DEFINITION

Water- hydrogen oxide is a binary compound of inorganic nature.

Formula - H 2 O. Molar mass - 18 g / mol. It can exist in three states of aggregation - liquid (water), solid (ice) and gaseous (water vapor).

Chemical properties of water

Water is the most common solvent. There is an equilibrium in a solution of water, therefore water is called ampholyte:

H 2 O ↔ H + + OH - ↔ H 3 O + + OH -.

Under the action of an electric current, water decomposes into hydrogen and oxygen:

H 2 O = H 2 + O 2.

At room temperature, water dissolves active metals with the formation of alkalis, while hydrogen also evolves:

2H 2 O + 2Na = 2NaOH + H 2.

Water is capable of interacting with fluorine and interhalogen compounds, and in the second case, the reaction proceeds at low temperatures:

2H 2 O + 2F 2 = 4HF + O 2.

3H 2 O + IF 5 = 5HF + HIO 3.

Salts formed by a weak base and a weak acid undergo hydrolysis when dissolved in water:

Al 2 S 3 + 6H 2 O = 2Al (OH) 3 ↓ + 3H 2 S.

Water is able to dissolve some substances, metals and non-metals when heated:

4H 2 O + 3Fe = Fe 3 O 4 + 4H 2;

H 2 O + C ↔ CO + H 2.

Water, in the presence of sulfuric acid, enters into interaction (hydration) reactions with unsaturated hydrocarbons - alkenes with the formation of saturated monohydric alcohols:

CH 2 = CH 2 + H 2 O → CH 3 -CH 2 -OH.

Physical properties of water

Water is a clear liquid (n.o.). The dipole moment is 1.84 D (due to the strong difference in the electronegativities of oxygen and hydrogen). Water has the highest specific heat value among all substances in the liquid and solid state of aggregation. Specific heat of fusion of water - 333.25 kJ / kg (0 С), vaporization - 2250 kJ / kg. Water is capable of dissolving polar substances. Water has a high surface tension and a negative electrical surface potential.

Receiving water

Water is obtained through a neutralization reaction, i.e. reactions of interaction between acids and alkalis:

H 2 SO 4 + 2KOH = K 2 SO 4 + H 2 O;

HNO 3 + NH 4 OH = NH 4 NO 3 + H 2 O;

2CH 3 COOH + Ba (OH) 2 = (CH 3 COO) 2 Ba + H 2 O.

One of the ways to obtain water is the reduction of metals with hydrogen from their oxides:

CuO + H 2 = Cu + H 2 O.

Examples of problem solving

EXAMPLE 1

Exercise	How much water should you take to prepare a 5% solution from a 20% acetic acid solution?
Solution	According to the determination of the mass fraction of a substance, a 20% solution of acetic acid is 80 ml of a solvent (water) 20 g of acid, and a 5% solution of acetic acid is 95 ml of a solvent (water) of 5 g of acid. Let's make the proportion: x = 20 × 95/5 = 380. Those. the new solution (5%) contains 380 ml of solvent. It is known that the original solution contained 80 ml of solvent. Therefore, to get a 5% solution of acetic acid from a 20% solution, you need to add: 380-80 = 300 ml of water.
Answer	Needs 300 ml of water.

EXAMPLE 2

Exercise	When organic matter with a mass of 4.8 g was burned, 3.36 liters of carbon dioxide (n.u.) and 5.4 g of water were formed. The density of organic matter in terms of hydrogen is 16. Determine the formula of organic matter.
Solution	Molar masses of carbon dioxide and water, calculated using the table of chemical elements of D.I. Mendeleev - 44 and 18 g / mol, respectively. Let's calculate the amount of the substance of the reaction products: n (CO 2) = V (CO 2) / V m; n (H 2 O) = m (H 2 O) / M (H 2 O); n (CO 2) = 3.36 / 22.4 = 0.15 mol; n (H 2 O) = 5.4 / 18 = 0.3 mol. Considering that in the composition of the CO 2 molecule there is one carbon atom, and in the composition of the H 2 O molecule there are 2 hydrogen atoms, the amount of substance and the masses of these atoms will be equal: n (C) = 0.15 mol; n (H) = 2 × 0.3 mol; m (C) = n (C) x M (C) = 0.15 x 12 = 1.8 g; m (H) = n (H) × M (H) = 0.3 × 1 = 0.3 g. Let us determine if there is oxygen in the composition of organic matter: m (O) = m (C x H y O z) - m (C) - m (H) = 4.8 - 0.6 - 1.8 = 2.4 g. The amount of substance of oxygen atoms: n (O) = 2.4 / 16 = 0.15 mol. Then, n (C): n (H): n (O) = 0.15: 0.6: 0.15. Divide by the smallest value, we get n (C): n (H): n (O) = 1: 4: 1. Therefore, the formula of organic matter is CH 4 O. The molar mass of organic matter calculated using the table of chemical elements of D.I. Mendeleev - 32 g / mol. The molar mass of organic matter, calculated using the value of its density for hydrogen: M (C x H y O z) = M (H 2) × D (H 2) = 2 × 16 = 32 g / mol. If the formulas of organic matter derived from combustion products and using density for hydrogen are different, then the ratio of molar masses will be greater than 1. Let's check this: M (C x H y O z) / M (CH 4 O) = 1. Therefore, the formula for organic matter is CH 4 O.
Answer	The formula for organic matter is CH 4 O.

Water (hydrogen oxide) is a binary inorganic compound with the chemical formula Н 2 O. A water molecule consists of two hydrogen atoms and one oxygen atoms, which are connected by a covalent bond.

Hydrogen peroxide.

Physical and chemical properties

The physical and chemical properties of water are determined by the chemical, electronic and spatial structure of H 2 O molecules.

The H and O atoms in the H 2 0 molecule are in their stable oxidation states, +1 and -2, respectively; therefore, water does not exhibit pronounced oxidizing or reducing properties. Please note: in metal hydrides, hydrogen is in the -1 oxidation state.

The Н 2 O molecule has an angular structure. H-O bonds very polar. On the O atom there is an excess negative charge, on the H atoms - excess positive charges. On the whole, the Н 2 O molecule is polar, i.e. dipole. This explains the fact that water is a good solvent for ionic and polar substances.

The presence of excess charges on the H and O atoms, as well as the lone electron pairs of the O atoms, causes the formation of hydrogen bonds between water molecules, as a result of which they combine into associates. The existence of these associates explains the abnormally high values ​​of mp. etc. kip. water.

Along with the formation of hydrogen bonds, the result of the mutual influence of H2O molecules on each other is their self-ionization:
in one molecule, a heterolytic break of the polar communication O-N, and the released proton is attached to the oxygen atom of another molecule. The resulting hydronium ion H 3 O + is essentially a hydrated hydrogen ion H + H 2 O, therefore, the simplified equation of water self-ionization is written as follows:

H 2 O ↔ H + + OH -

The dissociation constant of water is extremely small:

This indicates that water very slightly dissociates into ions, and therefore the concentration of undissociated H2O molecules is practically constant:

In pure water [H +] = [OH -] = 10 -7 mol / l. This means that water is a very weak amphoteric electrolyte, exhibiting no noticeable acidic or basic properties.
However, water has a strong ionizing effect on the electrolytes dissolved in it. Under the action of water dipoles, polar covalent bonds in the molecules of solutes are converted into ionic ones, the ions are hydrated, the bonds between them are weakened, as a result of which electrolytic dissociation occurs. For instance:
HCl + Н 2 O - Н 3 O + + Сl -

(strong electrolyte)

(or excluding hydration: HCl → H + + Cl -)

CH 3 COOH + H 2 O ↔ CH 3 COO - + H + (weak electrolyte)

(or CH 3 COOH ↔ CH 3 COO - + H +)

According to the Brønsted-Lowry theory of acids and bases, in these processes water exhibits the properties of a base (proton acceptor). According to the same theory, water acts as an acid (proton donor) in reactions, for example, with ammonia and amines:

NH 3 + H 2 O ↔ NH 4 + + OH -

CH 3 NH 2 + H 2 O ↔ CH 3 NH 3 + + OH -

Redox reactions involving water

I. Reactions in which water plays the role of an oxidizing agent

These reactions are possible only with strong reducing agents, which are able to reduce the hydrogen ions that are part of water molecules to free hydrogen.

1) Interaction with metals

a) Under normal conditions, H 2 O interacts only with the gap. and shch.-zem. metals:

2Na + 2Н + 2 О = 2NaOH + H 0 2

Ca + 2Н + 2 О = Ca (OH) 2 + H 0 2

b) At high temperatures, H 2 O reacts with some other metals, for example:

Mg + 2Н + 2 О = Mg (OH) 2 + H 0 2

3Fe + 4Н + 2 О = Fe 2 O 4 + 4H 0 2

c) Al and Zn displace Н 2 from water in the presence of alkalis:

2Al + 6Н + 2 О + 2NaOH = 2Na + 3H 0 2

2) Interaction with low EO non-metals (reactions occur under harsh conditions)

C + H + 2 O = CO + H 0 2 ("water gas")

2P + 6H + 2 O = 2HPO 3 + 5H 0 2

In the presence of alkalis, silicon displaces hydrogen from water:

Si + H + 2 O + 2NaOH = Na 2 SiO 3 + 2H 0 2

3) Interaction with metal hydrides

NaH + H + 2 O = NaOH + H 0 2

CaH 2 + 2H + 2 O = Ca (OH) 2 + 2H 0 2

4) Interaction with carbon monoxide and methane

CO + H + 2 O = CO 2 + H 0 2

2CH 4 + O 2 + 2H + 2 O = 2CO 2 + 6H 0 2

Reactions are used industrially to produce hydrogen.

II. Reactions in which water plays the role of a reducing agent

These reactions are possible only with very strong oxidants, which are capable of oxidizing the oxygen CO CO 2, which is part of water, to free oxygen O 2 or to peroxide anions 2-. In an exceptional case (in the reaction with F 2), oxygen is formed with c o. +2.

1) Interaction with fluorine

2F 2 + 2H 2 O -2 = O 0 2 + 4HF

2F 2 + H 2 O -2 = O +2 F 2 + 2HF

2) Interaction with atomic oxygen

H 2 O -2 + O = H 2 O - 2

3) Interaction with chlorine

At high T, a reversible reaction occurs

2Cl 2 + 2H 2 O -2 = O 0 2 + 4HCl

III. Reactions of intramolecular oxidation - reduction of water.

Electric shock or high temperature decomposition of water into hydrogen and oxygen can occur:

2H + 2 O -2 = 2H 0 2 + O 0 2

Thermal decomposition is a reversible process; the degree of thermal decomposition of water is low.

Hydration reactions

I. Hydration of ions. The ions formed during the dissociation of electrolytes in aqueous solutions attach a certain number of water molecules and exist in the form of hydrated ions. Some ions form such strong bonds with water molecules that their hydrates can exist not only in solution, but also in a solid state. This explains the formation of crystalline hydrates such as CuSO4 5H 2 O, FeSO 4 7H 2 O, etc., as well as aqua complexes: CI 3, Br 4, etc.

II. Hydration of oxides

III. Hydration of organic compounds containing multiple bonds

Hydrolysis reactions

I. Hydrolysis of salts

Reversible hydrolysis:

a) by salt cation

Fe 3+ + H 2 O = FeOH 2+ + H +; (acidic medium. pH

b) by salt anion

CO 3 2 - + H 2 O = HCO 3 - + OH -; (alkaline medium. pH> 7)

c) by cation and by salt anion

NH 4 + + CH 3 COO - + H 2 O = NH 4 OH + CH 3 COOH (medium close to neutral)

Irreversible hydrolysis:

Al 2 S 3 + 6H 2 O = 2Аl (OH) 3 ↓ + 3H 2 S

II. Hydrolysis of metal carbides

Al 4 C 3 + 12Н 2 O = 4Аl (OH) 3 ↓ + 3CH 4 netane

CaC 2 + 2H 2 O = Ca (OH) 2 + C 2 H 2 acetylene

III. Hydrolysis of silicides, nitrides, phosphides

Mg 2 Si + 4H 2 O = 2Mg (OH) 2 ↓ + SiH 4 silane

Ca 3 N 2 + 6Н 2 O = ЗСа (ОН) 2 + 2NH 3 ammonia

Cu 3 P 2 + 6Н 2 O = ЗСu (ОН) 2 + 2РН 3 phosphine

IV. Hydrolysis of halogens

Cl 2 + H 2 O = HCl + HClO

Br 2 + H 2 O = HBr + HBrO

V. Hydrolysis of organic compounds

Classes of organic substances	Hydrolysis products (organic)
Haloalkanes (alkyl halides)
Aryl halides
Dihaloalkanes	Aldehydes or ketones
Metal alcoholates
Carboxylic acid halides	Carboxylic acids
Carboxylic acid anhydrides	Carboxylic acids
Complex esters of carboxylic acids	Carboxylic acids and alcohols
	Glycerin and higher carboxylic acids
Di- and polysaccharides	Monosaccharides
Peptides and proteins	α-Amino acids
Nucleic acids

The most important derivatives of oxygen are its compounds with hydrogen - water Н2О and Н2О2.
Let's consider both compounds and first of all the most common of them - water.

The structure of the water molecule and the polar nature of the bond between hydrogen and oxygen atoms were discussed in. water is 18. In the gaseous state (in the form of vapor), water is lighter than air, the average of which is 29. However, under normal conditions, water is a liquid that has a much higher density. This is due to the fact that water molecules are combined (associated) with each other by an additional special type of bond - hydrogen bond.

The hydrogen bond is so named because it necessarily requires the presence of a hydrogen ion. In a water molecule, where common electron pairs are strongly displaced towards oxygen, hydrogen atoms are practically devoid of electrons and represent a bare nucleus. Such a nucleus (for hydrogen, this is a proton) is attracted by the electron shells of oxygen atoms of neighboring molecules, and a bond is formed between the molecules. Unlike other types of chemical bonds, denoted by dashes in structural formulas, hydrogen bonds are denoted by a dotted line

A hydrogen bond is different from a chemical bond. It is much weaker than the latter. However, the hydrogen bond cannot be considered simply intermolecular bonding, it is much stronger.
A hydrogen bond can arise not only between water molecules. It is often found in organic matter.

■ 30. Explain the mechanism of hydrogen bond formation.
31. List the types of chemical bonds known to you.
32. What type of chemical bond is the water molecule built on?
33. What is the reason for the association of the water molecule?

By physical properties water is a liquid that is colorless, tasteless and odorless.
Water has the highest density (1 g / cm3) at 4 °. As the temperature rises and falls, the density of the water decreases (so ice floats on water). The melting point of ice 0 ° and the boiling point of water 100 ° are the main points of the centigrade temperature scale. Water is an excellent solvent for liquids, gases and solids. Water conducts electricity very poorly. The specific heat capacity of water is the mostthe largest among all solids and liquids.

Water in nature

Water is very widespread in nature. About 3/4 of the surface the globe busy with water. These are oceans, seas, surface flowing fresh waters, lakes, fresh and salt, glaciers, underground waters, water vapor; constantly present in the atmosphere in greater or lesser amounts, as well as crystallization water, which is part of the crystalline hydrates.

Since water is a good solvent, natural waters always contain a variety of dissolved substances. Seawater contains in a dissolved state many different salts, including NaCl, magnesium sulfate MgSO4, etc., which give it a bitter salty. Underground waters flowing through rocks dissolve various, and these solutions emerging on the surface are called mineral springs.

There are especially many mineral springs in the Caucasus. From the water of carbon dioxide sources they improve and. Carbon dioxide is dissolved under pressure in these waters. Sulphurous waters in Matsesta and Pyatigorsk are cold and hot, contain and. Hydrogen sulfide baths lower blood pressure and improve heart function. The ferrous waters of Zheleznovodsk and Lipetsk are recommended for oral administration with anemia. The lime waters of Kislovodsk are used for kidney diseases, The waters of the warm springs of Transbaikalia and Turkestan are used in in kind for baths with general weakness of the body, nervous diseases, skin diseases, etc.

If groundwater is located near the centers of volcanic activity, the water comes out to the surface hot in the form of so-called geysers. It is believed that there is a huge amount of hot water in the depths of the earth's crust. It can be used as a very cheap source of thermal energy.

Life on earth began with water, which we know now is the environment for the life of aquatic organisms, but it; absolutely necessary for all living organisms that cannot exist without water. The protoplasm of any cell is colloidal solution squirrel in water. The human body contains 65% water. If the human body loses 20% of water, the changes in the cells become irreversible and the person dies. A person can live without food for 30-40 days, and without water, no more than 7 days. Plant life is also impossible without water. Water for green plants is a necessary component for photosynthesis.

■ 34. In what condition and where is water found in nature? Write it down in a notebook.

35. What are mineral springs, the composition of their water, what is the use in medicine?

Chemical properties of water

Water is an indifferent oxide. Water is an extremely weak electrolyte, dissociating according to the following scheme:
H2O ⇄ H + + OH -
Some of the most active (Na, K, Ca, Ba, Al) can displace from water:
2Na + 2H2O = 2NaOH + H2
2Na + 2Н + + 2OH - = 2Na + + 2OH - + H2
2Na + 2H + = 2Na + + H2
Red-hot water decomposes with the release of hydrogen and the formation of scale:
3Fe + 4H2O = Fe3O5 + 4H2

superheated steam

Elements with stronger than oxidizing properties, for example, are displaced from water:
Cl 0 2 + H2O -2 = 2HCl -1 +
Cl 0 2 + 2 e- → 2Сl -1
O -2 - 2 e- → O 0
Hot charcoal decomposes water to form water gas, which is basically a mixture of hydrogen and carbon monoxide
C + H2O = CO + H2
Water can react with basic and acidic oxides, forming bases and acids, d The release of heat when caustic alkalis and sulfuric acid are dissolved in water is also explained by the chemical reactions of water addition occurring between water and these substances.

Water can react with salts to form crystalline hydrates. For example, copper sulfate, which has a blue color, is the products of the combination of white copper sulfate with water according to the equation:
CuSO4 + 5H2O = СuSO4 = 5H2O + Q

Water is chemically very stable, but it can decompose when exposed to electric current.

Water actively enters into hydrolysis reactions with complex inorganic and organic substances.

■ 36. Why is water classified as an indifferent oxide?
37. Is the expression "sodium dissolves in water" correct?
38. Write the reaction equations for the interaction with water of basic and acidic oxides. With which of them does the water not react?
39. For what purpose is water subjected to electrolysis?
40. Water reacts with salts to form crystalline hydrates. Write the reaction equation for the formation of crystalline hydrate. What other type of interaction is possible between water and salts?
41. In a vessel with 200 g of water was placed 9.2 g of sodium. What substance was formed in this case? Is it soluble? If it is soluble, what is its percentage in the resulting solution?
42. To 50 g of 30% sulfuric acid was added 5 g of sulfuric anhydride. What is the concentration of sulfuric acid?
43. Among those listed in the properties of water, indicate those that can be used to obtain hydrogen.
44. What volume of hydrogen can be obtained by the interaction of 5 kg of iron with superheated steam, if 10% of the weight of iron comes is reduced to scale, and 20% of the produced hydrogen is lost?
45. How much copper oxide can be reduced by hydrogen obtained in the previous problem?

The water that is part of the crystals is called crystallization water. It is chemically bound to a substance and gives the crystal the appropriate properties. For example, copper kynopoc, CuSO4 · 5H2O in the form of a crystalline hydrate with five water molecules has a bright blue color, which it loses on ignition due to the removal of crystallization water (Fig. 45). Natural CaSО4 · 2H2О, with low heating, separates one water molecule, turning into a compound of the composition 2CaSО4 · H2O, called hemihydrate gypsum. This one has the ability to "grasp", that is, when mixed with water, it attaches the missing water molecule to itself and solidifies, forming dihydrous CaSO4 · 2H2O:
2CaSО4 H2O + 3H2O = 2 (CaSO4 2H2O)
This reaction has found wide application in medicine when applying plaster casts.
However, if the gypsum is calcined until the water is completely removed
CaSO4 2H2O2 = CaSO4 + 2H2O

Rice. 45. Dehydration of copper sulfate 1- copper sulfate 2- water released during heating

then the reaction becomes irreversible and water no longer adds to calcium sulfate.
Crystalline hydrates are chemical compounds of salt with water. They are referred to as complex compounds. There are many more crystalline hydrates, for example, Glauber's salt
Na2SО4 · 10H2O, iron vitriol FeSО4 · 7H2O, etc.

■ 46. ​​How much water and crystalline hydrate Na2SO4 · 10H2O should be taken to prepare 200 g of 3% sodium sulfate solution?
47. In the laboratory, anhydrous alcohol is used to absolve alcohol, with which the alcohol is boiled until it acquires a blue color. What kind of reaction occurs when this happens? How much will the weight of 25 g of copper sulfate increase if we assume that 75% of the sulfate has turned into copper sulfate?
What percentage of water was contained in alcohol, if 150 g of alcohol was subjected to absolution?
48.20 a FeSO4 · 7H2O was dissolved in 180 g of water. What is the concentration of the resulting solution?
49. What is two-water gypsum, semi-aqueous gypsum? What are their uses in medicine?
50. What water is called crystallization water?

Methods for purifying natural waters

Natural water does not always meet all the requirements that humans place on it. Therefore, water is treated differently for different purposes.
Drinking water should be frequent, clear, odorless and free of pathogenic bacteria. Natural water intended for drinking enters the water treatment plants of the city water supply system, where the oka passes through a system of treatment facilities (Fig. 46). First, it passes through metal filters to

cleaning from mechanical impurities, then enters the sedimentation tanks, where small particles polluting it gradually settle. To accelerate their sedimentation, a coagulant is usually added to the sedimentation tanks - a substance that makes suspensions and colloidal particles coagulate and settle. Aluminum chloride AlCl3 or aluminum sulfate Al2 (SO4) 3 is used as a coagulant.

Rice. 46. Wastewater treatment plant system of a water treatment plant. 1-filter; 2-settling tank; 3-mixers; 4 - pumping; 5 - water intake; 6 - chlorination; 7 - sediment; 8 - adding alum.

After settling, the water is filtered through sand, bone charcoal and fabric filters, after which soluble salts and microorganisms remain in it, among which there may be pathogenic bacteria. To destroy them, a little chlorine water is added to the water in an amount that kills bacteria, but is harmless to humans. After that, the water enters the so-called reservoirs. pure water, where it is kept for some time in order for the effect of chlorine to fully manifest itself. Purified water is supplied to consumers through the water supply system.

In rural areas, water usually does not go through such a complex treatment system, but is taken directly from wells or other natural bodies of water. Such water must be boiled, and in the case of massive gastrointestinal diseases, it must be added a small amount of bleach solution.

Rice. 47.
1- Wurtz flask with water; Liebig 2-water refrigerator: 3 - alonge; 4- receptacle for distilled water; 5 - thermometer.

Distilled water is used in chemical laboratories and medicine. To completely remove salts, water is distilled in so-called distillation stills. The principle of distillation of water can be observed in a laboratory setup (Fig. 47). The water is boiling in a flask. The resulting steam through the gas outlet pipe enters the Liebig water cooler 2, where the steam condenses and flows through the drain 3 into the receiving vessel 4. The resulting water is called distilled. It is completely salt-free and harmful to drink. The distiller works in the same way (fig. 48).

Rice. 48.

■ 51. What is distillation and for what purposes is distilled water used? 52. What are the requirements for drinking water? 53. How can water be purified: a) from mechanical impurities; b) from dissolved salts; c) from colloidal particles?

§ 54. Hydrogen peroxide

- an oxide richer in oxygen compared to water. The peroxide formula is H2O2, but this does not mean that it is monovalent in this compound. In a hydrogen peroxide molecule, there is one common electron pair between two oxygen atoms. Oxygen atoms connected in this way are contained not only in hydrogen peroxide, but also in any other peroxide and are called the "peroxide chain"

The presence of a peroxide chain makes the molecule unstable. Indeed, under the most insignificant influences - storage in a lighted room, heating, the action of the MnO2 catalyst - hydrogen peroxide decomposes, turning into water, with the release of oxygen
2H2O2 = 2H2O + O2
This reaction can be accompanied by an explosion.
A 30% hydrogen peroxide solution is called perhydrol.

It can cause severe burns if it comes into contact with the skin. Net has a density of 1.46 g / s3 and a freezing point of -1.7 °. A solution of hydrogen peroxide has an acidic reaction, which gives reason to consider it as a very weak diacid.
Some metal peroxides such as Na2O2; ВаО2, can be considered not only as, but also as a kind of salt of hydrogen peroxide. Hydrogen peroxide can be obtained from these compounds by the action of a stronger acid:
ВаО2 + H2SO4 = BaSO4 + H2O2

The behavior of hydrogen peroxide in redox reactions is discussed in § 32. When interacting with organic substances, hydrogen peroxide behaves like. Anhydrous hydrogen peroxide causes burns and spontaneous combustion of combustible materials. With burns with hydrogen peroxide, a characteristic White spot”And then an ulcer may form. A first aid measure, as with acid burns, is to rinse with plenty of water.

Hydrogen peroxide is used as a disinfectant in medicine for rinsing, rinsing and as a hemostatic agent in the form of a 3% solution. In addition, it is used to bleach hair, wool, silk, horns, etc. Hydrogen peroxide is also used to restore paintings painted with lead whitewash, which gradually darken in air, since under the action of air hydrogen sulfide, black lead sulfide is formed in the paint ... Hydrogen peroxide oxidizes lead sulfide to sulfate according to the following scheme:
PbS + H2O2 → PbSO4 + H2O
Such pictures are wiped with a weak solution of hydrogen peroxide.
Store hydrogen peroxide in dark glass flasks in a cool room, in the dark to slow down the ongoing decay.

■ 54. Give examples of reactions in which hydrogen peroxide would exhibit the properties of an oxidizing agent.

55, Give examples of reactions in which hydrogen peroxide would exhibit the properties of a reducing agent.

56. Where and how should hydrogen peroxide be stored in laboratories? Why?
57. What are the first aid measures for burns with hydrogen peroxide?

58. In the presence of manganese dioxide, oxygen can be obtained from hydrogen peroxide. Draw a device that can use this process.

59. How many grams of barium peroxide is required to obtain 5 moles of pure hydrogen peroxide?
60. Hydrogen peroxide dissociates as acids. Write the equation for the two-step dissociation of this acid.

61. Where and how is hydrogen peroxide used and how is it related to its properties?

Air

Our planet is surrounded by air, which is necessary for breathing for all creatures living on earth. A person passes through his lungs about 13,000 liters of air per day.
The air shell of the earth is called the atmosphere (from the words "atmos" - air, "sefira" - a ball). The air contains 78% (by volume) nitrogen, 21% oxygen, 0.96%

Rice. 49. Diagram of air composition

Inert gases, mainly argon and neon, as well as helium, krypton and xenon, 0.03-0.04% carbon dioxide and 0.01% hydrogen. The air composition is shown in Fig. 49. Medium air is equal to 29. e.
In addition, the composition of the atmosphere includes accidental impurities, as well as variable components - water vapor, nitrogen, ozone, as well as dust and local air pollution that sometimes occur during intensive work of enterprises in a certain area, as well as during the operation of transport.

The amount of dust in the air can be very high, especially in large cities. Dust disturbs the transparency of the air and contributes to the formation of fogs, since water droplets condense on the dust particles. Various microorganisms can be in the air. Among them there may be disease-causing ones. Hence, it is clear how important air purification in cities is, how important it is to ensure that the air does not pollute Industrial enterprises and transport.
To clean the air inside the premises, special air conditioning devices are used: it is filtered, humidified to the desired state, removed from dust and bacteria, and maintained at the most favorable temperature.
1 m3 of air at 0 ° weighs 1.293 kg, with an increase in altitude, the density of air becomes less. At -193 °, the air turns into a liquid state. Since air is a mixture of gases with different boiling points, it can be divided into its constituent parts according to boiling points, or, as they say, subjected to fractional distillation.

The energy of compressed air is widely used, which is obtained by increasing the pressure of atmospheric air using compressors. When compressed air is blown into the blast furnace, the oxygen supply increases and the combustion becomes more intense.
Liquid air is a bluish cloudy liquid. Liquid oxygen gives it a blue color, and it can be cloudy because at the temperature of liquid air, carbon dioxide becomes solid. If you filter it, then the air will be transparent.
Under the influence of the low temperature of liquid air, some bodies acquire special, completely new properties. For example, it acquires the elasticity of steel, becomes so hard that it is possible to hammer nails with a hammer made of it, rubber becomes fragile, like, and breaks apart from the impact. Many at the temperature of liquid air acquire the properties of superconductivity. If an electric current is excited in a metal ring, then the galvanometer connected to it will show the presence of an electric current for a very long time.

Interestingly, most of the bacteria in liquid air do not die, but plunges into a state of suspended animation.
If a combustible material is impregnated with liquid air, which either does not ignite or burns very weakly in ordinary air, for example sawdust or coal powder, then when ignited, they instantly burn out with the release of a large amount of gases, therefore, liquid air is widely used in blasting operations. For this, cardboard cartridges are stuffed with sawdust, placed in explosion chambers, impregnated with liquid air and set on fire. A violent explosion occurs. If the explosion did not occur, then after a while the air from the cartridge evaporates, and it becomes safe again, unlike any other explosive.

Liquid air is obtained at high pressure and low temperature.
Compressed air is used in pneumatic devices and various pneumatic equipment, as well as in caisson work. The caisson is a huge air-tight and waterproof concrete box, inside which several people can be. On one side, the caisson is open. It is lowered with the open side into the water to the very bottom, reinforced with a load so that it does not float, and water is forced out of it with compressed air. To displace water, the air pressure in the caisson is brought to 4 atm. At this pressure, the air in a large number dissolves in the blood. With a sharp decrease in pressure, for example, when rising to the surface, its excess quickly leaves the blood in the form of bubbles, which can clog the blood vessels and even reach the heart. In severe cases, this so-called decompression sickness can be fatal. Therefore, the rise from the caisson is carried out gradually so that the dissolved air comes out in small portions.

Read the description of the model carefully and look at the sketch.

In accordance with the sketch, make changes to the drawing of the base of the straight skirt.

Transfer the lines of the style to the colored paper template.

Use colored paper to make fabric layouts.

Paste the details into the "simulation result".

Apply the necessary inscriptions for cutting on the parts of the pattern.

Drawing in М 1: 4 for modeling

Operational control card

	Control criteria
	1. Drawing lines of the style on the drawing of the base
	Pocket line drawing
	Changing the position of the dart on the front panel of the skirt
	Indication of the inscriptions "close the dart", "cut off the side part"
	Allowance for the slot along the line of the middle of the rear panel 50 ÷ 80 mm
	Fastening allowance along the line of the middle of the front panel 30 ÷ 40 mm.
	Making a complete set of pattern parts (front and rear skirt panel, side part of the front panel)
	2. Preparing the pattern for cutting:
	Front panel
	Part name
	Number of details
	The direction of the common thread
	Rear panel
	Part name
	Number of details
	The direction of the common thread
	Machining allowances for all cuts
	Side part of the front panel
	Part name
	Number of details
	The direction of the common thread
	Machining allowances for all cuts
	Total:

Line drawing