Collier Encyclopedia. Chlorine gas, physical properties of chlorine, chemical properties of chlorine Distribution of chlorine in nature physical properties

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=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 really 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

Chlorine(from the Greek. χλωρός - "green") - a chemical element of group VII of the periodic system of Mendeleev, atomic number 17, atomic mass 35.453. It is denoted by the symbol Cl (lat. Chlorum). Reactive nonmetal. Included in the group of halogens. The simple substance chlorine under normal conditions is a yellowish-green poisonous gas heavier than air, with a pungent odor. The chlorine molecule is diatomic (formula Cl 2).

The connection with hydrogen - gaseous hydrogen chloride - was first obtained by Joseph Priestley in 1772. Chlorine was obtained for the first time in 1774 by the Swedish chemist Carl Wilhelm Scheele by the interaction of hydrochloric acid with pyrolusite MnO 2. 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, attempts to isolate chlorine remained unsuccessful until the work of the English chemist Humphry Davy, who in 1810 managed to decompose table salt into sodium and chlorine by electrolysis, proving the elemental nature of the latter and calling it chlorine (from the Greek chloros - yellow-green). In 1813 J.L. Gay-Lussac proposed the name chlorine for this element.

Like fluorine, the bulk of chlorine came to the earth's surface from the hot bowels of the Earth. Even at present, millions of tons of both HCl and HF are released annually with volcanic gases. Even more significant was such a separation in past epochs.
The primary form of chlorine on the earth's surface corresponds to its extreme dispersion. As a result of the work of water, which for many millions of years destroyed rocks and washed out of them all soluble constituents, chlorine compounds accumulated in the seas. The drying of the latter led to the formation in many places of the globe of powerful deposits of NaCl, which serves as the feedstock for the production of chlorine compounds.
Chlorine occurs in nature only in the form of compounds. The average content of chlorine in the earth's crust is 1.7×10 -2% by weight, in acid igneous rocks - granites 2.4×10 -2, in basic and ultrabasic 5×10 -3. Water migration plays a major role in the history of chlorine in the earth's crust. In the form of 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) is 97, the main one being NaCl halite, known as table salt. There are also large deposits of potassium and magnesium chlorides and mixed chlorides: sylvin KCl, sylvinite (Na, K) Cl, carnallite KCl × MgCl 2 × 6H 2 O, kainite KCl × MgSO 4 × ZH 2 O, bischofite MgCl 2 × 6H 2 O In the history of the Earth, the supply of HCl contained in volcanic gases to the upper parts of the earth's crust was of great importance. In nature, there are two isotopes of chlorine 35 Cl and 37 Cl.

Under normal conditions, chlorine is a yellow-green gas with a suffocating odor. Chlorine has t bp - 34.05 ° C, t melt - 101 ° C. The density of gaseous chlorine under normal conditions is 3.214 g/l; saturated steam at 0 °C 12.21 g/l; liquid chlorine at a boiling point of 1.557 g/cm 3 ; solid chlorine at -102 ° C 1.9 g / cm 3. Saturated vapor pressure of chlorine at 0 °C 0.369; at 25 °C 0.772; at 100 °C 3.814 MN / m 2 or 3.69, respectively; 7.72; 38.14 kgf / cm 2. Heat of fusion 90.3 kJ/kg (21.5 cal/g); heat of vaporization 288 kJ/kg (68.8 cal/g); heat capacity of gas at constant pressure 0.48 kJ/(kg×K) . Chlorine dissolves well in TiCl 4 , SiCl 4 , SnCl 4 and some organic solvents (especially hexane and carbon tetrachloride). The chlorine molecule is diatomic (Cl 2). The degree of thermal dissociation of Cl 2 +243 kJ → 2Cl at 1000 K is 2.07 × 10 -4%, at 2500 K - 0.909%.
The external electronic configuration of the Cl3s2 atom is 3p5. In accordance with this, chlorine in compounds exhibits oxidation states -1, +1, +3, +4, +5, +6 and +7. The covalent radius of the atom is 0.99A, the ionic radius of Cl is 1.82A, the electron affinity of the chlorine atom is 3.65 eV, and the ionization energy is 12.97 eV.
Chemically chlorine is very active, combines directly with almost all metals (with some only in the presence of moisture or when heated) and with non-metals (except carbon, nitrogen, oxygen, inert gases), forming the corresponding chlorides, reacts with many compounds, replaces hydrogen in saturated hydrocarbons and joins unsaturated compounds. Chlorine displaces bromine and iodine from their compounds with hydrogen and metals; from compounds of chlorine with these elements, it is displaced by fluorine. Alkali metals in the presence of traces of moisture interact with chlorine with ignition, most metals react with dry chlorine only when heated. Steel, as well as some metals, is resistant to dry chlorine at low temperatures, so they are used for the manufacture of equipment and storage for dry chlorine. Phosphorus ignites in an atmosphere of chlorine, forming PCl3, and with further chlorination - PCl 5; sulfur with chlorine, when heated, gives S 2 Cl 2, SCl 2 and other S n Cl m. Arsenic, antimony, bismuth, strontium, tellurium interact vigorously with chlorine. A mixture of chlorine and hydrogen burns with a colorless or yellow-green flame to form hydrogen chloride (this is a chain reaction). The maximum temperature of the hydrogen-chlorine flame is 2200 °C. Mixtures of chlorine with hydrogen containing from 5.8 to 88.3% H 2 are explosive.
With oxygen, chlorine forms oxides: Cl 2 O, ClO 2, Cl 2 O 6, Cl 2 O 7, Cl 2 O 8, as well as hypochlorites (salts of hypochlorous acid), chlorites, chlorates and perchlorates. All oxygen compounds of chlorine form explosive mixtures with easily oxidized substances. Chlorine oxides are unstable and can explode spontaneously, hypochlorites decompose slowly during storage, chlorates and perchlorates can explode under the influence of initiators.
Chlorine in water is hydrolyzed, forming hypochlorous and hydrochloric acids: Cl 2 + H 2 O → HClO + HCl. When chlorinating aqueous solutions of alkalis in the cold, hypochlorites and chlorides are formed: 2NaOH + Cl 2 \u003d NaClO + NaCl + H 2 O, and when heated - chlorates. Chlorine is obtained by chlorination of dry calcium hydroxide. When ammonia reacts with chlorine, nitrogen trichloride is formed. When chlorinating organic compounds, chlorine either replaces hydrogen: R-H + Cl 2 \u003d RCl + HCl, or joins through multiple bonds:
>C=C< + Сl 2 → СlС-ССl
forming various chlorine-containing organic compounds.
Chlorine forms interhalogen compounds with other halogens. Fluorides СlF, СlF 3 , СlF 5 are very reactive; for example, in a ClF 3 atmosphere, glass wool ignites spontaneously. Known compounds of chlorine with oxygen to fluorine are chlorine oxyfluorides: СlО 3 F, СlО 2 F 3 , СlOF, СlОF 3 and fluorine perchlorate FСlO 4 .

Chlorine began to be produced industrially in 1785 by the interaction of hydrochloric acid with manganese dioxide or pyrolusite. In 1867, the English chemist G. Deacon developed a method for producing chlorine by oxidizing HCl with atmospheric oxygen in the presence of a catalyst. Since the late 19th and early 20th centuries, chlorine has been produced by electrolysis of aqueous solutions of alkali metal chlorides. By these methods, in the 70s of the 20th century, 90 - 95% of the chlorine in the world was produced. Small amounts of chlorine are produced incidentally in the production of magnesium, calcium, sodium, and lithium by electrolysis of molten chlorides. In 1975, the world production of chlorine was about 23 million tons.
Two main methods of electrolysis of NaCl aqueous solutions are used: 1) in electrolyzers with a solid cathode and a porous filter diaphragm; 2) in electrolyzers with a mercury cathode. According to both methods, chlorine gas is released on a graphite or oxide titanium-ruthenium anode. According to the first method, hydrogen is released at the cathode and a solution of NaOH and NaCl is formed, from which commercial caustic soda is 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 solution of NaOH, hydrogen and pure mercury are obtained, which again goes into production. Both methods give 1.125 tons of NaOH per 1 ton of chlorine.
Diaphragm electrolysis requires less capital investment to organize the production of chlorine, and produces cheaper NaOH. The mercury cathode method makes it possible to obtain very pure NaOH, but the loss of mercury leads to environmental pollution. In 1970, the mercury cathode method accounted for 62.2% of the world's chlorine production, the solid cathode method 33.6%, and other methods 4.3%. After 1970, solid cathode electrolysis with an ion-exchange membrane began to be used, which made it possible to obtain pure NaOH without the use of mercury.
To obtain chlorine in small quantities in laboratories, reactions based on the oxidation of hydrogen chloride with strong oxidizing agents are usually used, manganese dioxide or potassium permanganate is usually used:
2KMnO 4 + 16HCl → 2KCl + 2MnCl 2 + 5Cl 2 + 8H 2 O

One of the important branches of the chemical industry is the chlorine industry. The main quantities of chlorine are processed at the place of its production into chlorine-containing compounds. Chlorine is stored and transported in liquid form in cylinders, barrels, railway tanks or in specially equipped ships.
The main consumers of chlorine are organic technology (obtaining chlorine-containing organic compounds) and the pulp and paper industry (bleaching). Significantly less chlorine is consumed in the production of inorganic compounds, sanitary needs, water chlorination and other areas. Chlorine is also used for the chlorination of certain ores in order to extract titanium, niobium, zirconium, and others. The recently proposed use of chlorine for the treatment of metals is interesting: under its action with a sufficiently heated (infrared radiation) surface, all roughness is removed in the form of volatile chlorides. This method of chemical grinding is especially applicable to products with a complex profile. It was also shown that a chlorine jet easily cuts through sufficiently heated sheets of heat-resistant alloys.
Chlorine has been used as a chemical in the military, as well as for the production of other chemical warfare agents: mustard gas and phosgene.

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

Chlorine poisoning is possible in the chemical, pulp and paper, textile, and pharmaceutical industries. Chlorine irritates the mucous membranes of the eyes and respiratory tract. Secondary infection usually joins the primary inflammatory changes. Acute poisoning develops almost immediately. When inhaling medium and low concentrations of chlorine, chest tightness and pain, dry cough, rapid breathing, pain in the eyes, lacrimation, increased levels of leukocytes in the blood, body temperature, etc. are noted. Bronchopneumonia, toxic pulmonary edema, depression, convulsions are possible. . In mild cases, recovery occurs in 3-7 days. As long-term consequences, catarrhs of the upper respiratory tract, recurrent broichitis, pneumosclerosis are observed; possible activation of pulmonary tuberculosis. With prolonged inhalation of small concentrations of chlorine, similar, but slowly developing forms of the disease are observed. Prevention of poisoning: sealing of production facilities, equipment, effective ventilation, if necessary, the use of a gas mask. The maximum permissible concentration of chlorine in the air of production, premises is 1 mg/m3. The production of chlorine, bleach and other chlorine-containing compounds refers to industries with harmful working conditions.

The history of elemental chlorine is relatively short; it dates back to 1774. It is very likely that alchemists 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.

Chlorine was first described in detail by the Swedish chemist K. Schelle in the interaction of pyrolusite with hydrochloric acid in his treatise on pyrolusite.

4HCl + MnO2 = Cl2 + MnCl2 + 2H2O

Schelle 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.

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.

Gay-Lussac gave the new element a shorter name - chlorine.

part: general characteristics

1. Location in the table D.I. Mendeleev

Chlorine (from the Greek member - “green”) is 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).

2. The structure of the atom (CI)

The valence level of the chlorine atom contains 1 unpaired electron: 1SI 2SI 2p6 3SI 3p5, so the valence equal to 1 for the chlorine atom is very stable. Due to the presence of an unoccupied orbital of the d-sublevel in the chlorine atom, the chlorine atom can also exhibit other valences. Scheme of the formation of excited states of the atom:

3. Physical properties

Under normal conditions, chlorine is a yellow-green gas with a suffocating odor. When cooled, chlorine turns into a liquid at a temperature of about 239 K, and then crystallizes below 113 K. Some of its physical properties are presented in the table.

4. Chemical properties
4.1 Interaction with non-metals

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

In the light or when heated, it actively reacts (sometimes with an explosion) with hydrogen by a radical mechanism. A mixture of chlorine and hydrogen in small concentrations burns with a colorless or yellow-green flame.

5Cl2 + 2P > 2PCl5
2S + Cl2 > S2Cl2

With oxygen, chlorine forms oxides in which it exhibits an oxidation state from +1 to +7: Cl2O, ClO2, Cl2O6, Cl2O7. They have a pungent odor, are thermally and photochemically unstable, and prone to explosive decomposition.

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

Cl2 + 3F2(e) > 2ClF3

4.2 Reaction with metals

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

Cl2 + 2Na > 2NaCl

3Cl2 + 2Sb > 2SbCl3
3Cl2 + 2Fe > 2FeCl3

Now on the video we can observe the reactions of chlorine with some elements

Burning candles in chlorine

The interaction of chlorine with metals: a) with iron

Interaction with complex substances

Displacement by a more active halogen of a less active one from its salt

4.3 Other properties

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

Cl2 + 2HBr > Br2 + 2HCl

Cl2 + 2NaI > I2 + 2NaCl

When reacted with carbon monoxide, phosgene is formed:

Cl2 + CO > COCl2

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

Cl2 + H2O > HCl + HClO

3Cl2 + 6NaOH > 5NaCl + NaClO3 + 3H2O

By chlorination of dry calcium hydroxide, bleach is obtained:

Cl2 + Ca(OH)2 > CaCl(OCl) + H2O

The action of chlorine on ammonia can be obtained nitrogen trichloride:

4NH3 + 3Cl2 > NCl3 + 3NH4Cl
4.4 Oxidizing properties of chlorine

Chlorine is a very strong oxidizing agent.

Cl2 + H2S > 2HCl + S

4.5 Reactions with organic substances

With saturated compounds:

CH3-CH3 + Cl2 > C2H6-xClx + HCl

Attaches to unsaturated compounds by multiple bonds:

CH2=CH2 + Cl2 > Cl-CH2-CH2-Cl

Aromatic compounds replace a hydrogen atom with chlorine in the presence of catalysts (eg AlCl3 or FeCl3).

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 - 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 were digging 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 - they hit 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 called poschlordiethyl sulfide was used for the first time in the area of \u200b\u200bthis city.

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 othertoxic 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 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 humans date back to about 3-4 millennium BC. And 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 13th century, n. e., 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. Judging by the description, this gas is very similar to.

It was first described in detail by the Swedish chemist Scheele in his treatise on pyrolusite. By heating the mineral 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 and (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, Bertollet suggested that this gas be considered the 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 Davy, who in 1807 decomposed table salt with an electric current into an alkali metal and a 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.

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 Ypres. Crécy (Battle of Crécy in 1346 saw the first use of firearms by English troops in Europe.) 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, with a flat north-easterly wind, 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 died. 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.

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...

History of chlorine

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 human use of salt date back to approximately 3...4 millennium BC. And 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.

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.

Chlorine was first described in detail 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.

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 is a simple substance, an element, and called it chloric gas or chlorine (from the Greek χλωροζ 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, glycerin and fluoroplast are obtained; 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 pungent 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 chlorine gas 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 hardens at 101.6°C. Under increased pressure, chlorine can be liquidized at higher temperatures up to +144°C. Chlorine is highly soluble in dichloroethane and some other chlorine-containing organic solvents.

Element #17 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. The most common minerals containing chlorine, halite NaCI, 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 of all "wine ” (or “merit”) that the chlorine content in 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 10 22 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 nine isotopes of this element are known, but only two chlorine-35 and chlorine-37 are found in nature. The first is about three times more than the second.

The remaining seven 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.

How is chlorine obtained?

The first thing you notice when you get to the chlorine plant is the numerous power lines. Chlorine production consumes a lot of electricity it is needed in order to decompose natural chlorine compounds.

Naturally, the main chlorine raw material is rock salt. If the chlorine plant is located near the river, then salt is not imported by rail, but by barges - it is more economical. Salt is an inexpensive product, but a lot of it is consumed: to get a ton of chlorine, you need about 1.7 ... 1.8 tons of salt.

Salt goes to warehouses. Three six-month stocks of raw materials are stored here chlorine production, as a rule, large-tonnage.

Salt is crushed and dissolved in warm water. This brine is pumped through the pipeline to the cleaning shop, where in huge tanks, the height of a three-story house, the brine is cleaned from impurities of calcium and magnesium salts and clarified (allowed to settle). The pure concentrated sodium chloride solution is pumped to the main chlorine production shop to the electrolysis shop.

In an aqueous solution, salt molecules are converted into Na + and Cl ions. The Cl ion differs from the chlorine atom only in that it has one extra electron. This means that in order to obtain elemental chlorine, it is necessary to tear off this extra electron. This happens in the cell on a positively charged electrode (anode). Electrons seem to be “sucked off” from it: 2Cl → Cl 2 + 2ē. The anodes are made of graphite, because any metal (except platinum and its analogues), taking away excess electrons from chlorine ions, quickly corrodes and collapses.

There are two types of technological design for the production of chlorine: diaphragm and mercury. In the first case, a perforated iron sheet serves as the cathode, and the cathode and anode spaces of the cell are separated by an asbestos diaphragm. On the iron cathode, hydrogen ions are discharged and an aqueous solution of caustic soda is formed. If mercury is used as a cathode, then sodium ions are discharged on it and sodium amalgam is formed, which is then decomposed by water. Hydrogen and caustic soda are obtained. In this case, a separating diaphragm is not needed, and the alkali is more concentrated than in diaphragm electrolyzers.

So, the production of chlorine is simultaneously the production of caustic soda and hydrogen.

Hydrogen is removed through metal pipes, and chlorine through glass or ceramic pipes. Freshly prepared chlorine is saturated with water vapor and is therefore particularly aggressive. Subsequently, it is first cooled with cold water in high towers lined with ceramic tiles from the inside and filled with ceramic nozzles (the so-called Raschig rings), and then dried with concentrated sulfuric acid. It is the only chlorine desiccant and one of the few liquids with which chlorine does not interact.

Dry chlorine is no longer so aggressive, it does not destroy, for example, steel equipment.

Chlorine is usually transported in a liquid state in railway tanks or cylinders under pressure up to 10 atm.

In Russia, the production of chlorine was first organized as early as 1880 at the Bondyuzhsky plant. Chlorine was then obtained in principle in the same way that Scheele had obtained it in his time by reacting hydrochloric acid with pyrolusite. All chlorine produced was used to produce bleach. In 1900, for the first time in Russia, a workshop for the electrolytic production of chlorine was put into operation at the Donsoda plant. The capacity of this workshop was only 6 thousand tons per year. In 1917, all chlorine plants in Russia produced 12,000 tons of chlorine. And in 1965, about 1 million tons of chlorine were produced in the USSR ...

One of many

All the variety of practical applications of chlorine can be expressed without much stretch in one phrase: chlorine is necessary for the production of chlorine products, i.e. substances containing “bound” chlorine. But speaking of these same chlorine products, you can’t get off with one phrase. They are very different both in properties and in purpose.

The limited volume of our article does not allow us to talk about all the compounds of chlorine, but without a story about at least some of the substances that require chlorine, our “portrait” of element No. 17 would be incomplete and unconvincing.

Take, for example, organochlorine insecticides, substances that kill harmful insects 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 more than 100 years later, in the 30s of our century.

Now hexachlorane is obtained by chlorinating benzene. Like hydrogen, benzene reacts very slowly with chlorine in the dark (and in the absence of catalysts), but in bright light, the benzene chlorination reaction (C 6 H 6 + 3Cl 2 → C 6 H 6 Cl 6) proceeds quite quickly.

Hexachloran, like many other insecticides, is used in the form of dusts with fillers (talc, kaolin), or in the form of suspensions and emulsions, or, finally, in the form of aerosols. Hexachloran is especially effective in seed dressing and in pest control of vegetable and fruit crops. The consumption of hexachlorane is only 1...3 kg per hectare, the economic effect of its use is 10...15 times higher than the costs. Unfortunately, hexachlorane is not harmless to humans...

PVC

If you ask any student to list the plastics known to him, he will be one of the first to name polyvinyl chloride (otherwise, vinyl plastic). From the point of view of a chemist, PVC (as polyvinyl chloride is often referred to in the literature) is a polymer in the molecule of which hydrogen and chlorine atoms are “strung” on a chain of carbon atoms:

There may be several thousand links in this chain.

And from a consumer point of view, PVC is insulation for wires and raincoats, linoleum and gramophone records, protective varnishes and packaging materials, chemical equipment and foam plastics, toys and instrument parts.

Polyvinyl chloride is formed during the polymerization of vinyl chloride, which is most often obtained by treating acetylene with hydrogen chloride: HC ≡ CH + HCl → CH 2 = CHCl. There is another way to obtain vinyl chloride - thermal cracking of dichloroethane.

CH 2 Cl CH 2 Cl → CH 2 \u003d CHCl + HCl. Of interest is the combination of these two methods, when HCl is used in the production of vinyl chloride by the acetylene method, which is released during the cracking of dichloroethane.

Vinyl chloride is a colorless gas with a pleasant, somewhat heady, ethereal odor that polymerizes easily. To obtain a polymer, liquid vinyl chloride is injected under pressure into warm water, where it is crushed into tiny droplets. So that they do not merge, a little gelatin or polyvinyl alcohol is added to the water, and in order for the polymerization reaction to develop, the polymerization initiator, benzoyl peroxide, is also introduced there. After a few hours, the droplets harden and a suspension of the polymer in water is formed. The polymer powder is separated on a filter or centrifuge.

Polymerization usually occurs at a temperature of 40 to 60°C, and the lower the polymerization temperature, the longer the resulting polymer molecules...

We talked about only two substances, for which element No. 17 is required. Only about two out of many hundreds. There are many such examples. And they all say that chlorine is not only a poisonous and dangerous gas, but a very important, very useful element.

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 lube!

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, then a third ... But the most striking thing was that the chemical properties of chloroacetic acids differed little from acetic acid itself. The class of reactions discovered by Dumas was completely inexplicable by the then prevailing electrochemical hypothesis and the theory of Berzelius radicals (in the words of the French chemist Laurent, the discovery of chloroacetic acid was like a meteor that destroyed the whole old school). Berzelius, his students and followers vigorously disputed the correctness of Dumas' work. A mocking letter from the famous German chemist Friedrich Wöhler under the pseudonym S.C.H. appeared in the German journal Annalen der Chemie und Pharmacie. Windier (in German "Schwindler" means "liar", "deceiver"). It reported that the author was able to replace in fiber (C 6 H 10 O 5) and all carbon atoms. hydrogen and oxygen to chlorine, and the properties of fiber did not change. And what 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 water form a crystalline hydrate of the 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 arranged 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.

Chlorine poisoning

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 ° / o, then acute poisoning can occur, the first sign of which is attacks of severe coughing. In case of chlorine poisoning, absolute rest is necessary; it is useful to inhale oxygen, or ammonia (sniffing 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%.

Not 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.

Chlorine analysis

To determine the chlorine content, an air sample is passed through absorbers with an acidified solution of potassium iodide. (Chlorine displaces iodine, the amount of the latter is easily determined by titration 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 certain 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.

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At present, anodes made of titanium dioxide modified with platinum metal oxides, primarily ruthenium dioxide RuO 2 , are considered to be the "gold standard" of anodes for chlorine production. Ruthenium-titanium oxide anodes (ORTA) are known in the English literature under the names MMO (mixed metal oxide) or DSA (dimensionally stable anode). A film of doped titanium dioxide is produced directly on the surface of a titanium metal substrate. Despite the high cost, ORTA have undeniable advantages over graphite anodes:

A several times higher allowable current density makes it possible to reduce the size of the equipment;
- there are practically no anode corrosion products, which drastically simplifies electrolyte cleaning;
- anodes have excellent corrosion resistance, are able to work in industrial conditions for more than a year without replacement (repair).

For the manufacture of anodes chlorine production prospects and other materials. However, this is a topic for a separate (and large) publication (- ed. note).

Due to the toxicity and high cost of mercury, the third variant of electrolyzers is being actively developed - the membrane one, which is currently the main one in developed countries. In this embodiment, the cathode and anode spaces are separated by an ion-exchange membrane that is permeable to sodium ions but does not allow anions to pass through. In this case, as in the mercury process, contamination of the alkaline catholyte with chloride is excluded.

The material for the manufacture of membranes for chlorine production is Nafion (Nafion) - an ionomer based on polytetrafluoroethylene with grafted groups of perfluorovinyl sulfonic ether. This material, developed in the 60s of the last century by DuPont, is distinguished by excellent chemical, thermal and mechanical resistance and satisfactory conductivity. Until now, it remains the material of choice in the construction of many electrochemical installations (- ed.).

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