Hydrogen in nature (0.9% in the Earth's crust). Physical and chemical properties of hydrogen

Hydrogen is a special element that occupies two cells at once in the periodic system of Mendeleev. It is located in two groups of elements with opposite properties, and this feature makes it unique. Hydrogen is a simple substance and integral part many complex compounds, it is an organogenic and biogenic element. It is worth familiarizing yourself in detail with its main features and properties.

Hydrogen in Mendeleev's periodic system

The main features of hydrogen indicated in:

• the element's serial number is 1 (there are the same number of protons and electrons);
• atomic mass is 1.00795;
• hydrogen has three isotopes, each of which has special properties;
• due to the content of only one electron, hydrogen is able to exhibit reducing and oxidizing properties, and after the donation of an electron, hydrogen has a free orbital, which takes part in the composition chemical bonds according to the donor-acceptor mechanism;
• hydrogen is a light element with a low density;
• hydrogen is a strong reducing agent, it opens the group alkali metals in the first group of the main subgroup;
• when hydrogen reacts with metals and other strong reducing agents, it accepts their electron and becomes an oxidizing agent. Such compounds are called hydrides. According to the indicated feature, hydrogen conditionally belongs to the group of halogens (in the table it is given above fluorine in brackets), with which it has similarities.

Hydrogen as a simple substance

Hydrogen is a gas whose molecule consists of two. This substance was discovered in 1766 by the British scientist Henry Cavendish. He proved that hydrogen is a gas that explodes when it interacts with oxygen. After studying hydrogen, chemists found that this substance is the lightest of all known to man.

Another scientist, Lavoisier, gave the element the name "hydrogenium", which in Latin means "giving birth to water." In 1781, Henry Cavendish proved that water is a combination of oxygen and hydrogen. In other words, water is the product of the reaction of hydrogen with oxygen. The combustible properties of hydrogen were known even to ancient scientists: the corresponding records were left by Paracelsus, who lived in the 16th century.

Molecular hydrogen is a naturally occurring gaseous compound common in nature, which consists of two atoms and when a burning splinter is brought up. A hydrogen molecule can decay into atoms that turn into helium nuclei, since they are able to participate in nuclear reactions. Such processes regularly occur in space and on the Sun.

Hydrogen and its physical properties

Hydrogen has the following physical parameters:

• boils at -252.76 °C;
• melts at -259.14 °C; *within the indicated temperature limits, hydrogen is an odorless, colorless liquid;
• hydrogen is slightly soluble in water;
• hydrogen can theoretically go into a metallic state when provided special conditions (low temperatures and high pressure)
• pure hydrogen is an explosive and combustible substance;
• hydrogen is able to diffuse through the thickness of metals, therefore it dissolves well in them;
• hydrogen is 14.5 times lighter than air;
• at high pressure snow-like crystals of solid hydrogen can be obtained.

Chemical properties of hydrogen

Laboratory methods:

• interaction of dilute acids with active metals and metals of medium activity;
• hydrolysis of metal hydrides;
• reaction with water of alkali and alkaline earth metals.

Hydrogen compounds:

Hydrogen halides; volatile hydrogen compounds of non-metals; hydrides; hydroxides; hydrogen hydroxide (water); hydrogen peroxide; organic compounds (proteins, fats, carbohydrates, vitamins, lipids, essential oils, hormones). Click to see safe experiments on the study of the properties of proteins, fats and carbohydrates.

To collect the resulting hydrogen, you need to keep the test tube turned upside down. Hydrogen cannot be collected like carbon dioxide, because it is much lighter than air. Hydrogen quickly evaporates, and when mixed with air (or in a large accumulation) it explodes. Therefore, it is necessary to invert the tube. Immediately after filling, the tube is closed with a rubber stopper.

To check the purity of hydrogen, you need to bring a lit match to the neck of the test tube. If a deaf and quiet pop occurs, the gas is clean, and air impurities are minimal. If the pop is loud and whistling, the gas in the test tube is dirty, it contains a large proportion of foreign components.

Attention! Do not try to repeat these experiments yourself!

The hydrogen atom, compared with the atoms of other elements, has the simplest structure: it consists of one proton.

generating atomic nucleus, and one electron located in the ls orbital. The uniqueness of the hydrogen atom lies in the fact that its only valence electron is directly in the field of action of the atomic nucleus, since it is not shielded by other electrons. This provides it with specific properties. He can in chemical reactions donate an electron, forming an H + cation (like alkali metal atoms), or add an electron from a partner to form an H- anion (like halogen atoms). Therefore, hydrogen in the periodic system is placed more often in group IA, sometimes in group VIIA, but there are variants of tables where hydrogen does not belong to any of the groups of the periodic table.

The hydrogen molecule is diatomic - H2. Hydrogen is the lightest of all gases. Due to the non-polarity and high strength of the H2 molecule (E St\u003d 436 kJ / mol) under normal conditions, hydrogen actively interacts only with fluorine, and when illuminated, also with chlorine and bromine. When heated, it reacts with many non-metals, chlorine, bromine, oxygen, sulfur, showing reducing properties, and interacting with alkali and alkaline earth metals, it is an oxidizing agent and forms hydrides of these metals:

Among all organogens, hydrogen has the lowest relative electronegativity (0E0 = 2.1), therefore, in natural compounds, hydrogen always exhibits an oxidation state of +1. From the standpoint of chemical thermodynamics, hydrogen in living systems containing water cannot form either molecular hydrogen (Н 2) or hydride ion (Н~). Molecular hydrogen at normal conditions it is chemically inactive and at the same time highly volatile, which is why it cannot be retained by the body and participate in metabolism. The hydride ion is chemically extremely active and immediately interacts even with a very small amount of water to form molecular hydrogen. Therefore, hydrogen in the body is either in the form of compounds with other organogens, or in the form of an H + cation.

Hydrogen with organogenic elements forms only covalent bonds. According to the degree of polarity, these bonds are arranged in the following order:

This series is very important for chemistry natural compounds, since the polarity of these bonds and their polarizability predetermine the acidic properties of the compounds, i.e., dissociation with the formation of a proton.

acid properties. Depending on the nature of the element forming X-N connection, there are 4 types of acids:

OH-acids (carboxylic acids, phenols, alcohols);

SH-acids (thiols);

NH-acids (amides, imides, amines);

CH-acids (hydrocarbons and their derivatives).

Given the high polarizability S-H connections can be made next row acids according to the ability to dissociate:

The concentration of hydrogen cations in the aquatic environment determines its acidity, which is expressed using the pH value pH = -lg (Sec. 7.5). Most physiological environments of the body have a reaction close to neutral (pH = 5.0-7.5), only in gastric juice pH = 1.0-2.0. This provides, on the one hand, an antimicrobial effect, killing many microorganisms brought into the stomach with food; on the other hand, acidic environment has a catalytic effect in the hydrolysis of proteins, polysaccharides and other biosubstrates, contributing to the production of the necessary metabolites.

redox properties. Due to the high positive charge density, the hydrogen cation is a rather strong oxidizing agent (f° = 0 V), oxidizing active and medium activity metals when interacting with acids and water:

There are no such strong reducing agents in living systems, and the oxidizing power of hydrogen cations in a neutral medium (pH = 7) is significantly reduced (f° = -0.42 V). Therefore, in the body, the hydrogen cation does not exhibit oxidizing properties, but actively participates in redox reactions, contributing to the conversion of the starting substances into reaction products:

In all the examples given, the hydrogen atoms did not change their oxidation state +1.

Reducing properties are characteristic of molecular and especially atomic hydrogen, i.e. hydrogen at the moment of release directly in the reaction medium, as well as for the hydride ion:

However, there are no such reducing agents (H2 or H-) in living systems, and therefore there are no such reactions. The opinion found in the literature, including textbooks, that hydrogen is the carrier of the reducing properties of organic compounds does not correspond to reality; Thus, in living systems, the reduced form of dehydrogenase coenzyme, in which carbon atoms, rather than hydrogen atoms, act as a reducer of biosubstrates (Sec. 9.3.3).

complexing properties. Due to the presence of a free atomic orbital in the hydrogen cation and the high polarizing effect of the H + cation itself, it is an active complexing ion. So, in an aqueous medium, a hydrogen cation forms a hydronium ion H3O +, and in the presence of ammonia, an ammonium ion NH4:

Tendency to form associates. Highly polar hydrogen atoms O-H connections and N--H form hydrogen bonds (Sec. 3.1). The strength of a hydrogen bond (from 10 to 100 kJ/mol) depends on the magnitude of the localized charges and the length of the hydrogen bond, i.e., on the distance between the atoms of the electronegative elements involved in its formation. For amino acids, carbohydrates, proteins, nucleic acids the following lengths of hydrogen bonds are characteristic, pm:

Due to hydrogen bonds, reversible intermolecular interactions arise between the substrate and the enzyme, between individual groups in natural polymers, which determine their secondary, tertiary, and quaternary structures (Sections 21.4, 23.4). The hydrogen bond plays a leading role in the properties of water as a solvent and reagent.

Water and its properties. Water is the most important compound of hydrogen. All chemical reactions in the body occur only in the aquatic environment, life without water is impossible. Water as a solvent was considered in Sec. 6.1.

Acid-base properties. Water as a reagent from the standpoint of acid-base properties is a true ampholyte (Section 8.1). This manifests itself both in the hydrolysis of salts (Section 8.3.1) and in the dissociation of acids and bases in an aqueous medium (Section 8.3.2).

Quantitative characteristic acidity aquatic environments is pH value pH.

Water as an acid-base reagent is involved in the hydrolysis reactions of biosubstrates. For example, hydrolysis of adenosine triphosphate serves as a source of stored energy for the body, enzymatic hydrolysis of unnecessary proteins serves to obtain amino acids, which are the starting material for the synthesis of necessary proteins. At the same time, H+ cations or OH– anions are acid-base catalysts for biosubstrate hydrolysis reactions (Sections 21.4, 23.4).

redox properties. In a water molecule, both hydrogen and oxygen are in stable oxidation states. Therefore, water does not exhibit pronounced redox properties. Redox reactions are possible when water interacts only with very active reducing agents or very active oxidizing agents, or under conditions of strong activation of the reagents.

Water can be an oxidizing agent due to hydrogen cations when interacting with strong reducing agents, such as alkali and alkaline earth metals or their hydrides:

At high temperatures interaction of water with less active reducing agents is possible:

In living systems, their water component never acts as an oxidizing agent, since this would lead to the destruction of these systems due to the formation and irreversible removal of molecular hydrogen from organisms.

Water can act as a reducing agent due to oxygen atoms, for example, when interacting with such a strong oxidizing agent as fluorine:

Under the influence of light and with the participation of chlorophyll, the process of photosynthesis proceeds in plants with the formation of O2 from water (Sec. 9.3.6):

In addition to direct participation in redox transformations, water and its dissociation products H + and OH- take part as a medium that contributes to the occurrence of many redox reactions due to its high polarity ( = 79) and the participation of the ions formed by it in the transformations of initial substances into final (Section 9.1).

complexing properties. Due to the presence of two lone electron pairs at the oxygen atom, the water molecule is a fairly active monodentate ligand, which forms a complex oxonium ion H 3 0 + with a hydrogen cation, and fairly stable aqua complexes with metal cations in aqueous solutions, for example [Ca (H 2 0) 6 ] 2+ , [ Fe(H 2 0) 6 ] 3+ , 2+ . In these complex ions, the node molecules are covalently bonded to the complexing agents rather strongly. Alkali metal cations do not form aqua complexes, but form hydrated cations due to electrostatic forces. Time settled life water molecules in the hydration shells of these cations does not exceed 0.1 s, and their composition in terms of the number of water molecules can easily change.

Tendency to form associates. Due to the high polarity, which promotes electrostatic interaction and the formation of hydrogen bonds, water molecules even in pure water (Sec. 6.1) form intermolecular associates that differ in structure, the number of molecules and the time of their settled life in the associates, as well as the lifetime of the associates themselves. In this way, pure water is an open complex dynamic system. Under the influence of external factors: radioactive, ultraviolet and laser radiation, elastic waves, temperature, pressure, electric, magnetic and electromagnetic fields from artificial and natural sources (space, Sun, Earth, living objects) - water changes its structural and informational properties, and consequently, its biological and physiological functions change.

In addition to self-association, water molecules hydrate ions, polar molecules, and macromolecules, forming hydration shells around them, thereby stabilizing them in solution and promoting their dissolution (Sec. 6.1). Substances whose molecules are non-polar and relatively small can only slightly dissolve in water, filling the voids of its associates with a certain structure. In this case, as a result of hydrophobic interaction, nonpolar molecules structure the hydration shell surrounding them, turning it into a structured associate, usually with an ice-like structure, inside which this nonpolar molecule is located.

In living organisms, two categories of water can be distinguished - "bound" and "free", the latter, apparently, is only in the intercellular fluid (Sec. 6.1). bound water, in turn, is subdivided into "structured" (strongly bound) and "destructured" (weakly bound or loose) water. Probably, all of the above external factors affect the state of water in the body, changing the ratios: "structured" / "destructured" and "bound" / "free" water, as well as its structural and dynamic parameters. This is manifested in changes in the physiological state of the body. It is possible that intracellular water continuously undergoes regulated, mainly by proteins, pulsating transitions from a "structured" to a "destructured" state. These transitions are interconnected with the expulsion of spent metabolites (slags) from the cell and the absorption of necessary substances. FROM modern point of vision, water is involved in the formation of a single intracellular structure, due to which the orderliness of life processes is achieved. Therefore, according to the figurative expression of A. Szent-Gyorgyi, water in the body is the "matrix of life."

Water in nature. Water is the most important and widespread substance on Earth. Surface the globe 75% covered with water. The volume of the World Ocean is 1.4 billion km 3 . The same amount of water is found in minerals in the form of water of crystallization. The atmosphere contains 13 thousand km 3 of water. At the same time, the reserves of fresh water suitable for drinking and domestic needs are quite limited (the volume of all freshwater reservoirs is 200 thousand km 3). Fresh water, used in everyday life, contains various impurities from 0.05 to 1 g / l, most often these are salts: bicarbonates, chlorides, sulfates, including soluble calcium and magnesium salts, the presence of which makes water hard (section 14.3). At present, security water resources and cleaning Wastewater are the most pressing environmental issues.

In ordinary water, there is about 0.02% heavy water D2O (D - deuterium). It accumulates during the evaporation or electrolysis of ordinary water. Heavy water is toxic. Heavy water is used to study the movement of water in living organisms. With its help, it was established that the speed of water movement in the tissues of some plants reaches 14 m/h, and the water drunk by a person is completely distributed over his organs and tissues in 2 hours and is completely removed from the body only after two weeks. Living organisms contain from 50 to 93% water, which is an indispensable participant in all life processes. Life is impossible without water. With a life expectancy of 70 years, a person consumes about 70 tons of water with food and drink.

In scientific and medical practice widely used distilled water- colorless transparent liquid, odorless and tasteless, pH = 5.2-6.8. This is a pharmacopoeial preparation for the preparation of many dosage forms.

Water for injections(pyrogenic water) - also a pharmacopoeial preparation. This water does not contain pyrogenic substances. Pyrogens are substances of bacterial origin - metabolites or waste products of bacteria that, when entering the body, cause chills, fever, headaches, and impaired cardiovascular activity. Apyrogenic water is prepared by double distillation of the node (bidistillate) under aseptic conditions and used within 24 hours.

Concluding the section, it is necessary to emphasize the features of hydrogen as a biogenic element. In living systems, hydrogen always exhibits an oxidation state of +1 and occurs either as a polar covalent bond with other biogenic elements, or as an H + cation. The hydrogen cation is a carrier of acidic properties and an active complexing agent that interacts with free electron pairs of atoms of other organogens. From the standpoint of redox properties, bound hydrogen under the conditions of the body does not show the properties of either an oxidizing agent or a reducing agent, however, the hydrogen cation actively participates in many redox reactions, without changing its oxidation state, but contributing to the conversion of biosubstrates into reaction products. Hydrogen bonded to electronegative elements forms hydrogen bonds.

The most abundant element in the universe is hydrogen. In the matter of stars, it has the form of nuclei - protons - and is the material for thermonuclear processes. Almost half of the mass of the Sun also consists of H 2 molecules. Its content in the earth's crust reaches 0.15%, and atoms are present in the composition of oil, natural gas, water. Together with oxygen, nitrogen and carbon, it is an organogenic element that is part of all living organisms on Earth. In our article, we will study the physical and Chemical properties hydrogen, we define the main areas of its application in industry and its importance in nature.

Position in the periodic system of chemical elements of Mendeleev

The first element to open the periodic table is hydrogen. Its atomic mass is 1.0079. It has two stable (protium and deuterium) and one radioactive isotope (tritium). Physical properties determined by the place of the non-metal in the table chemical elements. Under normal conditions, hydrogen (its formula is H 2) is a gas that is almost 15 times lighter than air. The structure of an element's atom is unique: it consists of only a nucleus and one electron. The molecule of a substance is diatomic, the particles in it are connected using a covalent non-polar bond. Its energy intensity is quite high - 431 kJ. This explains the low chemical activity of the compound under normal conditions. The electronic formula of hydrogen is: H:H.

The substance has whole line properties that have no analogues among other non-metals. Let's consider some of them.

Solubility and thermal conductivity

Metals conduct heat best, but hydrogen approaches them in terms of thermal conductivity. The explanation for the phenomenon lies in the very high speed thermal motion of light molecules of a substance, therefore, in a hydrogen atmosphere, a heated object cools 6 times faster than in air. The compound can dissolve well in metals, for example, almost 900 volumes of hydrogen can be absorbed by one volume of palladium. Metals can enter into chemical reactions with H 2 in which the oxidizing properties of hydrogen are manifested. In this case, hydrides are formed:

2Na + H 2 \u003d 2 NaH.

In this reaction, the atoms of an element accept electrons from metal particles, turning into anions with a unit negative charge. A simple substance H 2 in this case is an oxidizing agent, which is usually not typical for it.

Hydrogen as a reducing agent

What unites metals and hydrogen is not only high thermal conductivity, but also the ability of their atoms to chemical processes donate their own electrons, that is, oxidize. For example, basic oxides react with hydrogen. The redox reaction ends with the release of pure metal and the formation of water molecules:

CuO + H 2 \u003d Cu + H 2 O.

The interaction of a substance with oxygen during heating also leads to the production of water molecules. The process is exothermic and is accompanied by the release a large number thermal energy. If a gas mixture of H 2 and O 2 reacts in a ratio of 2: 1, then it is called because it explodes when ignited:

2H 2 + O 2 \u003d 2H 2 O.

Water is and plays an important role in the formation of the Earth's hydrosphere, climate, and weather. It provides the circulation of elements in nature, supports all the life processes of organisms - the inhabitants of our planet.

Interaction with non-metals

The most important chemical properties of hydrogen are its reactions with non-metallic elements. At normal conditions are chemically inert enough, so the substance can only react with halogens, for example, with fluorine or chlorine, which are the most active among all non-metals. So, a mixture of fluorine and hydrogen explodes in the dark or in the cold, and with chlorine - when heated or in the light. The reaction products will be hydrogen halides, the aqueous solutions of which are known as fluoride and chloride acids. C interacts at a temperature of 450-500 degrees, a pressure of 30-100 MPa and in the presence of a catalyst:

N₂ + 3H₂ ⇔ p, t, kat ⇔ 2NH₃.

The considered chemical properties of hydrogen have great importance for industry. For example, you can get a valuable chemical product - ammonia. It is the main raw material for the production of nitrate acid and nitrogen fertilizers: urea, ammonium nitrate.

organic matter

Between carbon and hydrogen leads to the production of the simplest hydrocarbon - methane:

C + 2H 2 = CH 4.

The substance is the most important component of the natural substance and is used as a valuable type of fuel and raw material for the industry of organic synthesis.

In the chemistry of carbon compounds, an element is included in a huge number of substances: alkanes, alkenes, carbohydrates, alcohols, etc. Many reactions of organic compounds with H 2 molecules are known. They are wearing common name hydrogenation or hydrogenation. So, aldehydes can be reduced with hydrogen to alcohols, unsaturated hydrocarbons - to alkanes. For example, ethylene is converted to ethane:

C 2 H 4 + H 2 \u003d C 2 H 6.

Important practical value have such chemical properties of hydrogen as, for example, the hydrogenation of liquid oils: sunflower, corn, rapeseed. It leads to the production of solid fat - lard, which is used in the production of glycerin, soap, stearin, durum varieties margarine. For improvement appearance and palatability food product, milk, animal fats, sugar, vitamins are added to it.

In our article, we studied the properties of hydrogen and found out its role in nature and human life.

DEFINITION

Hydrogen- the first element of the Periodic system of chemical elements of D.I. Mendeleev. The symbol is N.

Atomic mass - 1 a.m.u. The hydrogen molecule is diatomic - H 2.

Electronic configuration hydrogen atom - 1s 1. Hydrogen belongs to the s-element family. In its compounds, it exhibits oxidation states -1, 0, +1. Natural hydrogen consists of two stable isotopes - protium 1 H (99.98%) and deuterium 2 H (D) (0.015%) - and a radioactive isotope of tritium 3 H (T) (trace amounts, half-life - 12.5 years) .

Chemical properties of hydrogen

Under normal conditions, molecular hydrogen exhibits a relatively low reactivity, which is explained by the high bond strength in the molecule. When heated, it interacts with almost all simple substances formed by elements of the main subgroups (except noble gases, B, Si, P, Al). In chemical reactions, it can act both as a reducing agent (more often) and an oxidizing agent (less often).

Hydrogen manifests reducing agent properties(H 2 0 -2e → 2H +) in the following reactions:

1. Reactions of interaction with simple substances - non-metals. Hydrogen reacts with halogens, moreover, the reaction of interaction with fluorine under normal conditions, in the dark, with an explosion, with chlorine - under illumination (or UV irradiation) by a chain mechanism, with bromine and iodine only when heated; oxygen(a mixture of oxygen and hydrogen in a 2:1 volume ratio is called "explosive gas"), gray, nitrogen and carbon:

H 2 + Hal 2 \u003d 2HHal;

2H 2 + O 2 \u003d 2H 2 O + Q (t);

H 2 + S \u003d H 2 S (t \u003d 150 - 300C);

3H 2 + N 2 ↔ 2NH 3 (t = 500C, p, kat = Fe, Pt);

2H 2 + C ↔ CH 4 (t, p, kat).

2. Reactions of interaction with complex substances. Hydrogen reacts with oxides of low-active metals, and it is able to reduce only metals that are in the activity series to the right of zinc:

CuO + H 2 \u003d Cu + H 2 O (t);

Fe 2 O 3 + 3H 2 \u003d 2Fe + 3H 2 O (t);

WO 3 + 3H 2 \u003d W + 3H 2 O (t).

Hydrogen reacts with non-metal oxides:

H 2 + CO 2 ↔ CO + H 2 O (t);

2H 2 + CO ↔ CH 3 OH (t = 300C, p = 250 - 300 atm., kat = ZnO, Cr 2 O 3).

Hydrogen enters into hydrogenation reactions with organic compounds the class of cycloalkanes, alkenes, arenes, aldehydes and ketones, etc. All these reactions are carried out under heating, under pressure, platinum or nickel is used as catalysts:

CH 2 \u003d CH 2 + H 2 ↔ CH 3 -CH 3;

C 6 H 6 + 3H 2 ↔ C 6 H 12;

C 3 H 6 + H 2 ↔ C 3 H 8;

CH 3 CHO + H 2 ↔ CH 3 -CH 2 -OH;

CH 3 -CO-CH 3 + H 2 ↔ CH 3 -CH (OH) -CH 3.

Hydrogen as an oxidizing agent(H 2 + 2e → 2H -) acts in reactions with alkali and alkaline earth metals. In this case, hydrides are formed - crystalline ionic compounds in which hydrogen exhibits an oxidation state of -1.

2Na + H 2 ↔ 2NaH (t, p).

Ca + H 2 ↔ CaH 2 (t, p).

Physical properties of hydrogen

Hydrogen is a light colorless gas, odorless, density at n.o. - 0.09 g / l, 14.5 times lighter than air, t bale = -252.8C, t pl = - 259.2C. Hydrogen is poorly soluble in water and organic solvents, it is highly soluble in some metals: nickel, palladium, platinum.

According to modern cosmochemistry, hydrogen is the most abundant element in the universe. The main form of existence of hydrogen in outer space are individual atoms. Hydrogen is the 9th most abundant element on Earth. The main amount of hydrogen on Earth is in a bound state - in the composition of water, oil, natural gas, coal, etc. In the form of a simple substance, hydrogen is rarely found - in the composition of volcanic gases.

Getting hydrogen

There are laboratory and industrial methods for producing hydrogen. Laboratory methods include the interaction of metals with acids (1), as well as the interaction of aluminum with aqueous solutions of alkalis (2). Among the industrial methods for producing hydrogen, the electrolysis of aqueous solutions of alkalis and salts (3) and the conversion of methane (4) play an important role:

Zn + 2HCl = ZnCl 2 + H 2 (1);

2Al + 2NaOH + 6H 2 O = 2Na +3 H 2 (2);

2NaCl + 2H 2 O = H 2 + Cl 2 + 2NaOH (3);

CH 4 + H 2 O ↔ CO + H 2 (4).

Examples of problem solving

EXAMPLE 1

Exercise	When 23.8 g of metallic tin interacted with an excess of hydrochloric acid, hydrogen was released, in an amount sufficient to obtain 12.8 g of metallic copper. Determine the oxidation state of tin in the resulting compound.
Solution	Based on the electronic structure of the tin atom (...5s 2 5p 2), we can conclude that tin is characterized by two oxidation states - +2, +4. Based on this, we will compose the equations of possible reactions: Sn + 2HCl = H 2 + SnCl 2 (1); Sn + 4HCl = 2H 2 + SnCl 4 (2); CuO + H 2 \u003d Cu + H 2 O (3). Find the amount of copper substance: v (Cu) \u003d m (Cu) / M (Cu) \u003d 12.8 / 64 \u003d 0.2 mol. According to equation 3, the amount of hydrogen substance: v (H 2) \u003d v (Cu) \u003d 0.2 mol. Knowing the mass of tin, we find its amount of substance: v (Sn) \u003d m (Sn) / M (Sn) \u003d 23.8 / 119 \u003d 0.2 mol. Let's compare the amounts of tin and hydrogen substances according to equations 1 and 2 and according to the condition of the problem: v 1 (Sn): v 1 (H 2) = 1:1 (equation 1); v 2 (Sn): v 2 (H 2) = 1:2 (equation 2); v(Sn): v(H 2) = 0.2:0.2 = 1:1 (problem condition). Therefore, tin reacts with hydrochloric acid according to equation 1 and the oxidation state of tin is +2.
Answer	The oxidation state of tin is +2.

EXAMPLE 2

Exercise	The gas released by the action of 2.0 g of zinc per 18.7 ml of 14.6% hydrochloric acid (solution density 1.07 g/ml) was passed by heating over 4.0 g of copper (II) oxide. What is the mass of the resulting solid mixture?
Solution	When zinc acts on hydrochloric acid hydrogen is released: Zn + 2HCl \u003d ZnCl 2 + H 2 (1), which, when heated, reduces copper (II) oxide to copper (2): CuO + H 2 \u003d Cu + H 2 O. Find the amount of substances in the first reaction: m (p-ra Hcl) = 18.7. 1.07 = 20.0 g; m(HCl) = 20.0. 0.146 = 2.92 g; v (HCl) \u003d 2.92 / 36.5 \u003d 0.08 mol; v(Zn) = 2.0/65 = 0.031 mol. Zinc is deficient, so the amount of hydrogen released is: v (H 2) \u003d v (Zn) \u003d 0.031 mol. In the second reaction, hydrogen is deficient because: v (CuO) \u003d 4.0 / 80 \u003d 0.05 mol. As a result of the reaction, 0.031 mol of CuO will turn into 0.031 mol of Cu, and the mass loss will be: m (СuО) - m (Сu) \u003d 0.031 × 80 - 0.031 × 64 \u003d 0.50 g. The mass of the solid mixture of CuO with Cu after passing hydrogen will be: 4.0-0.5 = 3.5 g
Answer	The mass of the solid mixture of CuO with Cu is 3.5 g.

Hydrogen (tracing paper from Latin: lat. Hydrogenium - hydro = "water", gen = "generating"; hydrogenium - "generating water"; denoted by the symbol H) - the first element of the periodic system of elements. Widely distributed in nature. The cation (and nucleus) of the most common isotope of hydrogen 1 H is the proton. The properties of the 1 H nucleus make it possible to widely use NMR spectroscopy in the analysis of organic substances.

Three isotopes of hydrogen have their own names: 1 H - protium (H), 2 H - deuterium (D) and 3 H - tritium (radioactive) (T).

The simple substance hydrogen - H 2 - is a light colorless gas. In a mixture with air or oxygen, it is combustible and explosive. Non-toxic. Let's dissolve in ethanol and a number of metals: iron, nickel, palladium, platinum.

Story

The release of combustible gas during the interaction of acids and metals was observed in the 16th and XVII centuries at the dawn of the formation of chemistry as a science. Mikhail Vasilyevich Lomonosov also directly pointed to its isolation, but already definitely realizing that this was not phlogiston. The English physicist and chemist Henry Cavendish studied this gas in 1766 and called it "combustible air". When burned, "combustible air" produced water, but Cavendish's adherence to the theory of phlogiston prevented him from drawing the right conclusions. The French chemist Antoine Lavoisier, together with the engineer J. Meunier, using special gasometers, in 1783 carried out the synthesis of water, and then its analysis, decomposing water vapor with red-hot iron. Thus, he established that "combustible air" is part of the water and can be obtained from it.

origin of name

Lavoisier gave hydrogen the name hydrogène (from other Greek ὕδωρ - water and γεννάω - I give birth) - “giving birth to water”. The Russian name "hydrogen" was proposed by the chemist M.F. Solovyov in 1824 - by analogy with "oxygen" by M.V. Lomonosov.

Prevalence

In the Universe
Hydrogen is the most abundant element in the universe. It accounts for about 92% of all atoms (8% are helium atoms, the share of all other elements combined is less than 0.1%). Thus, hydrogen is the main component stars and interstellar gas. Under conditions of stellar temperatures (for example, the surface temperature of the Sun is ~ 6000 °C), hydrogen exists in the form of plasma; in interstellar space, this element exists in the form of individual molecules, atoms, and ions and can form molecular clouds that differ significantly in size, density, and temperature.

Earth's crust and living organisms
The mass fraction of hydrogen in the earth's crust is 1% - this is the tenth most common element. However, its role in nature is determined not by mass, but by the number of atoms, the share of which among other elements is 17% (second place after oxygen, the proportion of atoms of which is ~ 52%). Therefore, the importance of hydrogen in the chemical processes occurring on Earth is almost as great as that of oxygen. Unlike oxygen, which exists on Earth in both bound and free states, practically all hydrogen on Earth is in the form of compounds; only a very small amount of hydrogen in the form of a simple substance is found in the atmosphere (0.00005% by volume).
Hydrogen is a constituent of almost all organic substances and is present in all living cells. In living cells, by the number of atoms, hydrogen accounts for almost 50%.

Receipt

Industrial methods of obtaining simple substances depend on the form in which the corresponding element is in nature, that is, what can be the raw material for its production. So, oxygen, available in a free state, is obtained in a physical way- release from liquid air. Almost all hydrogen is in the form of compounds, so chemical methods are used to obtain it. In particular, decomposition reactions can be used. One of the ways to produce hydrogen is the reaction of decomposition of water by electric current.
The main industrial method for producing hydrogen is the reaction with water of methane, which is part of natural gas. It is carried out at high temperature:
CH 4 + 2H 2 O \u003d CO 2 + 4H 2 −165 kJ

One of the laboratory methods for producing hydrogen, which is sometimes used in industry, is the decomposition of water by electric current. Hydrogen is usually produced in the laboratory by reacting zinc with hydrochloric acid.