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

Methods of obtaining

Based on the oxidation process of Cl - anions

2Cl - - 2e - = Cl 2 0

Industrial

Electrolysis of aqueous solutions of chlorides, more often NaCl:

2NaCl + 2H 2 O = Cl 2 + 2NaOH + H 2

Laboratory

Oxidation of conc. HCI with various oxidizing agents:

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

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

6HCl + KClO 3 = 3Cl 2 + KCl + 3H 2 O

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

Chemical properties

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

Cl 2 0 + 2e - = 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

Low-active metals are more easily oxidized by wet chlorine or its aqueous solutions:

Cl 2 + Cu = CuCl 2

3Cl 2 + 2Au = 2AuCl 3

Reactions with nonmetals

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

Nonmetal halides are formed. The most important reaction is interaction with hydrogen.

Cl 2 + H 2 = 2HC1

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

3Cl 2 + 2P = 2PCl 3 (or PCl 5 - in excess of Cl 2)

2Cl 2 + Si = SiCl 4

3Cl 2 + I 2 = 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 = I 2 + 2KCl

Cl 2 + 2HI = I 2 + 2HCl

Cl 2 + H 2 S = S + 2HCl

3Cl 2 + 2NH 3 = N 2 + 6HCl

Disproportionation of chlorine in water and aqueous solutions of alkalis

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

Cl 2 + H 2 O = HCl + HClO hypochlorous acid

Cl 2 + 2KOH = KCl + KClO + H 2 O

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

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

These reactions have important, since they lead to the production of oxygen chlorine compounds:

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

Interaction of chlorine with organic substances

a) replacement of hydrogen atoms in OM molecules

b) attachment of Cl 2 molecules at the site of rupture of multiple carbon-carbon bonds

H 2 C=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 - hydrogen chloride. At rev. T - colorless. a gas with a pungent odor, liquefies quite easily (mp -114°C, bp -85°C). Anhydrous HCl, in both gaseous and liquid states, is non-electrically conductive and chemically inert towards metals, metal oxides and hydroxides, as well as 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 low-active ones as Cu and Ag.
The reducing properties of the chloride anion in HCl also appear 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 reacts reversibly with oxygen:

2HCl + F 2 = Cl 2 + 2HF

4HCl + O 2 = 2Сl 2 + 2H 2 O

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

Methods of obtaining

1. Synthesis from simple substances:

H 2 + Cl 2 = 2HCl

2. Formed as a by-product during chlorination of hydrocarbons:

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

3. In the laboratory it is obtained by the action of conc. H 2 SO 4 for chlorides:

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

H 2 SO 4 (conc.) + 2NaCl = 2HCl + Na 2 SO 4 (at very high heating)

Aqueous solution of HCl - strong acid (hydrochloric or hydrochloric)

HCl is very soluble in water: at vol. In 1 liter of H 2 O ~ 450 liters of gas are dissolved (dissolution is accompanied by the release of a significant amount of heat). The 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 disintegrate into ions, i.e. an aqueous solution of HCl is a strong acid.

Chemical properties of hydrochloric acid

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

HCl → H + + Cl -

Interaction:

a) with metals (up to H):

2HCl 2 + Zn = ZnCl 2 + H 2

b) with basic and amphoteric oxides:

2HCl + CuO = CuCl 2 + H 2 O

6HCl + Al 2 O 3 = 2AlCl 3 + ZN 2 O

c) with bases and amphoteric hydroxides:

2HCl + Ca(OH) 2 = CaCl 2 + 2H 2 O

3HCl + Al(OH) 3 = AlCl 3 + ZH 2 O

d) with salts of weaker acids:

2HCl + CaCO 3 = CaCl 2 + CO 2 + H 3 O

HCl + C 6 H 5 ONa = C 6 H 5 OH + NaCl

e) with ammonia:

HCl + NH 3 = NH 4 Cl

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

2Cl - - 2e - = Cl 2 0

For reaction equations, see "Production of chlorine." Special meaning has an ORR between hydrochloric and nitric acids:

Reactions with organic compounds

Interaction:

a) with amines (as organic bases)

R-NH 2 + HCl → + Cl -

b) with amino acids (as amphoteric compounds)

Chlorine oxides and oxoacids

Acidic oxides

Acids

Salts

Chemical properties

1. All chlorine oxoacids and their salts are strong oxidizing agents.

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

Bleaching powder

Chloric (bleaching) lime - a mixture of hypochlorite and calcium chloride, has a bleaching and disinfectant effect. Sometimes considered as an example of a mixed salt containing simultaneously the anions of two acids:

Javel water

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

The physical properties of chlorine are considered: the density of chlorine, its thermal conductivity, specific heat and dynamic viscosity at various temperatures. The physical properties of Cl 2 are presented in the form of tables for the liquid, solid and gaseous states of this halogen.

Basic physical properties of chlorine

Chlorine is included in group VII of the third period of the periodic table of elements at number 17. It belongs to the subgroup of halogens, has relative atomic and molecular masses of 35.453 and 70.906, respectively. At temperatures above -30°C, chlorine is a greenish-yellow gas with a characteristic strong, irritating odor. It liquefies easily under normal pressure (1.013 10 5 Pa), when cooled to -34 ° C, and forms a transparent amber liquid that solidifies at a temperature of -101 ° C.

Due to its high chemical activity, free chlorine does not occur in nature, but exists only in the form of compounds. It is found mainly in the mineral halite (), and is also part of such minerals as sylvite (KCl), carnallite (KCl MgCl 2 6H 2 O) and sylvinite (KCl NaCl). The chlorine content in the earth's crust approaches 0.02% of the total number of atoms of the earth's crust, where it is found in the form of two isotopes 35 Cl and 37 Cl in a percentage ratio of 75.77% 35 Cl and 24.23% 37 Cl.

Physical properties of chlorine - table of main indicators

Property	Meaning
Melting point, °C	-100,5
Boiling point, °C	-30,04
Critical temperature, °C	144
Critical pressure, Pa	77.1 10 5
Critical density, kg/m 3	573
Gas density (at 0°C and 1.013 10 5 Pa), kg/m 3	3,214
Saturated steam density (at 0°C and 3.664 10 5 Pa), kg/m 3	12,08
Density of liquid chlorine (at 0°C and 3.664 10 5 Pa), kg/m 3	1468
Density of liquid chlorine (at 15.6°C and 6.08 10 5 Pa), kg/m 3	1422
Density of solid chlorine (at -102°C), kg/m 3	1900
Relative density of gas in air (at 0°C and 1.013 10 5 Pa)	2,482
Relative density of saturated steam in air (at 0°C and 3.664 10 5 Pa)	9,337
Relative density of liquid chlorine at 0°C (relative to water at 4°C)	1,468
Specific volume of gas (at 0°C and 1.013 10 5 Pa), m 3 /kg	0,3116
Specific volume of saturated steam (at 0°C and 3.664 10 5 Pa), m 3 /kg	0,0828
Specific volume of liquid chlorine (at 0°C and 3.664 10 5 Pa), m 3 /kg	0,00068
Chlorine vapor pressure at 0°C, Pa	3.664 10 5
Dynamic viscosity of gas at 20°C, 10 -3 Pa s	0,013
Dynamic viscosity of liquid chlorine at 20°C, 10 -3 Pa s	0,345
Heat of fusion of solid chlorine (at melting point), kJ/kg	90,3
Heat of vaporization (at boiling point), kJ/kg	288
Heat of sublimation (at melting point), kJ/mol	29,16
Molar heat capacity C p of gas (at -73…5727°C), J/(mol K)	31,7…40,6
Molar heat capacity C p of liquid chlorine (at -101…-34°C), J/(mol K)	67,1…65,7
Gas thermal conductivity coefficient at 0°C, W/(m K)	0,008
Thermal conductivity coefficient of liquid chlorine at 30°C, W/(m K)	0,62
Gas enthalpy, kJ/kg	1,377
Enthalpy of saturated steam, kJ/kg	1,306
Enthalpy of liquid chlorine, kJ/kg	0,879
Refractive index at 14°C	1,367
Specific electrical conductivity at -70°С, S/m	10 -18
Electron affinity, kJ/mol	357
Ionization energy, kJ/mol	1260

Chlorine Density

Under normal conditions, chlorine is a heavy gas with a density approximately 2.5 times higher. Density of gaseous and liquid chlorine under normal conditions (at 0°C) is equal to 3.214 and 1468 kg/m3, respectively. When liquid or gaseous chlorine is heated, its density decreases due to an increase in volume due to thermal expansion.

Density of chlorine gas

The table shows the density of chlorine in the gaseous state at various temperatures (ranging from -30 to 140°C) and normal atmospheric pressure (1.013·10 5 Pa). The density of chlorine changes with temperature—it decreases when heated. For example, at 20°C the density of chlorine is 2.985 kg/m3, and when the temperature of this gas increases to 100°C, the density value decreases to a value of 2.328 kg/m 3.

Density of chlorine gas at different temperatures

t, °С	ρ, kg/m 3	t, °С	ρ, kg/m 3
-30	3,722	60	2,616
-20	3,502	70	2,538
-10	3,347	80	2,464
0	3,214	90	2,394
10	3,095	100	2,328
20	2,985	110	2,266
30	2,884	120	2,207
40	2,789	130	2,15
50	2,7	140	2,097

As pressure increases, the density of chlorine increases. The tables below show the density of chlorine gas in the temperature range from -40 to 140°C and pressure from 26.6·10 5 to 213·10 5 Pa. With increasing pressure, the density of chlorine in the gaseous state increases proportionally. For example, an increase in chlorine pressure from 53.2·10 5 to 106.4·10 5 Pa at a temperature of 10°C leads to a twofold increase in the density of this gas.

The density of chlorine gas at various temperatures and pressures is from 0.26 to 1 atm.

↓ t, °С | P, kPa →	26,6	53,2	79,8	101,3
-40	0,9819	1,996	—	—
-30	0,9402	1,896	2,885	3,722
-20	0,9024	1,815	2,743	3,502
-10	0,8678	1,743	2,629	3,347
0	0,8358	1,678	2,528	3,214
10	0,8061	1,618	2,435	3,095
20	0,7783	1,563	2,35	2,985
30	0,7524	1,509	2,271	2,884
40	0,7282	1,46	2,197	2,789
50	0,7055	1,415	2,127	2,7
60	0,6842	1,371	2,062	2,616
70	0,6641	1,331	2	2,538
80	0,6451	1,292	1,942	2,464
90	0,6272	1,256	1,888	2,394
100	0,6103	1,222	1,836	2,328
110	0,5943	1,19	1,787	2,266
120	0,579	1,159	1,741	2,207
130	0,5646	1,13	1,697	2,15
140	0,5508	1,102	1,655	2,097

The density of chlorine gas at various temperatures and pressures is from 1.31 to 2.1 atm.

↓ t, °С | P, kPa →	133	160	186	213
-20	4,695	5,768	—	—
-10	4,446	5,389	6,366	7,389
0	4,255	5,138	6,036	6,954
10	4,092	4,933	5,783	6,645
20	3,945	4,751	5,565	6,385
30	3,809	4,585	5,367	6,154
40	3,682	4,431	5,184	5,942
50	3,563	4,287	5,014	5,745
60	3,452	4,151	4,855	5,561
70	3,347	4,025	4,705	5,388
80	3,248	3,905	4,564	5,225
90	3,156	3,793	4,432	5,073
100	3,068	3,687	4,307	4,929
110	2,985	3,587	4,189	4,793
120	2,907	3,492	4,078	4,665
130	2,832	3,397	3,972	4,543
140	2,761	3,319	3,87	4,426

Density of liquid chlorine

Liquid chlorine can exist in a relatively narrow temperature range, the boundaries of which lie from minus 100.5 to plus 144 ° C (that is, from the melting point to the critical temperature). Above a temperature of 144°C, chlorine will not turn into a liquid state under any pressure. The density of liquid chlorine in this temperature range varies from 1717 to 573 kg/m3.

Density of liquid chlorine at different temperatures

t, °С	ρ, kg/m 3	t, °С	ρ, kg/m 3
-100	1717	30	1377
-90	1694	40	1344
-80	1673	50	1310
-70	1646	60	1275
-60	1622	70	1240
-50	1598	80	1199
-40	1574	90	1156
-30	1550	100	1109
-20	1524	110	1059
-10	1496	120	998
0	1468	130	920
10	1438	140	750
20	1408	144	573

Specific heat capacity of chlorine

The specific heat capacity of chlorine gas C p in kJ/(kg K) in the temperature range from 0 to 1200°C and normal atmospheric pressure can be calculated using the formula:

where T is the absolute temperature of chlorine in degrees Kelvin.

It should be noted that under normal conditions the specific heat of chlorine is 471 J/(kg K) and increases when heated. The increase in heat capacity at temperatures above 500°C becomes insignificant, and at high temperatures The specific heat capacity of chlorine remains virtually unchanged.

The table shows the results of calculating the specific heat of chlorine using the above formula (the calculation error is about 1%).

Specific heat capacity of chlorine gas as a function of temperature

t, °С	C p , J/(kg K)	t, °С	C p , J/(kg K)
0	471	250	506
10	474	300	508
20	477	350	510
30	480	400	511
40	482	450	512
50	485	500	513
60	487	550	514
70	488	600	514
80	490	650	515
90	492	700	515
100	493	750	515
110	494	800	516
120	496	850	516
130	497	900	516
140	498	950	516
150	499	1000	517
200	503	1100	517

At temperatures close to absolute zero, chlorine is in a solid state and has a low specific heat capacity (19 J/(kg K)). As the temperature of solid Cl 2 increases, its heat capacity increases and reaches a value of 720 J/(kg K) at minus 143°C.

Liquid chlorine has a specific heat capacity of 918...949 J/(kg K) in the range from 0 to -90 degrees Celsius. The table shows that the specific heat capacity of liquid chlorine is higher than that of gaseous chlorine and decreases with increasing temperature.

Thermal conductivity of chlorine

The table shows the values ​​of the thermal conductivity coefficients of chlorine gas at normal atmospheric pressure in the temperature range from -70 to 400°C.

The thermal conductivity coefficient of chlorine under normal conditions is 0.0079 W/(m deg), which is 3 times less than at the same temperature and pressure. Heating chlorine leads to an increase in its thermal conductivity. Thus, at a temperature of 100°C, the value of this physical property of chlorine increases to 0.0114 W/(m deg).

Thermal conductivity of chlorine gas

t, °С	λ, W/(m deg)	t, °С	λ, W/(m deg)
-70	0,0054	50	0,0096
-60	0,0058	60	0,01
-50	0,0062	70	0,0104
-40	0,0065	80	0,0107
-30	0,0068	90	0,0111
-20	0,0072	100	0,0114
-10	0,0076	150	0,0133
0	0,0079	200	0,0149
10	0,0082	250	0,0165
20	0,0086	300	0,018
30	0,009	350	0,0195
40	0,0093	400	0,0207

Chlorine viscosity

The coefficient of dynamic viscosity of gaseous chlorine in the temperature range 20...500°C can be approximately calculated using the formula:

where η T is the coefficient of dynamic viscosity of chlorine at a given temperature T, K;
η T 0 - coefficient of dynamic viscosity of chlorine at temperature T 0 = 273 K (at normal conditions);
C is the Sutherland constant (for chlorine C = 351).

Under normal conditions, the dynamic viscosity of chlorine is 0.0123·10 -3 Pa·s. When heated, the physical property of chlorine, such as viscosity, takes on higher values.

Liquid chlorine has a viscosity an order of magnitude higher than gaseous chlorine. For example, at a temperature of 20°C, the dynamic viscosity of liquid chlorine has a value of 0.345·10 -3 Pa·s and decreases with increasing temperature.

Sources:

1. Barkov S. A. Halogens and the manganese subgroup. Elements of group VII of the periodic table of D. I. Mendeleev. A manual for students. M.: Education, 1976 - 112 p.
2. Tables of physical quantities. Directory. Ed. acad. I. K. Kikoina. M.: Atomizdat, 1976 - 1008 p.
3. Yakimenko L. M., Pasmanik M. I. Handbook on the production of chlorine, caustic soda and basic chlorine products. Ed. 2nd, per. and others. M.: Chemistry, 1976 - 440 p.

Chlorine

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

◁ Chlorine (see).

chlorine

(lat. Chlorum), a chemical element of group VII of the periodic table, belongs to the halogens. The name comes 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 temperatures it easily liquefies under a pressure of 0.6 MPa. Chemically very active (oxidizing agent). The main minerals are halite (rock salt), sylvite, bischofite; sea ​​water contains chlorides of sodium, potassium, magnesium and other elements. They are 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”), 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 of 35 (in a mixture of 75.77% by mass) and 37 (24.23%). Outer electron layer 3 configuration s 2 p 5 . In compounds it exhibits mainly oxidation states –1, +1, +3, +5 and +7 (valences I, III, V and VII). (cm. Located in the third period in group VIIA of Mendeleev’s periodic table of elements, belongs to the halogens.
HALOGEN)
The radius of the neutral chlorine atom is 0.099 nm, the ionic radii are, respectively (the values ​​of the coordination number are indicated in parentheses): Cl - 0.167 nm (6), Cl 5+ 0.026 nm (3) and Clr 7+ 0.022 nm (3) and 0.041 nm ( 6). The sequential ionization energies of the neutral chlorine atom are, respectively, 12.97, 23.80, 35.9, 53.5, 67.8, 96.7 and 114.3 eV. Electron affinity 3.614 eV. According to the Pauling scale, the electronegativity of chlorine is 3.16.
History of discovery
The most important chemical compound of 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 chlorine gas. To dissolve the “king of metals” - gold - they used “aqua regia” - a mixture of hydrochloric and nitric acids, the interaction of which releases chlorine. (cm. For the first time, chlorine gas was obtained and described in detail by the Swedish chemist K. Scheele SCHEELE Karl Wilhelm) (cm. in 1774. He heated hydrochloric acid with the mineral pyrolusite PYROLUSITE) (cm. MnO 2 and observed the release of a yellow-green gas with a pungent odor. Since the theory of phlogiston dominated in those days, Scheele considered the new gas as “dephlogistonized hydrochloric acid,” i.e., as an oxide (oxide) of hydrochloric acid. A. Lavoisier (cm. LAVOISIER Antoine Laurent) considered the gas as an oxide of the element “muria” (hydrochloric acid was called muric acid, from the Latin muria - brine). The same point of view was first shared by the English scientist G. Davy (cm. DAVY Humphrey), who spent a lot of time breaking down “murium oxide” into simple substances. He failed, 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 suggest calling it chlorine in accordance with the yellow-green color of the gas. 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 was suggested that this element should be called “halogen” (i.e., salt-producing), but over time it became the general name for all elements of group VIIA.
Being in nature
The chlorine content in the earth's crust is 0.013% by weight; it is present in noticeable concentrations in the form of the Cl – ion. sea ​​water(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, sylvine (cm. SYLVIN) KCl, sylvinite (Na, K)Cl, kainite (cm. KAINIT) KCl MgSO 4 3H 2 O, bischofite (cm. BISCHOFIT) MgCl 2 ·6H 2 O and many others. Chlorine can be found in a variety of rocks and soil.
Receipt
To obtain chlorine gas, electrolysis of a strong aqueous solution of NaCl is used (sometimes KCl is used). Electrolysis is carried out using a cation exchange membrane separating the cathode and anode spaces. Moreover, due to the process
2NaCl + 2H 2 O = 2NaOH + H 2 + Cl 2
three valuable chemical products are obtained at once: chlorine at the anode, hydrogen at the cathode (cm. HYDROGEN), and alkali accumulates in the electrolyzer (1.13 tons of NaOH for every ton of chlorine produced). The production of chlorine by electrolysis requires large amounts of electricity: from 2.3 to 3.7 MW is consumed to produce 1 ton of chlorine.
To obtain chlorine in the laboratory, they use the reaction of concentrated hydrochloric acid with any strong oxidizing agent (potassium permanganate KMnO 4, potassium dichromate K 2 Cr 2 O 7, potassium chlorate KClO 3, bleach CaClOCl, manganese (IV) oxide MnO 2). It is most convenient to use potassium permanganate for these purposes: in this case, the reaction proceeds without heating:
2KMnO 4 + 16HCl = 2KСl + 2MnCl 2 + 5Cl 2 + 8H 2 O.
If necessary, chlorine in liquefied (under pressure) form is transported in railway tanks or in steel cylinders. Chlorine cylinders have a special marking, but even without it, a chlorine cylinder can be easily distinguished from cylinders with other non-toxic gases. The bottom of chlorine cylinders is shaped like 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, ionization potential is 11.48 eV. The energy of dissociation 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 an equilibrium is established:
Сl 2 + H 2 O H + = Сl - + HOСl.
In order to shift this equilibrium to the left, i.e., 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 dissociation energy of Cl 2 molecules into atoms and the high electron affinity of the chlorine atom, chemically chlorine is highly active. It reacts directly 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:
3Сl 2 + 2Аl = 2А1Сl 3
and iron:
2Fe + 3Cl 2 = 2FeCl 3.
Chlorine reacts with hydrogen H2 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 appears:
H 2 + Cl 2 = 2HCl.
A solution of hydrogen chloride in water is called hydrochloric acid (cm. HYDROCHLORIC ACID)(hydrochloric) acid. The maximum mass concentration of hydrochloric acid is about 38%. Salts of hydrochloric acid - chlorides (cm. CHLORIDE), for example, ammonium chloride NH 4 Cl, calcium chloride CaCl 2, barium chloride BaCl 2 and others. Many chlorides are highly soluble in water. Silver chloride AgCl is practically insoluble in water and in acidic aqueous solutions. A qualitative reaction to the presence of chloride ions in a solution is the formation of a white AgCl precipitate with Ag + ions, practically insoluble in a nitric acid medium:
CaCl 2 + 2AgNO 3 = 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 (forming, depending on the reaction conditions, compounds PCl 3 or PCl 5), arsenic, boron and other non-metals. Chlorine does not react directly with oxygen, nitrogen, carbon (numerous chlorine compounds 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 bromine, so chlorine displaces bromide ion from bromide solutions, for example:
Cl 2 + 2NaBr = Br 2 + 2NaCl
Chlorine undergoes substitution reactions with many organic compounds, for example, with methane CH4 and benzene C6H6:
CH 4 + Cl 2 = CH 3 Cl + HCl or C 6 H 6 + Cl 2 = C 6 H 5 Cl + HCl.
A chlorine molecule is capable of attaching via multiple bonds (double and triple) to organic compounds, for example, to ethylene C 2 H 4:
C 2 H 4 + Cl 2 = CH 2 Cl CH 2 Cl.
Chlorine interacts with aqueous solutions of alkalis. If the reaction occurs at room temperature, chloride (for example, potassium chloride KCl) and hypochlorite are formed (cm. HYPOCHLORITES)(for example, potassium hypochlorite KClO):
Cl 2 + 2KOH = KClO + KCl + H 2 O.
When chlorine interacts with a hot (temperature about 70-80°C) alkali solution, the corresponding chloride and chlorate are formed (cm. CHLORATES), For example:
3Cl 2 + 6KOH = 5KCl + 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 weak, unstable hypochlorous acid (cm. Hypochlorous acid) HClO. Its salts are hypochlorites, for example, NaClO - sodium hypochlorite. Hypochlorites are strong oxidizing agents 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 to release chlorine oxide (I) Cl 2 O:
2HClO = 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 the low-stable acid of medium strength HClO 2. This acid is called chloric acid, its salts are called chlorites (cm. CHLORITES (salts)), for example, NaClO 2 - sodium chlorite.
The oxidation state of chlorine +4 corresponds to only one compound - chlorine dioxide ClO 2.
The oxidation state of chlorine +5 corresponds to strong, stable only in aqueous solutions at concentrations below 40%, perchloric 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 ClO 3 (exists in the form of a dimer Cl 2 O 6).
The oxidation state of chlorine +7 corresponds to 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. The oxide corresponding to the oxidation state of chlorine is +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 global production amounts to 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, separating and purifying metals, etc. Chlorine is used to disinfect water (chlorination (cm. CHLORINATION)) and for many other purposes.
Biological role
Chlorine is one of the most important biogenic elements (cm. BIOGENIC ELEMENTS) and is part of all living organisms. Some plants, the so-called halophytes, are not only able to grow in highly saline soils, but also accumulate large quantities of chlorides. Microorganisms (halobacteria, etc.) and animals are known that live in conditions of high salinity. Chlorine is one of the main elements of water-salt metabolism in animals and humans, determining physical and chemical processes in the tissues of the body. It is involved in maintaining acid-base balance in tissues, osmoregulation (cm. OSMOREGULATION)(chlorine is the main osmotically active substance in blood, lymph and other body fluids), being mainly outside the cells. In plants, chlorine takes part in oxidative reactions and photosynthesis.
Human muscle tissue contains 0.20-0.52% chlorine, bone tissue - 0.09%; in the blood - 2.89 g/l. The average person's body (body weight 70 kg) contains 95 g of chlorine. Every day a person receives 3-6 g of chlorine from food, which more than covers the need for this element.
Features of working with chlorine
Chlorine is a poisonous asphyxiating gas; if it enters the lungs, it causes burns of lung tissue and 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. POISONIC SUBSTANCES), used by Germany in the First world war. When working with chlorine, you should use protective clothing, a gas mask, and gloves. On a short time You can protect your respiratory organs from chlorine getting into them with a cloth bandage moistened with a solution of sodium sulfite Na 2 SO 3 or sodium thiosulfate Na 2 S 2 O 3 . The maximum permissible concentration of chlorine in the air of working premises is 1 mg/m 3, in the air of populated areas 0.03 mg/m 3.

encyclopedic Dictionary. 2009 .

Synonyms:

See what “chlorine” is in other dictionaries:

Chlorine, eh... Russian word stress

chlorine- chlorine, and... Russian spelling dictionary

chlorine- chlorine/... Morphemic-spelling dictionary

- (Greek chloros greenish yellow). A chemically simple, gaseous body, greenish-yellow in color, pungent, irritating odor, having the ability to discolor plant matter. Dictionary foreign words, included in the Russian language... Dictionary of foreign words of the Russian language

- (symbol C1), a widespread non-metallic element, one of the HALOGENS (elements of the seventh group of the periodic table), first discovered in 1774. It is part of table salt (NaCl). Chlorine is a greenish yellow... ... Scientific and technical encyclopedic dictionary

CHLORINE- CHLORINE, C12, chemical. element, atomic number 17, atomic weight 35.457. Being in group VII of the III period, chlorine atoms have 7 outer electrons, due to which X behaves like a typical monovalent metalloid. X. divided into isotopes with atomic... ... Great Medical Encyclopedia

Chlorine- usually obtained by electrolysis of alkali metal chlorides, in particular sodium chloride. Chlorine is a greenish-yellow, asphyxiating, corrosive gas that is 2.5 times denser than air, slightly soluble in water, and easily liquefied. Usually transported... Official terminology

Chlorine- (Chlorum), Cl, chemical element of group VII of the periodic table, atomic number 17, atomic mass 35.453; refers to halogens; yellow-green gas, boiling point 33.97°C. Used in the production of polyvinyl chloride, chloroprene rubber,... ... Illustrated Encyclopedic Dictionary

CHLORINE, chlorine, pl. no, husband (from Greek chloros green) (chemical). Chemical element, asphyxiating gas, used. in technology, in sanitation as a disinfectant and in warfare as a poisonous substance. Ushakov's explanatory dictionary. D.N. Ushakov. 1935 1940 … Ushakov's Explanatory Dictionary

Chlorine... The initial part of complex words, introducing the meaning of the words: chlorine, chloride (organochlorine, chloroacetone, chlorobenzene, chloromethane, etc.). Ephraim's explanatory dictionary. T. F. Efremova. 2000... Modern explanatory dictionary of the Russian language by Efremova

Books

• Russian theater or Complete collection of all Russian theatrical works. Part 24. Operas: Guardian Professor. - I. Knyazhnin. Misfortune from the carriage. - Dushinka's joy. - Sailor jokes. - . Chlor Tsarevich, , . The book is a reprint of 1786. Despite the fact that serious work has been done to restore the original quality of the publication, some pages may...

Chlorine(from the Greek χλωρ?ς - “green”) - an element of the main subgroup of the seventh group, the third period of the periodic table of chemical elements of D. I. Mendeleev, with atomic number 17. Denoted by the symbol Cl(lat. Chlorum). Chemically active non-metal. It is part of the group of halogens (originally the name “halogen” was used by the German chemist Schweiger for chlorine [literally, “halogen” is translated as salt), but it did not catch on, and subsequently became common for group VII of elements, which includes chlorine).

The simple substance chlorine (CAS number: 7782-50-5) under normal conditions is a poisonous gas of yellowish-green color, with a pungent odor. The chlorine molecule is diatomic (formula Cl 2).

History of the discovery of chlorine

Gaseous anhydrous hydrogen chloride was first collected by J. Prisley in 1772. (over liquid mercury). Chlorine was first obtained in 1774 by Scheele, who described its release during the interaction of pyrolusite with hydrochloric acid in his treatise on pyrolusite:

4HCl + MnO2 = Cl2 + MnCl2 + 2H2O

Scheele noted the odor of chlorine, similar to that of aqua regia, its ability to react with gold and cinnabar, and its bleaching properties.

However, Scheele, in accordance with the phlogiston theory that was dominant in chemistry at that time, suggested that chlorine is dephlogisticated hydrochloric acid, that is, the oxide of hydrochloric acid. Berthollet and Lavoisier suggested that chlorine is an oxide of the element Muria, however, attempts to isolate it remained unsuccessful until the work of Davy, who managed to decompose table salt into sodium and chlorine by electrolysis.

Distribution in nature

There are two isotopes of chlorine found in nature: 35 Cl and 37 Cl. In the earth's crust, chlorine is the most common halogen. Chlorine is very active - it directly combines with almost all elements of the periodic table. Therefore, in nature it is found only in the form of compounds in the minerals: halite NaCl, sylvite KCl, sylvinite KCl NaCl, bischofite MgCl 2 6H2O, carnallite KCl MgCl 2 6H 2 O, kainite KCl MgSO 4 3H 2 O. The largest reserves of chlorine are contained in the salts of the waters of the seas and oceans (the content in sea water is 19 g/l). Chlorine accounts for 0.025% of the total number of atoms in the earth's crust, the clarke number of chlorine is 0.017%, and the human body contains 0.25% chlorine ions by mass. In the human and animal bodies, chlorine is found mainly in intercellular fluids (including blood) and plays important role in the regulation of osmotic processes, as well as in processes associated with the work of nerve cells.

Physical and physico-chemical properties

Under normal conditions, chlorine is a yellow-green gas with a suffocating odor. Some of its physical properties are presented in the table.

Some physical properties of chlorine

Property	Meaning
Color (gas)	Yellow-green
Boiling temperature	−34 °C
Melting temperature	−100 °C
Decomposition temperature (dissociations into atoms)	~1400 °C
Density (gas, n.s.)	3.214 g/l
Electron affinity of an atom	3.65 eV
First ionization energy	12.97 eV
Heat capacity (298 K, gas)	34.94 (J/mol K)
Critical temperature	144 °C
Critical pressure	76 atm
Standard enthalpy of formation (298 K, gas)	0 (kJ/mol)
Standard entropy of formation (298 K, gas)	222.9 (J/mol K)
Melting enthalpy	6.406 (kJ/mol)
Enthalpy of boiling	20.41 (kJ/mol)
Energy of homolytic cleavage of the X-X bond	243 (kJ/mol)
Energy of heterolytic cleavage of the X-X bond	1150 (kJ/mol)
Ionization energy	1255 (kJ/mol)
Electron affinity energy	349 (kJ/mol)
Atomic radius	0.073 (nm)
Electronegativity according to Pauling	3,20
Electronegativity according to Allred-Rochow	2,83
Stable oxidation states	-1, 0, +1, +3, (+4), +5, (+6), +7

Chlorine gas liquefies relatively easily. Starting from a pressure of 0.8 MPa (8 atmospheres), chlorine will be liquid already at room temperature. When cooled to −34 °C, chlorine also becomes liquid at normal atmospheric pressure. Liquid chlorine is a yellow-green liquid that is very corrosive (due to the high concentration of molecules). By increasing the pressure, it is possible to achieve the existence of liquid chlorine up to a temperature of +144 °C (critical temperature) at a critical pressure of 7.6 MPa.

At temperatures below −101 °C, liquid chlorine crystallizes into an orthorhombic lattice with the space group Cmca and parameters a=6.29 Å b=4.50 Å, c=8.21 Å. Below 100 K, the orthorhombic modification of crystalline chlorine becomes tetragonal, having a space group P4 2/ncm and lattice parameters a=8.56 Å and c=6.12 Å.

Solubility

The degree of dissociation of the chlorine molecule Cl 2 → 2Cl. At 1000 K it is 2.07×10 −4%, and at 2500 K it is 0.909%.

The threshold for the perception of odor in air is 0.003 (mg/l).

In terms of electrical conductivity, liquid chlorine ranks among the strongest insulators: it conducts current almost a billion times worse than distilled water, and 10 22 times worse than silver. The speed of sound in chlorine is approximately one and a half times less than in air.

Chemical properties

Structure of the electron shell

The valence level of a chlorine atom contains 1 unpaired electron: 1s 2 2s 2 2p 6 3s 2 3p 5, so a valence of 1 for a chlorine atom is very stable. Due to the presence of an unoccupied d-sublevel orbital in the chlorine atom, the chlorine atom can exhibit other valences. Scheme of formation of excited states of an atom:

Chlorine compounds are also known in which the chlorine atom formally exhibits valency 4 and 6, for example ClO 2 and Cl 2 O 6. However, these compounds are radicals, meaning they have one unpaired electron.

Interaction with metals

Chlorine reacts directly with almost all metals (with some only in the presence of moisture or when heated):

Cl 2 + 2Na → 2NaCl 3Cl 2 + 2Sb → 2SbCl 3 3Cl 2 + 2Fe → 2FeCl 3

Interaction with non-metals

With non-metals (except carbon, nitrogen, oxygen and inert gases), it forms the corresponding chlorides.

In the light or when heated, it reacts actively (sometimes with explosion) with hydrogen according to a radical mechanism. Mixtures of chlorine with hydrogen, containing from 5.8 to 88.3% hydrogen, explode upon irradiation to form hydrogen chloride. A mixture of chlorine and hydrogen in small concentrations burns with a colorless or yellow-green flame. Maximum temperature hydrogen-chlorine flame 2200 °C.:

Cl 2 + H 2 → 2HCl 5Cl 2 + 2P → 2PCl 5 2S + Cl 2 → S 2 Cl 2

With oxygen, chlorine forms oxides in which it exhibits an oxidation state from +1 to +7: Cl 2 O, ClO 2, Cl 2 O 6, Cl 2 O 7. They have a pungent odor, are thermally and photochemically unstable, and are prone to explosive decomposition.

When reacting with fluorine, not chloride is formed, but fluoride:

Cl 2 + 3F 2 (ex.) → 2ClF 3

Other properties

Chlorine displaces bromine and iodine from their compounds with hydrogen and metals:

Cl 2 + 2HBr → Br 2 + 2HCl Cl 2 + 2NaI → I 2 + 2NaCl

When reacting with carbon monoxide, phosgene is formed:

Cl 2 + CO → COCl 2

When dissolved in water or alkalis, chlorine dismutates, forming hypochlorous (and when heated, perchloric) and hydrochloric acids, or their salts:

Cl 2 + H 2 O → HCl + HClO 3Cl 2 + 6NaOH → 5NaCl + NaClO 3 + 3H 2 O

Chlorination of dry calcium hydroxide produces bleach:

Cl 2 + Ca(OH) 2 → CaCl(OCl) + H 2 O

The effect of chlorine on ammonia, nitrogen trichloride can be obtained:

4NH 3 + 3Cl 2 → NCl 3 + 3NH 4 Cl

Oxidizing properties of chlorine

Chlorine is a very strong oxidizing agent.

Cl 2 + H 2 S → 2HCl + S

Reactions with organic substances

With saturated compounds:

CH 3 -CH 3 + Cl 2 → C 2 H 5 Cl + HCl

Attaches to unsaturated compounds via multiple bonds:

CH 2 =CH 2 + Cl 2 → Cl-CH 2 -CH 2 -Cl

Aromatic compounds replace a hydrogen atom with chlorine in the presence of catalysts (for example, AlCl 3 or FeCl 3):

C 6 H 6 + Cl 2 → C 6 H 5 Cl + HCl

Methods of obtaining

Industrial methods

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

MnO 2 + 4HCl → MnCl 2 + Cl 2 + 2H 2 O

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

4HCl + O 2 → 2H 2 O + 2Cl 2

Today, chlorine is produced on an industrial scale together with sodium hydroxide and hydrogen by electrolysis of a solution of table salt:

2NaCl + 2H 2 O → H 2 + Cl 2 + 2NaOH Anode: 2Cl − — 2е − → Cl 2 0 Cathode: 2H 2 O + 2e − → H 2 + 2OH −

Since the electrolysis of water occurs parallel to the electrolysis of sodium chloride, the overall equation can be expressed as follows:

1.80 NaCl + 0.50 H 2 O → 1.00 Cl 2 + 1.10 NaOH + 0.03 H 2

Three variants of the electrochemical method for producing chlorine are used. Two of them are electrolysis with a solid cathode: diaphragm and membrane methods, the third is electrolysis with a liquid mercury cathode (mercury production method). Among the electrochemical production methods, the easiest and most convenient method is electrolysis with a mercury cathode, but this method causes significant harm environment as a result of evaporation and leakage of metallic mercury.

Diaphragm method with solid cathode

The electrolyzer cavity is divided by a porous asbestos partition - a diaphragm - into cathode and anode spaces, where the cathode and anode of the electrolyzer are respectively located. Therefore, such an electrolyzer is often called diaphragm, and the production method is diaphragm electrolysis. A flow of saturated anolyte (NaCl solution) continuously enters the anode space of the diaphragm electrolyzer. As a result of the electrochemical process, chlorine is released at the anode due to the decomposition of halite, and hydrogen is released at the cathode due to the decomposition of water. In this case, the near-cathode zone is enriched with sodium hydroxide.

Membrane method with solid cathode

The membrane method is essentially similar to the diaphragm method, but the anode and cathode spaces are separated by a cation-exchange polymer membrane. The membrane production method is more efficient than the diaphragm method, but more difficult to use.

Mercury method with liquid cathode

The process is carried out in an electrolytic bath, which consists of an electrolyzer, a decomposer and a mercury pump, interconnected by communications. In the electrolytic bath, mercury circulates under the action of a mercury pump, passing through an electrolyzer and a decomposer. The cathode of the electrolyzer is a flow of mercury. Anodes - graphite or low-wear. Together with mercury, a stream of anolyte, a solution of sodium chloride, continuously flows through the electrolyzer. As a result of the electrochemical decomposition of chloride, chlorine molecules are formed at the anode, and at the cathode, the released sodium dissolves in mercury, forming an amalgam.

Laboratory methods

In laboratories, for the production of chlorine, processes based on the oxidation of hydrogen chloride with strong oxidizing agents (for example, manganese (IV) oxide, potassium permanganate, potassium dichromate) are usually used:

2KMnO 4 + 16HCl → 2KCl + 2MnCl 2 + 5Cl 2 +8H 2 O K 2 Cr 2 O 7 + 14HCl → 3Cl 2 + 2KCl + 2CrCl 3 + 7H 2 O

Chlorine storage

The chlorine produced is stored in special “tanks” or pumped into high-pressure steel cylinders. Cylinders with liquid chlorine under pressure have a special color - swamp color. It should be noted that during prolonged use of chlorine cylinders, extremely explosive nitrogen trichloride accumulates in them, and therefore, from time to time, chlorine cylinders must undergo routine washing and cleaning of nitrogen chloride.

Chlorine Quality Standards

According to GOST 6718-93 “Liquid chlorine. Technical specifications" the following grades of chlorine are produced

Application

Chlorine is used in many industries, science and household needs:

• In the production of polyvinyl chloride, plastic compounds, synthetic rubber, from which they make: wire insulation, window profiles, packaging materials, clothing and shoes, linoleum and gramophone records, varnishes, equipment and foam plastics, toys, instrument parts, building materials. Polyvinyl chloride is produced by the polymerization of vinyl chloride, which today is most often produced from ethylene by the chlorine-balanced method through the intermediate 1,2-dichloroethane.
• The bleaching properties of chlorine have been known for a long time, although it is not chlorine itself that “bleaches,” but atomic oxygen, which is formed during the breakdown of hypochlorous acid: Cl 2 + H 2 O → HCl + HClO → 2HCl + O.. This method of bleaching fabrics, paper, cardboard has been used for several centuries.
• Production of organochlorine insecticides - substances that kill insects harmful to crops, but are safe for plants. 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). This substance was first synthesized back in 1825 by Faraday, but it found practical application only more than 100 years later - in the 30s of the twentieth century.
• It was used as a chemical warfare agent, as well as for the production of other chemical warfare agents: mustard gas, phosgene.
• To disinfect water - “chlorination”. The most common method of disinfecting drinking water; is based on the ability of free chlorine and its compounds to inhibit the enzyme systems of microorganisms that catalyze redox processes. To disinfect drinking water, the following are used: chlorine, chlorine dioxide, chloramine and bleach. SanPiN 2.1.4.1074-01 establishes the following limits (corridor) of the permissible content of free residual chlorine in drinking water centralized water supply 0.3 - 0.5 mg/l. A number of scientists and even politicians in Russia criticize the very concept of chlorination of tap water, but cannot offer an alternative to the disinfecting aftereffect of chlorine compounds. The materials from which water pipes are made interact differently with chlorinated tap water. Free chlorine in tap water significantly reduces the service life of polyolefin-based pipelines: various types of polyethylene pipes, including cross-linked polyethylene, also known as PEX (PE-X). In the USA, to control the admission of pipelines made of polymer materials for use in water supply systems with chlorinated water, they were forced to adopt 3 standards: ASTM F2023 in relation to cross-linked polyethylene (PEX) pipes and hot chlorinated water, ASTM F2263 in relation to all polyethylene pipes and chlorinated water, and ASTM F2330 applied to multilayer (metal-polymer) pipes and hot chlorinated water. In terms of durability when interacting with chlorinated water, copper water pipes demonstrate positive results.
• Registered in the food industry as a food additive E925.
• In the chemical production of hydrochloric acid, bleach, bertholite 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 trying to limit the use of chlorine in everyday life, including because burning chlorine-containing waste produces a significant amount of dioxins.

Biological role

Chlorine is one of the most important biogenic elements and is part of all living organisms.

In animals and humans, chloride ions are involved in maintaining osmotic balance; chloride ion has an optimal radius for penetration through the cell membrane. This is precisely what explains its joint participation with sodium and potassium ions in creating constant osmotic pressure and regulating water-salt metabolism. Under the influence of GABA (a neurotransmitter), chlorine ions have an inhibitory effect on neurons by reducing the action potential. In the stomach, chlorine ions create a favorable environment for the action of proteolytic enzymes of gastric juice. Chloride channels are present in many cell types, mitochondrial membranes and skeletal muscle. These channels perform important functions in regulating fluid volume, transepithelial ion transport and stabilizing membrane potentials, and are involved in maintaining cell pH. Chlorine accumulates in visceral tissue, skin and skeletal muscles. Chlorine is absorbed mainly in the large intestine. The absorption and excretion of chlorine are closely related to sodium ions and bicarbonates, and to a lesser extent to mineralocorticoids and Na + /K + - ATPase activity. 10-15% of all chlorine accumulates in cells, of which 1/3 to 1/2 is in red blood cells. About 85% of chlorine is found in the extracellular space. Chlorine is excreted from the body mainly through urine (90-95%), feces (4-8%) and through the skin (up to 2%). Chlorine excretion is associated with sodium and potassium ions, and reciprocally with HCO 3 − (acid-base balance).

A person consumes 5-10 g of NaCl per day. The minimum human need for chlorine is about 800 mg per day. The baby receives the required amount of chlorine through mother's milk, which contains 11 mmol/l of chlorine. NaCl is necessary for the production of hydrochloric acid in the stomach, which promotes digestion and the destruction of pathogenic bacteria. Currently, the involvement of chlorine in the occurrence of certain diseases in humans is not well studied, mainly due to the small number of studies. Suffice it to say that even recommendations on the daily intake of chlorine have not been developed. Human muscle tissue contains 0.20-0.52% chlorine, bone tissue - 0.09%; in the blood - 2.89 g/l. The average person's body (body weight 70 kg) contains 95 g of chlorine. Every day a person receives 3-6 g of chlorine from food, which more than covers the need for this element.

Chlorine ions are vital for plants. Chlorine is involved in energy metabolism in plants, activating oxidative phosphorylation. It is necessary for the formation of oxygen during photosynthesis by isolated chloroplasts, and stimulates auxiliary processes of photosynthesis, primarily those associated with energy accumulation. Chlorine has a positive effect on the absorption of oxygen, potassium, calcium, and magnesium compounds by roots. Excessive concentration of chlorine ions in plants can also have a negative side, for example, reduce the chlorophyll content, reduce the activity of photosynthesis, and retard the growth and development of plants.

But there are plants that, in the process of evolution, either adapted to soil salinity, or, in the struggle for space, occupied empty salt marshes where there is no competition. Plants growing on saline soils are called halophytes; they accumulate chlorides during the growing season, and then get rid of the excess through leaf fall or release chlorides onto the surface of leaves and branches and receive a double benefit by shading the surfaces from sunlight.

Among microorganisms, halophiles - halobacteria - are also known, which live in highly saline waters or soils.

Features of operation and precautions

Chlorine is a toxic, asphyxiating gas that, if it enters the lungs, causes burns of lung tissue and suffocation. It has an irritating effect on the respiratory tract at a concentration in the air of about 0.006 mg/l (i.e., twice the threshold for the perception of the smell of chlorine). Chlorine was one of the first chemical agents used by Germany in World War I. When working with chlorine, you should use protective clothing, a gas mask, and gloves. For a short time, you can protect the respiratory organs from chlorine entering them with a cloth bandage moistened with a solution of sodium sulfite Na 2 SO 3 or sodium thiosulfate Na 2 S 2 O 3.

MPC of chlorine atmospheric air the following: average daily - 0.03 mg/m³; maximum single dose - 0.1 mg/m³; in the working premises of an industrial enterprise - 1 mg/m³.

DEFINITION

Chlorine is in the third period of the VII group of the main (A) subgroup of the Periodic table.

Belongs to elements of the p-family. Non-metal. The nonmetallic elements included in this group are collectively called halogens. Designation - Cl. Serial number - 17. Relative atomic mass - 35.453 amu.

Electronic structure of the chlorine atom

The chlorine atom consists of a positively charged nucleus (+17), consisting of 17 protons and 18 neutrons, around which 17 electrons move in 3 orbits.

Fig.1. Schematic structure of the chlorine atom.

The distribution of electrons among orbitals is as follows:

17Cl) 2) 8) 7 ;

1s 2 2s 2 2p 6 3s 2 3p 5 .

The outer energy level of the chlorine atom contains seven electrons, all of which are considered valence electrons. The energy diagram of the ground state takes the following form:

The presence of one unpaired electron indicates that chlorine is capable of exhibiting the +1 oxidation state. Several excited states are also possible due to the presence of vacant 3 d-orbitals. First, electrons 3 are vaporized p-sublevel and occupy free d-orbitals, and then electrons 3 s-sublevel:

This explains the presence of chlorine in three more oxidation states: +3, +5 and +7.

Examples of problem solving

EXAMPLE 1

Exercise	Given two elements with nuclear charges Z=17 and Z=18. The simple substance formed by the first element is a poisonous gas with a pungent odor, and the second is a non-toxic, odorless, non-respiratory gas. Write the electronic formulas for the atoms of both elements. Which one produces a poisonous gas?
Solution	The electronic formulas of the given elements will be written as follows: 17 Z 1 s 2 2s 2 2p 6 3s 2 3p 5 ; 18 Z 1 s 2 2s 2 2p 6 3s 2 3p 6 . Charge of the nucleus of an atom chemical element equal to its serial number in the Periodic Table. Therefore, it is chlorine and argon. Two chlorine atoms form a molecule of a simple substance - Cl 2, which is a poisonous gas with a pungent odor
Answer	Chlorine and argon.