Comparative characteristics of fluorine and chlorine. Oxygen - characteristic of the element, prevalence in nature, physical and chemical properties, obtaining Tasks for independent work

All chemical elements, depending on the structure and properties of atoms, are divided into metals, non-metals and noble gases. Also, simple substances formed by elements are classified into metals and non-metals, based on their physical and chemical properties. You met with metals in the previous chapter. Now let's move on to the consideration of non-metals.

The very word "non-metals" indicates that the properties of non-metal elements and their corresponding simple substances are opposite to the properties of metals.

If metal atoms are characterized by relatively large radii and a small number of electrons (1-3) at the outer level, non-metal atoms, on the contrary, are characterized by small atomic radii and the number of electrons at the outer energy level from 4 to 8 (boron has 3 electrons, but atoms this element have a small radius). Hence the striving of metal atoms to donate external electrons, i.e., reducing properties, and for non-metal atoms, the striving to receive the electrons missing up to the cherished eight, i.e., oxidizing properties. These properties are characterized by the position of non-metals in the electronegativity series. So, fluorine exhibits only oxidizing properties, and oxygen - reducing properties exclusively in relation to fluorine, etc.

Among the 114 known today chemical elements(of which 92 elements are found in nature) 22 elements are classified as non-metals. We have already talked about the location of metals and non-metals in the Periodic system of D. I. Mendeleev in the previous chapter. Here we note again that in the Periodic system of D. I. Mendeleev, metals are located mainly under the B-At diagonal, and non-metals are located along this diagonal and above it in the main subgroups (Fig. 71).

Rice. 71.
The position of non-metal chemical elements (marked in red) in the Periodic system of D. I. Mendeleev

The properties of simple substances formed by non-metals are very diverse. Although there are much fewer non-metals compared to metals, it is difficult to identify common characteristic features for them.

Judge for yourself: hydrogen H 2, oxygen O 2 and ozone O 2, fluorine F 2, chlorine Cl 2, nitrogen N 2 are gases under normal conditions, bromine Br 2 is a liquid, and boron, carbon (diamond and graphite), silicon, phosphorus (red and white), sulfur (plastic and rhombic), selenium, tellurium, iodine I 2, astatine are solids.

If the overwhelming majority of metals are characterized by a silvery-white color, then the color of non-metals - simple substances covers all the colors of the spectrum: red (red phosphorus, red-brown liquid bromine), yellow (sulfur), green (chlorine - yellow-green gas), violet (iodine vapor).

The melting points of non-metals lie in a very wide range: from 3800 ° C for graphite to -259 ° C for hydrogen. This feature of the properties of non-metals is a consequence of the formation of two types of crystal lattices: molecular (O 2, O 2, N 2, halogens, white phosphorus, etc.) and atomic (diamond, graphite, silicon, boron, etc.). The different structure of crystal lattices also explains the phenomenon of allotropy (remember what it is). For example, the element phosphorus forms a simple substance with a molecular crystal lattice - white phosphorus, the molecules of which have the composition P 4, and a simple substance with an atomic crystal lattice - red phosphorus P.

The second reason for allotropy is related to different number atoms in the molecules of simple substances. A typical example is simple substances formed by oxygen: oxygen O 2 and ozone O 3.

Unlike colorless oxygen O 2 , which has no smell, ozone is a light blue gas with a strong odor.

You already know from last year's course that the admixture of ozone in the air that appears after a thunderstorm gives a feeling of pleasant freshness; ozone is also contained in the air of pine forests and the sea coast.

In nature, ozone is formed by electrical discharges or the oxidation of organic resinous substances, as well as by the action of ultraviolet rays on oxygen. In the laboratory, it is obtained in special devices - ozonizers (Fig. 72) by acting on oxygen with a quiet (without sparks) electric discharge.

Rice. 72.
Ozonator

Ozone is a much stronger oxidizing agent than oxygen. Its use is based on the strong oxidizing ability of ozone: bleaching of fabrics, deodorization (odor removal) of fats and oils, disinfection of air and drinking water.

Ozone is very important for the preservation of all life on our planet. Recall that the ozone layer of the Earth (Fig. 73), located at an altitude of 20-25 km, delays ultraviolet radiation, which has a destructive effect on the cells of living organisms. Therefore, it is clear how important it is to preserve this very sensitive to the action of various chemical substances"ozone shield" of the planet from destruction.

Rice. 73.
Ozone layer Earth

Ozone is classified as a variable constituent of air. Also in late XVIII in. A. Lavoisier established that air is not a simple substance, but a mixture of gaseous non-metals: nitrogen N 2 (it accounts for 4/5 of the volume of air) and oxygen O 2 (with a volume fraction of 1/5). In the future, ideas about the composition of air were refined. Currently, there are constant, variable and random components of air.

The constant components of air are nitrogen, oxygen and noble gases (argon, helium, neon, etc.). Their content in the troposphere is the same (Table 6).

Table 6
Composition of air

The variable constituents of air are carbon dioxide (about 0.03% by volume), water vapor and ozone (about 0.00004% by volume). Their content can vary greatly depending on natural and industrial conditions.

Random components of air include dust, microorganisms, plant pollen, some gases, including those that form acid rain: oxides of sulfur, nitrogen, etc.

Air, free from variable and random components, is transparent, devoid of color, taste and smell, 1 liter of it at n. y. has a mass of 1.29 g. Molar mass air with a volume of 22.4 liters (1 mol) is equal to 29 g / mol.

Air is an ocean of gases at the bottom of which people, animals and plants live. It is essential for respiration and photosynthesis. The air oxygen dissolved in water serves for the respiration of the inhabitants of the aquatic environment (fish, aquatic plants).

The role of air in the processes of weathering (destruction) of rocks and for soil formation is great (Fig. 74). Under the action of air and bacteria, organic residues are mineralized - obsolete organic substances turn into mineral compounds and are again absorbed by plants.

Rice. 74.
As a result of weathering, rocks of a bizarre shape are formed.

Nitrogen, argon and oxygen are obtained from liquid air using different boiling points (Fig. 75). During the distillation of liquefied air, nitrogen is the first to evaporate.

Rice. 75.
Distillation of liquid air:
a - process diagram; c - industrial installation

New words and concepts

1. Metal elements and non-metal elements. The structure of atoms of non-metals.
2. Simple substances are metals and simple substances are non-metals.
3. Allotropy. oxygen and ozone.
4. Air composition.

Tasks for independent work

1. Determine how many times heavier (lighter) than air oxygen, carbon dioxide, hydrogen, i.e. determine the relative density of these gases in air (D air).
2. Knowing the volumetric composition of air, find the amount of substance of each gas: nitrogen and oxygen in 100 liters of air at n. y.
3. Determine the number of molecules: a) oxygen; b) nitrogen contained in 22.4 liters of air at n. y.
4. Calculate the volume of air (n.a.) that will be required to burn 20 m 3 of hydrogen sulfide if water and sulfur oxide (IV) are formed. Calculate the mass of this air.
5. Prepare a report on the use of oxygen.
6. What are ozone holes? How to prevent their occurrence?

Tests in chemistry Grade 9

Final test in chemistry grade 9

The variant was prepared by G. R. Subkhanova.

Option 1

1. The elements nitrogen and fluorine have the same

1) total number of electrons

2) the number of completed energy levels

3) the number of electrons in the outer level

4) the number of protons in the nucleus

Answer:

1. In the series of chemical elements B → C → N

1) the charge of the nuclei of atoms decreases

2) the acidic properties of the formed hydroxides increase

3) the number of electronic levels increases

4) electronegativity increases

5) the atomic radius increases

Answer:

1. have the same type of chemical bond

1) potassium sulfate and nitric oxide (I)

2) hydrogen bromide and aluminum oxide

3) copper and sodium chloride

4) oxygen and silicon

Answer:

1. When interacting with which of the following substances, hydrogen is an oxidizing agent?

1) oxygen

Answer:

1. The interaction of aluminum with iron(III) oxide refers to the reactions

1) compounds, redox

2) exchange, exothermic

3) redox, substitution

4) neutralization, endothermic

Answer:

1. The largest number of cations is formed upon complete dissociation of 1 mol

1) potassium phosphate

2) sodium nitrate

3) copper(II) sulfate

4) iron(III) chloride

Answer:

Answer:

1. Both sodium sulfate solution and sodium carbonate solution interact with

1) aluminum phosphate

2) zinc hydroxide

3) barium chloride

4) nitric acid

Answer:

1. Iron(III) oxide reacts with

1) aluminum hydroxide

2) magnesium chloride

3) nitric acid

4) aluminum oxide

Answer:

1. The following statements are true for acetylene:

1) a molecule consists of two carbon atoms and two hydrogen atoms

2) is a saturated hydrocarbon

3) carbon atoms in a molecule are connected by a double bond

4) reacts with chlorine

5) when decomposed, carbon dioxide and hydrogen are formed

Answer:

1. Establish a correspondence between the formula of a substance and the reagents with each of which it can interact.

FORMULA OF THE SUBSTANCE REAGENTS

A) H 2 1) CuO, N 2

B) HBr 2) NO 2, Na 2 SO 4

C) CuCl 2 3) Si, H 2 O

Answer:

Answer:

1. The transformation scheme is given: AlCl 3 → Al(OH) 3 → X → NaAlO 2

Write the molecular equations of the reactions by which these transformations can be carried out.

Solution:

AlCl 3 + 3NaOH → Al(OH) 3 + 3NaCl

2Al(OH) 3 → Al 2 O 3 + 3H 2 O

Al 2 O 3 + Na 2 O→ 2NaAlO 2

1. After passing 2.24 liters of sulfur dioxide gas (n.a.) through a potassium hydroxide solution, 252.8 g of a potassium sulfite solution were obtained. Calculate the mass fraction of salt in the resulting solution.

Solution:

2KOH + SO 2 → K 2 SO 3 + H 2 O

2) Calculate the mass and amount of potassium sulfite substance obtained as a result of the reaction:

According to the reaction equationn(SO 2 ) = n(K 2 SO 3 ) = 0.1 mol

m (K 2 SO 3) \u003d n (K 2 SO 3) * M (K 2 SO 3) \u003d 0.1mole * 158 G/ mole = 15.8 G

3) Determine the mass fraction of potassium sulfite in solution:

Answer: 6.25%

Option 2

1. There are two elements in an atom energy levels filled with electrons, and the third one has 6 electrons. What is this element?

1) silicon

2) carbon

3) oxygen

Answer

1. In the series of chemical elements Be → Mg → Ca

1) decreases highest degree oxidation

2) the atomic radius increases

3) the value of electronegativity increases

4) the main properties of the formed hydroxides are enhanced

5) the number of electrons in the outer level decreases

Answer:

1. Chemical bond in the ammonium chloride molecule

1) covalent non-polar

2) covalent polar

4) hydrogen

Answer:

1. Carbon enters into a substitution reaction with

1) iron(III) oxide

2) oxygen

4) sulfuric acid

Answer:

Solution:

CuSO 4 + 2 KOH = Cu(Oh) 2 + K 2 SO 4 formation of a blue precipitate

Answer:

Solution:

Nitric acid is a strong acid. therefore, in an aqueous solution, it completely dissociates into ions.

Answer:

Solution:
Reactive metals react with water at room temperature

Answer:

Solution:

Ammonium chloride and barium sulfate react with silver nitrate, of which only ammonium chloride reacts with calcium hydroxide.

Answer:

Solution:

Ethylene is an unsaturated hydrocarbon (alkene) containing a double bond, so it can enter into a polymerization reaction.C2H4M=28g/mol

Solution:

Magnesium:Mg + I 2 \u003d MgI 2

Mg + CuCl 2 = MgCl 2 + Cu

Oxide sulfur(VI)-acid oxide:SO 3 + H 2 O \u003d H 2 SO 4

SO 3 + Na 2 O \u003d Na 2 SO 4

ZnBr 2 -salt:ZnBr 2 + Cl 2 = ZnCl 2 + Br 2

ZnBr 2 + 2KOH = Zn(OH) 2 + 2KBr

BUT	B	IN
1	2	4

1. Establish a correspondence between a gaseous substance and a laboratory method for its recognition. For each element in the first column, match the corresponding element in the second column.

Write down the numbers in response, arranging them in the order corresponding to the letters:

1. The transformation scheme is given: FeCl 2 → X → FeSO 4 → Fe

Write the molecular equations of the reactions by which these transformations can be carried out.

Solution:

FeCl 2 + 2KOH → Fe(OH) 2 + 2 KCl

Fe(OH) 2 + H 2 SO 4 → FeSO 4 + 2H 2 O

FeSO 4 + Zn → ZnSO 4 + Fe

1. When an excess of potassium carbonate solution reacted with a 10% solution of barium nitrate, 1.97 g of a precipitate fell out. Determine the mass of the barium nitrate solution taken for the experiment.

Solution:

1) Compose the reaction equation:

K 2 CO 3 + Ba(NO 3 ) 2 → BaCO 3 + 2 KNO 3

2) Calculate the amount of barium carbonate substance obtained as a result of the reaction:

According to the reaction equationn(BaCO 3 ) = n(Ba(NO 3 ) 2 = 0.01 mol

m(Ba(NO 3) 2) = n(Ba(NO 3) 2) * M((Ba(NO 3) 2) = 0.01mole * 261 G/ mole = 2.61 G

3) Determine the mass of the solution (Ba(NO 3 ) 2):

Answer: 26.1g



The elements fluorine, chlorine, bromine, iodine and astatine included in the main subgroup of group VII are called halogens. This name, which literally means "salt-forming", was given to the elements for their ability to interact with metals to form typical salts, such as sodium chloride NaCl.

The outer electron shell of halogen atoms contains seven electrons - two in s- and five in p-orbitals (ns2np5). Halogens have a significant electron affinity. their atoms easily attach an electron, forming singly charged negative ions with the electronic structure of the corresponding noble gas (ns2np6). The tendency to attach electrons characterizes halogens as typical non-metals. The similar structure of the outer electron shell determines the great similarity of halogens with each other, which is manifested both in their chemical properties and in the types and properties of the compounds they form. But, as a comparison of the properties of halogens shows, there are significant differences between them.

With an increase in the serial number of elements in the F - At series, the atomic radii increase, the electronegativity decreases, the non-metallic properties and the oxidizing ability of the elements weaken.

Unlike other halogens, fluorine in its compounds is always in the -1 oxidation state, since it has the highest electronegativity among all elements. The remaining halogens exhibit various oxidation states from -1 to +7.

With the exception of some oxides, which will be discussed below, all halogen compounds correspond to odd oxidation states. This pattern is due to the possibility of sequential excitation of paired electrons in Cl, Br, I, and At atoms to the d sublevel, which leads to an increase in the number of electrons involved in the formation covalent bonds, up to 3, 5 or 7.

Molecules of simple substances formed by halogen atoms are diatomic. As the atomic radius increases in the series F, Cl, Br, I, At, the polarizability of molecules increases. As a result, the intermolecular dispersion interaction is enhanced, which leads to an increase in the melting and boiling points of halogens.

In the series Cl 2 - Br 2 -I 2, the bond strength between atoms in a molecule gradually decreases. A decrease in the bond strength in halogen molecules is manifested in a decrease in their resistance to heating. Fluorine falls out of the general pattern: the bond strength between atoms in its molecule is less, and the degree thermal dissociation of molecules is higher than that of chlorine. Such anomalous properties of fluorine can be explained by the absence of a d-subshell in the outer electron shell of its atom. In the molecule of chlorine and other halogens, there are free d-orbitals, and therefore an additional donor-acceptor interaction takes place between the atoms, which strengthens the bond.

During the formation of the F 2 molecule, a decrease in the energy of electrons is achieved due to the interaction of 2p-AO with unpaired electrons of fluorine atoms (system 1 + 1). The remaining p-AOs of unshared electron pairs can be considered as not participating in the formation of a chemical bond. The chemical bond in the Cl 2 molecule, in addition to the similar interaction of valence 3d-AO of chlorine atoms (system 1 + 1), is also formed due to interactions of 3p-AO of the lone electron pair of one chlorine atom with the vacant 3d-AO of the other (system 2 + 0). As a result, the bond order in the C1 2 molecule is greater than in the F 2 molecule, and chemical bond- stronger.

Halogens, due to their high chemical activity, are in nature exclusively in a bound state - mainly in the form of salts of hydrohalic acids.

Fluorine occurs in nature most often in the form of the mineral fluorspar CaF 2 .

The most important natural compound chlorine is sodium chloride (common salt) NaCl, which serves as the main raw material for the production of other chlorine compounds.

All halogens have a very strong odor. Inhalation of them, even in small quantities, causes severe irritation of the respiratory tract and inflammation of the mucous membranes. Larger amounts of halogens can cause severe poisoning.

Halogens are relatively slightly soluble in water. One volume of water dissolves about 2.5 volumes at room temperature chlorine . This solution is called chlorine water.

Fluorine cannot be dissolved in water, as it vigorously decomposes it:

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

Fluorine and chlorine react intensively with many organic solvents: carbon disulfide, ethyl alcohol, diethyl ether, chloroform, benzene.

Chemical properties of halogens.

Free halogens exhibit extremely high chemical activity. They interact with almost all simple substances. The reactions of the combination of halogens with metals proceed especially quickly and with the release of a large amount of heat.

2Na + C1 2 = 2NaCl.

Copper, tin and many other metals are burned in chlorine to form the corresponding salts. In all these cases, the metal atoms donate electrons, i.e., they are oxidized, and the halogen atoms add electrons, i.e., they are reduced. This ability to accept electrons, pronounced in the halogen atoms, is their characteristic chemical property. Therefore, halogens are very energetic oxidizing agents.

The oxidizing properties of halogens are also manifested when they interact with complex substances. Let's give some examples.

1. When chlorine is passed through a solution of iron (II) chloride, the latter is oxidized into iron (III) chloride, as a result of which the solution turns from pale green to yellow:

2FeCl 2 + C1 2 = 2FeCl 3

Chemical activity fluorine exceptionally high. alkali metals, lead, iron ignite in an atmosphere of fluorine at room temperature. Fluorine does not act on some metals (Al, Fe, Ni. Cu, Zn) in the cold, since a protective layer of fluoride is formed on their surface. However, when heated, fluorine reacts with all metals, including gold and platinum.

With many non-metals (hydrogen, iodine, bromine, sulfur, phosphorus, arsenic, antimony, carbon, silicon, boron), fluorine interacts in the cold: reactions proceed with an explosion or with the formation of a flame:

H 2 (g) + F 2 (g) \u003d 2HF (g)

Si(K) + 2F 2 (r) = SiF 4 (r)

S(K) + 3F 2 (r) = SF 6 (r)

When heated, chlorine, krypton and xenon combine with fluorine, for example: Xe (g) + F 2 tr) \u003d XeF 2 (r)

Fluorine does not directly react only with oxygen, nitrogen and carbon (in the form of diamond).

The interaction of fluorine with complex substances proceeds very vigorously. In its atmosphere, stable substances such as glass (in the form of cotton wool) and water vapor burn:

Si0 2 (k) + 2F 2 (r) = SiF 4 (r) + 0 2 (g)

2Н 2 0(g) + 2F 2 (r) = 4HF(r) + 0 2 (g)

Free chlorine also exhibits very high chemical activity, although less than fluorine. It directly interacts with all simple substances, with the exception of oxygen, nitrogen and noble gases. Non-metals such as phosphorus, arsenic, antimony and silicon react with chlorine even at low temperatures; in this case, a large amount of heat is released. Vigorously proceeds the interaction of chlorine with active metals sodium, potassium, magnesium, etc. At room temperature without lighting, chlorine practically does not interact with hydrogen, but when heated or in bright sunshine the reaction proceeds by a chain mechanism with an explosion.

Receipt.

Fluorine, due to its high electronegativity, can be isolated from compounds only by electrolysis (a KF + 2HF melt is subjected to electrolysis. Electrolysis is carried out in a nickel vessel, which is the cathode, and coal serves as the anode).

Chlorine are currently obtained in large quantities by electrolysis of aqueous solutions of sodium or potassium chlorides.

In laboratories, chlorine is obtained by the action of various oxidizing agents on hydrochloric acid.

Mn0 2 + 4HC1 \u003d MnC1 2 + C1 2 + 2H 2 0.

Compounds of halogens with hydrogen.

The chemical bond in the molecules of hydrogen halides is polar covalent: the common electron pair is shifted to the halogen atom as more electronegative. The strength of the chemical bond in hydrogen halide molecules naturally decreases in the series HF - HC1 - HBr - HI: this manifests itself in a change in the enthalpy of dissociation of molecules into atoms.

In the transition, for example, from HF to HI, the degree of overlap of the electron clouds of hydrogen and halogen atoms decreases, and the overlap region is located at a greater distance from the nucleus of the halogen atom and is more strongly screened by the increased number of intermediate electron layers. In addition, in the series F - Cl - Br - I, the electronegativity of the halogen atom decreases. Therefore, in the HF molecule, the electron cloud of the hydrogen atom is shifted towards the halogen atom to the greatest extent, and in the molecules of HC1, HBr and HI - less and less. This also leads to a decrease in the overlap of interacting electron clouds and, thereby, to a weakening of the bond between atoms.

Hydrogen halides are very soluble in water. At 0°C one volume of water dissolves about 500 volumes HC1, 600 volumes of HBr and about 425 volumes of HI (at 10°C); hydrogen fluoride miscible with water in any ratio.

The dissolution of hydrogen halides is accompanied by their dissociation according to the acid type, and only hydrogen fluoride dissociated relatively weakly, while the rest are among the strongest acids.

Negative hydrogen halide ions, excluding fgorid-ion, have reducing properties, increasing in the series Cl-, Br_, I-.

The chloride ion is oxidized f torus, potassium permanganate, manganese dioxide and other strong oxidizing agents, for example:

16HC1 + 2KMp0 4 = 5C1 2 + 2KS1 + 2MnC1 2 + 8H 2 0.

A solution of hydrogen fluoride in water is called hydrofluoric acid.. This name comes from fluorspar, from which hydrogen fluoride is usually obtained by the action of concentrated sulfuric acid:

CaF 2 + H 2 S0 4 = CaS0 4 + 2HF.

Hydrogen fluoride reacts with most metals. However, in many cases, the resulting salt is poorly soluble, as a result of which a protective film appears on the metal surface.

A remarkable property of hydrogen fluoride and hydrofluoric acid is their ability to interact with silicon dioxide Si0 2 , which is part of the glass; as a result, gaseous silicon fluoride SiF 4 is formed:

Si0 2 + 4HF \u003d SiF 4 + 2H 2 0.

Hydrochloric acid obtained by dissolving hydrogen chloride in water. At present, the main method of industrial production of hydrogen chloride is the process of its synthesis from hydrogen and chlorine:

H 2 (g) + C1 2 (G) \u003d 2HC1 (G),

Large amounts of HCl are also obtained as a by-product of chlorination. organic compounds according to the scheme

RH + C1 2 = RC1 + HC1,

Halogens form a number of compounds with oxygen. However, all these compounds are unstable, they are not obtained by direct interaction of halogens with oxygen, but only indirectly. Such features of oxygen compounds of halogens are consistent with the fact that almost all of them are characterized by positive values ​​of the standard Gibbs energy of formation.

Of the oxygen-containing compounds of halogens, the most stable are salts of oxygen acids, the least stable are oxides and acids. In all oxygen-containing compounds, halogens, except for fluorine, exhibit a positive oxidation state, reaching seven.

Oxygen fluoride OF 2 can be obtained by passing fluorine into a chilled 2% NaOH solution. The reaction goes according to the equation:

2F 2 + 2NaOH \u003d 2NaF + H 2 0 + OF 2

As already mentioned, oxygen compounds chlorine can only be obtained by indirect methods. Considering the ways of their formation, let's start with the process of hydrolysis of chlorine, i.e., with a reversible reaction between chlorine and water

C1 2 (p) + H 2 0 (W)<->HC1(R) + HClO(r)

resulting in the formation of hydrochloric acid and hypochlorous acid HOC1.

Ticket 16

Chemistry of hydrogen

Hydrogen has three isotopes: protium, deuterium, or D, and tritium, or T. Their mass numbers are 1, 2, and 3. Protium and deuterium are stable, tritium is radioactive.

The hydrogen molecule consists of two atoms.

Hydrogen in the free state is found on Earth only in small quantities. Sometimes it is released along with other gases during volcanic eruptions, as well as from boreholes during oil extraction. But in the form of compounds, hydrogen is very common.

In industry, hydrogen is produced mainly from natural gas. This gas, which consists mainly of methane, is mixed with water vapor and oxygen. When a mixture of gases is heated to 800-900 ° C in the presence of a catalyst, a reaction occurs, which can be schematically represented by the equation:

2CH 4 + 0 2 + 2H 2 0 \u003d 2C0 2 + 6H 2.

In laboratories, hydrogen is mostly obtained by electrolysis of aqueous solutions of NaOH or KOH, the concentration of these solutions is chosen to match their maximum electrical conductivity. The electrodes are usually made from sheet nickel. This metal does not corrode in alkali solutions, even being an anode. If necessary, the resulting hydrogen is purified from water vapor and traces of oxygen. Among other laboratory methods, the most common method is the extraction of hydrogen from solutions of sulfuric or hydrochloric acids by the action of zinc on them.

Properties and application of hydrogen.

Hydrogen is a colorless, odorless gas. Hydrogen is very slightly soluble in water, but in some metals, such as nickel, palladium, platinum, it dissolves in significant quantities.

The solubility of hydrogen in metals is related to its ability to diffuse through metals. In addition, being the lightest gas, hydrogen has the highest diffusion rate: its molecules, faster than the molecules of all other gases, propagate in the medium of another substance and pass through various kinds of partitions. Especially great is its ability to diffuse at elevated pressure and high temperatures.

The chemical properties of hydrogen are largely determined by the ability of its atom to donate the only electron it has and turn into a positively charged ion. In this case, a feature of the hydrogen atom is manifested, which distinguishes it from the atoms of all other elements: the absence of intermediate electrons between the valence electron and the nucleus.

The hydrogen ion formed as a result of the loss of an electron by a hydrogen atom is a proton, the size of which is several orders of magnitude smaller than the size of the cations of all other elements. Therefore, the polarizing effect of the proton is very strong, as a result of which hydrogen is not able to form ionic compounds in which it would act as a cation. Its compounds, even with the most active non-metals, such as fluorine, are substances with a polar covalent bond.

The hydrogen atom is able not only to donate, but also to attach one electron. This produces a negatively charged hydrogen ion electron shell helium atom. In the form of such ions, hydrogen is found in compounds with certain active metals. Thus, hydrogen has a dual chemical nature, exhibiting both an oxidizing and a reducing ability. In most reactions, it acts as a reducing agent, forming compounds in which its oxidation state is +1. But in reactions with active metals, it acts as an oxidizing agent: its oxidation state in compounds with metals is -1.

Thus, giving one electron, hydrogen shows similarity with the metals of the first group of the periodic system, and adding an electron. - with non-metals of the seventh group. Therefore, the hydrogen periodic system usually placed either in the first group and at the same time in brackets in the seventh, or in the seventh group and in brackets in the first.

Hydrogen compounds with metals are called hydrides.

Hydrides of alkali and alkaline earth metals are salts. i.e., the chemical bond between the metal and hydrogen in them is ionic. Under the action of water on them, a redox reaction occurs, in which the hydride ion H - acts as a reducing agent, and the hydrogen of water - as an oxidizing agent:

H - - e~ \u003d H 0; H20 + e - \u003d H ° + OH -.

As a result of the reaction, hydrogen and a base are formed. For example, calcium hydride reacts with water according to the equation:

CaH 2 + 2H 2 0 \u003d 2H 2 + Ca (OH) 2.

If a lit match is brought to a jet of hydrogen coming out of some narrow hole, then the hydrogen ignites and burns with a non-luminous flame, forming water:

2H 2 + 0 2 \u003d 2H 2 0.

At low temperatures, hydrogen and oxygen practically do not interact. If you mix both gases and leave the mixture, then after a few years even signs of water cannot be found in it.

The low rate of interaction of hydrogen with oxygen at low temperatures is due to the high activation energy of this reaction. Hydrogen and oxygen molecules are very strong; the vast majority of collisions between them at room temperature are inefficient. Only at elevated temperatures, when kinetic energy of colliding molecules becomes large, some collisions of molecules become effective and lead to the formation of active centers.

At high temperatures, hydrogen can take oxygen from many compounds, including most metal oxides. For example, if hydrogen is passed over heated copper oxide, then copper is reduced:

CuO + H 2 \u003d Cu + H 2 0.

Atomic hydrogen: At high temperatures, hydrogen molecules dissociate into atoms:

H 2<=>2H.

This reaction can be carried out, for example, by heating a tungsten wire with a current in an atmosphere of highly rarefied hydrogen. The reaction is reversible, and the higher the temperature, the more the equilibrium is shifted to the right.

Atomic hydrogen is also obtained by the action of a quiet electric discharge on molecular hydrogen, which is under a pressure of about 70 Pa. The hydrogen atoms formed under these conditions do not immediately combine into molecules, which makes it possible to study their properties.

When hydrogen is decomposed into atoms, a large amount of heat is absorbed:

H 2 (g) \u003d 2H (G)

From this it is clear that hydrogen atoms must be much more active than its molecules. In order for molecular hydrogen to enter into any reaction, the molecules must break up into atoms, for which a large amount of energy must be expended. In the reactions of atomic hydrogen, such an expenditure of energy is not required.

Indeed, even at room temperature, atomic hydrogen reduces many metal oxides and combines directly with sulfur, nitrogen, and phosphorus; with oxygen it forms hydrogen peroxide.

Hydrogen peroxide.

Hydrogen peroxide (peroxide) is a colorless syrupy liquid. This is a very fragile substance that can decompose with an explosion into water and oxygen, and a large amount of heat is released:

2H 2 0 2(W) - 2H 2 O (W) + 0 2(G)

Aqueous solutions of hydrogen peroxide are more stable; in a cool place they can be stored for quite a long time.

Hydrogen peroxide is formed as an intermediate product during the combustion of hydrogen, but due to the high temperature of the hydrogen flame, it immediately decomposes into water and oxygen. However, if a hydrogen flame is directed at a piece of ice, traces of hydrogen peroxide can be found in the resulting water.

Hydrogen peroxide is also obtained by the action of atomic hydrogen on oxygen.

In hydrogen peroxide, hydrogen atoms are covalently bonded to oxygen atoms, between which a simple bond also occurs. The structure of hydrogen peroxide can be expressed as follows structural formula: BUT HE.

H 2 0 2 molecules have significant polarity, which is a consequence of their spatial structure.

Hydrogen peroxide reacts directly with some bases to form salts. So, under the action of hydrogen peroxide on an aqueous solution of barium hydroxide, a precipitate of the barium salt of hydrogen peroxide precipitates:

Ba (OH) 2 + H 2 0 2 \u003d Ba0 2 + 2H 2 0.

Salts of hydrogen peroxide are called peroxides or peroxides. They consist of positively charged metal ions and negatively charged O 2- ions. The oxidation state of oxygen in hydrogen peroxide is -1, therefore, hydrogen peroxide has the properties of both an oxidizing agent and a reducing agent, i.e., it exhibits redox duality. Nevertheless, oxidizing properties are more characteristic of it, since the standard potential of the electrochemical system

H 2 0 2 + 2H + + 2e~ = 2H 2 0,

Examples of reactions in which H 2 0 2 serves as an oxidizing agent are the oxidation of potassium nitrite

KNO 2 + H 2 0 2 = KN0 3 + H 2 O

and isolation of iodine from potassium iodide:

2KI + H 2 0 2 \u003d I 2 + 2KON.

As an example of the reducing ability of hydrogen peroxide, we point out the reactions of interaction of H 2 0 2 with silver oxide (I)

Ag 2 0 + H 2 0 2 \u003d 2Ag + H 2 0 + 0 2,