Basic properties of chlorine. Chlorine: properties, application, production. Chemical properties of chlorine

The main industrial method of production is concentrated NaCl (Fig. 96). In this case, (2Сl’ – 2e– = Сl 2) is released, and (2Н + 2e – = H2) is released in the cathode space and forms NaOH.

When obtained in a laboratory, they usually use the effect of MnO 2 or KMnO 4 on:

MnO 2 + 4HCl = MnCl 2 + Cl 2 + 2H 2 O

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

It is similar in its characteristic chemical function - it is also an active monovalent metalloid. However, it is less than that of. Therefore, the latter is capable of displacing connections.

Interaction with H 2 + Cl 2 = 2HCl + 44 kcal

under normal conditions it proceeds extremely slowly, but when the mixture is heated or strongly illuminated (direct sunlight, burning, etc.) it is accompanied.

NaCl + H 2 SO 4 = NaHSO 4 + HCl

NaCl + NaHSO 4 = Na 2 SO 4 + HCl

The first of them occurs partly already under normal conditions and almost entirely under low heating; the second occurs only at higher . To carry out the process, high-performance mechanical machines are used.

Cl 2 + H 2 O = HCl + HOCl

Being an unstable compound, HOCl slowly decomposes even in such a dilute state. are called hypochlorous acid, or . HOCl itself and its are very strong.

The easiest way to achieve this is by adding to the reaction mixture. Since, as H is formed, OH will be bound into undissociated ones and will shift to the right. Using, for example, NaOH we have:

Cl 2 + H 2 O<–––>HOCl + HCl

HOCl + HCl + 2NaOH –––>NaOCl + NaCl + 2H 2 O

or in general:

Cl 2 + 2NaOH –––>NaOCl + NaCl + H 2 O

As a result of interaction with, a mixture of hypochlorous and is obtained. The resulting (“”) has strong oxidizing properties and is widely used for bleaching and.

1) HOCl = HCl + O

2) 2HOСl = H 2 O + Cl 2 O

3) 3HOCl = 2HCl + HClO 3

All these processes can occur simultaneously, but their relative rates depend greatly on the existing conditions. By changing the latter, it is possible to ensure that the transformation goes almost entirely in one direction.

Under the influence of direct sunlight, decomposition occurs according to the first of them. It also occurs in the presence of those that can easily attach, and some (for example ").

The decomposition of HOCl according to the third type occurs especially easily when heated. Therefore, the effect on hot is expressed by the summary equation:

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

2КlO 3 + H 2 C 2 O 4 = K 2 CO 3 + CO 2 + H 2 O + 2ClO 2

greenish-yellow dioxide is formed (mp. - 59 °C, bp. + 10 °C). Free ClO 2 is unstable and can decompose with

Characteristics of elements of group VII of the main subgroup, using chlorine as an example

General characteristics of the subgroup

Table 1. Nomenclature of elements of subgroup VIIA

P-elements, typical, non-metals (astatine is a semi-metal), halogens.

Electron diagram of the element Hal (Hal ≠ F):

The elements of subgroup VIIA are characterized by the following valences:

Table 2. Valence

3. The elements of subgroup VIIA are characterized by the following oxidation states:

Table 3. Oxidation states of elements

Characteristics of a chemical element

Chlorine is an element of group VII A. Serial number 17

Relative atomic mass: 35.4527 a. e.m. (g/mol)

Number of protons, neutrons, electrons: 17,18,17

Atomic structure:

Electronic formula:

Typical oxidation states: -1, 0, +1, +3, +4, +5, +7

Ionization energy: 1254.9(13.01) kJ/mol (eV)

Electron affinity: 349 (kJ/mol)

Electronegativity according to Pauling: 3.20

Characteristics of a simple substance

Bond type: covalent non-polar

Diatomic molecule

Isotopes: 35 Cl (75.78%) and 37 Cl (24.22%)

Crystal lattice type: molecular

Thermodynamic parameters

Table 4

Physical properties

Table 5

Chemical properties

An aqueous solution of chlorine is highly dismutated (“chlorine water”)

Stage 1: Cl 2 + H 2 O = HCl + HOCl

Stage 2: HOCl = HCl + [O] – atomic oxygen

The oxidizing capacity in the subgroup decreases from fluorine to iodine = ˃

Chlorine is a strong oxidizing agent:

1. Interaction with simple substances

a) with hydrogen:

Cl 2 + H 2 = 2HCl

b) with metals:

Cl 2 + 2Na = 2NaCl

3Cl 2 + 2Fe = 2FeCl 3

c) with some less electronegative nonmetals:

3Cl 2 + 2P = 2PCl 3

Cl 2 + S = SCl 2

With oxygen, carbon and nitrogen, chlorine directly does not react!

2. Interaction with complex substances

a) with water: see above

b) with acids: does not react!

c) with alkali solutions:

in the cold: Cl 2 +2 NaOH = NaCl + NaClO + H 2 O

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

e) with many organic substances:

Cl 2 + CH 4 = CH 3 Cl + HCl

C 6 H 6 + Cl 2 = C 6 H 5 Cl + HCl

The most important chlorine compounds

Hydrogen chloride, hydrogen chloride(HCl) is a colorless, thermally stable gas (under normal conditions) with a pungent odor, fumes in moist air, easily dissolves in water (up to 500 volumes of gas per volume of water) to form hydrochloric (hydrochloric) acid. At −114.22 °C, HCl turns into a solid state. In the solid state, hydrogen chloride exists in the form of two crystalline modifications: orthorhombic, stable below, and cubic.

An aqueous solution of hydrogen chloride is called hydrochloric acid. When dissolved in water, the following processes occur:

HCl g + H 2 O l = H 3 O + l + Cl − l

The dissolution process is highly exothermic. With water, HCl forms an azeotropic mixture. It is a strong monoprotic acid. Interacts energetically with all metals in the voltage series to the left of hydrogen, with basic and amphoteric oxides, bases and salts, forming salts - chlorides:

Mg + 2 HCl → MgCl 2 + H 2

FeO + 2 HCl → FeCl 2 + H 2 O

When exposed to strong oxidizing agents or during electrolysis, hydrogen chloride exhibits reducing properties:

MnO 2 + 4 HCl → MnCl 2 + Cl 2 + 2 H 2 O

When heated, hydrogen chloride is oxidized by oxygen (catalyst - copper(II) chloride CuCl 2):

4 HCl + O 2 → 2 H 2 O +2 Cl 2

However, concentrated hydrochloric acid reacts with copper to form a monovalent copper complex:

2 Cu + 4 HCl → 2 H + H 2

A mixture of 3 parts by volume of concentrated hydrochloric acid and 1 part by volume of concentrated nitric acid is called “aqua regia”. Aqua regia can even dissolve gold and platinum. The high oxidative activity of aqua regia is due to the presence of nitrosyl chloride and chlorine in it, which are in equilibrium with the starting substances:

4 H 3 O + + 3 Cl − + NO 3 − = NOCl + Cl 2 + 6 H 2 O

Due to the high concentration of chloride ions in the solution, the metal binds into a chloride complex, which promotes its dissolution:

3 Pt + 4 HNO 3 + 18 HCl → 3 H 2 + 4 NO + 8 H 2 O

Hydrogen chloride is also characterized by addition reactions to multiple bonds (electrophilic addition):

R-CH=CH 2 + HCl → R-CHCl-CH 3

R-C≡CH + 2 HCl → R-CCl 2 -CH 3

Chlorine oxides- inorganic chemical compounds of chlorine and oxygen, with the general formula: Cl x O y.
Chlorine forms the following oxides: Cl 2 O, Cl 2 O 3, ClO 2, Cl 2 O 4, Cl 2 O 6, Cl 2 O 7. In addition, the following are known: the short-lived radical ClO, the chlorine peroxide radical ClOO and the chlorine tetroxide radical ClO 4 .
The table below shows the properties of stable chlorine oxides:

Table 6

Property	Cl2O	ClO2	ClOClO 3	Cl 2 O 6 (l)↔2ClO 3 (g)	Cl2O7
Color and condition at room. temperature	Yellow-brown gas	Yellow-green gas	Light yellow liquid	Dark red liquid	Colorless liquid
Chlorine oxidation state	(+1)	(+4)	(+1), (+7)	(+6)	(+7)
T. pl., °C	−120,6	−59	−117	3,5	−91,5
Boil temperature, °C	2,0		44,5
d(f, 0°C), g*cm -3	-	1,64	1,806	-	2,02
ΔH° sample (gas, 298 K), kJ*mol -1	80,3	102,6	~180	(155)
ΔG° sample (gas, 298 K), kJ*mol -1	97,9	120,6	-	-	-
S° sample (gas, 298 K), J*K -1 *mol -1	265,9	256,7	327,2	-	-
Dipole moment μ, D	0.78 ± 0.08	1.78 ± 0.01	-	-	0.72 ± 0.02

Chlorine oxide (I), Dichlor oxide, hypochlorous acid anhydride - a compound of chlorine in the oxidation state +1 with oxygen.

Under normal conditions, it is a brownish-yellow gas with a characteristic odor reminiscent of chlorine. At temperatures below 2 °C the liquid is golden-red in color. Toxic: affects the respiratory tract. Spontaneously slowly decomposes:

Explosive at high concentrations. Density under normal conditions is 3.22 kg/m³. Dissolves in carbon tetrachloride. Soluble in water to form weak hypochlorous acid:

Reacts quickly with alkalis:

Cl 2 O + 2NaOH (dil.) = 2NaClO + H 2 O

Chlorine dioxide- acid oxide. When dissolved in water, chlorous and perchloric acids are formed (disproportionation reaction). Dilute solutions are stable in the dark and decompose slowly in the light:

Chlorine dioxide- chlorine oxide ( IV), a compound of chlorine and oxygen, formula: ClO 2.

Under normal conditions, ClO 2 is a reddish-yellow gas with a characteristic odor. At temperatures below 10 °C ClO 2 is a red-brown liquid. Low stability, explodes in light, on contact with oxidizing agents and when heated. Let's dissolve well in water. Due to its explosive hazard, chlorine dioxide cannot be stored as a liquid.

Acidic oxide. When dissolved in water, chlorous and perchloric acids are formed (disproportionation reaction). Dilute solutions are stable in the dark and decompose slowly in the light:

The resulting chlorous acid is very unstable and decomposes:

Exhibits redox properties.

2ClO 2 + 5H 2 SO 4 (diluted) + 10FeSO 4 = 5Fe 2 (SO 4) 3 + 2HCl + 4H 2 O

ClO 2 + 2NaOH cold. = NaClO 2 + NaClO 3 + H 2 O

ClO 2 + O 3 = ClO 3 + O 2

ClO 2 reacts with many organic compounds and acts as a medium-strength oxidizing agent.

Hypochlorous acid- HClO, a very weak monobasic acid in which chlorine has an oxidation state of +1. Exists only in solutions.

In aqueous solutions, hypochlorous acid partially decomposes into a proton and the hypochlorite anion ClO − :

Unstable. Hypochlorous acid and its salts - hypochlorites- strong oxidizing agents. Reacts with hydrochloric acid HCl, forming molecular chlorine:

HClO + NaOH (diluted) = NaClO + H 2 O

Chlorous acid- HClO 2, a monobasic acid of medium strength.

Chlorous acid HClO 2 in its free form is unstable; even in a dilute aqueous solution it quickly decomposes:

Neutralized by alkalis.

HClO 2 + NaOH (dil. cold) = NaClO 2 + H 2 O

The anhydride of this acid is unknown.

An acid solution is prepared from its salts - chlorites formed as a result of the interaction of ClO 2 with alkali:

Exhibits redox properties.

5HClO2 + 3H2SO4 (diluted) + 2KMnO4 = 5HClO3 + 2MnSO4 + K2SO4 + 3H2O

Chloric acid- HClO 3, a strong monobasic acid in which chlorine has an oxidation state of +5. Not received in free form; in aqueous solutions at concentrations below 30% in the cold it is quite stable; in more concentrated solutions it decomposes:

Hypochlorous acid is a strong oxidizing agent; oxidizing capacity increases with increasing concentration and temperature. HClO 3 is easily reduced to hydrochloric acid:

HClO 3 + 5HCl (conc.) = 3Cl 2 + 3H 2 O

HClO 3 + NaOH (diluted) = NaClO 3 + H 2 O

When a mixture of SO 2 and air is passed through a strongly acidic solution, chlorine dioxide is formed:

In 40% perchloric acid, filter paper, for example, ignites.

8. Being in nature:

In the earth's crust, chlorine is the most common halogen. Since chlorine is very active, it occurs in nature only in the form of compounds in minerals.

Table 7. Finding in nature

Table 7. Mineral forms

The largest reserves of chlorine are contained in the salts of the waters of the seas and oceans.

Receipt

Chemical methods for producing chlorine are ineffective and expensive. Today they have mainly historical significance. 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

Method for producing chlorine by catalytic oxidation of hydrogen chloride with atmospheric oxygen.

Electrochemical methods

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

Application

· Window profile made from chlorine-containing polymers

· The main component of bleaches is Labarraco water (sodium hypochlorite)

· In the production of polyvinyl chloride, plastic compounds, synthetic rubber.

· Production of organochlorines. A significant portion of the chlorine produced is consumed to obtain plant protection products. One of the most important insecticides is hexachlorocyclohexane (often called hexachlorane).

· Used as a chemical warfare agent, as well as for the production of other chemical warfare agents: mustard gas, phosgene.

· For water disinfection - “chlorination”.

· Registered in the food industry as a food additive E925.

· In the chemical production of hydrochloric acid, bleach, berthollet salt, metal chlorides, poisons, medicines, fertilizers.

· In metallurgy for the production of pure metals: titanium, tin, tantalum, niobium.

· As an indicator of solar neutrinos in chlorine-argon detectors.

Many developed countries are striving to limit the use of chlorine in everyday life, including because the combustion of chlorine-containing waste produces a significant amount of dioxins.

Chlorine is a common element in nature; the chlorine content in the earth’s crust is » 0.02 wt. %. In the free state it is found in small quantities in volcanic gases. In nature, chlorine occurs mainly in the form of chlorides. Chlorine is part of many minerals, the most important of which are: NaCl - halite (rock salt), KCl - sylvite, KCl × MgCl 2 × 6 H 2 O - carnallite.

There is a lot of chlorine in sea water - an average of 1.9%. This happens because chlorine washed out of rocks cannot linger anywhere (almost all metal chlorides are soluble) and is carried by rivers into the seas and oceans. But one should not think that chlorine that gets into sea water cannot return to the continents. Wind plays an important role in the reverse migration of chlorine, carrying away salty dust from the surface of oceans, seas and salt lakes. So chlorine participates in the cycle of substances. But in arid and desert areas, as a result of intense evaporation of water, the concentration of chlorine in groundwater increases greatly. This is how salt marshes are formed, especially in the lowlands. Hundreds of millions of tons of chlorine are produced annually from various sources around the world.

Chloride solutions are an essential component of living organisms. The chlorine content in the human body is 0.25%, in blood plasma - 0.35%. The body of an adult contains more than 200 g of sodium chloride, of which 45 g is dissolved in the blood. There is often not enough chlorine in food and natural water for normal human development, which is why people have been adding salt to their food since ancient times. Chlorine is also introduced into animal feed. Plants, unlike animals, never experience chlorine deficiency.

Chlorine was probably obtained by alchemists, but its discovery is associated with the name of the famous Swedish chemist Carl Wilhelm Scheele. Numerous chlorine compounds were known, of course, long before Scheele. This element is part of many salts, including the most famous - table salt. In 1774, Scheele isolated chlorine in free form by heating the black mineral pyrolusite with concentrated hydrochloric acid: MnO 2 + 4HCl ® Cl 2 + MnCl 2 + 2H 2 O.

At first, chemists considered chlorine not as an element, but as a chemical compound of the unknown element muria (from the Latin muria - brine) with oxygen. It was believed that hydrochloric acid (it was called muric acid) contains chemically bound oxygen. However, numerous attempts to “tear” oxygen from chlorine led nowhere. As a result of similar experiments carried out by Humphry Davy, Joseph Louis Gay-Lussac and Louis Jacques Thenard, it became clear that chlorine does not contain oxygen and is a simple substance. The experiments of Gay-Lussac, who analyzed the quantitative ratio of gases in the reaction of chlorine with hydrogen, led to the same conclusion.

In 1811, Davy proposed the name “chlorin” for the new element - from the Greek. "chloros" - yellow-green. This is exactly the color of chlorine. A year later, Gay-Lussac “shortened” the name to “chlorine.” But still the British (and Americans) call this element “chlorine”, while the French call it chlore. The Germans also adopted the shortened name.

Chlorine(lat. Chlorum), Cl, chemical element of 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/m2, or 1 kgf/cm2) it is 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%). Radioactive isotopes with mass numbers 31-47 have been artificially obtained, 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 isotopic tracers.

Historical reference. Chlorine was first obtained in 1774 by K. Scheele by reacting 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 acidic igneous rocks - granites and others - 2.4·10 -2, in basic and ultrabasic rocks 5·10 -3. The main role in the history of chlorine in the earth's crust is played by water migration. In the form of Cl ion, it is found in the World Ocean (1.93%), underground brines and salt lakes. The number of its 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: sylvinite 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 a boiling point of -34.05°C, a melting point of -101°C. The density of chlorine gas 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/cm3; 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, respectively, 3.69; 7.72; 38.14 kgf/cm2. Heat of fusion 90.3 kJ/kg (21.5 cal/g); heat of evaporation 288 kJ/kg (68.8 cal/g); The heat capacity of gas at constant pressure is 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) of Chlorine at a partial pressure of 0.1 Mn/m2, or 1 kgf/cm2, in water 14.8 (0°C), 5.8 (30°C), 2.8 ( 70°С); in a solution of 300 g/l NaCl 1.42 (30°C), 0.64 (70°C). Below 9.6°C, Chlorine hydrates of variable composition Cl 2 ·nH 2 O (where n = 6-8) are formed in aqueous solutions; These are yellow cubic crystals that decompose with increasing temperature into Chlorine and water. Chlorine is highly soluble in TiCl 4, SiCl 4, SnCl 4 and some organic solvents (especially 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 = 2Cl at 1000 K is 2.07·10 -4%, at 2500 K 0.909%.

Chemical properties of Chlorine. External electronic configuration of the Cl 3s 2 Sp 5 atom. In accordance with this, Chlorine in compounds exhibits oxidation states of -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, directly combines 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; Of the compounds of chlorine with these elements, it is replaced by fluorine. Alkali metals in the presence of traces of moisture react with Chlorine with ignition; most metals react with dry Chlorine only when heated. Steel, as well as some metals, are resistant in an atmosphere of 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 PCl 3, and with further chlorination - PCl 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 with the formation of 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.

With oxygen, Chlorine forms oxides: 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 weakly stable and can spontaneously explode; hypochlorites slowly decompose during storage; chlorates and perchlorates can explode under the influence of initiators.

Chlorine in water hydrolyzes, forming hypochlorous and hydrochloric acids: Cl 2 + H 2 O = HClO + HCl. When aqueous solutions of alkalis are chlorinated in the cold, hypochlorites and chlorides are formed: 2NaOH + Cl 2 = NaClO + NaCl + H 2 O, and when heated, chlorates are formed. Chlorination of dry calcium hydroxide produces bleach.

When ammonia reacts with chlorine, nitrogen trichloride is formed. When chlorinating organic compounds, Chlorine either replaces hydrogen or joins 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 a ClF 3 atmosphere, glass wool spontaneously ignites. Known compounds of chlorine with oxygen and fluorine are Chlorine oxyfluorides: ClO 3 F, ClO 2 F 3, ClOF, ClOF 3 and fluorine perchlorate FClO 4.

Getting Chlorine. Chlorine began to be produced industrially in 1785 by reacting 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 and early 20th centuries, 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 by-product in the production of magnesium, calcium, sodium and lithium by electrolysis of molten chlorides. Two main methods of electrolysis of aqueous solutions of NaCl are used: 1) in electrolyzers with a solid cathode and a porous filter diaphragm; 2) in electrolyzers with a mercury cathode. In both methods, Chlorine gas 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 separated by subsequent processing. According to the second method, sodium amalgam is formed at 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 t of NaOH per 1 ton of Chlorine.

Electrolysis with a diaphragm requires less capital investment to organize the production of Chlorine and produces cheaper NaOH. The mercury cathode method produces very pure NaOH, but the loss of mercury pollutes the environment.

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 site 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. Industrial countries are characterized by the following approximate consumption of Chlorine: for the production of chlorine-containing organic compounds - 60-75%; inorganic compounds containing Chlorine, -10-20%; for bleaching pulp and fabrics - 5-15%; for sanitary needs and water chlorination - 2-6% of total production.

Chlorine is also used to chlorinate some ores 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 Chlorine content in plants (a lot of Chlorine in halophytes) ranges from thousandths of a percent to whole percent, in animals - tenths and hundredths of a percent. The daily requirement of an adult for Chlorine (2-4 g) is covered by food products. Chlorine is usually supplied in excess with food in the form of sodium chloride and potassium chloride. Bread, meat and dairy products are especially rich in Chlorine. In the animal body, Chlorine is the main osmotically active substance in blood plasma, lymph, cerebrospinal fluid and some tissues. Plays a role in water-salt metabolism, promoting tissue retention of water. 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 roots. Chlorine is necessary for the production of oxygen during photosynthesis by isolated chloroplasts. Most nutrient media for artificial plant cultivation do not contain chlorine. It is possible that very low concentrations of Chlorine are sufficient for plant development.

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. Primary inflammatory changes are usually accompanied by a secondary infection. Acute poisoning develops almost immediately. When inhaling medium and low concentrations of Chlorine, 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. are observed. Bronchopneumonia, toxic pulmonary edema, depressive states, convulsions are possible . In mild cases, recovery occurs within 3-7 days. As long-term consequences, catarrh 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 production facilities, equipment, effective ventilation, using a gas mask if necessary. The production of chlorine, bleach and other chlorine-containing compounds is classified as production with hazardous working conditions.

No matter how negatively we view public restrooms, nature dictates its own rules, and we have to visit them. In addition to natural (for a given place) odors, another common aroma is bleach used to disinfect the room. It got its name because of the main active ingredient in it - Cl. Let us learn about this chemical element and its properties, and also characterize chlorine by position in the periodic table.

How was this element discovered?

A chlorine-containing compound (HCl) was first synthesized in 1772 by the British priest Joseph Priestley.

Two years later, his Swedish colleague Karl Scheele was able to describe a method for isolating Cl using the reaction between hydrochloric acid and manganese dioxide. However, this chemist did not understand that as a result a new chemical element was synthesized.

It took scientists almost 40 years to learn how to produce chlorine in practice. This was first done by the British Humphry Davy in 1811. At the same time, he used a different reaction than his theoretic predecessors. Davy used electrolysis to break down NaCl (known to most as table salt) into its components.

After studying the resulting substance, the British chemist realized that it was elemental. After this discovery, Davy not only named it chlorine, but was also able to characterize chlorine, although it was very primitive.

Chlorine turned into chlorine (chlore) thanks to Joseph Gay-Lussac and in this form exists in French, German, Russian, Belarusian, Ukrainian, Czech, Bulgarian and some other languages ​​today. In English the name "chlorine" is still used, and in Italian and Spanish "chloro".

The element in question was described in more detail by Jens Berzelius in 1826. It was he who was able to determine its atomic mass.

What is chlorine (Cl)

Having considered the history of the discovery of this chemical element, it is worth learning more about it.

The name chlorine was derived from the Greek word χλωρός (“green”). It was given because of the yellowish-greenish color of this substance

Chlorine itself exists as a diatomic gas, Cl2, but it is practically never found in nature in this form. More often it appears in various compounds.

In addition to its distinctive hue, chlorine is characterized by a sweetish-acrid odor. It is a very toxic substance, therefore, when released into the air and inhaled by a person or animal, it can lead to their death within a few minutes (depending on the concentration of Cl).

Since chlorine is almost 2.5 times heavier than air, it will always be located below it, that is, near the ground. For this reason, if you suspect the presence of Cl, you should climb as high as possible, since there will be a lower concentration of this gas.

Also, unlike some other toxic substances, chlorine-containing substances have a characteristic color, which can allow them to be visually identified and action taken. Most standard gas masks help protect the respiratory system and mucous membranes from Cl. However, for complete safety, more serious measures must be taken, including neutralizing the toxic substance.

It is worth noting that it was with the use of chlorine as a poisonous gas by the Germans in 1915 that chemical weapons began their history. As a result of the use of almost 200 tons of the substance, 15 thousand people were poisoned in a few minutes. A third of them died almost instantly, a third received permanent damage, and only 5 thousand managed to escape.

Why is such a dangerous substance still not banned and is mined annually in millions of tons? It's all about its special properties, and to understand them, it is worth considering the characteristics of chlorine. The easiest way to do this is using the periodic table.

Characteristics of chlorine in the periodic system

Chlorine as a halogen

In addition to its extreme toxicity and pungent odor (characteristic of all representatives of this group), Cl is highly soluble in water. Practical confirmation of this is the addition of chlorine-containing detergents to pool water.

Upon contact with moist air, the substance in question begins to smoke.

Properties of Cl as a non-metal

When considering the chemical characteristics of chlorine, it is worth paying attention to its non-metallic properties.

It has the ability to form compounds with almost all metals and non-metals. An example is the reaction with iron atoms: 2Fe + 3Cl 2 → 2FeCl 3.

It is often necessary to use catalysts to carry out reactions. H2O can play this role.

Often reactions with Cl are endothermic (they absorb heat).

It is worth noting that in crystalline form (in powder form), chlorine interacts with metals only when heated to high temperatures.

Reacting with other non-metals (except O 2, N, F, C and inert gases), Cl forms compounds - chlorides.

When reacting with O 2, extremely unstable oxides are formed that are prone to decomposition. In them, the oxidation state of Cl can manifest itself from +1 to +7.

When interacting with F, fluorides are formed. Their degree of oxidation may be different.

Chlorine: characteristics of the substance in terms of its physical properties

In addition to chemical properties, the element in question also has physical properties.

Effect of temperature on the state of aggregation of Cl

Having examined the physical characteristics of the element chlorine, we understand that it is capable of transforming into different states of aggregation. It all depends on the temperature.

In its normal state, Cl is a gas with highly corrosive properties. However, it can easily liquefy. This is affected by temperature and pressure. For example, if it is 8 atmospheres and the temperature is +20 degrees Celsius, Cl 2 is an acid-yellow liquid. It is capable of maintaining this state of aggregation up to +143 degrees, if the pressure also continues to increase.

When it reaches -32 °C, the state of chlorine ceases to depend on pressure, and it continues to remain liquid.

Crystallization of the substance (solid state) occurs at -101 degrees.

Where does Cl exist in nature?

Having considered the general characteristics of chlorine, it is worth finding out where such a complex element can be found in nature.

Due to its high reactivity, it is almost never found in its pure form (which is why it took scientists years to learn how to synthesize it when they first studied this element). Typically, Cl is found in compounds in various minerals: halite, sylvite, kainite, bischofite, etc.

Most of all, it is found in salts extracted from sea or ocean water.

Effect on the body

When considering the characteristics of chlorine, it has already been said more than once that it is extremely toxic. Moreover, atoms of the substance are contained not only in minerals, but also in almost all organisms, from plants to humans.

Due to their special properties, Cl ions penetrate cell membranes better than others (therefore, more than 80% of all chlorine in the human body is located in the intercellular space).

Together with K, Cl is responsible for the regulation of water-salt balance and, as a consequence, for osmotic equality.

Despite such an important role in the body, in its pure form Cl 2 kills all living things - from cells to entire organisms. However, in controlled doses and with short-term exposure, it does not have time to cause damage.

A striking example of the latter statement is any swimming pool. As you know, water in such institutions is disinfected with Cl. Moreover, if a person rarely visits such an establishment (once a week or a month), it is unlikely that he will suffer from the presence of this substance in the water. However, employees of such institutions, especially those who spend almost the entire day in the water (rescuers, instructors), often suffer from skin diseases or have weakened immunity.

In connection with all this, after visiting the pools, you should definitely take a shower - to wash off possible chlorine residues from your skin and hair.

Human uses of Cl

Remembering from the characteristics of chlorine that it is a “capricious” element (when it comes to interaction with other substances), it will be interesting to know that it is quite often used in industry.

First of all, it is used to disinfect many substances.

Cl is also used in the manufacture of certain types of pesticides, which helps save crops from pests.

The ability of this substance to interact with almost all elements of the periodic table (characteristic of chlorine as a non-metal) helps with its help to extract certain types of metals (Ti, Ta and Nb), as well as lime and hydrochloric acid.

In addition to all of the above, Cl is used in the production of industrial substances (polyvinyl chloride) and medications (chlorhexidine).

It is worth mentioning that today a more effective and safe disinfectant has been found - ozone (O 3). However, its production is more expensive than chlorine, and this gas is even more unstable than chlorine (brief description of physical properties in 6-7 points). Therefore, few people can afford to use ozonation instead of chlorination.

How is chlorine produced?

Today, many methods are known for the synthesis of this substance. They all fall into two categories:

• Chemical.
• Electrochemical.

In the first case, Cl is obtained due to a chemical reaction. However, in practice they are very costly and ineffective.

Therefore, industry prefers electrochemical methods (electrolysis). There are three of them: diaphragm, membrane and mercury electrolysis.