· Biological role · Toxicity · Literature · Related articles · Comments · Notes · Official site ·

Chemical Methods

Chemical methods for obtaining chlorine are inefficient and costly. Today, they mainly historical meaning. It can be obtained by reacting potassium permanganate with hydrochloric acid:

Scheele method

Initially, the industrial method for producing chlorine was based on the Scheele method, that is, the reaction of pyrolusite with hydrochloric acid:

Deacon method

In 1867, Deacon developed a method for producing chlorine by catalytic oxidation of hydrogen chloride with atmospheric oxygen. The Deacon process is today used to recover chlorine from hydrogen chloride, a by-product of industrial chlorination of organic compounds.

Electrochemical methods

Today, chlorine is produced on an industrial scale together with sodium hydroxide and hydrogen by electrolysis of a sodium chloride solution, the main processes of which can be represented by the summary formula:

Three variants of the electrochemical method for producing chlorine are used. Two of them are solid cathode electrolysis: diaphragm and membrane method s, the third is electrolysis with a liquid mercury cathode (mercury production method). The quality of chlorine obtained by electrochemical methods differs little:

diaphragm method

Scheme of an old diaphragm electrolytic cell for the production of chlorine and lye: A- anode, IN- insulators, WITH- cathode, D- space filled with gases (above the anode - chlorine, above the cathode - hydrogen), M- diaphragm

The simplest of the electrochemical methods, in terms of organizing the process and structural materials for the electrolyzer, is the diaphragm method for producing chlorine.

The salt solution in the diaphragm cell is continuously fed into the anode space and flows through an asbestos diaphragm, usually mounted on a steel cathode mesh, to which, in some cases, a small amount of polymer fibers is added.

Diaphragm suction is performed by pumping pulp from asbestos fibers through the electrolyzer, which, getting stuck in the cathode grid, form an asbestos layer that plays the role of a diaphragm.

In many designs of electrolyzers, the cathode is completely immersed under the anolyte layer (electrolyte from the anode space), and the hydrogen released on the cathode grid is removed from under the cathode using gas pipes, without penetrating through the diaphragm into the anode space due to countercurrent.

Counterflow is a very important feature of the diaphragm cell design. It is thanks to the countercurrent flow directed from the anode space to the cathode space through a porous diaphragm that it becomes possible to separately obtain liquors and chlorine. The countercurrent flow is designed to counteract the diffusion and migration of OH - ions into the anode space. If the countercurrent is insufficient, then hypochlorite ion (ClO -) begins to form in the anode space in large quantities, which, after that, can be oxidized at the anode to the chlorate ion ClO 3 - . The formation of chlorate ion seriously reduces the current efficiency of chlorine and is the main side process in this method. The release of oxygen is also harmful, which, in addition, leads to the destruction of the anodes and, if they are made of carbon materials, the ingress of phosgene impurities into the chlorine.

Anode: - main process Cathode: - main process

Graphite or carbon electrodes can be used as an anode in diaphragm electrolyzers. To date, they have mainly been replaced by titanium anodes with a ruthenium oxide-titanium coating (ORTA anodes) or other low-consumption anodes.

Table salt, sodium sulfate and other impurities, when their concentration in solution increases above their solubility limit, precipitate. The caustic solution is decanted from the precipitate and transferred as a finished product to the warehouse or the evaporation stage is continued to obtain a solid product, followed by melting, flaking or granulation.

The reverse, that is, table salt crystallized into a precipitate, is returned back to the process, preparing the so-called reverse brine from it. From it, in order to avoid the accumulation of impurities in solutions, impurities are separated before preparing the return brine.

The loss of anolyte is replenished by adding fresh brine obtained by underground leaching of salt layers of halite, bischofite and other minerals containing sodium chloride, and in addition by dissolving them in special containers at the place of production. Before mixing it with the reverse brine, fresh brine is cleaned of mechanical suspensions and a significant part of calcium and magnesium ions.

The resulting chlorine is separated from water vapor, compressed and fed either to the production of chlorine-containing products or to liquefaction.

Due to its relative simplicity and low cost, the diaphragm method for producing chlorine is still widely used in industry.

Scheme of a diaphragm electrolyzer.

Membrane method

The membrane method of chlorine production is the most energy efficient, but at the same time it is difficult to organize and operate.

From the point of view of electrochemical processes, the membrane method is similar to the diaphragm method, but the anode and cathode spaces are completely separated by an anion-impermeable cation-exchange membrane. Therefore, in a membrane electrolyzer, in contrast to a diaphragm cell, there is not one stream, but two.

As in the diaphragm method, a salt solution flow enters the anode space. And in the cathode - deionized water. A stream of depleted anolyte flows from the cathode space, which also contains impurities of hypochlorite and chlorate ions and chlorine comes out, and from the anode space - lye and hydrogen, which practically do not contain impurities and are close to commercial concentration, which reduces energy costs for their evaporation and purification.

At the same time, the feeding solution of salt (both fresh and recycled) and water are preliminarily cleaned of any impurities as much as possible. Such thorough cleaning is determined by the high cost of polymeric cation exchange membranes and their vulnerability to impurities in the feed solution.

In addition, the limited geometric shape and, in addition, the low mechanical strength and thermal stability of ion-exchange membranes largely determine the relatively complex designs of membrane electrolysis plants. For the same reason, membrane plants require the most complex systems automatic control and management.

Scheme of a membrane electrolyzer.

Mercury method with liquid cathode

In a number of electrochemical methods for obtaining chlorine, the mercury method makes it possible to obtain the purest chlorine.

Scheme of a mercury electrolyzer.

The installation for mercury electrolysis consists of an electrolyser, an amalgam decomposer and a mercury pump, interconnected by mercury-conducting communications.

The cathode of the electrolyzer is a flow of mercury pumped by the pump. Anodes - graphite, carbon or low-wear (ORTA, TDMA or others). Together with mercury, a stream of sodium chloride feed solution continuously flows through the electrolyzer.

At the anode, chlorine ions are oxidized from the electrolyte, and chlorine is released:

- main process

Chlorine and anolyte are removed from the electrolyzer. The anolyte leaving the electrolyzer is saturated with fresh halite, the impurities introduced with it, as well as washed out from the anodes and structural materials, are removed from it, and returned to electrolysis. Before saturation, the chlorine dissolved in it is extracted from the anolyte.

The growing requirements for environmental safety of production and the high cost of metallic mercury lead to the gradual replacement of the mercury method by methods of obtaining chlorine with a solid cathode.

Laboratory methods

Due to the availability of chlorine, bottled liquefied chlorine is commonly used in laboratory practice. Chlorine can be obtained by the action of an acid on sodium hypochlorite:

In addition, oxygen is also released. If you use hydrochloric acid, then the reaction looks different:

To obtain chlorine in small quantities, processes based on the oxidation of hydrogen chloride with strong oxidizing agents (for example, manganese (IV) oxide, potassium permanganate, potassium dichromate, lead dioxide, Berthollet salt, etc.) are usually used, manganese dioxide or potassium permanganate:

If it is not possible to use cylinders, small electrolyzers with a conventional or valve electrode can be used to produce chlorine.

15.1. general characteristics halogens and chalcogens

Halogens ("giving birth to salts") are elements of group VIIA. These include fluorine, chlorine, bromine and iodine. This group also includes unstable, and therefore not naturally occurring, astatine. Sometimes hydrogen is also included in this group.
Chalcogens ("copper-producing") are elements of the VIA group. These include oxygen, sulfur, selenium, tellurium and the almost non-natural polonium.
Of the eight naturally occurring atoms elements of these two groups, the most common oxygen atoms ( w= 49.5%), followed by chlorine atoms in abundance ( w= 0.19%), then - sulfur ( w= 0.048%), then - fluorine ( w= 0.028%). The atoms of other elements are hundreds and thousands of times smaller. You already studied oxygen in the eighth grade (Chapter 10), of the other elements, chlorine and sulfur are the most important - you will get to know them in this chapter.
The orbital radii of the atoms of halogens and chalcogens are small and only for the fourth atoms of each group approach one angstrom. This leads to the fact that all these elements are elements that form non-metals and only tellurium and iodine show some signs of amphoterism.
The general valence electronic formula of halogens is ns 2 np 5 , and chalcogens - ns 2 np 4 . The small size of atoms does not allow them to donate electrons; on the contrary, the atoms of these elements tend to accept them, forming singly charged (for halogens) and doubly charged (for chalcogens) anions. Connecting with small atoms, the atoms of these elements form covalent bonds. Seven valence electrons enable halogen atoms (except fluorine) to form up to seven covalent bonds, and six valence electrons of chalcogen atoms - up to six covalent bonds.
In compounds of fluorine, the most electronegative element, only one oxidation state is possible, namely -I. Oxygen, as you know, has a maximum oxidation state of +II. For atoms of other elements, the highest oxidation state is equal to the group number.

Simple substances of elements of group VIIA are of the same type in structure. They are made up of diatomic molecules. Under normal conditions, fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. By chemical properties these substances are strong oxidizing agents. Due to the growth in the size of atoms with an increase in the atomic number, their oxidative activity decreases.
Of the simple substances of group VIA elements, under normal conditions, only oxygen and ozone, consisting of diatomic and triatomic molecules, are gaseous, respectively; the rest are solids. Sulfur consists of eight-atomic cyclic molecules S 8 , selenium and tellurium from polymer molecules Se n and Te n. In terms of their oxidizing activity, chalcogens are inferior to halogens: only oxygen is a strong oxidizing agent of them, while the rest exhibit oxidizing properties to a much lesser extent.

Compound hydrogen compounds halogens (NE) fully complies with the general rule, and chalcogens, in addition to the usual hydrogen compounds of the composition H 2 E, can also form more complex hydrogen compounds of the composition H 2 E n chain structure. In aqueous solutions, both hydrogen halides and other hydrogen chalcogens exhibit acidic properties. Their molecules are acid particles. Of these, only HCl, HBr and HI are strong acids.
For halogens formation oxides uncharacteristic, most of them are unstable, however, higher oxides of the composition E 2 O 7 are known for all halogens (except for fluorine, whose oxygen compounds are not oxides). All halogen oxides are molecular substances, chemically they are acidic oxides.
In accordance with their valence capabilities, chalcogens form two series of oxides: EO 2 and EO 3. All these oxides are acidic.

Hydroxides of halogens and chalcogens are oxoacids.

Make abbreviated electronic formulas and energy diagrams of atoms of elements of VIA and VIIA groups. Indicate the outer and valence electrons.

Chlorine is the most common and therefore the most important of the halogens.
In the earth's crust, chlorine is found in the composition of minerals: halite (rock salt) NaCl, sylvin KCl, carnallite KCl MgCl 2 6H 2 O and many others. The main industrial production method is the electrolysis of sodium or potassium chlorides.

The simple substance chlorine is a greenish gas with a pungent, suffocating odor. At -101 °C, it condenses into a yellow-green liquid. Chlorine is very poisonous, during the First World War they even tried to use it as a chemical warfare agent.
Chlorine is one of the strongest oxidizing agents. It reacts with most simple substances (exception: noble gases, oxygen, nitrogen, graphite, diamond and some others). As a result, halides are formed:
Cl 2 + H 2 \u003d 2HCl (when heated or in the light);
5Cl 2 + 2P = 2PCl 5 (when burned in excess chlorine);
Cl 2 + 2Na = 2NaCl (at room temperature);
3Cl 2 + 2Sb = 2SbCl 3 (at room temperature);
3Cl 2 + 2Fe \u003d 2FeCl 3 (when heated).
In addition, chlorine can also oxidize many complex substances, for example:
Cl 2 + 2HBr \u003d Br 2 + 2HCl (in gas phase and in solution)
Cl 2 + 2HI \u003d I 2 + 2HCl (in the gas phase and in solution);
Cl 2 + H 2 S = 2HCl + S (in solution);
Cl 2 + 2KBr = Br 2 + 2KCl (in solution);
Cl 2 + 3H 2 O 2 = 2HCl + 2H 2 O + O 2 (in concentrated solution);
Cl 2 + CO \u003d CCl 2 O (in the gas phase);
Cl 2 + C 2 H 4 \u003d C 2 H 4 Cl 2 (in the gas phase).
In water, chlorine partially dissolves (physically), and partially reacts reversibly with it (see § 11.4 c). With a cold solution of potassium hydroxide (and any other alkali), a similar reaction proceeds irreversibly:

Cl 2 + 2OH \u003d Cl + ClO + H 2 O.

As a result, a solution of chloride and potassium hypochlorite is formed. In the case of reaction with calcium hydroxide, a mixture of CaCl 2 and Ca(ClO) 2 is formed, called bleach.

With hot concentrated solutions of alkalis, the reaction proceeds differently:

3Cl 2 + 6OH = 5Cl + ClO 3 + 3H 2 O.

In the case of reaction with KOH, potassium chlorate, called Berthollet salt, is obtained in this way.
Hydrogen chloride is the only hydrogen bond chlorine. This colorless gas with a suffocating odor is highly soluble in water (it completely reacts with it, forming oxonium ions and chloride ions (see § 11.4). Its solution in water is called hydrochloric or hydrochloric acid. This is one of the most important products of chemical technology, since hydrochloric acid is consumed in many industries.It is of great importance for humans, in particular because it is contained in gastric juice, contributing to the digestion of food.
Hydrogen chloride used to be produced industrially by burning chlorine in hydrogen. At present, the need for hydrochloric acid is almost completely satisfied through the use of hydrogen chloride, which is formed as a by-product during the chlorination of various organic substances, for example, methane:

CH 4 + Cl 2 \u003d CH 3 + HCl

And laboratories produce hydrogen chloride from sodium chloride by treating it with concentrated sulfuric acid:
NaCl + H 2 SO 4 = HCl + NaHSO 4 (at room temperature);
2NaCl + 2H 2 SO 4 \u003d 2HCl + Na 2 S 2 O 7 + H 2 O (when heated).
Higher oxide chlorine Cl 2 O 7 - colorless oily liquid, molecular substance, acid oxide. As a result of reaction with water, it forms perchloric acid HClO 4 , the only oxoacid of chlorine that exists as an individual substance; the remaining oxoacids of chlorine are known only in aqueous solutions. Information about these chlorine acids is given in table 35.

Table 35

C/O chlorine	Formula acids	Name acids	Force acids	Name salts
		hydrochloric
		hypochlorous		hypochlorites
		chloride
		chlorine
				perchlorates

Most chlorides are soluble in water. The exceptions are AgCl, PbCl 2 , TlCl and Hg 2 Cl 2 . The formation of a colorless precipitate of silver chloride when a solution of silver nitrate is added to the test solution - qualitative reaction for chloride ion:

Ag + Cl = AgCl

Chlorine can be obtained from sodium or potassium chlorides in the laboratory:

2NaCl + 3H 2 SO 4 + MnO 2 = 2NaHSO 4 + MnSO 4 + 2H 2 O + Cl 2

As an oxidizing agent in the production of chlorine by this method, you can use not only manganese dioxide, but also KMnO 4 , K 2 Cr 2 O 7 , KClO 3 .
Sodium and potassium hypochlorites are found in various household and industrial bleaches. Bleach is also used as a bleach and is also used as a disinfectant.
Potassium chlorate is used in the manufacture of matches, explosives and pyrotechnic compositions. When heated, it decomposes:
4KClO 3 \u003d KCl + 3KClO 4;
2KClO 3 = 2KCl + O 2 (in the presence of MnO 2).
Potassium perchlorate also decomposes, but at a higher temperature: KClO 4 \u003d KCl + 2O 2.

1.Compose molecular reaction equations for which ionic equations are given in the text of the paragraph.
2. Make the equations of the reactions given in the text of the paragraph descriptively.
3. Make equations of reactions that characterize the chemical properties of a) chlorine, b) hydrogen chloride (and hydrochloric acid), c) potassium chloride and d) barium chloride.
Chemical properties of chlorine compounds

Various allotropic modifications are stable under different conditions element sulfur. Under normal conditions simple matter sulfur is a yellow brittle crystalline substance, consisting of eight-atomic molecules:

This is the so-called rhombic sulfur (or -sulfur) S 8. (The name comes from a crystallographic term characterizing the symmetry of the crystals of this substance). When heated, it melts (113 ° C), turning into a mobile yellow liquid, consisting of the same molecules. With further heating, the cycles are broken and very long polymer molecules are formed - the melt darkens and becomes very viscous. This is the so-called -sulfur S n. Sulfur boils (445 ° C) in the form of diatomic molecules S 2, similar in structure to oxygen molecules. The structure of these molecules, as well as oxygen molecules, cannot be described in terms of the covalent bond model. In addition, there are other allotropic modifications of sulfur.
In nature, there are deposits of native sulfur, from which it is mined. Most of the sulfur that is mined is used to produce sulfuric acid. Part of sulfur is used in agriculture for plant protection. Purified sulfur is used in medicine for the treatment of skin diseases.
From hydrogen compounds sulfur, hydrogen sulfide (monosulfan) H 2 S is of the greatest importance. It is a colorless poisonous gas with the smell of rotten eggs. It is slightly soluble in water. Physical dissolution. To a small extent, protolysis of hydrogen sulfide molecules occurs in an aqueous solution, and to an even lesser extent, hydrosulfide ions formed in this case (see Appendix 13). However, a solution of hydrogen sulfide in water is called hydrosulfide acid (or hydrogen sulfide water).

Hydrogen sulfide burns in air:

2H 2 S + 3O 2 \u003d 2H 2 O + SO 2 (with excess oxygen).

A qualitative reaction to the presence of hydrogen sulfide in the air is the formation of black lead sulfide (blackening of filter paper moistened with a solution of lead nitrate:

H 2 S + Pb 2 + 2H 2 O \u003d PbS + 2H 3O

The reaction proceeds in this direction due to the very low solubility of lead sulfide.

In addition to hydrogen sulfide, sulfur forms other sulfanes H 2 S n, for example, disulfan H 2 S 2 , similar in structure to hydrogen peroxide. It is also a very weak acid; its salt is pyrite FeS 2 .

In accordance with the valence capabilities of its atoms, sulfur forms two oxide: SO 2 and SO 3 . Sulfur dioxide (trivial name - sulphur dioxide) is a colorless gas with a pungent odor that causes coughing. Sulfur trioxide (the old name is sulfuric anhydride) is a solid, extremely hygroscopic non-molecular substance, which turns into a molecular substance when heated. Both oxides are acidic. When reacted with water, they form sulfur and sulfuric acids, respectively. acids.
In dilute solutions, sulfuric acid is a typical strong acid with all their characteristic properties.
Pure sulfuric acid, as well as its concentrated solutions, are very strong oxidizing agents, and the oxidizing atoms here are not hydrogen atoms, but sulfur atoms, passing from the oxidation state + VI to the oxidation state + IV. As a result, OVR with concentrated sulfuric acid usually produces sulfur dioxide, for example:

Cu + 2H 2 SO 4 \u003d CuSO 4 + SO 2 + 2H 2 O;
2KBr + 3H 2 SO 4 \u003d 2KHSO 4 + Br 2 + SO 2 + 2H 2 O.

Thus, even metals that are in the voltage series to the right of hydrogen (Cu, Ag, Hg) react with concentrated sulfuric acid. At the same time, some fairly active metals (Fe, Cr, Al, etc.) do not react with concentrated sulfuric acid, this is due to the fact that a dense protective film is formed on the surface of such metals under the action of sulfuric acid, preventing further oxidation. This phenomenon is called passivation.
Being a dibasic acid, sulfuric acid forms two rows salts: medium and sour. Acid salts are isolated only for alkaline elements and ammonium, the existence of other acid salts is doubtful.
Most medium sulfates are soluble in water and, since the sulfate ion is practically not an anionic base, they do not undergo anionic hydrolysis.
Modern industrial methods for the production of sulfuric acid are based on the production of sulfur dioxide (1st stage), its oxidation to trioxide (2nd stage) and the interaction of sulfur trioxide with water (3rd stage).

Sulfur dioxide is obtained by burning sulfur or various sulfides in oxygen:

S + O 2 \u003d SO 2;
4FeS 2 + 11O 2 \u003d 2Fe 2 O 3 + 8SO 2.

The process of roasting sulfide ores in non-ferrous metallurgy is always accompanied by the formation of sulfur dioxide, which is used to produce sulfuric acid.
Under normal conditions, sulfur dioxide cannot be oxidized with oxygen. Oxidation is carried out by heating in the presence of a catalyst, vanadium(V) oxide or platinum. Although the reaction

2SO 2 + O 2 2SO 3 + Q

reversible, the yield reaches 99%.
If the resulting gas mixture of sulfur trioxide with air is passed through pure water, most of the sulfur trioxide is not absorbed. To prevent losses, the gas mixture is passed through sulfuric acid or its concentrated solutions. In this case, disulfuric acid is formed:

SO 3 + H 2 SO 4 \u003d H 2 S 2 O 7.

A solution of disulfuric acid in sulfuric acid is called oleum and is often represented as a solution of sulfur trioxide in sulfuric acid.
By diluting oleum with water, both pure sulfuric acid and its solutions can be obtained.

1.Compose structural formulas
a) sulfur dioxide, b) sulfur trioxide,
c) sulfuric acid, d) disulfuric acid.

Chlorine(lat. Chlorum), Cl, chemical element group VII of the periodic system of Mendeleev, atomic number 17, atomic mass 35.453; belongs to the halogen family. Under normal conditions (0°C, 0.1 MN/m 2 , or 1 kgf/cm 2) a yellow-green gas with a sharp irritating odor. Natural Chlorine consists of two stable isotopes: 35 Cl (75.77%) and 37 Cl (24.23%). Artificially obtained radioactive isotopes with mass numbers 31-47, in particular: 32, 33, 34, 36, 38, 39, 40 with half-lives (T ½) respectively 0.31; 2.5; 1.56 sec; 3.1 10 5 years; 37.3, 55.5 and 1.4 min. 36 Cl and 38 Cl are used as tracers.

Historical reference. Chlorine was obtained for the first time in 1774 by K. Scheele by the interaction of hydrochloric acid with pyrolusite MnO 2 . However, only in 1810, G. Davy established that chlorine is an element and named it chlorine (from the Greek chloros - yellow-green). In 1813, J. L. Gay-Lussac proposed the name Chlorine for this element.

Distribution of chlorine in nature. Chlorine occurs in nature only in the form of compounds. The average content of Chlorine in the earth's crust (clarke) is 1.7·10 -2% by mass, in acid igneous rocks - granites and others 2.4·10 -2, in basic and ultrabasic 5·10 -3 . Water migration plays a major role in the history of chlorine in the earth's crust. In the form of Cl ion - it is found in the World Ocean (1.93%), underground brines and salt lakes. The number of own minerals (mainly natural chlorides) is 97, the main one being halite NaCl (Rock salt). Large deposits of potassium and magnesium chlorides and mixed chlorides are also known: sylvin KCl, sylvinite (Na,K)Cl, carnalite KCl MgCl 2 6H 2 O, kainite KCl MgSO 4 3H 2 O, bischofite MgCl 2 6H 2 O In the history of the Earth, the supply of HCl contained in volcanic gases to the upper parts of the earth's crust was of great importance.

Physical properties of chlorine. Chlorine has t bp -34.05°C, t pl -101°C. The density of gaseous chlorine under normal conditions is 3.214 g/l; saturated steam at 0°C 12.21 g/l; liquid chlorine at a boiling point of 1.557 g/cm 3 ; solid chlorine at - 102°C 1.9 g/cm 3 . Saturated vapor pressure of Chlorine at 0°C 0.369; at 25°C 0.772; at 100°C 3.814 MN/m 2 or 3.69 respectively; 7.72; 38.14 kgf / cm 2. Heat of fusion 90.3 kJ/kg (21.5 cal/g); heat of vaporization 288 kJ/kg (68.8 cal/g); heat capacity of gas at constant pressure 0.48 kJ/(kg K) . Critical constants of Chlorine: temperature 144°C, pressure 7.72 MN/m2 (77.2 kgf/cm2), density 573 g/l, specific volume 1.745·10 -3 l/g. Solubility (in g / l) Chlorine at a partial pressure of 0.1 MN / m 2, or 1 kgf / cm 2, in water 14.8 (0 ° C), 5.8 (30 ° C), 2.8 ( 70°C); in a solution of 300 g/l NaCl 1.42 (30°C), 0.64 (70°C). Below 9.6°C in aqueous solutions, chlorine hydrates of variable composition Cl 2 ·nH 2 O are formed (where n = 6-8); These are yellow crystals of cubic syngony, decomposing when the temperature rises into Chlorine and water. Chlorine dissolves well in TiCl 4 , SiCl 4 , SnCl 4 and some organic solvents (especially in hexane C 6 H 14 and carbon tetrachloride CCl 4). The chlorine molecule is diatomic (Cl 2). The degree of thermal dissociation of Cl 2 + 243 kJ \u003d 2Cl at 1000 K is 2.07 10 -4%, at 2500 K 0.909%.

Chemical properties of chlorine. External electronic configuration of the atom Cl 3s 2 Зр 5 . In accordance with this, chlorine in compounds exhibits oxidation states -1, +1, +3, +4, +5, +6 and +7. The covalent radius of the atom is 0.99Å, the ionic radius of Cl is 1.82Å, the electron affinity of the Chlorine atom is 3.65 eV, and the ionization energy is 12.97 eV.

Chemically, chlorine is very active, it combines directly with almost all metals (with some only in the presence of moisture or when heated) and with non-metals (except carbon, nitrogen, oxygen, inert gases), forming the corresponding chlorides, reacts with many compounds, replaces hydrogen in saturated hydrocarbons and joins unsaturated compounds. Chlorine displaces bromine and iodine from their compounds with hydrogen and metals; from the compounds of chlorine with these elements, it is displaced by fluorine. Alkali metals in the presence of traces of moisture interact with chlorine with ignition, most metals react with dry chlorine only when heated. Steel, as well as some metals, is resistant to dry chlorine at low temperatures, so they are used for the manufacture of equipment and storage facilities for dry chlorine. Phosphorus ignites in an atmosphere of chlorine, forming РCl 3 , and upon further chlorination - РCl 5 ; sulfur with Chlorine, when heated, gives S 2 Cl 2, SCl 2 and other S n Cl m. Arsenic, antimony, bismuth, strontium, tellurium interact vigorously with chlorine. A mixture of chlorine and hydrogen burns with a colorless or yellow-green flame to form hydrogen chloride (this is a chain reaction).

The maximum temperature of the hydrogen-chlorine flame is 2200°C. Mixtures of chlorine with hydrogen containing from 5.8 to 88.5% H 2 are explosive.

Chlorine forms oxides with oxygen: Cl 2 O, ClO 2 , Cl 2 O 6 , Cl 2 O 7 , Cl 2 O 8 , as well as hypochlorites (salts of hypochlorous acid), chlorites, chlorates and perchlorates. All oxygen compounds of chlorine form explosive mixtures with easily oxidized substances. Chlorine oxides are unstable and can explode spontaneously, hypochlorites decompose slowly during storage, chlorates and perchlorates can explode under the influence of initiators.

Chlorine in water is hydrolyzed, forming hypochlorous and hydrochloric acids: Cl 2 + H 2 O \u003d HClO + HCl. When chlorinating aqueous solutions of alkalis in the cold, hypochlorites and chlorides are formed: 2NaOH + Cl 2 \u003d NaClO + NaCl + H 2 O, and when heated - chlorates. By chlorination of dry calcium hydroxide, bleach is obtained.

When ammonia reacts with chlorine, nitrogen trichloride is formed. In the chlorination of organic compounds, chlorine either replaces hydrogen or adds via multiple bonds, forming various chlorine-containing organic compounds.

Chlorine forms interhalogen compounds with other halogens. Fluorides ClF, ClF 3 , ClF 3 are very reactive; for example, in an atmosphere of ClF 3 glass wool ignites spontaneously. Chlorine compounds with oxygen and fluorine are known - Chlorine oxyfluorides: ClO 3 F, ClO 2 F 3 , ClOF, ClOF 3 and fluorine perchlorate FClO 4 .

Getting Chlorine. Chlorine began to be produced in industry in 1785 by the interaction of hydrochloric acid with manganese (II) oxide or pyrolusite. In 1867, the English chemist G. Deacon developed a method for producing chlorine by oxidizing HCl with atmospheric oxygen in the presence of a catalyst. Since the late 19th - early 20th century, chlorine has been produced by electrolysis of aqueous solutions of alkali metal chlorides. These methods produce 90-95% of Chlorine in the world. Small amounts of chlorine are obtained incidentally in the production of magnesium, calcium, sodium, and lithium by electrolysis of molten chlorides. Two main methods of electrolysis of NaCl aqueous solutions are used: 1) in electrolyzers with a solid cathode and a porous filter diaphragm; 2) in electrolyzers with a mercury cathode. According to both methods, gaseous chlorine is released on a graphite or oxide titanium-ruthenium anode. According to the first method, hydrogen is released at the cathode and a solution of NaOH and NaCl is formed, from which commercial caustic soda is isolated by subsequent processing. According to the second method, sodium amalgam is formed on the cathode, when it is decomposed with pure water in a separate apparatus, a NaOH solution, hydrogen and pure mercury are obtained, which again goes into production. Both methods give 1.125 tons of NaOH per 1 ton of Chlorine.

Diaphragm electrolysis requires less capital investment for chlorine production and produces cheaper NaOH. The mercury cathode method produces very pure NaOH, but the loss of mercury pollutes the environment.

The use of chlorine. One of the important branches of the chemical industry is the chlorine industry. The main quantities of chlorine are processed at the place of its production into chlorine-containing compounds. Chlorine is stored and transported in liquid form in cylinders, barrels, railway tanks or in specially equipped vessels. For industrial countries, the following approximate consumption of chlorine is typical: for the production of chlorine-containing organic compounds - 60-75%; inorganic compounds containing Chlorine, -10-20%; for bleaching of pulp and fabrics - 5-15%; for sanitary needs and water chlorination - 2-6% of the total output.

Chlorine is also used for the chlorination of some ores in order to extract titanium, niobium, zirconium and others.

Chlorine in the body Chlorine is one of the biogenic elements, a constant component of plant and animal tissues. The content of chlorine in plants (a lot of chlorine in halophytes) - from thousandths of a percent to whole percent, in animals - tenths and hundredths of a percent. daily requirement an adult in Chlorine (2-4 g) is covered by food. With food, Chlorine is usually supplied in excess in the form of sodium chloride and potassium chloride. Bread, meat and dairy products are especially rich in Chlorine. In animals, chlorine is the main osmotically active substance in blood plasma, lymph, cerebrospinal fluid, and some tissues. Plays a role in water-salt metabolism, contributing to the retention of water by tissues. Regulation of acid-base balance in tissues is carried out along with other processes by changing the distribution of Chlorine between the blood and other tissues. Chlorine is involved in energy metabolism in plants, activating both oxidative phosphorylation and photophosphorylation. Chlorine has a positive effect on the absorption of oxygen by the roots. Chlorine is necessary for the production of oxygen during photosynthesis by isolated chloroplasts. Chlorine is not included in most nutrient media for artificial cultivation of plants. It is possible that very low concentrations of Chlorine are sufficient for the development of plants.

Chlorine poisoning is possible in the chemical, pulp and paper, textile, pharmaceutical industries and others. Chlorine irritates the mucous membranes of the eyes and respiratory tract. Secondary infection usually joins the primary inflammatory changes. Acute poisoning develops almost immediately. Inhalation of medium and low concentrations of chlorine causes tightness and pain in the chest, dry cough, rapid breathing, pain in the eyes, lacrimation, increased levels of leukocytes in the blood, body temperature, etc. Possible bronchopneumonia, toxic pulmonary edema, depression, convulsions . In mild cases, recovery occurs in 3-7 days. As long-term consequences, catarrhs ​​of the upper respiratory tract, recurrent bronchitis, pneumosclerosis and others are observed; possible activation of pulmonary tuberculosis. With prolonged inhalation of small concentrations of Chlorine, similar, but slowly developing forms of the disease are observed. Prevention of poisoning: sealing of production facilities, equipment, effective ventilation, if necessary, the use of a gas mask. The production of chlorine, bleach and other chlorine-containing compounds belongs to industries with harmful working conditions.

Cl 2 at vol. T - yellow-green gas with a sharp suffocating odor, heavier than air - 2.5 times, slightly soluble in water (~ 6.5 g / l); X. R. in nonpolar organic solvents. It is found free only in volcanic gases.

How to get

Based on the process of oxidation of anions Cl -

2Cl - - 2e - = Cl 2 0

Industrial

Electrolysis of aqueous solutions of chlorides, more often - NaCl:

2NaCl + 2H 2 O \u003d Cl 2 + 2NaOH + H 2

Laboratory

Oxidation conc. HCI various oxidizing agents:

4HCI + MnO 2 \u003d Cl 2 + MpCl 2 + 2H 2 O

16HCl + 2KMnO 4 \u003d 5Cl 2 + 2MnCl 2 + 2KCl + 8H 2 O

6HCl + KClO 3 \u003d ZCl 2 + KCl + 3H 2 O

14HCl + K 2 Cr 2 O 7 \u003d 3Cl 2 + 2CrCl 3 + 2KCl + 7H 2 O

Chemical properties

Chlorine is a very strong oxidizing agent. Oxidizes metals, non-metals and complex substances, while turning into very stable anions Cl -:

Cl 2 0 + 2e - \u003d 2Cl -

Reactions with metals

Active metals in an atmosphere of dry chlorine gas ignite and burn; in this case, metal chlorides are formed.

Cl 2 + 2Na = 2NaCl

3Cl 2 + 2Fe = 2FeCl 3

Inactive metals are more easily oxidized by wet chlorine or its aqueous solutions:

Cl 2 + Cu \u003d CuCl 2

3Cl 2 + 2Au = 2AuCl 3

Reactions with non-metals

Chlorine does not directly interact only with O 2, N 2, C. Reactions proceed with other non-metals under various conditions.

Non-metal halides are formed. The most important is the reaction of interaction with hydrogen.

Cl 2 + H 2 \u003d 2HC1

Cl 2 + 2S (melt) = S 2 Cl 2

ЗCl 2 + 2Р = 2РCl 3 (or РCl 5 - in excess of Cl 2)

2Cl 2 + Si = SiCl 4

3Cl 2 + I 2 \u003d 2ICl 3

Displacement of free non-metals (Br 2, I 2, N 2, S) from their compounds

Cl 2 + 2KBr = Br 2 + 2KCl

Cl 2 + 2KI \u003d I 2 + 2KCl

Cl 2 + 2HI \u003d I 2 + 2HCl

Cl 2 + H 2 S \u003d S + 2HCl

ZCl 2 + 2NH 3 \u003d N 2 + 6HCl

Disproportionation of chlorine in water and aqueous solutions of alkalis

As a result of self-oxidation-self-healing, some chlorine atoms are converted into Cl - anions, while others in a positive oxidation state are part of the ClO - or ClO 3 - anions.

Cl 2 + H 2 O \u003d HCl + HClO hypochlorous to-ta

Cl 2 + 2KOH \u003d KCl + KClO + H 2 O

3Cl 2 + 6KOH = 5KCl + KClO 3 + 3H 2 O

3Cl 2 + 2Ca (OH) 2 \u003d CaCl 2 + Ca (ClO) 2 + 2H 2 O

These reactions are important because they lead to the production of oxygen compounds of chlorine:

KClO 3 and Ca (ClO) 2 - hypochlorites; KClO 3 - potassium chlorate (bertolet salt).

Interaction of chlorine with organic substances

a) substitution of hydrogen atoms in OB molecules

b) attachment of Cl 2 molecules at the point of breaking of multiple carbon-carbon bonds

H 2 C \u003d CH 2 + Cl 2 → ClH 2 C-CH 2 Cl 1,2-dichloroethane

HC≡CH + 2Cl 2 → Cl 2 HC-CHCl 2 1,1,2,2-tetrachloroethane

Hydrogen chloride and hydrochloric acid

Hydrogen chloride gas

Physical and chemical properties

HCl is hydrogen chloride. At rev. T - colorless. gas with a pungent odor, liquefies quite easily (mp. -114°С, bp. -85°С). Anhydrous HCl, both in gaseous and liquid states, is non-conductive, chemically inert with respect to metals, metal oxides and hydroxides, and also to many other substances. This means that in the absence of water, hydrogen chloride does not exhibit acidic properties. Only at very high temperatures does gaseous HCl react with metals, even such inactive ones as Cu and Ag.
The reducing properties of the chloride anion in HCl also manifest themselves to a small extent: it is oxidized by fluorine at vol. T, and also at high T (600°C) in the presence of catalysts, it reversibly reacts with oxygen:

2HCl + F 2 \u003d Cl 2 + 2HF

4HCl + O 2 \u003d 2Cl 2 + 2H 2 O

Gaseous HCl is widely used in organic synthesis (hydrochlorination reactions).

How to get

1. Synthesis from simple substances:

H 2 + Cl 2 \u003d 2HCl

2. Formed as a by-product during hydrocarbon chlorination:

R-H + Cl 2 = R-Cl + HCl

3. In the laboratory, they receive the action of conc. H 2 SO 4 for chlorides:

H 2 SO 4 (conc.) + NaCl \u003d 2HCl + NaHSO 4 (with low heating)

H 2 SO 4 (conc.) + 2NaCl \u003d 2HCl + Na 2 SO 4 (with very strong heating)

An aqueous solution of HCl is a strong acid (hydrochloric, or hydrochloric)

HCl is very soluble in water: at vol. T in 1 l of H 2 O dissolves ~ 450 l of gas (dissolution is accompanied by the release of a significant amount of heat). A saturated solution has a mass fraction of HCl equal to 36-37%. This solution has a very pungent, suffocating odor.

HCl molecules in water almost completely decompose into ions, i.e., an aqueous solution of HCl is a strong acid.

Chemical properties of hydrochloric acid

1. HCl dissolved in water exhibits all the general properties of acids due to the presence of H + ions

HCl → H + + Cl -

Interaction:

a) with metals (up to H):

2HCl 2 + Zn \u003d ZnCl 2 + H 2

b) with basic and amphoteric oxides:

2HCl + CuO \u003d CuCl 2 + H 2 O

6HCl + Al 2 O 3 \u003d 2AlCl 3 + ZN 2 O

c) with bases and amphoteric hydroxides:

2HCl + Ca (OH) 2 \u003d CaCl 2 + 2H 2 O

3HCl + Al(OH) 3 \u003d AlCl 3 + ZN 2 O

d) with salts of weaker acids:

2HCl + CaCO 3 \u003d CaCl 2 + CO 2 + H 3 O

HCl + C 6 H 5 ONa \u003d C 6 H 5 OH + NaCl

e) with ammonia:

HCl + NH 3 \u003d NH 4 Cl

Reactions with strong oxidizing agents F 2 , MnO 2 , KMnO 4 , KClO 3 , K 2 Cr 2 O 7 . Anion Cl - is oxidized to free halogen:

2Cl - - 2e - = Cl 2 0

For reaction equations, see "Getting Chlorine". Of particular importance is the OVR between hydrochloric and nitric acid ami:

Reactions with organic compounds

Interaction:

a) with amines (as organic bases)

R-NH 2 + HCl → + Cl -

b) with amino acids (as amphoteric compounds)

Oxides and oxoacids of chlorine

Acid oxides

acids

salt

Chemical properties

1. All oxoacids of chlorine and their salts are strong oxidizers.

2. Almost all compounds decompose when heated due to intramolecular oxidation-reduction or disproportionation.

Bleaching powder

Chlorine (whitewash) lime - a mixture of hypochlorite and calcium chloride, has a bleaching and disinfecting effect. Sometimes it is considered as an example of a mixed salt, which simultaneously contains anions of two acids:

Javel water

Aqueous solution of chloride and potassium hapochlorite KCl + KClO + H 2 O

Chlorine

CHLORINE-A; m.[from Greek. chlōros - pale green] A chemical element (Cl), a greenish-yellow asphyxiating gas with a pungent odor (used as a poison and disinfectant). Chlorine compounds. Chlorine poisoning.

◁ Chlorine (see).

chlorine

(lat. Chlorum), a chemical element of group VII of the periodic system, refers to halogens. The name is from the Greek chlōros, yellow-green. Free chlorine consists of diatomic molecules (Cl 2); yellow-green gas with a pungent odor; density 3.214 g/l; t pl -101°C; t kip -33.97°C; at ordinary temperature, it is easily liquefied under a pressure of 0.6 MPa. Chemically very active (oxidizing agent). The main minerals are halite (rock salt), sylvin, bischofite; sea ​​water contains chlorides of sodium, potassium, magnesium and other elements. Used in the production of chlorine-containing organic compounds (60-75%), inorganic substances(10-20%), for bleaching cellulose and fabrics (5-15%), for sanitary needs and disinfection (chlorination) of water. Toxic.

CHLORINE

CHLORINE (lat. Chlorum), Cl (read "chlorine"), a chemical element with atomic number 17, atomic mass 35.453. In its free form, it is a yellow-green heavy gas with a sharp, suffocating odor (hence the name: Greek chloros - yellow-green).
Natural chlorine is a mixture of two nuclides (cm. NUCLIDE) with mass numbers 35 (in a mixture of 75.77% by mass) and 37 (24.23%). Outer electron layer configuration 3 s 2 p 5 . In compounds, it mainly exhibits oxidation states –1, +1, +3, +5 and +7 (valences I, III, V and VII). Located in the third period in group VIIA of the periodic system of elements of Mendeleev, refers to halogens (cm. HALOGENS).
The radius of the neutral chlorine atom is 0.099 nm, the ionic radii are equal, respectively (in parentheses are the values ​​of the coordination number): Cl - 0.167 nm (6), Cl 5+ 0.026 nm (3) and Clr 7+ 0.022 nm (3) and 0.041 nm ( 6). The successive ionization energies of the neutral chlorine atom are 12.97, 23.80, 35.9, 53.5, 67.8, 96.7, and 114.3 eV, respectively. Electron affinity 3.614 eV. On the Pauling scale, the electronegativity of chlorine is 3.16.
Discovery history
The most important chemical compound chlorine - table salt (chemical formula NaCl, chemical name sodium chloride) - has been known to man since ancient times. There is evidence that the extraction of table salt was carried out as early as 3-4 thousand years BC in Libya. It is possible that, using table salt for various manipulations, alchemists also encountered gaseous chlorine. To dissolve the "king of metals" - gold - they used "aqua regia" - a mixture of hydrochloric and nitric acids, the interaction of which releases chlorine.
For the first time, chlorine gas was obtained and described in detail by the Swedish chemist K. Scheele (cm. SCHEELE Karl Wilhelm) in 1774. He heated hydrochloric acid with the mineral pyrolusite (cm. PYROLUSITE) MnO 2 and observed the evolution of a yellow-green gas with a pungent odor. Since in those days the theory of phlogiston dominated (cm. PHLOGISTON), new gas Scheele considered it as "dephlogistinated hydrochloric acid", i.e. as an oxide (oxide) of hydrochloric acid. A. Lavoisier (cm. Lavoisier Antoine Laurent) considered gas as an oxide of the element "muria" (hydrochloric acid was called muriic acid, from Latin muria - brine). The same point of view was first shared by the English scientist G. Davy (cm. DEVI Humphrey), who spent a lot of time decomposing "murium oxide" into simple substances. He did not succeed, and by 1811 Davy came to the conclusion that this gas is a simple substance, and a chemical element corresponds to it. Davy was the first to propose, in accordance with the yellow-green color of the gas, to call it chlorine (chlorine). The name "chlorine" was given to the element in 1812 by the French chemist J. L. Gay-Lussac (cm. GAY LUSSAC Joseph Louis); it is accepted in all countries except Great Britain and the USA, where the name introduced by Davy has been preserved. It has been suggested that this element should be called "halogen" (i.e., producing salts), but it eventually became the common name for all elements of group VIIA.
Being in nature
The content of chlorine in the earth's crust is 0.013% by mass, in a noticeable concentration it is in the form of Cl ion - present in sea water (on average, about 18.8 g / l). Chemically, chlorine is highly active and therefore does not occur in free form in nature. It is part of such minerals that form large deposits, such as table or rock salt (halite (cm. HALITE)) NaCl, carnallite (cm. CARNALLITE) KCl MgCl 2 6H 21 O, sylvite (cm. SILVIN) KCl, sylvinite (Na, K)Cl, kainite (cm. Cainite) KCl MgSO 4 3H 2 O, bischofite (cm. BISHOPHIT) MgCl 2 6H 2 O and many others. Chlorine can be found in a variety of rocks, in the soil.
Receipt
To obtain gaseous chlorine, electrolysis of a strong aqueous solution of NaCl is used (sometimes KCl is used). The electrolysis is carried out using a cation exchange membrane separating the cathode and anode spaces. At the same time, through the process
2NaCl + 2H 2 O \u003d 2NaOH + H 2 + Cl 2
three valuable chemical products are obtained at once: at the anode - chlorine, at the cathode - hydrogen (cm. HYDROGEN), and alkali accumulates in the cell (1.13 tons of NaOH for every ton of chlorine produced). The production of chlorine by electrolysis requires large expenditures of electricity: from 2.3 to 3.7 MW is spent on obtaining 1 ton of chlorine.
To obtain chlorine in the laboratory, the reaction of concentrated hydrochloric acid with some strong oxidizing agent (potassium permanganate KMnO 4, potassium dichromate K 2 Cr 2 O 7, potassium chlorate KClO 3 , bleach CaClOCl, manganese oxide (IV) MnO 2) is used. It is most convenient to use potassium permanganate for these purposes: in this case, the reaction proceeds without heating:
2KMnO 4 + 16HCl \u003d 2KCl + 2MnCl 2 + 5Cl 2 + 8H 2 O.
If necessary, chlorine in a liquefied (under pressure) form is transported in railway tanks or in steel cylinders. Chlorine cylinders have a special marking, but even in the absence of such a chlorine cylinder, it is easy to distinguish it from cylinders with other non-toxic gases. The bottom of chlorine cylinders has the shape of a hemisphere, and a cylinder with liquid chlorine cannot be placed vertically without support.
Physical and chemical properties
Under normal conditions, chlorine is a yellow-green gas, the gas density at 25 ° C is 3.214 g / dm 3 (about 2.5 times the density of air). The melting point of solid chlorine is -100.98°C, the boiling point is -33.97°C. The standard electrode potential Cl 2 /Cl - in an aqueous solution is +1.3583 V.
In the free state, it exists in the form of diatomic Cl 2 molecules. The internuclear distance in this molecule is 0.1987 nm. The electron affinity of the Cl 2 molecule is 2.45 eV, the ionization potential is 11.48 eV. The dissociation energy of Cl 2 molecules into atoms is relatively low and amounts to 239.23 kJ/mol.
Chlorine is slightly soluble in water. At a temperature of 0°C, the solubility is 1.44 wt.%, at 20°C - 0.711°C wt.%, at 60°C - 0.323 wt. %. A solution of chlorine in water is called chlorine water. IN chlorine water equilibrium is established:
Cl 2 + H 2 O H + = Cl - + HOCl.
In order to shift this equilibrium to the left, i.e., to reduce the solubility of chlorine in water, either sodium chloride NaCl or some non-volatile strong acid (for example, sulfuric) should be added to the water.
Chlorine is highly soluble in many non-polar liquids. Liquid chlorine itself serves as a solvent for substances such as Bcl 3 , SiCl 4 , TiCl 4 .
Due to the low energy of dissociation of Cl 2 molecules into atoms and the high electron affinity of the chlorine atom, chlorine is chemically highly active. It enters into direct interaction with most metals (including, for example, gold) and many non-metals. So, without heating, chlorine reacts with alkaline (cm. ALKALI METALS) and alkaline earth metals (cm. ALKALINE EARTH METALS), with antimony:
2Sb + 3Cl 2 = 2SbCl 3
When heated, chlorine reacts with aluminum:
3Cl 2 + 2Al = 2A1Cl 3
and iron:
2Fe + 3Cl 2 \u003d 2FeCl 3.
Chlorine reacts with hydrogen H 2 either when ignited (chlorine burns quietly in a hydrogen atmosphere), or when a mixture of chlorine and hydrogen is irradiated with ultraviolet light. In this case, hydrogen chloride gas HCl is formed:
H 2 + Cl 2 \u003d 2HCl.
A solution of hydrogen chloride in water is called hydrochloric (cm. HYDROCHLORIC ACID)(hydrochloric) acid. The maximum mass concentration of hydrochloric acid is about 38%. Salts of hydrochloric acid - chlorides (cm. Chlorides), for example, ammonium chloride NH 4 Cl, calcium chloride CaCl 2 , barium chloride BaCl 2 and others. Many chlorides are highly soluble in water. Practically insoluble in water and in acidic aqueous solutions of silver chloride AgCl. A qualitative reaction to the presence of chloride ions in a solution is the formation of a white AgCl precipitate with Ag + ions, which is practically insoluble in a nitric acid medium:
CaCl 2 + 2AgNO 3 \u003d Ca (NO 3) 2 + 2AgCl.
At room temperature, chlorine reacts with sulfur (the so-called sulfur monochloride S 2 Cl 2 is formed) and fluorine (the compounds ClF and ClF 3 are formed). When heated, chlorine interacts with phosphorus (depending on the reaction conditions, PCl 3 or PCl 5 compounds are formed), arsenic, boron and other non-metals. Chlorine does not directly react with oxygen, nitrogen, carbon (numerous compounds of chlorine with these elements are obtained indirectly) and inert gases (in Lately scientists have found ways to activate such reactions and carry them out “directly”). With other halogens, chlorine forms interhalogen compounds, for example, very strong oxidizing agents - fluorides ClF, ClF 3, ClF 5. The oxidizing power of chlorine is higher than that of bromine, so chlorine displaces the bromide ion from bromide solutions, for example:
Cl 2 + 2NaBr \u003d Br 2 + 2NaCl
Chlorine enters into substitution reactions with many organic compounds, for example, with methane CH 4 and benzene C 6 H 6:
CH 4 + Cl 2 = CH 3 Cl + Hcl or C 6 H 6 + Cl 2 = C 6 H 5 Cl + Hcl.
The chlorine molecule is capable of adding multiple bonds (double and triple) to organic compounds, for example, to ethylene C 2 H 4:
C 2 H 4 + Cl 2 = CH 2 ClCH 2 Cl.
Chlorine interacts with aqueous solutions of alkalis. If the reaction proceeds at room temperature, then chloride (for example, potassium chloride KCl) and hypochlorite are formed. (cm. HYPOCHLORITES)(for example, potassium hypochlorite KClO):
Cl 2 + 2KOH \u003d KClO + KCl + H 2 O.
When chlorine interacts with a hot (temperature of about 70-80 ° C) alkali solution, the corresponding chloride and chlorate are formed (cm. CHLORATES), For example:
3Cl 2 + 6KOH \u003d 5KSl + KClO 3 + 3H 2 O.
When chlorine interacts with a wet slurry of calcium hydroxide Ca (OH) 2, bleach is formed (cm. BLEACHING POWDER)("bleach") CaClOCl.
The oxidation state of chlorine +1 corresponds to a weak, unstable hypochlorous acid (cm. hypochlorous acid) HClO. Its salts are hypochlorites, for example, NaClO is sodium hypochlorite. Hypochlorites are the strongest oxidizers and are widely used as bleaching and disinfecting agents. When hypochlorites, in particular bleach, interact with carbon dioxide CO 2, volatile hypochlorous acid is formed among other products (cm. hypochlorous acid), which can decompose with the release of chlorine oxide (I) Cl 2 O:
2HClO \u003d Cl 2 O + H 2 O.
It is the smell of this gas, Cl 2 O, that is the characteristic smell of bleach.
The oxidation state of chlorine +3 corresponds to a low-stable acid of medium strength HclO 2. This acid is called chloride, its salts are chlorites. (cm. CHLORITES (salts)), for example, NaClO 2 - sodium chlorite.
The oxidation state of chlorine +4 corresponds to only one compound - chlorine dioxide СlО 2.
The oxidation state of chlorine +5 corresponds to strong, stable only in aqueous solutions at a concentration below 40%, chloric acid (cm. hypochlorous acid) HClO 3 . Its salts are chlorates, for example, potassium chlorate KClO 3 .
The oxidation state of chlorine +6 corresponds to only one compound - chlorine trioxide СlО 3 (exists in the form of a dimer Сl 2 О 6).
The oxidation state of chlorine +7 corresponds to a very strong and fairly stable perchloric acid (cm. PERCHLORIC ACID) HClO 4 . Its salts are perchlorates (cm. PERCHLORATES), for example, ammonium perchlorate NH 4 ClO 4 or potassium perchlorate KClO 4 . It should be noted that perchlorates of heavy alkali metals - potassium, and especially rubidium and cesium are slightly soluble in water. Oxide corresponding to the oxidation state of chlorine +7 - Cl 2 O 7.
Among compounds containing chlorine in positive oxidation states, hypochlorites have the strongest oxidizing properties. For perchlorates, oxidizing properties are uncharacteristic.
Application
Chlorine is one of the most important products of the chemical industry. Its world production is tens of millions of tons per year. Chlorine is used to produce disinfectants and bleaches (sodium hypochlorite, bleach and others), hydrochloric acid, chlorides of many metals and non-metals, many plastics (polyvinyl chloride (cm. polyvinyl chloride) and others), chlorine-containing solvents (dichloroethane CH 2 ClCH 2 Cl, carbon tetrachloride CCl 4, etc.), for opening ores, separation and purification of metals, etc. Chlorine is used to disinfect water (cm. CHLORINATION)) and for many other purposes.
Biological role
Chlorine is one of the most important biogenic elements (cm. BIOGENIC ELEMENTS) and is found in all living organisms. Some plants, the so-called halophytes, are not only able to grow on highly saline soils, but also accumulate chlorides in large quantities. Microorganisms (halobacteria, etc.) and animals living in conditions of high salinity of the environment are known. Chlorine is one of the main elements of the water-salt metabolism of animals and humans, which determines the physicochemical processes in the tissues of the body. It is involved in maintaining the acid-base balance in tissues, osmoregulation (cm. OSMO-REGULATION)(chlorine is the main osmotically active substance of blood, lymph, and other body fluids), being mainly outside the cells. In plants, chlorine is involved in oxidative reactions and photosynthesis.
Human muscle tissue contains 0.20-0.52% chlorine, bone - 0.09%; in the blood - 2.89 g / l. In the body of an average person (body weight 70 kg) 95 g of chlorine. Every day with food, a person receives 3-6 g of chlorine, which in excess covers the need for this element.
Features of working with chlorine
Chlorine is a poisonous suffocating gas that, if it enters the lungs, causes a burn of the lung tissue, suffocation. It has an irritating effect on the respiratory tract at a concentration in the air of about 0.006 mg / l. Chlorine was one of the first chemical poisons (cm. POISONING SUBSTANCES) used by Germany in the First world war. When working with chlorine, protective clothing, gas masks, and gloves should be used. On a short time to protect the respiratory organs from the ingress of chlorine, you can use a rag bandage moistened with a solution of sodium sulfite Na 2 SO 3 or sodium thiosulfate Na 2 S 2 O 3. MPC of chlorine in the air of working premises 1 mg / m 3, in the air settlements 0.03 mg / m 3.

encyclopedic Dictionary. 2009 .

Synonyms: