Hydrogen. Physical and chemical properties, receipt. Chemistry organics Hydrogen oxygen equation

10.1 Hydrogen

The name "hydrogen" refers to both a chemical element and a simple substance. Element hydrogen consists of hydrogen atoms. Simple substance hydrogen consists of hydrogen molecules.

a) Chemical element hydrogen

In the natural series of elements, the ordinal number of hydrogen is 1. In the system of elements, hydrogen is in the first period in the IA or VIIA group.

Hydrogen is one of the most abundant elements on Earth. The molar fraction of hydrogen atoms in the atmosphere, hydrosphere and lithosphere of the Earth (all together this is called the earth's crust) is 0.17. It is found in water, many minerals, petroleum, natural gas, plants and animals. The human body contains on average about 7 kilograms of hydrogen.

There are three isotopes of hydrogen:
a) light hydrogen - protium,
b) heavy hydrogen - deuterium(D),
c) superheavy hydrogen - tritium(T).

Tritium is an unstable (radioactive) isotope; therefore, it practically does not occur in nature. Deuterium is stable, but very little of it: w D = 0.015% (based on the mass of all terrestrial hydrogen). Therefore, the atomic mass of hydrogen differs very little from 1 D (1.00794 D).

b) Hydrogen atom

From the previous sections of the chemistry course, you already know the following characteristics of the hydrogen atom:

The valence capabilities of the hydrogen atom are determined by the presence of one electron in a single valence orbital. A high ionization energy makes a hydrogen atom not prone to give up an electron, and a not too high energy of affinity for an electron leads to a slight tendency to accept it. Consequently, in chemical systems the formation of the H cation is impossible, and the compounds with the H anion are not very stable. Thus, for a hydrogen atom, the most characteristic is the formation of a covalent bond with other atoms due to its one unpaired electron. And in the case of the formation of an anion, and in the case of the formation of a covalent bond, the hydrogen atom is monovalent.
In a simple substance, the oxidation state of hydrogen atoms is zero, in most compounds, hydrogen exhibits an oxidation state of + I, and only in hydrides of the least electronegative elements of hydrogen has an oxidation state of –I.
Information on the valence capabilities of the hydrogen atom is given in table 28. The valence state of the hydrogen atom bound by one covalent bond to any atom is indicated in the table by the symbol "H-".

Table 28.The valence capabilities of the hydrogen atom

Valence state		Examples of chemicals
	I 0 –I	HCl, H 2 O, H 2 S, NH 3, CH 4, C 2 H 6, NH 4 Cl, H 2 SO 4, NaHCO 3, KOH H 2 B 2 H 6, SiH 4, GeH 4
		NaH, KH, CaH 2, BaH 2

c) Hydrogen molecule

The diatomic hydrogen molecule H 2 is formed when hydrogen atoms are bound by the only covalent bond possible for them. The bond is formed by the exchange mechanism. By the way the electron clouds overlap, this is s-bond (Fig.10.1 a). Since the atoms are the same, the bond is non-polar.

Interatomic distance (more precisely, the equilibrium interatomic distance, because atoms vibrate) in a hydrogen molecule r(H – H) = 0.74 A (fig.10.1 v), which is much less than the sum of the orbital radii (1.06 A). Consequently, the electron clouds of the bonded atoms overlap deeply (Fig.10.1 b), and the bond in the hydrogen molecule is strong. This is also evidenced by the rather large value of the binding energy (454 kJ / mol).
If we characterize the shape of the molecule by the boundary surface (similar to the boundary surface of the electron cloud), then we can say that the hydrogen molecule has the shape of a slightly deformed (elongated) sphere (Fig.10.1 G).

d) Hydrogen (substance)

Under normal conditions, hydrogen is a colorless and odorless gas. In small quantities, it is non-toxic. Solid hydrogen melts at 14 K (–259 ° C), and liquid hydrogen boils at 20 K (–253 ° C). Low melting and boiling points, a very small temperature range for the existence of liquid hydrogen (only 6 ° C), as well as small values of the molar heats of fusion (0.117 kJ / mol) and vaporization (0.903 kJ / mol) indicate that intermolecular bonds in hydrogen very weak.
The density of hydrogen r (H 2) = (2 g / mol) :( 22.4 l / mol) = 0.0893 g / l. For comparison: the average density of air is 1.29 g / l. That is, hydrogen is 14.5 times lighter than air. It is practically insoluble in water.
At room temperature, hydrogen is inactive, but when heated it reacts with many substances. In these reactions, hydrogen atoms can both increase and decrease their oxidation state: Н 2 + 2 e- = 2Н -I, Н 2 - 2 e- = 2H + I.
In the first case, hydrogen is an oxidizing agent, for example, in reactions with sodium or calcium: 2Na + H 2 = 2NaH, ( t) Ca + H 2 = CaH 2. ( t)
But the reducing properties of hydrogen are more characteristic: O 2 + 2H 2 = 2H 2 O, ( t)
CuO + H 2 = Cu + H 2 O. ( t)
When heated, hydrogen is oxidized not only by oxygen, but also by some other non-metals, for example, fluorine, chlorine, sulfur, and even nitrogen.
In the laboratory, hydrogen is obtained as a result of the reaction

Zn + H 2 SO 4 = ZnSO 4 + H 2.

Iron, aluminum and some other metals can be used instead of zinc, and some other dilute acids can be used instead of sulfuric acid. The resulting hydrogen is collected in a test tube by the method of displacement of water (see Fig.10.2 b) or simply into an inverted flask (fig.10.2 a).

In industry, hydrogen is obtained in large quantities from natural gas (mainly methane) by its interaction with water vapor at 800 ° C in the presence of a nickel catalyst:

CH 4 + 2H 2 O = 4H 2 + CO 2 ( t, Ni)

or coal is treated at high temperature with water vapor:

2H 2 O + C = 2H 2 + CO 2. ( t)

Pure hydrogen is obtained from water by decomposing it with an electric current (subjecting it to electrolysis):

2H 2 O = 2H 2 + O 2 (electrolysis).

e) Hydrogen compounds

Hydrides (binary compounds containing hydrogen) are divided into two main types:
a) volatile (molecular) hydrides,
b) salt-like (ionic) hydrides.
Elements IVA - VIIA of groups and boron form molecular hydrides. Of these, only hydrides of elements that form non-metals are stable:

B 2 H 6; CH 4; NH 3; H 2 O; HF
SiH 4; PH 3; H 2 S; HCl
AsH 3; H 2 Se; HBr
H 2 Te; HI
With the exception of water, all these compounds are gaseous substances at room temperature, hence their name - "volatile hydrides".
Some of the elements that form non-metals are also found in more complex hydrides. For example, carbon forms compounds with general formulas C n H 2 n+2, C n H 2 n, C n H 2 n–2 and others, where n can be very large (these compounds are studied by organic chemistry).
Ionic hydrides include hydrides of alkali, alkaline earth elements and magnesium. Crystals of these hydrides consist of H anions and metal cations in the highest oxidation state Me or Me 2 (depending on the group of the system of elements).

LiH
NaH	MgH 2
KH	CaH 2
RbH	SrH 2
CsH	BaH 2

Both ionic and almost all molecular hydrides (except for H 2 O and HF) are reducing agents, but ionic hydrides exhibit reducing properties much stronger than molecular ones.
In addition to hydrides, hydrogen is part of hydroxides and some salts. You will get acquainted with the properties of these more complex hydrogen compounds in the following chapters.
The main consumers of the hydrogen produced in the industry are plants for the production of ammonia and nitrogen fertilizers, where ammonia is obtained directly from nitrogen and hydrogen:

N 2 + 3H 2 2NH 3 ( R, t, Pt - catalyst).

In large quantities, hydrogen is used to obtain methyl alcohol (methanol) by the reaction 2H 2 + CO = CH 3 OH ( t, ZnO - catalyst), as well as in the production of hydrogen chloride, which is obtained directly from chlorine and hydrogen:

H 2 + Cl 2 = 2HCl.

Sometimes hydrogen is used in metallurgy as a reducing agent in the production of pure metals, for example: Fe 2 O 3 + 3H 2 = 2Fe + 3H 2 O.

1. What particles are the nuclei of a) protium, b) deuterium, c) tritium?
2.Compare the ionization energy of the hydrogen atom with the ionization energy of the atoms of other elements. According to this characteristic, which element is the closest to hydrogen?
3. Do the same for the electron affinity energy
4. Compare the direction of polarization of the covalent bond and the oxidation state of hydrogen in the compounds: a) BeH 2, CH 4, NH 3, H 2 O, HF; b) CH 4, SiH 4, GeH 4.
5. Write down the simplest, molecular, structural and spatial formula of hydrogen. Which one is most commonly used?
6. It is often said: "Hydrogen is lighter than air." What does this mean? When can this expression be taken literally, and when not?
7. Make the structural formulas of potassium and calcium hydrides, as well as ammonia, hydrogen sulfide and hydrogen bromide.
8. Knowing the molar heats of fusion and vaporization of hydrogen, determine the values of the corresponding specific quantities.
9.For each of the four reactions illustrating the main Chemical properties hydrogen, make up an electronic balance. Note oxidants and reducing agents.
10. Determine the mass of zinc required to obtain 4.48 liters of hydrogen in the laboratory.
11. Determine the mass and volume of hydrogen that can be obtained from a 30 m 3 mixture of methane and water vapor, taken in a volume ratio of 1: 2, with a yield of 80%.
12. Make up the equations of the reactions occurring in the interaction of hydrogen a) with fluorine, b) with sulfur.
13. The following reaction schemes illustrate the main chemical properties of ionic hydrides:

a) MH + O 2 MOH ( t); b) MH + Cl 2 MCl + HCl ( t);
c) MH + H 2 O MOH + H 2; d) MH + HCl (p) MCl + H 2
Here M is lithium, sodium, potassium, rubidium, or cesium. Write the equations of the corresponding reactions if M is sodium. Illustrate the chemical properties of calcium hydride with reaction equations.
14. Using the electronic balance method, construct equations for the following reactions to illustrate the reducing properties of some molecular hydrides:
a) HI + Cl 2 HCl + I 2 ( t); b) NH 3 + O 2 H 2 O + N 2 ( t); c) CH 4 + O 2 H 2 O + CO 2 ( t).

10.2 Oxygen

As with hydrogen, the word "oxygen" is the name of both a chemical element and a simple substance. In addition to a simple substance " oxygen"(dioxygen) the chemical element oxygen forms another simple substance called " ozone"(trioxygen). These are allotropic modifications of oxygen. The substance oxygen consists of molecules of oxygen O 2, and the substance ozone consists of molecules of ozone O 3.

a) Chemical element oxygen

In the natural series of elements, the ordinal number of oxygen is 8. In the system of elements, oxygen is in the second period in the VIA group.
Oxygen is the most abundant element on earth. In the earth's crust, every second atom is an oxygen atom, that is, the molar fraction of oxygen in the atmosphere, hydrosphere and lithosphere of the Earth is about 50%. Oxygen (substance) - component air. The volume fraction of oxygen in the air is 21%. Oxygen (an element) is a part of water, many minerals, as well as plants and animals. The human body contains an average of 43 kg of oxygen.
Natural oxygen consists of three isotopes (16 O, 17 O and 18 O), of which the lightest isotope 16 O is the most abundant. Therefore, the atomic mass of oxygen is close to 16 D (15.9994 D).

b) Oxygen atom

You are familiar with the following characteristics of the oxygen atom.

Table 29.Oxygen atom valence

Valence state		Examples of chemicals
		Al 2 O 3, Fe 2 O 3, Cr 2 O 3 *

	–II –I 0 + I + II	H 2 O, SO 2, SO 3, CO 2, SiO 2, H 2 SO 4, HNO 2, HClO 4, COCl 2, H 2 O 2 O 2 ** O 2 F 2 OF 2
		NaOH, KOH, Ca (OH) 2, Ba (OH) 2 Na 2 O 2, K 2 O 2, CaO 2, BaO 2
		Li 2 O, Na 2 O, MgO, CaO, BaO, FeO, La 2 O 3

* These oxides can also be considered ionic compounds.
** Oxygen atoms in a molecule are not in a given valence state; this is just an example of a substance with an oxidation state of oxygen atoms equal to zero
The high ionization energy (like hydrogen) excludes the formation of a simple cation from the oxygen atom. The electron affinity energy is quite high (almost twice that of hydrogen), which provides a greater tendency for the oxygen atom to attach electrons and the ability to form O 2A anions. But the energy of affinity for an electron of an oxygen atom is still less than that of halogen atoms and even other elements of group VIA. Therefore, oxygen anions ( oxide ions) exist only in compounds of oxygen with elements, the atoms of which donate electrons very easily.
By socializing two unpaired electrons, the oxygen atom can form two covalent bonds. Due to the impossibility of excitation, two lone pairs of electrons can only enter into a donor-acceptor interaction. Thus, without taking into account the multiplicity of the bond and hybridization, the oxygen atom can be in one of five valence states (Table 29).
The most characteristic of the oxygen atom is the valence state with W k = 2, that is, the formation of two covalent bonds due to two unpaired electrons.
The very high electronegativity of the oxygen atom (higher - only for fluorine) leads to the fact that in most of its compounds oxygen has an oxidation state of –II. There are substances in which oxygen exhibits other values of the oxidation state, some of which are shown in Table 29 as examples, and the comparative stability is shown in Fig. 10.3.

c) Oxygen molecule

It has been experimentally established that the diatomic oxygen molecule O 2 contains two unpaired electrons. Using the method of valence bonds, such an electronic structure of this molecule cannot be explained. Nevertheless, the bond in the oxygen molecule is close in properties to covalent. The oxygen molecule is non-polar. Interatomic distance ( r o – o = 1.21 A = 121 nm) is less than the distance between atoms linked by a simple bond. The molar binding energy is quite high and amounts to 498 kJ / mol.

d) Oxygen (substance)

Under normal conditions oxygen is a colorless and odorless gas. Solid oxygen melts at 55 K (–218 ° C), and liquid oxygen boils at 90 K (–183 ° C).
Intermolecular bonds in solid and liquid oxygen are somewhat stronger than in hydrogen, as evidenced by the wider temperature range for the existence of liquid oxygen (36 ° C) and higher than that of hydrogen, molar heats of fusion (0.446 kJ / mol) and vaporization (6, 83 kJ / mol).
Oxygen is slightly soluble in water: at 0 ° C, only 5 volumes of oxygen (gas!) Dissolve in 100 volumes of water (liquid!).
The high tendency of oxygen atoms to attach electrons and high electronegativity lead to the fact that oxygen exhibits only oxidizing properties. These properties are especially pronounced at high temperatures.
Oxygen reacts with many metals: 2Ca + O 2 = 2CaO, 3Fe + 2O 2 = Fe 3 O 4 ( t);
non-metals: C + O 2 = CO 2, P 4 + 5O 2 = P 4 O 10,
and complex substances: CH 4 + 2O 2 = CO 2 + 2H 2 O, 2H 2 S + 3O 2 = 2H 2 O + 2SO 2.

Most often, as a result of such reactions, various oxides are obtained (see Chapter II § 5), but active alkali metals, for example sodium, are converted into peroxides by combustion:

2Na + O 2 = Na 2 O 2.

Structural formula of the resulting sodium peroxide (Na) 2 (O-O).
A smoldering splinter, placed in oxygen, flares up. It is a convenient and easy way to detect pure oxygen.
In industry, oxygen is obtained from air by rectification (complex distillation), and in the laboratory by subjecting some oxygen-containing compounds to thermal decomposition, for example:
2KMnO 4 = K 2 MnO 4 + MnO 2 + O 2 (200 ° C);
2KClO 3 = 2KCl + 3O 2 (150 ° C, MnO 2 - catalyst);
2KNO 3 = 2KNO 2 + 3O 2 (400 ° C)
and, in addition, by catalytic decomposition of hydrogen peroxide at room temperature: 2H 2 O 2 = 2H 2 O + O 2 (MnO 2 is a catalyst).
Pure oxygen is used in industry to intensify those processes in which oxidation occurs and to create a high-temperature flame. In rocketry, liquid oxygen is used as an oxidizer.
Oxygen is of great importance for maintaining the life of plants, animals and humans. Under normal conditions, a person has enough oxygen to breathe. But in conditions when there is not enough air, or it is absent altogether (in airplanes, during diving work, in spaceships, etc.), special gas mixtures containing oxygen. Oxygen is also used in medicine for diseases that cause difficulty in breathing.

e) Ozone and its molecules

Ozone O 3 is the second allotropic modification of oxygen.
The triatomic ozone molecule has an angular structure, the middle between the two structures, displayed by the following formulas:

Ozone is a dark blue gas with a pungent odor. Due to its strong oxidative activity, it is poisonous. Ozone is one and a half times "heavier" than oxygen and slightly more than oxygen, we will dissolve in water.
Ozone is formed in the atmosphere from oxygen during electrical lightning discharges:

3O 2 = 2O 3 ().

At normal temperatures, ozone slowly converts to oxygen, and when heated, this process proceeds with an explosion.
Ozone is contained in the so-called "ozone layer" of the earth's atmosphere, protecting all life on earth from the harmful effects of solar radiation.
In some cities, ozone is used instead of chlorine for disinfection (disinfection) of drinking water.

Draw the structural formulas of the following substances: OF 2, H 2 O, H 2 O 2, H 3 PO 4, (H 3 O) 2 SO 4, BaO, BaO 2, Ba (OH) 2. Name these substances. Describe the valence states of oxygen atoms in these compounds.
Determine the valence and oxidation state of each of the oxygen atoms.
2. Make the equations of combustion reactions in oxygen of lithium, magnesium, aluminum, silicon, red phosphorus and selenium (selenium atoms are oxidized to the oxidation state + IV, the atoms of other elements - to the highest oxidation state). What classes of oxides do the products of these reactions belong to?
3. How many liters of ozone can be obtained (under normal conditions) a) from 9 liters of oxygen, b) from 8 g of oxygen?

Water is the most abundant substance in the earth's crust. The mass of the earth's water is estimated at 10 18 tons. Water is the basis of the hydrosphere of our planet, in addition, it is contained in the atmosphere, in the form of ice forms the polar caps of the Earth and alpine glaciers, and is also part of various rocks. The mass fraction of water in the human body is about 70%.
Water is the only substance that has its own special names in all three states of aggregation.

The electronic structure of a water molecule (Fig.10.4 a) we have studied in detail earlier (see § 7.10).
Due to the polarity of the O – H bonds and the angular shape, the water molecule is electric dipole.

To characterize the polarity of an electric dipole, a physical quantity called " electric moment of an electric dipole " or simply " dipole moment ".

In chemistry, the dipole moment is measured in Debyes: 1 D = 3.34. 10-30 Cl. m

In a water molecule there are two polar covalent bonds, that is, two electric dipoles, each of which has its own dipole moment (and). The total dipole moment of the molecule is equal to the vector sum of these two moments (Fig.10.5):

(H 2 O) = ,

where q 1 and q 2 - partial charges (+) on hydrogen atoms, and and - interatomic O - H distances in the molecule. Because q 1 = q 2 = q, a, then

The experimentally determined dipole moments of the water molecule and some other molecules are given in the table.

Table 30.Dipole moments of some polar molecules

Molecule	Molecule	Molecule

Given the dipole nature of the water molecule, it is often schematically depicted as follows:
Pure water is a colorless liquid, tasteless and odorless. Some of the main physical characteristics of water are given in the table.

Table 31.Some physical characteristics of water

Large values of the molar heats of fusion and vaporization (an order of magnitude higher than those of hydrogen and oxygen) indicate that water molecules, both in solid and liquid matter, are quite tightly bound together. These connections are called " hydrogen bonds ".

ELECTRIC DIPOLE, DIPOLE MOMENT, BONDING POLARITY, MOLECULE POLARITY.
How many valence electrons of an oxygen atom take part in the formation of bonds in a water molecule?
2.When overlapping of which orbitals are bonds formed between hydrogen and oxygen in a water molecule?
3. Make a diagram of the formation of bonds in the hydrogen peroxide molecule H 2 O 2. What can you say about the spatial structure of this molecule?
4. The interatomic distances in HF, HCl and HBr molecules are 0.92, respectively; 1.28 and 1.41. Using the dipole moment table, calculate and compare the partial charges on the hydrogen atoms in these molecules.
5. The interatomic distances S - H in the hydrogen sulfide molecule are equal to 1.34, and the angle between the bonds is 92 °. Determine the values of the partial charges on the sulfur and hydrogen atoms. What can you say about hybridization of the valence orbitals of the sulfur atom?

10.4. Hydrogen bond

As you already know, due to the significant difference in the electronegativity of hydrogen and oxygen (2.10 and 3.50), the hydrogen atom in the water molecule has a large positive partial charge ( q h = 0.33 e), and the oxygen atom has an even greater negative partial charge ( q h = -0.66 e). Recall also that the oxygen atom has two lone pairs of electrons per sp 3-hybrid AO. The hydrogen atom of one water molecule is attracted to the oxygen atom of another molecule, and, in addition, the half-empty 1s-AO of the hydrogen atom partially accepts a pair of electrons from the oxygen atom. As a result of these interactions between molecules, special kind intermolecular bonds - hydrogen bond.
In the case of water, hydrogen bonding can be schematically represented as follows:

In the last structural formula, three dots (dotted line, not electrons!) Show the hydrogen bond.

The hydrogen bond exists not only between water molecules. It is formed if two conditions are met:
1) there is a strongly polar N – E bond in the molecule (E is the symbol of an atom of a sufficiently electronegative element),
2) there is an E atom in the molecule with a large negative partial charge and a lone pair of electrons.
The element E can be fluorine, oxygen and nitrogen. Hydrogen bonds are much weaker if E is chlorine or sulfur.
Examples of substances with a hydrogen bond between molecules: hydrogen fluoride, solid or liquid ammonia, ethyl alcohol, and many others.

In liquid hydrogen fluoride, its molecules are linked by hydrogen bonds in rather long chains, and three-dimensional networks are formed in liquid and solid ammonia.
In terms of strength, the hydrogen bond is intermediate between chemical bond and other types of intermolecular bonds. The molar energy of a hydrogen bond usually ranges from 5 to 50 kJ / mol.
In solid water (i.e. ice crystals), all hydrogen atoms are hydrogen bonded to oxygen atoms, with each oxygen atom forming two hydrogen bonds (using both lone pairs of electrons). This structure makes ice "looser" in comparison with liquid water, where some of the hydrogen bonds are broken, and the molecules are able to "pack" somewhat more densely. This feature of the structure of ice explains why, unlike most other substances, water in a solid state has a lower density than in a liquid state. Water reaches its maximum density at 4 ° С - at this temperature, a lot of hydrogen bonds break, and thermal expansion not yet very strongly affecting the density.
Hydrogen bonds are very important in our life. Let's imagine for a moment that hydrogen bonds have ceased to form. Here are some of the consequences:

water at room temperature would become gaseous, as its boiling point would drop to about –80 ° C;
all reservoirs would freeze from the bottom, since the density of ice would be greater than the density of liquid water;
the double helix of DNA would cease to exist and much more.

The examples given are enough to understand that in this case, nature on our planet would become completely different.

HYDROGEN BONDING, CONDITIONS OF ITS FORMATION.
Formula ethyl alcohol CH 3 –CH 2 –O – H. Between which atoms of different molecules of this substance are hydrogen bonds formed? Draw up structural formulas to illustrate their formation.
2. Hydrogen bonds exist not only in individual substances, but also in solutions. Show with the help of structural formulas how hydrogen bonds are formed in an aqueous solution of a) ammonia, b) hydrogen fluoride, c) ethanol (ethyl alcohol). = 2H 2 O.
Both of these reactions occur in water constantly and at an equal rate, therefore, there is an equilibrium in water: 2H 2 O AH 3 O + OH.
This balance is called equilibrium of autoprotolysis water.

The direct reaction of this reversible process is endothermic, therefore, when heated, autoprotolysis increases, while at room temperature the equilibrium is shifted to the left, that is, the concentration of H 3 O and OH ions is negligible. What are they equal to?
According to the law of the acting masses

But due to the fact that the number of reacted water molecules is insignificant in comparison with the total number of water molecules, it can be assumed that the water concentration during autoprotolysis practically does not change, and 2 = const Such a low concentration of oppositely charged ions in clean water explains why this liquid, although bad, still conducts an electric current.

AUTOPROTOLYSIS OF WATER, CONSTANT OF AUTOPROTOLYSIS (IONIC PRODUCT) OF WATER.
The ionic product of liquid ammonia (boiling point –33 ° C) is 2 · 10 –28. Make up the equation for the autoprotolysis of ammonia. Determine the concentration of ammonium ions in pure liquid ammonia. Which of the substances has the highest electrical conductivity, water or liquid ammonia?

1. Obtaining hydrogen and its combustion (reducing properties).
2. Obtaining oxygen and combustion of substances in it (oxidizing properties).

Oxygen- one of the most common elements on Earth. It makes up about half the weight of the earth's crust, the outer shell of the planet. When combined with hydrogen, it forms water, which covers more than two-thirds of the earth's surface.

We can neither see oxygen nor taste or smell it. However, it makes up a fifth of the air and is vital. To live, we, like animals and plants, need to breathe.

Oxygen is an indispensable participant chemical reactions, going inside any microscopic cell of a living organism, as a result of which nutrients are broken down and the energy necessary for life is released. That is why oxygen is so necessary for every living being (with the exception of a few types of microbes).

When burning, substances combine with oxygen, releasing energy in the form of heat and light.

Hydrogen

The most common element in the universe is hydrogen... It accounts for the bulk of most stars. On Earth, most of the hydrogen (chemical symbol H) is bound with oxygen (O) to form water (H20). Hydrogen is the simplest and lightest chemical element, since each of its atoms consists of only one proton and one electron.

At the beginning of the 20th century, airships and large aircraft were filled with hydrogen. However, hydrogen is highly flammable. After several disasters caused by fires, hydrogen was no longer used in airships. Today another light gas is used in aeronautics - non-combustible helium.

Hydrogen combines with carbon to form substances called hydrocarbons. These include products derived from natural gas and crude oil, such as propane and butane gases or liquid gasoline. Hydrogen also combines with carbon and oxygen to form carbohydrates. The starch in potatoes and rice and the sugar in beets are carbohydrates.

The sun and other stars are mostly made of hydrogen. In the center of the star, monstrous temperatures and pressures cause hydrogen atoms to merge with each other and turn into another gas - helium. At the same time, a huge amount of energy is released in the form of heat and light.

Industrial methods of obtaining simple substances depend on the form in which the corresponding element is found in nature, that is, what can be the raw materials for its production. So, oxygen available in a free state is obtained physically- release from liquid air. Almost all hydrogen is in the form of compounds, therefore, to obtain it, they use chemical methods... In particular, decomposition reactions can be used. One of the methods for producing hydrogen is the reaction of water decomposition by electric current.

The main industrial method for producing hydrogen is the reaction of methane with water, which is part of natural gas. It is carried out at a high temperature (it is easy to make sure that no reaction occurs when methane is passed even through boiling water):

CH 4 + 2H 2 0 = CO 2 + 4H 2 - 165 kJ

In the laboratory, to obtain simple substances, they do not necessarily use natural raw materials, but select those starting materials from which it is easier to isolate the required substance. For example, in a laboratory, oxygen is not obtained from the air. The same applies to the production of hydrogen. One of the laboratory methods for producing hydrogen, which is sometimes used in industry, is the decomposition of water by electric current.

Usually in the laboratory, hydrogen is produced by the interaction of zinc with hydrochloric acid.

In industry

1.Electrolysis of aqueous solutions of salts:

2NaCl + 2H 2 O → H 2 + 2NaOH + Cl 2

2.Passing water vapor over hot coke at a temperature of about 1000 ° C:

H 2 O + C ⇄ H 2 + CO

3.Natural gas.

Steam conversion: CH 4 + H 2 O ⇄ CO + 3H 2 (1000 ° C) Catalytic oxidation with oxygen: 2CH 4 + O 2 ⇄ 2CO + 4H 2

4. Cracking and reforming of hydrocarbons in the process of oil refining.

In the laboratory

1.The action of dilute acids on metals. To carry out such a reaction, zinc and hydrochloric acid are most often used:

Zn + 2HCl → ZnCl 2 + H 2

2.Interaction of calcium with water:

Ca + 2H 2 O → Ca (OH) 2 + H 2

3.Hydrolysis of hydrides:

NaH + H 2 O → NaOH + H 2

4.The action of alkalis on zinc or aluminum:

2Al + 2NaOH + 6H 2 O → 2Na + 3H 2 Zn + 2KOH + 2H 2 O → K 2 + H 2

5.By electrolysis. During the electrolysis of aqueous solutions of alkalis or acids, hydrogen is evolved at the cathode, for example:

2H 3 O + + 2e - → H 2 + 2H 2 O

Bioreactor for hydrogen production

Physical properties

Gaseous hydrogen can exist in two forms (modifications) - in the form of ortho - and para-hydrogen.

In a molecule of orthohydrogen (mp -259.10 ° C, bp b. -252.89 ° C) - opposite to each other (antiparallel).

Allotropic forms of hydrogen can be separated by adsorption on active carbon at the temperature of liquid nitrogen. At very low temperatures, the equilibrium between orthohydrogen and parahydrogen is almost entirely shifted towards the latter. At 80 K, the ratio of forms is approximately 1: 1. Desorbed parahydrogen on heating is converted into orthohydrogen until a mixture equilibrium at room temperature is formed (ortho-pair: 75:25). Without a catalyst, the transformation is slow, which makes it possible to study the properties of individual allotropic forms. The hydrogen molecule is diatomic - Н₂. Under normal conditions, it is a colorless, odorless and tasteless gas. Hydrogen is the lightest gas, its density is many times less than that of air. Obviously, the smaller the mass of the molecules, the higher their speed at the same temperature. As the lightest, hydrogen molecules move faster than molecules of any other gas and thus can transfer heat faster from one body to another. It follows that hydrogen has the highest thermal conductivity among gaseous substances. Its thermal conductivity is about seven times higher than the thermal conductivity of air.

Chemical properties

Hydrogen molecules H₂ are quite strong, and in order for hydrogen to react, a lot of energy must be expended: H 2 = 2H - 432 kJ Therefore, at ordinary temperatures, hydrogen reacts only with very active metals, for example, with calcium, forming calcium hydride: Ca + H 2 = CaH 2 and with the only non-metal - fluorine, forming hydrogen fluoride: F 2 + H 2 = 2HF With most metals and non-metals, hydrogen reacts at elevated temperatures or under another action, for example, under lighting. It can "take away" oxygen from some oxides, for example: CuO + Н 2 = Cu + Н 2 0 The written equation reflects the reduction reaction. Reduction reactions are called processes as a result of which oxygen is taken away from the compound; substances that take away oxygen are called reducing agents (while they themselves are oxidized). Further, another definition of the concepts "oxidation" and "reduction" will be given. And this definition, historically the first, retains its significance at the present time, especially in organic chemistry. The reduction reaction is the opposite of the oxidation reaction. Both of these reactions always proceed simultaneously as one process: during the oxidation (reduction) of one substance, the reduction (oxidation) of the other must necessarily occur simultaneously.

N 2 + 3H 2 → 2 NH 3

Forms with halogens hydrogen halides:

F 2 + H 2 → 2 HF, the reaction proceeds with an explosion in the dark and at any temperature, Cl 2 + H 2 → 2 HCl, the reaction proceeds with an explosion, only in the light.

Reacts with soot under strong heating:

C + 2H 2 → CH 4

Interaction with alkali and alkaline earth metals

Hydrogen forms with active metals hydrides:

Na + H 2 → 2 NaH Ca + H 2 → CaH 2 Mg + H 2 → MgH 2

Hydrides- salty, solids, easily hydrolyzed:

CaH 2 + 2H 2 O → Ca (OH) 2 + 2H 2

Interaction with metal oxides (usually d-elements)

Oxides are reduced to metals:

CuO + H 2 → Cu + H 2 O Fe 2 O 3 + 3H 2 → 2 Fe + 3H 2 O WO 3 + 3H 2 → W + 3H 2 O

Hydrogenation of organic compounds

When hydrogen acts on unsaturated hydrocarbons in the presence of a nickel catalyst and an elevated temperature, a reaction occurs hydrogenation:

CH 2 = CH 2 + H 2 → CH 3 -CH 3

Hydrogen reduces aldehydes to alcohols:

CH 3 CHO + H 2 → C 2 H 5 OH.

Hydrogen Geochemistry

Hydrogen - basic construction material the universe. It is the most common element, and all elements are formed from it as a result of thermonuclear and nuclear reactions.

Free hydrogen H 2 is relatively rare in terrestrial gases, but in the form of water it plays an extremely important role in geochemical processes.

Hydrogen can be part of minerals in the form of ammonium ion, hydroxyl ion and crystal water.

In the atmosphere, hydrogen is continuously produced by the decomposition of water by solar radiation. It migrates to the upper atmosphere and escapes into space.

Application

Hydrogen energy

Atomic hydrogen is used for atomic hydrogen welding.

In the food industry, hydrogen is registered as food additive E949 like packing gas.

Features of treatment

When mixed with air, hydrogen forms an explosive mixture - the so-called explosive gas. This gas is most explosive when the volumetric ratio of hydrogen and oxygen is 2: 1, or hydrogen and air is approximately 2: 5, since the air contains about 21% oxygen. Hydrogen is also fire hazardous. Liquid hydrogen can cause severe frostbite if it comes into contact with the skin.

Explosive concentrations of hydrogen with oxygen arise from 4% to 96% by volume. When mixed with air from 4% to 75 (74)% by volume.

Use of hydrogen

In the chemical industry, hydrogen is used in the production of ammonia, soap and plastics. In the food industry, using hydrogen from liquid vegetable oils make margarine. Hydrogen is very light and always rises up in the air. Once airships and balloons were filled with hydrogen. But in the 30s. XX century there have been several horrific disasters as the airships exploded and burned. Nowadays, airships are filled with helium gas. Hydrogen is also used as rocket fuel. Hydrogen may someday be widely used as a fuel for cars and trucks. Hydrogen engines do not pollute the environment and only emit water vapor (although the production of hydrogen itself leads to some environmental pollution). Our sun is mostly made of hydrogen. Solar heat and light are the result of the release of nuclear energy from the fusion of hydrogen nuclei.

Using hydrogen as fuel (economic efficiency)

The most important characteristic of substances used as fuel is their calorific value. From the course general chemistry it is known that the reaction of interaction of hydrogen with oxygen occurs with the release of heat. If we take 1 mol of H 2 (2 g) and 0.5 mol of O 2 (16 g) under standard conditions and initiate a reaction, then according to the equation

H 2 + 0.5 O 2 = H 2 O

after the completion of the reaction, 1 mol of H 2 O (18 g) is formed with an energy release of 285.8 kJ / mol (for comparison: the heat of combustion of acetylene is 1300 kJ / mol, propane is 2200 kJ / mol). 1 m³ of hydrogen weighs 89.8 g (44.9 mol). Therefore, to obtain 1 m³ of hydrogen, 12832.4 kJ of energy will be spent. Taking into account that 1 kWh = 3600 kJ, we get 3.56 kWh of electricity. Knowing the tariff for 1 kWh of electricity and the cost of 1 m³ of gas, it can be concluded that it is advisable to switch to hydrogen fuel.

For example, an experimental model Honda FCX of the 3rd generation with a 156 liter hydrogen tank (contains 3.12 kg of hydrogen under a pressure of 25 MPa) travels 355 km. Accordingly, from 3.12 kg of H2, 123.8 kWh is obtained. Energy consumption per 100 km will be 36.97 kWh. Knowing the cost of electricity, the cost of gas or gasoline, their consumption for a car per 100 km, it is easy to calculate the negative economic effect of switching cars to hydrogen fuel. Let's say (Russia 2008), 10 cents per kWh of electricity leads to the fact that 1 m³ of hydrogen leads to a price of 35.6 cents, and taking into account the efficiency of water decomposition of 40-45 cents, the same amount of kWh from burning gasoline costs 12832.4kJ / 42000kJ / 0.7kg / l * 80 cents / l = 34 cents at retail prices, while for hydrogen we calculated the ideal option, excluding transportation, equipment depreciation, etc. For methane with a combustion energy of about 39 MJ per m³ the result will be two to four times lower due to the difference in price (1m³ for Ukraine costs $ 179, and for Europe $ 350). That is, the equivalent amount of methane will cost 10-20 cents.

However, we should not forget that when hydrogen is burned, we get pure water, from which it was extracted. That is, we have a renewable storehouse energy without harm to the environment, unlike gas or gasoline, which are the primary sources of energy.

Php on line 377 Warning: require (http: //www..php): failed to open stream: no suitable wrapper could be found in /hsphere/local/home/winexins/site/tab/vodorod.php on line 377 Fatal error: require (): Failed opening required "http: //www..php" (include_path = ".. php on line 377

In our Everyday life there are things that are so common that almost everyone knows about them. For example, everyone knows that water is a liquid, it is readily available and does not burn, therefore, it can extinguish fire. But have you ever wondered why this is so?

Image source: pixabay.com

Water is made up of hydrogen and oxygen atoms. Both of these elements support combustion. So, based on general logic (not scientific), it follows that water must also burn, right? However, this does not happen.

When does combustion occur?

Combustion is a chemical process in which molecules and atoms combine to release energy in the form of heat and light. To burn something, you need two things - fuel as a source of combustion (for example, a sheet of paper, a piece of wood, etc.) and an oxidizing agent (oxygen in the earth's atmosphere is the main oxidizing agent). We also need the heat necessary to reach the ignition temperature of the substance in order for the combustion process to begin.

Image source auclip.ru

For example, consider the process of burning paper using matches. In this case, paper will be a fuel, the gaseous oxygen contained in the air will act as an oxidizing agent, and the ignition temperature will be reached due to a burning match.

The structure of the chemical composition of water

Image source: water-service.com.ua

Water is made up of two hydrogen atoms and one oxygen atom. Its chemical formula is H2O. Now it is interesting to note that the two constituents of water are indeed highly flammable.

Why is hydrogen a flammable substance?

Hydrogen atoms have only one electron and therefore easily bind with other elements. As a rule, hydrogen occurs naturally in the form of a gas, the molecules of which consist of two atoms. This gas is highly reactive and oxidizes rapidly in the presence of an oxidizing agent, making it flammable.

Image source: myshared.ru

When hydrogen burns, a large amount of energy is released, so it is often used in liquefied form for launching spacecraft into space.

Oxygen supports combustion

As mentioned earlier, an oxidizing agent is required for any combustion. There are many chemical oxidants, including oxygen, ozone, hydrogen peroxide, fluorine, etc. Oxygen is the main oxidant that is found in excess in the Earth's atmosphere. It is generally the main oxidizing agent in most fires. That is why a constant supply of oxygen is needed to keep the fire going.

Water extinguishes fire

Water can extinguish fire for a number of reasons, one of which is that it is a non-combustible liquid, despite the fact that it consists of two elements that can individually create a fiery hell.

Water is the most common fire extinguishing agent. Image source: pixabay.com

As we said earlier, hydrogen is highly flammable, all that is needed is an oxidizing agent and an ignition temperature to start the reaction. Since oxygen is the most abundant oxidizing agent on Earth, it quickly combines with hydrogen atoms, releasing large amounts of light and heat, thus forming water molecules. This is how it works:

Note that a mixture of hydrogen with a small volume of oxygen or air is explosive and is called an oxyhydrogen gas, it burns extremely quickly with a loud pop, which is perceived as an explosion. The Hindenburg airship disaster in 1937 in New Jersey claimed dozens of lives as a result of the combustion of hydrogen that filled the airship shell. The flammability of hydrogen and its explosiveness in combination with oxygen is the main reason why we do not obtain water chemically in laboratories.

10.1 Hydrogen

The name "hydrogen" refers to both a chemical element and a simple substance. Element hydrogen consists of hydrogen atoms. Simple substance hydrogen consists of hydrogen molecules.

a) Chemical element hydrogen

In the natural series of elements, the ordinal number of hydrogen is 1. In the system of elements, hydrogen is in the first period in the IA or VIIA group.

There are three isotopes of hydrogen:
a) light hydrogen - protium,
b) heavy hydrogen - deuterium(D),
c) superheavy hydrogen - tritium(T).

b) Hydrogen atom

From the previous sections of the chemistry course, you already know the following characteristics of the hydrogen atom:

Table 28.The valence capabilities of the hydrogen atom

Valence state		Examples of chemicals
	I 0 –I	HCl, H 2 O, H 2 S, NH 3, CH 4, C 2 H 6, NH 4 Cl, H 2 SO 4, NaHCO 3, KOH H 2 B 2 H 6, SiH 4, GeH 4
		NaH, KH, CaH 2, BaH 2

c) Hydrogen molecule

d) Hydrogen (substance)

Zn + H 2 SO 4 = ZnSO 4 + H 2.

In industry, hydrogen is obtained in large quantities from natural gas (mainly methane) by its interaction with water vapor at 800 ° C in the presence of a nickel catalyst:

CH 4 + 2H 2 O = 4H 2 + CO 2 ( t, Ni)

or coal is treated at high temperature with water vapor:

2H 2 O + C = 2H 2 + CO 2. ( t)

Pure hydrogen is obtained from water by decomposing it with an electric current (subjecting it to electrolysis):

2H 2 O = 2H 2 + O 2 (electrolysis).

e) Hydrogen compounds

LiH
NaH	MgH 2
KH	CaH 2
RbH	SrH 2
CsH	BaH 2

N 2 + 3H 2 2NH 3 ( R, t, Pt - catalyst).

H 2 + Cl 2 = 2HCl.

Sometimes hydrogen is used in metallurgy as a reducing agent in the production of pure metals, for example: Fe 2 O 3 + 3H 2 = 2Fe + 3H 2 O.

1. What particles are the nuclei of a) protium, b) deuterium, c) tritium?
2.Compare the ionization energy of the hydrogen atom with the ionization energy of the atoms of other elements. According to this characteristic, which element is the closest to hydrogen?
3. Do the same for the electron affinity energy
4. Compare the direction of polarization of the covalent bond and the oxidation state of hydrogen in the compounds: a) BeH 2, CH 4, NH 3, H 2 O, HF; b) CH 4, SiH 4, GeH 4.
5. Write down the simplest, molecular, structural and spatial formula of hydrogen. Which one is most commonly used?
6. It is often said: "Hydrogen is lighter than air." What does this mean? When can this expression be taken literally, and when not?
7. Make the structural formulas of potassium and calcium hydrides, as well as ammonia, hydrogen sulfide and hydrogen bromide.
8. Knowing the molar heats of fusion and vaporization of hydrogen, determine the values of the corresponding specific quantities.
9.For each of the four reactions that illustrate the basic chemical properties of hydrogen, draw up an electronic balance. Note oxidants and reducing agents.
10. Determine the mass of zinc required to obtain 4.48 liters of hydrogen in the laboratory.
11. Determine the mass and volume of hydrogen that can be obtained from a 30 m 3 mixture of methane and water vapor, taken in a volume ratio of 1: 2, with a yield of 80%.
12. Make up the equations of the reactions occurring in the interaction of hydrogen a) with fluorine, b) with sulfur.
13. The following reaction schemes illustrate the main chemical properties of ionic hydrides:

10.2 Oxygen

a) Chemical element oxygen

In the natural series of elements, the ordinal number of oxygen is 8. In the system of elements, oxygen is in the second period in the VIA group.
Oxygen is the most abundant element on earth. In the earth's crust, every second atom is an oxygen atom, that is, the molar fraction of oxygen in the atmosphere, hydrosphere and lithosphere of the Earth is about 50%. Oxygen (substance) is an integral part of air. The volume fraction of oxygen in the air is 21%. Oxygen (an element) is a part of water, many minerals, as well as plants and animals. The human body contains an average of 43 kg of oxygen.
Natural oxygen consists of three isotopes (16 O, 17 O and 18 O), of which the lightest isotope 16 O is the most abundant. Therefore, the atomic mass of oxygen is close to 16 D (15.9994 D).

b) Oxygen atom

You are familiar with the following characteristics of the oxygen atom.

Table 29.Oxygen atom valence

Valence state		Examples of chemicals
		Al 2 O 3, Fe 2 O 3, Cr 2 O 3 *

	–II –I 0 + I + II	H 2 O, SO 2, SO 3, CO 2, SiO 2, H 2 SO 4, HNO 2, HClO 4, COCl 2, H 2 O 2 O 2 ** O 2 F 2 OF 2
		NaOH, KOH, Ca (OH) 2, Ba (OH) 2 Na 2 O 2, K 2 O 2, CaO 2, BaO 2
		Li 2 O, Na 2 O, MgO, CaO, BaO, FeO, La 2 O 3

c) Oxygen molecule

d) Oxygen (substance)

Most often, as a result of such reactions, various oxides are obtained (see Chapter II § 5), but active alkali metals, for example sodium, are converted into peroxides by combustion:

2Na + O 2 = Na 2 O 2.

Structural formula of the resulting sodium peroxide (Na) 2 (O-O).
A smoldering splinter, placed in oxygen, flares up. It is a convenient and easy way to detect pure oxygen.
In industry, oxygen is obtained from air by rectification (complex distillation), and in the laboratory by subjecting some oxygen-containing compounds to thermal decomposition, for example:
2KMnO 4 = K 2 MnO 4 + MnO 2 + O 2 (200 ° C);
2KClO 3 = 2KCl + 3O 2 (150 ° C, MnO 2 - catalyst);
2KNO 3 = 2KNO 2 + 3O 2 (400 ° C)
and, in addition, by catalytic decomposition of hydrogen peroxide at room temperature: 2H 2 O 2 = 2H 2 O + O 2 (MnO 2 is a catalyst).
Pure oxygen is used in industry to intensify those processes in which oxidation occurs and to create a high-temperature flame. In rocketry, liquid oxygen is used as an oxidizer.
Oxygen is of great importance for maintaining the life of plants, animals and humans. Under normal conditions, a person has enough oxygen to breathe. But in conditions when there is not enough air, or it is absent altogether (in airplanes, during diving operations, in spaceships, etc.), special gas mixtures containing oxygen are prepared for breathing. Oxygen is also used in medicine for diseases that cause difficulty in breathing.

e) Ozone and its molecules

Ozone O 3 is the second allotropic modification of oxygen.
The triatomic ozone molecule has an angular structure, the middle between the two structures, displayed by the following formulas:

3O 2 = 2O 3 ().

To characterize the polarity of an electric dipole, a physical quantity called " electric moment of an electric dipole " or simply " dipole moment ".

In chemistry, the dipole moment is measured in Debyes: 1 D = 3.34. 10-30 Cl. m

(H 2 O) = ,

where q 1 and q 2 - partial charges (+) on hydrogen atoms, and and - interatomic O - H distances in the molecule. Because q 1 = q 2 = q, a, then

The experimentally determined dipole moments of the water molecule and some other molecules are given in the table.

Table 30.Dipole moments of some polar molecules

Molecule	Molecule	Molecule

Table 31.Some physical characteristics of water

10.4. Hydrogen bond

As you already know, due to the significant difference in the electronegativity of hydrogen and oxygen (2.10 and 3.50), the hydrogen atom in the water molecule has a large positive partial charge ( q h = 0.33 e), and the oxygen atom has an even greater negative partial charge ( q h = -0.66 e). Recall also that the oxygen atom has two lone pairs of electrons per sp 3-hybrid AO. The hydrogen atom of one water molecule is attracted to the oxygen atom of another molecule, and, in addition, the half-empty 1s-AO of the hydrogen atom partially accepts a pair of electrons from the oxygen atom. As a result of these interactions between molecules, a special type of intermolecular bonds arises - a hydrogen bond.
In the case of water, hydrogen bonding can be schematically represented as follows:

In the last structural formula, three dots (dotted line, not electrons!) Show the hydrogen bond.

In liquid hydrogen fluoride, its molecules are linked by hydrogen bonds in rather long chains, and three-dimensional networks are formed in liquid and solid ammonia.
In terms of strength, a hydrogen bond is intermediate between a chemical bond and other types of intermolecular bonds. The molar energy of a hydrogen bond usually ranges from 5 to 50 kJ / mol.
In solid water (i.e. ice crystals), all hydrogen atoms are hydrogen bonded to oxygen atoms, with each oxygen atom forming two hydrogen bonds (using both lone pairs of electrons). This structure makes ice "looser" in comparison with liquid water, where some of the hydrogen bonds are broken, and the molecules are able to "pack" somewhat more densely. This feature of the structure of ice explains why, unlike most other substances, water in a solid state has a lower density than in a liquid state. Water reaches its maximum density at 4 ° C - at this temperature, a lot of hydrogen bonds break, and thermal expansion still does not have a very strong effect on the density.
Hydrogen bonds are very important in our life. Let's imagine for a moment that hydrogen bonds have ceased to form. Here are some of the consequences:

water at room temperature would become gaseous, as its boiling point would drop to about –80 ° C;
all reservoirs would freeze from the bottom, since the density of ice would be greater than the density of liquid water;
the double helix of DNA would cease to exist and much more.

The examples given are enough to understand that in this case, nature on our planet would become completely different.

HYDROGEN BONDING, CONDITIONS OF ITS FORMATION.
The formula of ethyl alcohol is CH 3 –CH 2 –O – H. Between which atoms of different molecules of this substance are hydrogen bonds formed? Draw up structural formulas to illustrate their formation.
2. Hydrogen bonds exist not only in individual substances, but also in solutions. Show with the help of structural formulas how hydrogen bonds are formed in an aqueous solution of a) ammonia, b) hydrogen fluoride, c) ethanol (ethyl alcohol). = 2H 2 O.
Both of these reactions occur in water constantly and at an equal rate, therefore, there is an equilibrium in water: 2H 2 O AH 3 O + OH.
This balance is called equilibrium of autoprotolysis water.

But due to the fact that the number of reacted water molecules is insignificant in comparison with the total number of water molecules, it can be assumed that the water concentration during autoprotolysis practically does not change, and 2 = const Such a low concentration of oppositely charged ions in pure water explains why this liquid, although poorly, still conducts an electric current.

1. Obtaining hydrogen and its combustion (reducing properties).
2. Obtaining oxygen and combustion of substances in it (oxidizing properties).