The use of chlorine. Chlorine is a very strong oxidizing agent. How is chlorine obtained?
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Chlorine(lat. chlorum), cl, chemical element of group vii of Mendeleev's periodic system, atomic number 17, atomic mass 35.453; belongs to the family halogens. Under normal conditions (0°C, 0.1 MN/m 2 or 1 kgf/cm 2) yellow-green gas with a sharp irritating odor. Natural H. consists of two stable isotopes: 35 cl (75.77%) and 37 cl (24.23%). Radioactive isotopes with mass numbers 32, 33, 34, 36, 38, 39, 40 and half-lives ( t1/2) 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 isotope indicators.
Historical reference. H. obtained for the first time in 1774 K. Scheele the interaction of hydrochloric acid with pyrolusite mno 2. However, only in 1810 Davy established that chlorine is an element and named it chlorine (from the Greek chlor o s - yellow-green). In 1813 J. L. Gay Lussac suggested the name X for this element.
distribution in nature. H. occurs in nature only in the form of compounds. The average content of Ch. in the earth's crust (clarke) 1.7? 10 -2% by weight, in acidic igneous rocks - granites, etc. 2.4? 10-2 , in basic and ultrabasic 5 ? 10 -3 . Water migration plays a major role in the history of Christianity in the earth's crust. In the form of the cl ion, it is found in the World Ocean (1.93%), underground brines and salt lakes. The number of own minerals (mainly natural chlorides) 97, the main one is halite naci . Large deposits of potassium and magnesium chlorides and mixed chlorides are also known: sylvin kcl, sylvinite(na, k) ci, carnallite kci? mgcl2? 6h2o, Cainite kci? mgso 4? 3h 2 o, bischofite mgci 2 ? 6h2o. In the history of the Earth, the influx of hcl contained in volcanic gases into the upper parts of the earth's crust was of great importance.
Physical and chemical properties. H. has t kip -34.05°С, t nl - 101°C. Density of gaseous Ch. under normal conditions 3.214 g/l; saturated steam at 0°C 12.21 g/l; liquid H. at a boiling point of 1.557 g/cm 3 ; solid cold at - 102°c 1.9 g/cm 3 . Saturated vapor pressure Ch. 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/cm 2 . Melting heat 90.3 kJ/kg (21,5 cal/g); heat of evaporation 288 kJ/kg (68,8 cal/g); heat capacity of gas at constant pressure 0.48 kJ/(kg? TO) . Critical constants H.: temperature 144°c, pressure 7.72 Mn/m 2 (77,2 kgf/cm 2) , density 573 g/l, specific volume 1.745? 10-3 l/g. Solubility (in g/l) X. at a partial pressure of 0.1 Mn/m 2 , or 1 kgf/cm 2 , in water 14.8 (0°C), 5.8 (30°c), 2.8 (70°c); in solution 300 g/l naci 1.42 (30°c), 0.64 (70°c). Below 9.6°C, chlorine hydrates form in aqueous solutions. Variable composition cl ? n h 2 o (where n = 6 × 8); these are yellow crystals of the cubic system, which decompose into chlorine and water when the temperature rises. Chlorine dissolves well in ticl 4, sic1 4, sncl 4, and some organic solvents (especially in hexane c 6 h 14 and carbon tetrachloride ccl 4). The X. molecule is diatomic (cl 2). The degree of thermal dissociation cl 2 + 243 kj u 2cl at 1000 K is 2.07? 10 -40%, at 2500 K 0.909%. External electronic configuration of the atom cl 3 s 2 3 p 5 . In accordance with this, H. in compounds exhibits oxidation states of -1, +1, +3, +4, +5, +6, and +7. The covalent radius of the atom is 0.99 å, the ionic radius cl is 1.82 å, the affinity of the X atom to the electron is 3.65 ev, ionization energy 12.97 ev.
Chemically, chlorine is very active; it combines directly with almost all metals (with some only in the presence of moisture or when heated) and with non-metals (except for carbon, nitrogen, oxygen, and inert gases), forming the corresponding chlorides, reacts with many compounds, replaces hydrogen in saturated hydrocarbons and joins unsaturated compounds. H. displaces bromine and iodine from their compounds with hydrogen and metals; it is displaced from chlorine compounds with these elements by fluorine. Alkali metals in the presence of traces of moisture interact with chlorine with ignition; most metals react with dry chlorine only when heated. Steel, as well as some metals, are stable in a dry chlorine atmosphere at low temperatures, so they are used to make equipment and storage facilities for dry chlorine. Phosphorus ignites in an atmosphere of chlorine, forming pcl 3 , and upon further chlorination, pcl 5 ; sulfur with H. when heated gives s 2 cl 2, scl 2, etc. s n cl m. Arsenic, antimony, bismuth, strontium, and tellurium react vigorously with chlorine. A mixture of chlorine and hydrogen burns with a colorless or yellow-green flame to form hydrogen chloride(it's a chain reaction)
The maximum temperature of the hydrogen-chlorine flame is 2200°c. Chlorine mixtures with hydrogen containing from 5.8 to 88.5% h 2 are explosive.
With oxygen, X. forms oxides: cl 2 o, clo 2, cl 2 o 6, cl 2 o 7, cl 2 o 8 , as well as hypochlorites (salts hypochlorous acid) , chlorites, chlorates and perchlorates. All oxygen compounds of chlorine form explosive mixtures with easily oxidized substances. Chlorine oxides are not stable and can explode spontaneously; hypochlorites decompose slowly during storage; chlorates and perchlorates can explode under the influence of initiators.
H. hydrolyzes in water, forming hypochlorous and hydrochloric acids: cl 2 + h 2 o u hclo + hcl. When chlorinating aqueous solutions of alkalis in the cold, hypochlorites and chlorides are formed: 2naoh + cl 2 \u003d nacio + naci + h 2 o, and when heated - chlorates. Chlorination of dry calcium hydroxide bleach.
When ammonia reacts with chlorine, nitrogen trichloride is formed. . During the chlorination of organic compounds, chlorine either replaces hydrogen: r-h + ci 2 = rcl + hci, or adds via multiple bonds to form various chlorine-containing organic compounds .
H. forms with other halogens interhalogen compounds. Fluorides clf, clf 3 , clf 5 are very reactive; for example, in an atmosphere of clp 3, glass wool ignites spontaneously. Compounds of chlorine with oxygen and fluorine are known - oxyfluorides X.: clo 3 f, clo 2 f 3, clof, clof 3 and fluorine perchlorate fclo 4.
Receipt. Chlorine began to be produced commercially in 1785 by the interaction of hydrochloric acid with manganese dioxide or pyrolusite. In 1867, the English chemist H. Deacon developed a method for producing chlorine by oxidizing hcl with atmospheric oxygen in the presence of a catalyst. From the end of the 19th - beginning of the 20th centuries. Chlorine is obtained by electrolysis of aqueous solutions of alkali metal chlorides. By these methods in the 70s. 20th century 90-95% of H. is produced in the world. Small amounts of chlorine are obtained incidentally in the production of magnesium, calcium, sodium, and lithium by electrolysis of molten chlorides. In 1975, world production of chlorine was about 25 million tons. T. Two main methods of electrolysis of aqueous solutions of naci are used: 1) in electrolyzers with a solid cathode and a porous filter diaphragm; 2) in electrolyzers with a mercury cathode. According to both methods, gaseous X is released on a graphite or oxide titanium-ruthenium anode. According to the first method, hydrogen is released at the cathode and a solution of naoh and nacl is formed, from which commercial caustic soda is isolated by subsequent processing. According to the second method, sodium amalgam is formed on the cathode, when it is decomposed with pure water in a separate apparatus, a naoh solution, hydrogen and pure mercury are obtained, which again goes into production. Both methods give 1 T X. 1.125 T naoh.
Diaphragm electrolysis requires less capital investment for the organization of chemical production and produces cheaper naoh. The mercury cathode method produces very pure naoh, but the loss of mercury pollutes the environment. In 1970, 62.2% of the world's chemical output was produced by the mercury cathode method, 33.6% by the solid cathode method, and 4.2% by other methods. After 1970, solid cathode electrolysis with an ion-exchange membrane began to be used, allowing pure naoh to be obtained without the use of mercury.
Application. One of the important branches of the chemical industry is the chlorine industry. The main amounts of chlorine are processed at the place of its production into chlorine-containing compounds. Store and transport H. in liquid form in cylinders, barrels, railroad. tanks or in specially equipped vessels. For industrial countries, the following approximate consumption of chlorine is typical: for the production of chlorine-containing organic compounds - 60-75%; inorganic compounds containing Ch. - 10-20%; for bleaching pulp and fabrics - 5-15%; for sanitary needs and water chlorination - 2-6% of the total output.
Chlorine is also used for the chlorination of certain ores in order to extract titanium, niobium, zirconium, and others.
L. M. Yakimenko.
H. in the body. H. is one of biogenic elements, permanent component of plant and animal tissues. The content of Ch. in plants (many Ch. in halophytes) - from thousandths of a percent to whole percent, in animals - tenths and hundredths of a percent. The daily requirement of an adult for H. (2-4 G) is covered by food. With food H. usually comes in excess in the form of sodium chloride and potassium chloride. X. bread, meat and dairy products are especially rich. Chlorine is the main osmotically active substance in the body of animals in blood plasma, lymph, cerebrospinal fluid, and some tissues. Plays a role in water-salt exchange, helping tissues retain water. The regulation of acid-base balance in tissues is carried out along with other processes by changing the distribution of cholesterol between the blood and other tissues. X. is involved in energy metabolism in plants, activating both oxidative phosphorylation, and photophosphorylation. Ch. has a positive effect on the absorption of oxygen by the roots. Ch. is necessary for the formation of oxygen in the process of photosynthesis isolated chloroplasts. Ch. is not included in most nutrient media for the artificial cultivation of plants. It is possible that very low concentrations of Ch are sufficient for plant development.
M. Ya. Shkolnik.
Poisoning X . possible in the chemical, pulp and paper, textile, pharmaceutical industries, etc. H. irritates the mucous membranes of the eyes and respiratory tract. Secondary infection usually joins the primary inflammatory changes. Acute poisoning develops almost immediately. When medium and low concentrations of chlorine are inhaled, chest tightness and pain, dry cough, rapid breathing, pain in the eyes, lacrimation, and an increase in the content of leukocytes in the blood, increase in body temperature, etc. are noted. Possible bronchopneumonia, toxic pulmonary edema, depression, convulsions. In mild cases, recovery occurs in 3-7 day As long-term consequences, catarrhs of the upper respiratory tract, recurrent bronchitis, pneumosclerosis, etc. are observed; possible activation of pulmonary tuberculosis. With prolonged inhalation of small concentrations of Ch., similar, but slowly developing forms of the disease are observed. Prevention of poisoning: sealing of production equipment, effective ventilation, if necessary, the use of a gas mask. Maximum permissible concentration of H. in the air of industrial premises 1 mg/m 3 . The production of chemical chloride, bleach, and other chlorine-containing compounds belongs to industries with harmful working conditions, where according to Sov. Legislation restricts the employment of women and minors.
A. A. Kasparov.
Lit.: Yakimenko L. M., Production of chlorine, caustic soda and inorganic chlorine products, M., 1974; Nekrasov B.V., Fundamentals of General Chemistry, 3rd ed., [vol.] 1, M., 1973; Harmful substances in industry, ed. N. V. Lazareva, 6th ed., vol. 2, L., 1971; comprehensive inorganic chemistry, ed. j. c. Bailar, v. 1-5, oxf. - , 1973.
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(according to Pauling)
/cm³
Chlorine (χλωρός - green) - an element of the main subgroup of the seventh group, the third period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 17. It is denoted by the symbol Cl (lat. Chlorum). Reactive nonmetal. It belongs to 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 take root, and subsequently became common for the VII group of elements, which includes chlorine).
The simple substance chlorine (CAS number: 7782-50-5) under normal conditions is a yellowish-green poisonous gas with a pungent odor. The chlorine molecule is diatomic (formula Cl2).
Chlorine atom diagram
Chlorine was first obtained in 1772 by Scheele, who described its release during the interaction of pyrolusite with hydrochloric acid in his treatise on pyrolusite:
4HCl + MnO 2 \u003d Cl 2 + MnCl 2 + 2H 2 O
Scheele noted the smell of chlorine, similar to the smell of aqua regia, its ability to interact with gold and cinnabar, as well as its bleaching properties.
However, Scheele, in accordance with the phlogiston theory prevailing in chemistry at that time, suggested that chlorine is dephlogisticated hydrochloric acid, that is, hydrochloric acid oxide. Berthollet and Lavoisier suggested that chlorine is an oxide of the element murium, but 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
In nature, there are two isotopes of chlorine 35 Cl and 37 Cl. Chlorine is the most abundant halogen in the earth's crust. Chlorine is very active - it combines directly with almost all elements of the periodic table. Therefore, in nature, it occurs only in the form of compounds in the composition of minerals: halite NaCl, sylvin 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.
Chlorine accounts for 0.025% of the total number of atoms in the earth's crust, the Clarke number of chlorine is 0.19%, and the human body contains 0.25% of chlorine ions by mass. In humans and animals, chlorine is found mainly in intercellular fluids (including blood) and plays an important role in the regulation of osmotic processes, as well as in processes associated with the functioning of nerve cells.
Isotopic composition
In nature, there are 2 stable isotopes of chlorine: with a mass number of 35 and 37. The proportions of their content are respectively 75.78% and 24.22%.
Isotope | Relative mass, a.m.u. | Half life | Decay type | nuclear spin |
---|---|---|---|---|
35Cl | 34.968852721 | stable | — | 3/2 |
36Cl | 35.9683069 | 301000 years | β-decay in 36 Ar | 0 |
37Cl | 36.96590262 | stable | — | 3/2 |
38Cl | 37.9680106 | 37.2 minutes | β-decay in 38 Ar | 2 |
39Cl | 38.968009 | 55.6 minutes | β-decay in 39 Ar | 3/2 |
40Cl | 39.97042 | 1.38 minutes | β-decay in 40 Ar | 2 |
41Cl | 40.9707 | 34 c | β-decay in 41 Ar | |
42Cl | 41.9732 | 46.8 s | β-decay in 42 Ar | |
43Cl | 42.9742 | 3.3 s | β-decay in 43 Ar |
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 |
---|---|
Boiling temperature | -34°C |
Melting temperature | -101°C |
Decomposition temperature (dissociations into atoms) |
~1400°С |
Density (gas, n.o.s.) | 3.214 g/l |
Affinity for the electron 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) |
Enthalpy of fusion | 6.406 (kJ/mol) |
Boiling enthalpy | 20.41 (kJ/mol) |
When cooled, chlorine turns into a liquid at a temperature of about 239 K, and then below 113 K it crystallizes into an orthorhombic lattice with a space group cmca and parameters a=6.29 b=4.50 , c=8.21 . Below 100 K, the orthorhombic modification of crystalline chlorine transforms into the tetragonal one, which has a space group P4 2 /ncm and lattice parameters a=8.56 and c=6.12 .
Solubility
Solvent | Solubility g/100 g |
---|---|
Benzene | Soluble |
Water (0 °C) | 1,48 |
Water (20°C) | 0,96 |
Water (25°C) | 0,65 |
Water (40°C) | 0,46 |
Water (60°C) | 0,38 |
Water (80°C) | 0,22 |
Carbon tetrachloride (0 °C) | 31,4 |
Carbon tetrachloride (19 °C) | 17,61 |
Carbon tetrachloride (40 °C) | 11 |
Chloroform | Highly soluble |
TiCl 4 , SiCl 4 , SnCl 4 | Soluble |
In the light or when heated, it actively reacts (sometimes with an explosion) with hydrogen by a radical mechanism. Mixtures of chlorine with hydrogen, containing from 5.8 to 88.3% hydrogen, explode when irradiated with the formation of hydrogen chloride. A mixture of chlorine and hydrogen in small concentrations burns with a colorless or yellow-green flame. The maximum temperature of the hydrogen-chlorine flame is 2200 °C.:
Cl 2 + H 2 → 2HCl 5Cl 2 + 2P → 2PCl 5 2S + Cl 2 → S 2 Cl 2 Cl 2 + 3F 2 (ex.) → 2ClF 3
Other properties
Cl 2 + CO → COCl 2When 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 Cl 2 + Ca(OH) 2 → CaCl(OCl) + H 2 O 4NH 3 + 3Cl 2 → NCl 3 + 3NH 4Cl
Oxidizing properties of chlorine
Cl 2 + H 2 S → 2HCl + SReactions with organic substances
CH 3 -CH 3 + Cl 2 → C 2 H 6-x Cl x + HClAttaches to unsaturated compounds by multiple bonds:
CH 2 \u003d 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
Chlorine methods for producing chlorine
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 2NaCl + 2H 2 O → H 2 + Cl 2 + 2NaOH Anode: 2Cl - - 2e - → Cl 2 0 Cathode: 2H 2 O + 2e - → H 2 + 2OH-
Since the electrolysis of water takes place in parallel with the electrolysis of sodium chloride, the total 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 cathode (mercury production method). Among the electrochemical production methods, mercury cathode electrolysis is the easiest and most convenient method, but this method causes significant environmental damage due to evaporation and leakage of metallic mercury.
Diaphragm method with solid cathode
The cavity of the cell is divided by a porous asbestos partition - diaphragm - into the cathode and anode space, where the cathode and anode of the cell are respectively located. Therefore, such an electrolyzer is often called diaphragm electrolysis, and the production method is diaphragm electrolysis. A stream of saturated anolyte (NaCl solution) continuously enters the anode space of the diaphragm cell. 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 it is 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, under the action of a mercury pump, mercury circulates, passing through the electrolyzer and the decomposer. The cathode of the cell is a stream 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 the released sodium dissolves in mercury at the cathode, forming an amalgam.
Laboratory methods
In laboratories, to obtain 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 produced chlorine is stored in special “tanks” or pumped into high-pressure steel cylinders. Cylinders with liquid chlorine under pressure have a special color - marsh 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 be routinely flushed and cleaned from nitrogen chloride.
Chlorine quality standards
According to GOST 6718-93 “Liquid chlorine. Specifications” the following grades of chlorine are produced
Application
Chlorine is used in many industries, science and domestic needs:
- In the production of polyvinyl chloride, plastic compounds, synthetic rubber, which are used to make: insulation for wires, window profiles, packaging materials, clothes and shoes, linoleum and gramophone records, varnishes, equipment and foam plastics, toys, instrument parts, building materials. Polyvinyl chloride is produced by polymerizing vinyl chloride, which today is most often obtained from ethylene in a chlorine-balanced method through an intermediate 1,2-dichloroethane.
- The bleaching properties of chlorine have been known since ancient times, although it is not chlorine itself that “bleaches”, but atomic oxygen, which is formed during the decomposition of hypochlorous acid: Cl 2 + H 2 O → HCl + HClO → 2HCl + O .. This method of bleaching fabrics, paper, Cardboard has been used for centuries.
- Production of organochlorine insecticides - substances that kill insects harmful to crops, but are safe for plants. A significant part of the produced chlorine is spent on obtaining plant protection products. One of the most important insecticides is hexachlorocyclohexane (often referred to as hexachlorane). This substance was first synthesized back in 1825 by Faraday, but found practical application only after more than 100 years - in the 30s of our century.
- It was used as a chemical warfare agent, as well as for the production of other chemical warfare agents: mustard gas, phosgene.
- For water disinfection - "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. For the disinfection of drinking water, chlorine, chlorine dioxide, chloramine and bleach are used. SanPiN 2.1.4.1074-01 establishes the following limits (corridor) for the permissible content of free residual chlorine in drinking water from 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 they 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 life of pipelines based on polyolefins: polyethylene pipes of various types, including cross-linked polyethylene, more commonly known as PEX (PEX, PE-X). In the USA, in order to control the admission of pipelines made of polymeric materials for use in water supply systems with chlorinated water, 3 standards were forced to be adopted: ASTM F2023 for pipes, membranes and skeletal muscles. These channels perform important functions in the regulation of fluid volume, transepithelial ion transport and stabilization of 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, to a lesser extent with mineralocorticoids and the activity of Na + /K + - ATP-ase. 10-15% of all chlorine is accumulated in cells, from this amount from 1/3 to 1/2 - in erythrocytes. About 85% of chlorine is in the extracellular space. Chlorine is excreted from the body mainly with urine (90-95%), feces (4-8%) and through the skin (up to 2%). The excretion of chlorine 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 infant receives the necessary amount of chlorine through the 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. At present, the role of chlorine in the occurrence of certain diseases in humans is not well understood, 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 - 0.09%; in the blood - 2.89 g / l. In the body of an average person (body weight 70 kg) 95 g of chlorine. Every day with food, a person receives 3-6 g of chlorine, which in excess covers the need for this element.
Chlorine ions are vital for plants. Chlorine is involved in energy metabolism in plants by activating oxidative phosphorylation. It is necessary for the formation of oxygen in the process of photosynthesis by isolated chloroplasts, stimulates auxiliary processes of photosynthesis, primarily those associated with the accumulation of energy. Chlorine has a positive effect on the absorption of oxygen, potassium, calcium, and magnesium compounds by the roots. An excessive concentration of chlorine ions in plants can also have a negative side, for example, reduce the content of chlorophyll, reduce the activity of photosynthesis, retard the growth and development of Baskunchak chlorine plants). Chlorine was one of the first chemical poisons used
– With the help of analytical laboratory equipment, laboratory and industrial electrodes, in particular: reference electrodes ESr-10101 analyzing the content of Cl- and K +.
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No matter how negatively we feel about public restrooms, nature dictates its own rules, and you have to visit them. In addition to natural (for this place) odors, another familiar aroma is bleach used to disinfect the room. It got its name because of the main active ingredient in it - Cl. Let's learn about this chemical element and its properties, and also give a description of chlorine by position in the periodic system.
How this item was discovered
For the first time a chlorine-containing compound (HCl) was synthesized in 1772 by the British priest Joseph Priestley.
After 2 years, his Swedish colleague Karl Scheele managed to describe a method for isolating Cl using the reaction between hydrochloric acid and manganese dioxide. However, this chemist did not understand that a new chemical element was being synthesized as a result.
It took scientists almost 40 years to learn how to extract chlorine in practice. This was first done by the British Humphrey Davy in 1811. In doing so, he used a different reaction than his theoretic predecessors. Davy broke down NaCl (known to most as table salt) by electrolysis.
After studying the resulting substance, the British chemist realized that it was elemental. After this discovery, Davy not only named it - chlorine (chlorine), but was also able to characterize chlorine, although it was very primitive.
Chlorine turned into chlorine (chlore) thanks to Joseph Gay-Lussac and exists in this form in French, German, Russian, Belarusian, Ukrainian, Czech, Bulgarian and some other languages today. In English to this day, the name "chlorin" is used, and in Italian and Spanish "chloro".
The element under consideration 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 exists on its own as a diatomic gas Cl 2, but in this form it practically does not occur in nature. More often it appears in various compounds.
In addition to the distinctive shade, chlorine is characterized by a sweetish-pungent odor. It is a very toxic substance, therefore, if it enters the air and is 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 below it, that is, near the ground itself. 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 acted upon. Most standard gas masks help protect the respiratory organs and mucous membranes from Cl damage. However, for complete safety, more serious measures must be taken, up to the neutralization of 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 millions of tons are mined annually? 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 with the periodic table.
Characterization of chlorine in the periodic system
![](https://i1.wp.com/syl.ru/misc/i/ai/339304/1975821.jpg)
Chlorine as halogen
In addition to extreme toxicity and a pungent odor (characteristic of all representatives of this group), Cl is highly soluble in water. A 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
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. This role can be played by H 2 O.
Often, reactions with Cl are endothermic (they absorb heat).
It should be noted 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, oxides are formed that are extremely unstable and prone to decay. 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 can be different.
Chlorine: a characteristic of a substance in terms of its physical properties
In addition to chemical properties, the element under consideration also has physical properties.
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Effect of temperature on the aggregate state of Cl
Having considered the physical characteristics of the chlorine element, we understand that it is able to go into different states of aggregation. It all depends on the temperature regime.
In its normal state, Cl is a highly corrosive gas. However, he can easily liquefy. This is affected by temperature and pressure. For example, if it is equal to 8 atmospheres, and the temperature is +20 degrees Celsius, Cl 2 is an acid yellow liquid. It is able to maintain this state of aggregation up to +143 degrees, if the pressure also continues to rise.
Upon reaching -32 ° C, the state of chlorine ceases to depend on pressure, and it continues to remain liquid.
Crystallization of a substance (solid state) occurs at -101 degrees.
Where in nature exists Cl
Having considered the general characteristics of chlorine, it is worth finding out where such a difficult element can be found in nature.
Due to its high reactivity, it is almost never found in its pure form (therefore, at the beginning of the study of this element, scientists took years to learn how to synthesize it). Usually Cl is found in compounds in various minerals: halite, sylvin, 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 poisonous. At the same time, atoms of matter 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 the water-salt balance and, as a result, for osmotic equality.
Despite such an important role in the body, pure 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 vivid example of the last statement is any pool. As you know, water in such institutions is disinfected with Cl. At the same time, if a person rarely visits such an institution (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 stay in the water almost all day (rescuers, instructors) often suffer from skin diseases or have a weakened immune system.
In connection with all this, after visiting the pools, it is imperative to take a shower - to wash off possible chlorine residues from the skin and hair.
Human use of Cl
Keeping in mind from the characterization of chlorine that it is a "capricious" element (when it comes to interacting 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 (a characteristic of chlorine as a non-metal) helps to extract certain types of metals (Ti, Ta and Nb), as well as lime and hydrochloric acid with its help.
In addition to all of the above, Cl is used in the production of industrial substances (polyvinyl chloride) and medicines (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 (a brief description of the physical properties in 6-7 p.). Therefore, few can afford to use ozonation instead of chlorination.
How is chlorine produced?
Today, many methods are known for the synthesis of this substance. All of them fall into two categories:
- Chemical.
- Electrochemical.
In the first case, Cl is obtained as a result of a chemical reaction. However, in practice they are very costly and inefficient.
Therefore, electrochemical methods (electrolysis) are preferred in industry. There are three of them: diaphragm, membrane and mercury electrolysis.
In the west of Flanders lies a tiny town. Nevertheless, its name is known throughout the world and will long remain in the memory of mankind as a symbol of one of the greatest crimes against humanity. This town is Ypres. Crecy - Ypres - Hiroshima - milestones on the way to turning war into a giant machine of destruction.
At the beginning of 1915, the so-called Ypres ledge formed on the western front line. The allied Anglo-French troops northeast of Ypres wedged into the territory occupied by the German army. The German command decided to launch a counterattack and level the front line. On the morning of April 22, when a flat northeast blew, the Germans began an unusual preparation for the offensive - they carried out the first gas attack in the history of wars. On the Ypres sector of the front, 6,000 cylinders of chlorine were simultaneously opened. Within five minutes, a huge, weighing 180 tons, poisonous yellow-green cloud formed, which slowly moved towards the enemy's trenches.
Nobody expected this. The troops of the French and British were preparing for an attack, for artillery shelling, the soldiers dug in securely, but in front of the destructive chlorine cloud they were absolutely unarmed. The deadly gas penetrated into all the cracks, into all the shelters. The results of the first chemical attack (and the first violation of the 1907 Hague Convention on the Non-Use of Poisonous Substances!) were stunning - chlorine struck about 15 thousand people, and about 5 thousand - to death. And all this - in order to level the front line 6 km long! Two months later, the Germans launched a chlorine attack on the eastern front as well. And two years later, Ypres increased its notoriety. During a heavy battle on July 12, 1917, a poisonous substance, later called mustard gas, was used for the first time in the area of \u200b\u200bthis city. Mustard is a derivative of chlorine, dichlorodiethyl sulfide.
We recalled these episodes of history, connected with one small town and one chemical element, in order to show how dangerous element No. 17 can be in the hands of militant madmen. This is the darkest page in the history of chlorine. But it would be completely wrong to see in chlorine only a poisonous substance and a raw material for the production of other poisonous substances...
The history of elemental chlorine is relatively short, dating back to 1774. The history of chlorine compounds is as old as the world. Suffice it to recall that sodium chloride is table salt. And, apparently, even in prehistoric times, the ability of salt to preserve meat and fish was noticed.
The most ancient archaeological finds - evidence of the use of salt by man date back to about 3-4 millennium BC. But the most ancient description of the extraction of rock salt is found in the writings of the Greek historian Herodotus (V century BC). Herodotus describes the mining of rock salt in Libya. In the oasis of Sinah in the center of the Libyan desert was the famous temple of the god Ammon-Ra. That is why Libya was called "Ammonia", and the first name of rock salt was "sal ammoniacum". Later, starting around the thirteenth century. AD, this name was assigned to ammonium chloride.
Pliny the Elder's Natural History describes a method for separating gold from base metals by calcining with salt and clay. And one of the first descriptions of the purification of sodium chloride is found in the writings of the great Arab physician and alchemist Jabir ibn Hayyan (in European spelling - Geber).
It is very likely that alchemists also encountered elemental chlorine, since in the countries of the East already in the 9th, and in Europe in the 13th century. "royal vodka" was known - a mixture of hydrochloric and nitric acids. The book Hortus Medicinae by the Dutchman Van Helmont, published in 1668, says that when ammonium chloride and nitric acid are heated together, a certain gas is obtained. Based on the description, this gas is very similar to chlorine.
in detail chlorine was first described by the Swedish chemist Scheele in his treatise on pyrolusite. By heating the mineral pyrolusite with hydrochloric acid, Scheele noticed the smell characteristic of aqua regia, collected and studied the yellow-green gas that gave rise to this smell, and studied its interaction with certain substances. Scheele was the first to discover the effect of chlorine on gold and cinnabar (in the latter case, sublimate is formed) and the bleaching properties of chlorine.
Scheele did not consider the newly discovered gas to be a simple substance and called it "dephlogistinated hydrochloric acid". In modern terms, Scheele, and after him other scientists of that time, believed that the new gas was hydrochloric acid oxide.
Somewhat later, Bertholet and Lavoisier suggested that this gas be considered an oxide of some new element, murium. For three and a half decades, chemists have unsuccessfully tried to isolate the unknown murium.
A supporter of "murium oxide" was at first also Davy, who in 1807 decomposed table salt with an electric current into the alkali metal sodium and yellow-green gas. However, three years later, after many fruitless attempts to obtain muria, Davy came to the conclusion that the gas discovered by Scheele was a simple substance, an element, and called it chloric gas or chlorine (from Greek - yellow-green). And three years later, Gay-Lussac gave the new element a shorter name - chlorine. True, back in 1811, the German chemist Schweiger proposed another name for chlorine - “halogen” (literally it translates as salt), but this name did not take root at first, and later became common for a whole group of elements, which includes chlorine.
"Personal card" of chlorine
To the question, what is chlorine, you can give at least a dozen answers. First, it is a halogen; secondly, one of the strongest oxidizing agents; thirdly, an extremely poisonous gas; fourthly, the most important product of the main chemical industry; fifthly, raw materials for the production of plastics and pesticides, rubber and artificial fibers, dyes and medicines; sixth, the substance with which titanium and silicon are obtained, glycerin and fluoroplast; seventh, a means for purifying drinking water and bleaching fabrics ...
This listing could be continued.
Under normal conditions, elemental chlorine is a rather heavy, yellow-green gas with a sharp, characteristic odor. The atomic weight of chlorine is 35.453, and the molecular weight is 70.906, because the chlorine molecule is diatomic. One liter of gaseous chlorine under normal conditions (temperature 0 ° C and pressure 760 mmHg) weighs 3.214 g. When cooled to a temperature of - 34.05 ° C, chlorine condenses into a yellow liquid (density 1.56 g / cm 3), and at a temperature of - 101.6 ° C hardens. Under increased pressure, chlorine can be turned into a liquid and at higher temperatures up to +144°C. Chlorine is highly soluble in dichloroethane and some other chlorine-containing organic solvents.
Element number 17 is very active - it connects directly with almost all elements of the periodic system. Therefore, in nature, it occurs only in the form of compounds. The most common minerals containing chlorine, halite NaCl, sylvinite KCl NaCl, bischofite MgCl 2 -6H 2 O, carnallite KCl-MgCl 2 -6H 2 O, kainite KCl-MgSO 4 -3H 2 O. This is their first "wine" (or "credit") that the chlorine content of the earth's crust is 0.20% by weight. For non-ferrous metallurgy, some relatively rare chlorine-containing minerals are very important, for example, horn silver AgCl.
In terms of electrical conductivity, liquid chlorine ranks among the strongest insulators: it conducts current almost a billion times worse than distilled water, and 1022 times worse than silver.
The speed of sound in chlorine is about one and a half times less than in air.
And finally - about the isotopes of chlorine.
Now ten isotopes of this element are known, but only two are found in nature - chlorine-35 and chlorine-37. The first is about three times more than the second.
The remaining eight isotopes were obtained artificially. The shortest-lived of them - 32 Cl has a half-life of 0.306 seconds, and the longest-lived - 36 Cl - 310 thousand years.
ELEMENTARY CALCULATION. When chlorine is obtained by electrolysis of a sodium chloride solution, hydrogen and sodium hydroxide are simultaneously obtained: 2NaCl + 2H 2 O \u003d H 2 + Cl 2 + 2NaOH. Of course, hydrogen is a very important chemical product, but there are cheaper and more convenient ways to produce this substance, such as the conversion of natural gas ... But caustic soda is obtained almost exclusively by electrolysis of sodium chloride solutions - other methods account for less than 10%. Since the production of chlorine and NaOH are completely interconnected (as follows from the reaction equation, the production of one gram-molecule - 71 g of chlorine - is invariably accompanied by the production of two gram-molecules - 80 g of electrolytic alkali), knowing the productivity of the workshop (or plant, or state) in terms of alkali , you can easily calculate how much chlorine it produces. Each ton of NaOH is "accompanied" by 890 kg of chlorine.
OH AND LUBRICANT! Concentrated sulfuric acid is practically the only liquid that does not interact with chlorine. Therefore, for compressing and pumping chlorine, factories use pumps in which sulfuric acid plays the role of a working fluid and at the same time a lubricant.
Pseudonym of Friedrich Wöhler. Investigating the interaction of organic substances with chlorine, the French chemist of the XIX century. Jean Dumas made an amazing discovery: chlorine is able to replace hydrogen in the molecules of organic compounds. For example, when chlorinating acetic acid, first one hydrogen of the methyl group is replaced by chlorine, then another, third. But the most striking thing was that the chemical properties of chloroacetic acids were not much different from acetic acid itself. The class of reactions discovered by Dumas was completely inexplicable by the then dominant electrochemical hypothesis and the theory of Berzelius radicals. Berzelius, his students and followers vigorously disputed the correctness of Dumas' work. In the German journal Annalen der Chemie und Pharmacie, a mocking letter appeared from the famous German chemist Friedrich Wöhler under the pseudonym S. C. H. Windier (in German, “Schwindler” means “liar”, “deceiver”). It reported that the author managed to replace in fiber (C 6 H 10 O 5), all carbon, hydrogen and oxygen atoms by chlorine, and the properties of the fiber did not change. And that now in London they make warm girdles from cotton wool, consisting of pure chlorine.
CHLORINE AND WATER. Chlorine is visibly soluble in water. At 20°C, 2.3 volumes of chlorine dissolve in one volume of water. Aqueous solutions of chlorine (chlorine water) - yellow. But over time, especially when stored in the light, they gradually discolor. This is explained by the fact that dissolved chlorine partially interacts with water, hydrochloric and hypochlorous acids are formed: Cl 2 + H 2 O → HCl + HOCl. The latter is unstable and gradually decomposes into HCl and oxygen. Therefore, a solution of chlorine in water gradually turns into a solution of hydrochloric acid.
But at low temperatures, chlorine and iodine form a crystalline hydrate of an unusual composition - Cl 2 * 5 3 / 4 H 2 O. These greenish-yellow crystals (stable only at temperatures below 10 ° C) can be obtained by passing chlorine through ice water. The unusual formula is explained by the structure of the crystalline hydrate, and it is determined primarily by the structure of ice. In the crystal lattice of ice, H 2 O molecules can be located in such a way that regularly spaced voids appear between them. The elementary cubic cell contains 46 water molecules, between which there are eight microscopic voids. In these voids, chlorine molecules settle. The exact formula of chlorine hydrate should therefore be written as follows: 8Cl 2 * 46H 2 O.
POISONING WITH CHLORINE. The presence of about 0.0001% chlorine in the air irritates the mucous membranes. Constant exposure to such an atmosphere can lead to bronchial disease, sharply impairs appetite, and gives a greenish tint to the skin. If the chlorine content in the air is 0.1%, then acute poisoning can occur, the first sign of which is bouts of severe coughing. In case of chlorine poisoning, absolute rest is necessary; it is useful to inhale oxygen or ammonia (smelling ammonia), or vapors of alcohol with ether. According to existing sanitary standards, the content of chlorine in the air of industrial premises should not exceed 0.001 mg / l, i.e. 0.00003%.
HE ONLY POISON. "Everyone knows that wolves are greedy." That chlorine is poisonous - too. However, in small doses, poisonous chlorine can sometimes serve as an antidote. So, victims of hydrogen sulfide are given to sniff unstable bleach. By interacting, the two poisons are mutually neutralized.
ANALYSIS FOR CHLORINE. To determine the chlorine content, an air sample is passed through absorbers with an acidified solution of potassium iodide. (Chlorine displaces pod, the amount of the latter is easily determined by filtration with a solution of Na 2 S 2 O 3.) To determine the microquantities of chlorine in the air, a colorimetric method is often used, based on a sharp change in the color of some compounds (benzidine, orthotoluidine, methyl orange) during their oxidation with chlorine . For example, a colorless acidified solution of benzidine turns yellow, and a neutral one turns blue. The color intensity is proportional to the amount of chlorine.
Chlorine was probably also obtained by alchemists, but its discovery and first research is inextricably linked with the name of the famous Swedish chemist Carl Wilhelm Scheele. Scheele discovered five chemical elements - barium and manganese (together with Johan Gan), molybdenum, tungsten, chlorine, and independently of other chemists (albeit later) - three more: oxygen, hydrogen and nitrogen. Not a single chemist could subsequently repeat this achievement. At the same time, Scheele, already elected a member of the Royal Swedish Academy of Sciences, was a simple pharmacist in Köping, although he could have taken a more honorable and prestigious position. Frederick II the Great himself, the Prussian king, offered him a position as professor of chemistry at the University of Berlin. Refusing such tempting offers, Scheele said: "I cannot eat more than I need, and what I earn here in Köping is enough for me to live on."
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 free chlorine 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 murium (from the Latin muria - brine) with oxygen. It was believed that hydrochloric acid (it was called muriic) contains chemically bound oxygen. This was “testified”, in particular, by the following fact: when a solution of chlorine was left in the light, oxygen was released from it, and hydrochloric acid remained in the solution. However, numerous attempts to “tear off” oxygen from chlorine have led to nothing. So, no one managed to get carbon dioxide by heating chlorine with coal (which at high temperatures “takes away” oxygen from many compounds containing it). As a result of similar experiments carried out by Humphrey Davy, Joseph Louis Gay-Lussac and Louis Jacques Tenard, 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 the color of chlorine. The same root is in the word "chlorophyll" (from the Greek "chloros" and "phyllon" - leaf). A year later, Gay-Lussac "shortened" the name to "chlorine". But until now, the British (and Americans) call this element "chlorine" (chlorine), while the French - chlorine (chlore). The Germans, the “legislators” of chemistry, also adopted the abbreviated name for almost the entire 19th century. (in German chlorine - Chlor). In 1811, the German physicist Johann Schweiger proposed the name "halogen" for chlorine (from the Greek "hals" - salt, and "gennao" - I give birth). Subsequently, this term was assigned not only to chlorine, but also to all its analogues in the seventh group - fluorine, bromine, iodine, astatine.
An interesting demonstration of the combustion of hydrogen in an atmosphere of chlorine: sometimes an unusual side effect occurs during the experiment: a buzz is heard. Most often, the flame buzzes when a thin tube carrying hydrogen is lowered into a conical vessel filled with chlorine; the same is true for spherical flasks, but in cylinders the flame usually does not buzz. This phenomenon was called "singing flame".
In an aqueous solution, chlorine partially and rather slowly reacts with water; at 25 ° C, the equilibrium: Cl 2 + H 2 O HClO + HCl is established within two days. Hypochlorous acid decomposes in the light: HClO ® HCl + O. A bleaching effect is attributed to atomic oxygen (absolutely dry chlorine does not have such an ability).
Chlorine in its compounds can exhibit all oxidation states - from -1 to +7. With oxygen, chlorine forms a number of oxides, all of them in their pure form are unstable and explosive: Cl 2 O is a yellow-orange gas, ClO 2 is a yellow gas (below 9.7 ° C is a bright red liquid), chlorine perchlorate Cl 2 O 4 (ClO –ClO 3, light yellow liquid), Cl 2 O 6 (O 2 Cl–O–ClO 3, bright red liquid), Cl 2 O 7 is a colorless highly explosive liquid. Unstable oxides Cl 2 O 3 and ClO 3 were obtained at low temperatures. ClO 2 oxide is produced on an industrial scale and is used instead of chlorine for pulp bleaching and disinfection of drinking water and waste water. With other halogens, chlorine forms a number of so-called interhalogen compounds, for example, ClF, ClF 3 , ClF 5 , BrCl, ICl, ICl 3 .
Chlorine and its compounds with a positive oxidation state are strong oxidizing agents. In 1822, the German chemist Leopold Gmelin, by oxidation with chlorine, obtained red from yellow blood salt: 2K 4 + Cl 2 ® K 3 + 2KCl. Chlorine easily oxidizes bromides and chlorides with the release of free bromine and iodine.
Chlorine in different oxidation states forms a number of acids: HCl - hydrochloric (hydrochloric, salts - chlorides), HClO - hypochlorous (salts - hypochlorites), HClO 2 - chloride (salts - chlorites), HClO 3 - chloric (salts - chlorates), HClO 4 - chlorine (salts - perchlorates). In its pure form, of the oxygenic acids, only perchloric acid is stable. Of the salts of oxygen acids, hypochlorites, sodium chlorite NaClO 2 - for bleaching fabrics, for the manufacture of compact pyrotechnic oxygen sources ("oxygen candles"), potassium chlorates (berthollet salt), calcium and magnesium (for combating agricultural pests, as components of pyrotechnic compositions and explosives, in the production of matches), perchlorates - components of explosives and pyrotechnic compositions; ammonium perchlorate is a component of solid rocket propellants.
Chlorine reacts with many organic compounds. It quickly adds to unsaturated compounds with double and triple carbon-carbon bonds (the reaction with acetylene goes with an explosion), and in the light - to benzene. Under certain conditions, chlorine can replace hydrogen atoms in organic compounds: R–H + Cl 2 ® RCl + HCl. This reaction has played a significant role in the history of organic chemistry. In the 1840s, the French chemist Jean Baptiste Dumas discovered that when chlorine reacted with acetic acid, the reaction
CH 3 COOH + Cl 2 ® CH 2 ClCOOH + HCl. With an excess of chlorine, trichloroacetic acid CCl 3 COOH is formed. However, many chemists reacted to the work of Dumas incredulously. Indeed, according to the then generally accepted theory of Berzelius, positively charged hydrogen atoms could not be replaced by negatively charged chlorine atoms. This opinion was held at that time by many prominent chemists, among whom were Friedrich Wöhler, Justus Liebig and, of course, Berzelius himself.
In order to ridicule Dumas, Wöhler passed on to his friend Liebig an article on behalf of a certain S. Windler (Schwindler is a swindler in German) about a new successful application of the reaction allegedly discovered by Dumas. In the article, Wöhler, with obvious mockery, wrote about how in manganese acetate Mn (CH 3 COO) 2 it was possible to replace all elements, in accordance with their valency, with chlorine, resulting in a yellow crystalline substance consisting of chlorine alone. It was further said that in England, by successively replacing all atoms in organic compounds with chlorine atoms, ordinary fabrics are converted into chlorine ones, and that things retain their appearance. A footnote pointed out that the London shops briskly traded in material consisting of chlorine alone, as this material is very good for nightcaps and warm underpants.
The reaction of chlorine with organic compounds leads to the formation of many organochlorine products, among which are widely used solvents methylene chloride CH 2 Cl 2, chloroform CHCl 3, carbon tetrachloride CCl 4, trichlorethylene CHCl \u003d CCl 2, tetrachlorethylene C 2 Cl 4. In the presence of moisture, chlorine discolors the green leaves of plants, many dyes. This has been used since the 18th century. for bleaching fabrics.
Chlorine as a poisonous gas.
Scheele, who received chlorine, noted its very unpleasant pungent odor, difficulty breathing and coughing. As it was later found out, a person smells chlorine even if one liter of air contains only 0.005 mg of this gas, and at the same time it already irritates the respiratory tract, destroying the cells of the mucous membrane of the respiratory tract and lungs. The concentration of 0.012 mg / l is difficult to tolerate; if the concentration of chlorine exceeds 0.1 mg / l, it becomes life-threatening: breathing quickens, becomes convulsive, and then increasingly rare, and after 5–25 minutes, breathing stops. The maximum permissible concentration in the air of industrial enterprises is 0.001 mg / l, and in the air of residential areas - 0.00003 mg / l.
Petersburg Academician Toviy Yegorovich Lovitz, repeating Scheele's experiment in 1790, accidentally released a significant amount of chlorine into the air. After inhaling it, he lost consciousness and fell, then for eight days he suffered from excruciating pain in his chest. Fortunately, he recovered. Almost died, poisoned by chlorine, and the famous English chemist Davy. Experiments with even a small amount of chlorine are dangerous, as they can cause severe lung damage. It is said that the German chemist Egon Wiberg began one of his lectures on chlorine with the words: “Chlorine is a poisonous gas. If I get poisoned during another demonstration, please take me out into the fresh air. But the lecture will, unfortunately, have to be interrupted. If you release a lot of chlorine into the air, it becomes a real disaster. This was experienced during the First World War by the Anglo-French troops. On the morning of April 22, 1915, the German command decided to carry out the first gas attack in the history of wars: when the wind blew towards the enemy, the valves of 5730 cylinders were simultaneously opened on a small six-kilometer front near the Belgian town of Ypres, each of which contained 30 kg of liquid chlorine. Within 5 minutes, a huge yellow-green cloud formed, which slowly moved away from the German trenches towards the allies. The English and French soldiers were completely defenseless. The gas penetrated through the cracks into all the shelters, there was no escape from it: after all, the gas mask had not yet been invented. As a result, 15,000 people were poisoned, of which 5,000 died. A month later, on May 31, the Germans repeated the gas attack on the eastern front against the Russian troops. This happened in Poland near the city of Bolimov. At the front of 12 km, 264 tons of a mixture of chlorine with much more poisonous phosgene (carbonic acid chloride COCl 2) were released from 12 thousand cylinders. The royal command knew what happened at Ypres, and yet the Russian soldiers did not have any means of protection! As a result of the gas attack, the losses amounted to 9146 people, of which only 108 - as a result of rifle and artillery shelling, the rest were poisoned. At the same time, 1183 people died almost immediately.
Soon chemists pointed out how to escape from chlorine: you need to breathe through a gauze bandage soaked in a solution of sodium thiosulfate (this substance is used in photography, it is often called hyposulfite). Chlorine reacts very quickly with a solution of thiosulfate, oxidizing it:
Na 2 S 2 O 3 + 4Cl 2 + 5H 2 O ® 2H 2 SO 4 + 2NaCl + 6HCl. Of course, sulfuric acid is also not a harmless substance, but its dilute aqueous solution is much less dangerous than poisonous chlorine. Therefore, thiosulfate in those years had another name - "antichlor", but the first thiosulfate gas masks were not very effective.
In 1916, the Russian chemist, future academician Nikolai Dmitrievich Zelinsky invented a truly effective gas mask in which poisonous substances were retained by a layer of activated carbon. Such coal with a very developed surface could retain much more chlorine than gauze impregnated with hyposulfite. Fortunately, the "chlorine attacks" remained only a tragic episode in history. After the World War, chlorine had only peaceful professions.
The use of chlorine.
Huge amounts of chlorine - tens of millions of tons - are produced annually all over the world. Only in the USA by the end of the 20th century. annually, about 12 million tons of chlorine were obtained by electrolysis (10th place among chemical industries). Its bulk (up to 50%) is spent on the chlorination of organic compounds - to obtain solvents, synthetic rubber, polyvinyl chloride and other plastics, chloroprene rubber, pesticides, medicines, and many other necessary and useful products. The rest is consumed for the synthesis of inorganic chlorides, in the pulp and paper industry for bleaching wood pulp, for water purification. In relatively small quantities, chlorine is used in the metallurgical industry. With its help, very pure metals are obtained - titanium, tin, tantalum, niobium. By burning hydrogen in chlorine, hydrogen chloride is obtained, and from it - hydrochloric acid. Chlorine is also used for the production of bleaching agents (hypochlorites, bleach) and water disinfection by chlorination.
Ilya Leenson