognize certain chemicals are called qualitative reactions.

For alkalis, there are also qualitative reactions, with the help of which solutions of alkalis can be recognized among solutions of other substances. These are the reactions of alkalis with special substances - indicators (lat. "Pointers"). If you add a few drops of the indicator solution to the alkali solution, then it will change its color

Homework: paragraph 19, exercises 2-6, table 4