History reference
Hydrogen is the first element of PSCE D.I. Mendeleev.
The Russian name for hydrogen indicates that it "gives birth to water"; Latin " hydrogenium" means the same.
For the first time, the release of combustible gas during the interaction of certain metals with acids was observed by Robert Boyle and his contemporaries in the first half of the 16th century.
But hydrogen was discovered only in 1766 by the English chemist Henry Cavendish, who found that when metals interact with dilute acids, a certain “combustible air” is released. Observing the combustion of hydrogen in air, Cavendish found that the result is water. This was in 1782.
In 1783, the French chemist Antoine-Laurent Lavoisier isolated hydrogen by decomposing water with hot iron. In 1789, hydrogen was isolated from the decomposition of water under the action of an electric current.
Prevalence in nature
Hydrogen is the main element of space. For example, the Sun is made up of 70% of its mass hydrogen. There are several tens of thousands of times more hydrogen atoms in the Universe than all the atoms of all metals combined.In the earth's atmosphere, too, there is some hydrogen in the form of a simple substance - a gas of composition H 2. Hydrogen is much lighter than air and is therefore found in the upper atmosphere.
But there is much more bound hydrogen on Earth: after all, it is part of water, the most common complex substance on our planet. Hydrogen bound into molecules contains both oil and natural gas, many minerals and rocks. Hydrogen is a constituent of all organic substances.
Characteristics of the element hydrogen.
Hydrogen has a dual nature, for this reason, in some cases, hydrogen is placed in the alkali metal subgroup, and in others, in the halogen subgroup.
Electronic configuration 1s 1 . A hydrogen atom consists of one proton and one electron.
The hydrogen atom is able to lose an electron and turn into an H + cation, and in this it is similar to alkali metals.
The hydrogen atom can also attach an electron, thus forming an anion H - , in this respect, hydrogen is similar to halogens.
Always monovalent in compounds
CO: +1 and -1.
Physical properties of hydrogen
Hydrogen is a gas, colorless, tasteless and odorless. 14.5 times lighter than air. Slightly soluble in water. It has high thermal conductivity. At t= -253 °C it liquefies, at t= -259 °C it solidifies. Hydrogen molecules are so small that they can slowly diffuse through many materials - rubber, glass, metals, which is used in the purification of hydrogen from other gases.Three isotopes of hydrogen are known: - protium, - deuterium, - tritium. The main part of natural hydrogen is protium. Deuterium is part of the heavy water that enriches the surface waters of the ocean. Tritium is a radioactive isotope.
Chemical properties of hydrogen
Hydrogen is a non-metal and has a molecular structure. The hydrogen molecule consists of two atoms linked by a non-polar covalent bond. The binding energy in a hydrogen molecule is 436 kJ/mol, which explains the low chemical activity of molecular hydrogen.
Interaction with halogens. At ordinary temperature, hydrogen reacts only with fluorine:
With chlorine - only in the light, forming hydrogen chloride, with bromine the reaction proceeds less vigorously, with iodine it does not go to the end even at high temperatures.
Interaction with oxygen when heated, when ignited, the reaction proceeds with an explosion: 2H 2 + O 2 \u003d 2H 2 O.
A mixture of 1 part oxygen and 2 parts hydrogen is an "explosive mixture", the most explosive.
Interaction with sulfur - when heated H 2 + S = H 2 S.
interaction with nitrogen. When heated, at high pressure and in the presence of a catalyst:
Interaction with nitric oxide (II). Used in purification systems in the production of nitric acid: 2NO + 2H 2 = N 2 + 2H 2 O.
Interaction with metal oxides. Hydrogen is a good reducing agent, it restores many metals from their oxides: CuO + H 2 = Cu + H 2 O.
Atomic hydrogen is a strong reducing agent. It is formed from molecular in an electrical discharge under low pressure conditions. It has a high restorative activity hydrogen at the time of release formed when a metal is reduced with an acid.
Interaction with active metals . At high temperature, it combines with alkali and alkaline earth metals and forms white crystalline substances - metal hydrides, showing the properties of an oxidizing agent: 2Na + H 2 = 2NaH;
Getting hydrogen
In the laboratory:
The interaction of metal with dilute solutions of sulfuric and hydrochloric acids,
The interaction of aluminum or silicon with aqueous solutions of alkalis:
Si + 2NaOH + H 2 O \u003d Na 2 SiO 3 + 2H 2.
In industry:
Electrolysis of aqueous solutions of sodium and potassium chlorides or electrolysis of water in the presence of hydroxides:
2H 2 O \u003d 2H 2 + O 2.
conversion method. First, water gas is obtained by passing water vapor through hot coke at 1000 ° C:
Then carbon monoxide (II) is oxidized to carbon monoxide (IV) by passing a mixture of water gas with excess water vapor over a Fe 2 O 3 catalyst heated to 400–450 ° С:
CO + H 2 O \u003d CO 2 + H 2.
The resulting carbon monoxide (IV) is absorbed by water, in this way 50% of industrial hydrogen is obtained.
Methane conversion: CH 4 + H 2 O \u003d CO + 3H 2.
Thermal decomposition of methane at 1200 °C: CH 4 = C + 2H 2 .
Deep cooling (down to -196 °С) of coke oven gas. At this temperature, all gaseous substances, except hydrogen, condense.
The use of hydrogen is based on its physical and chemical properties:
as a light gas, it is used to fill balloons (mixed with helium);
oxygen-hydrogen flame is used to obtain high temperatures when welding metals;
as a reducing agent is used to obtain metals (molybdenum, tungsten, etc.) from their oxides;
for the production of ammonia and artificial liquid fuels, for the hydrogenation of fats.
§3. Reaction equation and how to write it
Interaction hydrogen With oxygen, as Sir Henry Cavendish established, leads to the formation of water. Let's use this simple example to learn how to write equations of chemical reactions.
What comes from hydrogen and oxygen, we already know:
H 2 + O 2 → H 2 O
Now we take into account that the atoms of chemical elements in chemical reactions do not disappear and do not appear from nothing, do not turn into each other, but combine in new combinations to form new molecules. This means that in the equation of the chemical reaction of atoms of each type there must be the same number before reactions ( left from the equal sign) and after the end of the reaction ( on right from the equal sign), like this:
2H 2 + O 2 \u003d 2H 2 O
That's what it is reaction equation - conditional record of an ongoing chemical reaction using formulas of substances and coefficients.
This means that in the above reaction two moles hydrogen should react with by one mole oxygen, and the result will be two moles water.
Interaction hydrogen With oxygen- not a simple process at all. It leads to a change in the oxidation states of these elements. To select coefficients in such equations, one usually uses the method " electronic balance".
When water is formed from hydrogen and oxygen, this means that hydrogen changed its oxidation state from 0 before +I, a oxygen- from 0 before −II. At the same time, several (n) electrons:
Hydrogen donating electrons serves here reducing agent, and oxygen accepting electrons - oxidizing agent.
Oxidizing and reducing agents
Now let's see how the processes of giving and receiving electrons look like separately. Hydrogen, having met with the "robber" - oxygen, loses all its property - two electrons, and its oxidation state becomes equal to +I:
H 2 0 − 2 e− = 2Н + I
Happened oxidation half-reaction equation hydrogen.
And the bandit oxygen About 2, having taken the last electrons from the unfortunate hydrogen, is very pleased with his new oxidation state -II:
O 2 + 4 e− = 2O − II
This reduction half-reaction equation oxygen.
It remains to add that both the "bandit" and his "victim" have lost their chemical identity and from simple substances - gases with diatomic molecules H 2 and About 2 turned into components of a new chemical substance - water H 2 O.
Further, we will argue as follows: how many electrons the reductant gave to the oxidizing bandit, that is how much he received. The number of electrons donated by the reducing agent must be equal to the number of electrons accepted by the oxidizing agent..
So you need equalize the number of electrons in the first and second half-reactions. In chemistry, the following conditional form of writing the equations of half-reactions is accepted:
2 H 2 0 − 2 e− = 2Н + I |
|
1 O 2 0 + 4 e− = 2O − II |
Here, the numbers 2 and 1 to the left of the curly bracket are factors that will help ensure that the number of given and received electrons is equal. We take into account that in the equations of half-reactions 2 electrons are given away, and 4 are accepted. To equalize the number of received and given electrons, the least common multiple and additional factors are found. In our case, the least common multiple is 4. Additional factors will be 2 for hydrogen (4: 2 = 2), and for oxygen - 1 (4: 4 = 1)
The resulting multipliers will serve as the coefficients of the future reaction equation:
2H 2 0 + O 2 0 \u003d 2H 2 + I O -II
Hydrogen oxidized not only when meeting oxygen. Approximately the same effect on hydrogen and fluorine F2, halogen and the famous "robber", and seemingly harmless nitrogen N 2:
H 2 0 + F 2 0 = 2H + I F −I |
3H 2 0 + N 2 0 \u003d 2N -III H 3 + I |
This results in hydrogen fluoride HF or ammonia NH3.
In both compounds, the oxidation state hydrogen becomes equal +I, because he gets partners in the molecule "greedy" for someone else's electronic good, with high electronegativity - fluorine F and nitrogen N. At nitrogen the value of electronegativity is considered equal to three conventional units, and y fluorine in general, the highest electronegativity among all chemical elements is four units. So it's no wonder they leave the poor hydrogen atom without any electronic environment.
But hydrogen maybe restore- accept electrons. This happens if alkali metals or calcium, in which the electronegativity is less than that of hydrogen, participate in the reaction with it.
In Lesson 22 " Chemical properties of hydrogen» from the course « Chemistry for dummies» find out with what substances hydrogen reacts; find out what chemical properties hydrogen has.
Hydrogen enters into chemical reactions with simple and complex substances. However, under normal conditions, hydrogen is inactive. For its interaction with other substances, it is necessary to create conditions: increase the temperature, apply a catalyst, etc.
Reactions of hydrogen with simple substances
When heated, hydrogen enters into a combination reaction with simple substances - oxygen, chlorine, nitrogen, sulfur.
If you set fire to pure hydrogen in air, coming out of the gas outlet tube, it burns with an even, barely noticeable flame. Now let's place a tube with burning hydrogen in a jar of oxygen (Fig. 95).
The combustion of hydrogen continues, while drops of water formed as a result of the reaction are visible on the walls of the jar:
When hydrogen burns, a lot of heat is released. The temperature of the oxygen-hydrogen flame reaches more than 2000 °C.
The chemical reaction of hydrogen with oxygen refers to compound reactions. As a result of the reaction, hydrogen oxide (water) is formed. This means that hydrogen was oxidized by oxygen, i.e. we can also call this reaction an oxidation reaction.
If, however, a small amount of hydrogen is collected in a test tube turned upside down by displacing air, and then a burning match is brought to its hole, then a loud “barking” sound of a small explosion of a mixture of hydrogen and air will be heard. Such a mixture is called "explosive".
On a note: The ability of hydrogen in a mixture with air to form "explosive gas" has often been the cause of accidents in balloons filled with hydrogen. Violation of the tightness of the ball shell led to a fire and even an explosion. Nowadays, balloons are filled with helium or constantly pumped hot air.
In an atmosphere of chlorine, hydrogen burns to form a complex substance - hydrogen chloride. In this case, the reaction proceeds:
The reaction of hydrogen with nitrogen occurs at elevated temperature and pressure in the presence of a catalyst. As a result of the reaction, ammonia NH 3 is formed:
If a stream of hydrogen is directed to sulfur melted in a test tube, then the smell of rotten eggs will be felt at its hole. This is how hydrogen sulfide gas H 2 S smells - the product of the reaction of hydrogen with sulfur:
On a note: Hydrogen is able not only to dissolve in some metals, but also togyrate with them. This forms chemical compounds called hydrides (NaH - sodium hydride). Hydrides of some metals are used as fuel in solid-fuel rocket engines, as well as in the production of thermonuclear energy.
Reactions of hydrogen with complex substances
Hydrogen reacts at elevated temperatures not only with simple but also with complex substances. Consider, as an example, its reaction with copper (II) oxide CuO (Fig. 96).
Let us pass hydrogen over the heated powder of copper(II) oxide CuO. As the reaction proceeds, the color of the powder changes from black to brownish red. This is the color of the simple copper substance Cu. During the reaction, droplets of liquid appear on the cold parts of the test tube. This is another product of the reaction - water H 2 O. Note that, in contrast to the simple substance of copper, water is a complex substance.
The equation for the reaction of copper(II) oxide with hydrogen:
Hydrogen in reaction with copper(II) oxide exhibits the ability to take away oxygen from the metal oxide, thereby restoring the metal from this oxide. As a result, there copper recovery from the complex substance CuO to metallic copper (Cu).
Recovery reactions- These are reactions in which complex substances donate oxygen atoms to other substances.
A substance that removes oxygen atoms is called a reducing agent. In the reaction with copper(II) oxide, the reducing agent is hydrogen. Hydrogen also reacts with oxides of some other metals, such as PbO, HgO, MoO 3 , WO 3 and others. Oxidation and reduction are always interconnected. If one substance (H 2) is oxidized, then the other (CuO) is reduced, and vice versa.
Lesson summary:
- When heated, hydrogen reacts with oxygen, chlorine, nitrogen, and sulfur.
- Restoration is the giving of oxygen atoms by complex substances to other substances.
- The processes of oxidation and reduction are interconnected.
I hope lesson 22 " Chemical properties of hydrogen' was clear and informative. If you have any questions, write them in the comments.
Characterization of s-elements
The block of s-elements includes 13 elements, common to which is the building up in their atoms of the s-sublevel of the external energy level.
Although hydrogen and helium are classified as s-elements due to the specific nature of their properties, they should be considered separately. Hydrogen, sodium, potassium, magnesium, calcium are vital elements.
Compounds of s-elements exhibit common patterns in properties, which is explained by the similarity of the electronic structure of their atoms. All external electrons are valence and take part in the formation of chemical bonds. Therefore, the maximum oxidation state of these elements in compounds is number electrons in the outer layer and, accordingly, is equal to the number of the group in which this element is located. The oxidation state of s-element metals is always positive. Another feature is that after the separation of the electrons of the outer layer, an ion with a noble gas shell remains. With an increase in the serial number of the element, atomic radius, the ionization energy decreases (from 5.39 eV y Li to 3.83 eV y Fr), and the reducing activity of the elements increases.
The vast majority of compounds of s-elements are colorless (unlike compounds of d-elements), since the transition of d-electrons from low energy levels to higher energy levels, which causes color, is excluded.
Compounds of elements of groups IA - IIA are typical salts; in an aqueous solution, they almost completely dissociate into ions and are not subject to cation hydrolysis (except for Be 2+ and Mg 2+ salts).
hydrogen hydride ionic covalent
For ions of s-elements, complex formation is not typical. Crystalline complexes of s - elements with ligands H 2 O-crystalline hydrates have been known since ancient times, for example: Na 2 B 4 O 7 10H 2 O-borax, KАl (SO 4) 2 12H 2 O-alum. Water molecules in crystalline hydrates are grouped around the cation, but sometimes completely surround the anion. Due to the small charge of the ion and the large radius of the ion, alkali metals are least prone to the formation of complexes, including aqua complexes. Lithium, beryllium, and magnesium ions act as complexing agents in complex compounds of low stability.
Hydrogen. Chemical properties of hydrogen
Hydrogen is the lightest s-element. Its electronic configuration in the ground state is 1S 1 . A hydrogen atom consists of one proton and one electron. The peculiarity of hydrogen is that its valence electron is located directly in the sphere of action of the atomic nucleus. Hydrogen does not have an intermediate electron layer, so hydrogen cannot be considered an electronic analogue of alkali metals.
Like alkali metals, hydrogen is a reducing agent and exhibits an oxidation state of +1. The spectra of hydrogen are similar to those of alkali metals. Hydrogen is similar to alkali metals in its ability to give a hydrated positively charged ion H + in solutions.
Like the halogen, the hydrogen atom is missing one electron. This is the reason for the existence of the hydride ion H - .
In addition, like halogen atoms, hydrogen atoms are characterized by a high ionization energy (1312 kJ/mol). Thus, hydrogen occupies a special position in the Periodic Table of the Elements.
Hydrogen is the most abundant element in the universe, accounting for up to half the mass of the sun and most stars.
On the sun and other planets, hydrogen is in the atomic state, in the interstellar medium in the form of partially ionized diatomic molecules.
Hydrogen has three isotopes; protium 1 H, deuterium 2 D and tritium 3 T, with tritium being a radioactive isotope.
Hydrogen molecules are distinguished by high strength and low polarizability, small size and low mass, and have high mobility. Therefore, hydrogen has very low melting points (-259.2 o C) and boiling points (-252.8 o C). Due to the high dissociation energy (436 kJ/mol), the decomposition of molecules into atoms occurs at temperatures above 2000 o C. Hydrogen is a colorless gas, odorless and tasteless. It has a low density - 8.99·10 -5 g/cm At very high pressures, hydrogen passes into the metallic state. It is believed that on the distant planets of the solar system - Jupiter and Saturn, hydrogen is in a metallic state. There is an assumption that the composition of the earth's core also includes metallic hydrogen, where it is at the superhigh pressure created by the earth's mantle.
Chemical properties. At room temperature, molecular hydrogen reacts only with fluorine, when irradiated with light - with chlorine and bromine, when heated with O 2, S, Se, N 2, C, I 2.
The reactions of hydrogen with oxygen and halogens proceed according to the radical mechanism.
Interaction with chlorine is an example of an unbranched reaction when irradiated with light (photochemical activation), when heated (thermal activation).
Cl + H 2 \u003d HCl + H (chain development)
H + Cl 2 \u003d HCl + Cl
An explosion of explosive gas - a hydrogen-oxygen mixture - is an example of a branched chain process, when the initiated chain includes not one, but several stages:
H 2 + O 2 \u003d 2OH
H + O 2 \u003d OH + O
O + H 2 \u003d OH + H
OH + H 2 \u003d H 2 O + H
The explosive process can be avoided by working with pure hydrogen.
Since hydrogen is characterized by positive (+1) and negative (-1) oxidation states, hydrogen can exhibit both reducing and oxidizing properties.
The reducing properties of hydrogen are manifested when interacting with non-metals:
H 2 (g) + Cl 2 (g) \u003d 2HCl (g),
2H 2 (g) + O 2 (g) \u003d 2H 2 O (g),
These reactions proceed with the release of a large amount of heat, which indicates a high energy (strength) of the H-Cl, H-O bonds. Therefore, hydrogen exhibits reducing properties with respect to many oxides, halides, for example:
This is the basis for the use of hydrogen as a reducing agent for obtaining simple substances from halide oxides.
An even stronger reducing agent is atomic hydrogen. It is formed from molecular in an electron discharge under low pressure conditions.
Hydrogen has a high reducing activity at the moment of release during the interaction of a metal with an acid. Such hydrogen reduces CrCl 3 to CrCl 2:
2CrCl 3 + 2HCl + 2Zn = 2CrCl 2 + 2ZnCl 2 + H 2 ^
The interaction of hydrogen with nitric oxide (II) is important:
2NO + 2H 2 = N 2 + H 2 O
Used in purification systems in the production of nitric acid.
As an oxidizing agent, hydrogen interacts with active metals:
In this case, hydrogen behaves like a halogen, forming similar halides hydrides.
Hydrides of group I s-elements have an ionic structure of the NaCl type. Chemically, ionic hydrides behave like basic compounds.
The covalent ones include hydrides of non-metallic elements less electronegative than hydrogen itself, for example, hydrides of the composition SiH 4, BH 3, CH 4. By chemical nature, non-metal hydrides are acidic compounds.
A characteristic feature of the hydrolysis of hydrides is the release of hydrogen, the reaction proceeds according to the redox mechanism.
Basic hydride
acid hydride
Due to the release of hydrogen, the hydrolysis proceeds completely and irreversibly (?Н<0, ?S>0). In this case, basic hydrides form an alkali, and acidic acids.
The standard potential of the system is B. Therefore, the H ion is a strong reducing agent.
In the laboratory, hydrogen is obtained by reacting zinc with 20% sulfuric acid in a Kipp apparatus.
Technical zinc often contains small impurities of arsenic and antimony, which are reduced by hydrogen at the time of release to toxic gases: arsine SbH 3 and stabyne SbH Such hydrogen can be poisonous. With chemically pure zinc, the reaction proceeds slowly due to overvoltage and a good hydrogen current cannot be obtained. The rate of this reaction is increased by adding crystals of copper sulphate, the reaction is accelerated by the formation of a galvanic Cu-Zn pair.
More pure hydrogen is formed by the action of alkali on silicon or aluminum when heated:
In industry, pure hydrogen is obtained by electrolysis of water containing electrolytes (Na 2 SO 4 , Ba (OH) 2).
A large amount of hydrogen is formed as a by-product during the electrolysis of an aqueous solution of sodium chloride with a diaphragm separating the cathode and anode space,
The largest amount of hydrogen is obtained by gasification of solid fuel (anthracite) with superheated steam:
Or conversion of natural gas (methane) by superheated steam:
The resulting mixture (synthesis gas) is used in the production of many organic compounds. The yield of hydrogen can be increased by passing synthesis gas over the catalyst, while CO is converted to CO 2 .
Application. A large amount of hydrogen is consumed in the synthesis of ammonia. For the production of hydrogen chloride and hydrochloric acid, for the hydrogenation of vegetable fats, for the reduction of metals (Mo, W, Fe) from oxides. Hydrogen-oxygen flames are used for welding, cutting and melting metals.
Liquid hydrogen is used as rocket fuel. Hydrogen fuel is environmentally friendly and more energy-intensive than gasoline, so it may replace petroleum products in the future. Already, several hundred cars are running on hydrogen in the world. The problems of hydrogen energy are associated with the storage and transportation of hydrogen. Hydrogen is stored in underground tankers in a liquid state under a pressure of 100 atm. Transporting large quantities of liquid hydrogen poses a serious hazard.
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.
The electronic configuration of the hydrogen atom is 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 for 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 of 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 is 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 degree of oxidation 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 reacts with 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. |