It is widely used in industry, agriculture, for medicinal and household needs. The annual production of chlorine in the world is 55.5 million tons: due to such a widespread distribution of this substance, accidents associated with its leakage are quite frequent (they occur both at industrial facilities and during the transportation of chlorine).

Often, not only an industrial facility is damaged, but also areas outside it (due to the physical and chemical properties of chlorine: it is 2.5 times heavier than air, therefore it accumulates in lowlands, water sources are exposed to contamination, since chlorine is very soluble in water).

Therefore, knowledge of economic facilities that produce or use chlorine, symptoms of chlorine poisoning, first aid skills, as well as knowledge of PPE used in the contaminated area is especially relevant today.

Before examining chlorine as a hazardous substance, identifying the symptoms of poisoning with this chemical and determining what pre-medical and first aid is, it is necessary to become familiar with its general characteristics and areas of use.

Chlorine (from Greek - “green”). Chemical formula – Cl2 (molecular weight – 70.91). The compound with chlorine (hydrogen chloride gas) was first prepared by D. Priestley in 1772. Chlorine in “pure form” was obtained two years later by K.V. Scheele.

The density of liquid chlorine is 1560 kg/m3. It is non-flammable and reactive: in light at elevated temperatures (for example, in the event of a fire) it interacts with hydrogen (explosion), which can result in the formation of a more dangerous gas - phosgene.

Chlorine is used in many areas of industry, science and, often, in everyday life. We list the areas of use of chlorine in industry:

– it is used in the production of polyvinyl chloride, synthetic rubber, plastic compounds (these materials are used for the manufacture of linoleum, clothing, shoes, wire insulation, etc.);

– in the pulp and paper industry, chlorine is used to bleach paper and cardboard (it is also used to bleach fabrics);

– it is involved in the production of organochlorine insecticides (these substances, which destroy harmful insects on crops, are used in agriculture);

– it is used in the process of disinfection (“chlorination”) of drinking water and wastewater treatment;

– it is widely used in the chemical production of berthollet salt, medicines, bleach, poisons, hydrochloric acid, metal chlorides;

– in metallurgy it is used for the production of pure metals;

– this substance is used as an indicator of solar neutrinos.

Chlorine is stored in cylindrical tanks (10...250 m3) and spherical (600...2,000 m3) tanks under its own vapor pressure (up to 1.8 MPa). It liquefies under pressure at normal temperatures. Transported in containers, cylinders, tanks that act as temporary storage facilities.

DEFINITION

Chlorine– chemical element of group VII of period 3 of the Periodic Table of Chemical Elements D.I. Mendeleev. Non-metal.

Refers to elements of the p-family. Halogen. The serial number is 17. The structure of the external electronic level is 3s 2 3 p 5. Relative atomic mass – 35.5 amu. The chlorine molecule is diatomic – Cl 2 .

Chemical properties of chlorine

Chlorine reacts with simple metals:

Cl 2 + 2Sb = 2SbCl 3 (t);

Cl 2 + 2Fe = 2FeCl 3;

Cl 2 + 2Na = 2NaCl.

Chlorine interacts with simple substances, non-metals. Thus, when interacting with phosphorus and sulfur, the corresponding chlorides are formed, with fluorine - fluorides, with hydrogen - hydrogen chloride, with oxygen - oxides, etc.:

5Cl 2 + 2P = 2HCl 5;

Cl 2 + 2S = SCl 2;

Cl 2 + H 2 = 2HCl;

Cl 2 + F 2 = 2ClF.

Chlorine is able to displace bromine and iodine from their compounds with hydrogen and metals:

Cl 2 + 2HBr = Br 2 + 2HCl;

Cl 2 + 2NaI = I 2 + 2NaCl.

Chlorine is able to dissolve in water and alkalis, and chlorine disproportionation reactions occur, and the composition of the reaction products depends on the conditions under which it is carried out:

Cl 2 + H 2 O ↔ HCl + HClO;

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

3 Cl 2 + 6NaOH = 5NaCl + NaClO 3 + 3H 2 O.

Chlorine reacts with a non-salt-forming oxide - CO to form a substance with a trivial name - phosgene, with ammonia to form ammonium trichloride:

Cl 2 + CO = COCl 2;

3 Cl 2 + 4NH 3 = NCl 3 + 3NH 4 Cl.

In reactions, chlorine exhibits the properties of an oxidizing agent:

Cl 2 + H 2 S = 2HCl + S.

Chlorine reacts with organic substances of the class of alkanes, alkenes and arenes:

CH 3 -CH 3 + Cl 2 = CH 3 -CH 2 -Cl + HCl (condition - UV radiation);

CH 2 = CH 2 + Cl 2 = CH 2 (Cl)-CH 2 -Cl;

C 6 H 6 + Cl 2 = C 6 H 5 -Cl + HCl (kat = FeCl 3, AlCl 3);

C 6 H 6 + 6Cl 2 = C 6 H 6 Cl 6 + 6HCl (condition – UV radiation).

Physical properties of chlorine

Chlorine is a yellow-green gas. Thermally stable. When chilled water is saturated with chlorine, solid clarate is formed. It dissolves well in water and is highly susceptible to dismutation (“chlorine water”). Dissolves in carbon tetrachloride, liquid SiCl 4 and TiCl 4. Poorly soluble in saturated sodium chloride solution. Does not react with oxygen. Strong oxidizing agent. Boiling point - -34.1C, melting point - -101.03C.

Getting chlorine

Previously, chlorine was obtained by the Scheele method (the reaction of manganese (VI) oxide with hydrochloric acid) or by the Deacon method (the reaction of hydrogen chloride with oxygen):

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

4HCl + O 2 = 2H 2 O + 2 Cl 2.

Nowadays, the following reactions are used to produce chlorine:

NaOCl + 2HCl = NaCl + Cl 2 + H 2 O;

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

2NaCl + 2H 2 O = 2NaOH + Cl 2 + H 2 (condition – electrolysis).

Use of chlorine

Chlorine has found wide application in various fields of industry, as it is used in the production of polymeric materials (polyvinyl chloride), bleaches, organochlorine insecticides (hexachlorane), chemical warfare agents (phosgene), for water disinfection, in the food industry, in metallurgy, etc.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Exercise	What volume, mass and amount of chlorine substance will be released (n.s.) when 17.4 g of manganese (IV) oxide reacts with hydrochloric acid taken in excess?
Solution	Let us write the reaction equation for the interaction of manganese (IV) oxide with hydrochloric acid: 4HCl + MnO 2 = MnCl 2 + Cl 2 + 2H 2 O. Molar masses of manganese (IV) oxide and chlorine, calculated using the table of chemical elements by D.I. Mendeleev – 87 and 71 g/mol, respectively. Let's calculate the amount of manganese (IV) oxide: n(MnO 2) = m(MnO 2) / M(MnO 2); n(MnO 2) = 17.4 / 87 = 0.2 mol. According to the reaction equation n(MnO 2): n(Cl 2) = 1:1, therefore, n(Cl 2) = n(MnO 2) = 0.2 mol. Then the mass and volume of chlorine will be equal: m(Cl 2) = 0.2 × 71 = 14.2 g; V(Cl 2) = n(Cl 2) × V m = 0.2 × 22.4 = 4.48 l.
Answer	The amount of chlorine substance is 0.2 mol, weight is 14.2 g, volume is 4.48 l.

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 (at the Battle of Crecy in 1346, English troops used firearms for the first time in Europe.) Ypres Hiroshima milestones on the way to turning war into a gigantic machine of destruction.

At the beginning of 1915, the so-called Ypres salient was formed on the western front line. Allied Anglo-French forces northeast of Ypres penetrated 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 steady nor'easter blowing, the Germans began unusual preparations for an offensive - they carried out the first gas attack in the history of war. On the Ypres sector of the front, 6,000 chlorine cylinders were opened simultaneously. Within five minutes, a huge, weighing 180 tons, poisonous yellow-green cloud formed, which slowly moved towards the enemy trenches.

Nobody expected this. The French and British troops were preparing for an attack, for artillery shelling, the soldiers dug in securely, but in front of the destructive chlorine cloud they were completely unarmed. The deadly gas penetrated into all cracks and into all shelters. The results of the first chemical attack (and the first violation of the 1907 Hague Convention on the Non-Use of Toxic Substances!) were stunning: chlorine struck about 15 thousand people, and about 5 thousand died. And all this in order to level the 6 km long front line! Two months later, the Germans launched a chlorine attack on the eastern front. And two years later, Ypres increased its notoriety. During a difficult battle on July 12, 1917, a toxic substance, later called mustard gas, was used for the first time in the area of ​​this city. Mustard gas is a chlorine derivative, dichlorodiethyl sulfide.

We recall these episodes of history associated 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 chapter in the history of chlorine.

But it would be completely wrong to see chlorine only as a toxic substance and a raw material for the production of other toxic 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 remember 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 (5th century BC). Herodotus describes the mining of rock salt in Libya. In the oasis of Sinach in the center of the Libyan Desert there was the famous temple of the god Ammon-Ra. That is why Libya was called “Ammonia”, and the first name for rock salt was “sal ammoniacum”. Later, starting around the 13th 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 calcination with salt and clay. And one of the first descriptions of the purification of sodium chloride is found in the works 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 century, and in Europe in the 13th century. “Aqua regia” was known - a mixture of hydrochloric and nitric acids. In the book of the Dutchman Van Helmont, Hortus Medicinae, published in 1668, it is said 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 chlorine.

Chlorine was first described in detail by the Swedish chemist Scheele in his treatise on pyrolusite. While heating the mineral pyrolusite with hydrochloric acid, Scheele noticed an odor characteristic of aqua regia, collected and examined the yellow-green gas that gave rise to this odor, 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 “dephlogisticated hydrochloric acid.” In modern language, Scheele, and after him other scientists of that time, believed that the new gas was the oxide of hydrochloric acid.

Somewhat later, Bertholet and Lavoisier proposed to consider this gas an oxide of a certain new element “murium”. For three and a half decades, chemists tried unsuccessfully to isolate the unknown muria.

At first, Davy was also a supporter of “murium oxide,” 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 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 translated as salt), but this name did not catch on 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. Firstly, it is halogen; secondly, one of the most powerful 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 fiber, dyes and medicines; sixthly, the substance with which titanium and silicon, glycerin and fluoroplastic are obtained; seventh, a means for purifying drinking water and bleaching fabrics...

This list could be continued.

Under normal conditions, elemental chlorine is a rather heavy yellow-green gas with a strong, 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 mm Hg) 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 it hardens. At elevated pressures, chlorine can be liquefied and at higher temperatures up to +144°C. Chlorine is highly soluble in dichloroethane and some other chlorinated organic solvents.

Element No. 17 is very active; it combines directly with almost all elements of the periodic table. Therefore, in nature it is found only in the form of compounds. The most common minerals containing chlorine are 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 primarily their “fault” " (or "merit") that the chlorine content in the earth's crust is 0.20% by weight. Some relatively rare chlorine-containing minerals, for example horn silver AgCl, are very important for non-ferrous metallurgy.

In terms of electrical conductivity, liquid chlorine ranks among the strongest insulators: it conducts current almost a billion times worse than distilled water, and 10 22 times worse than silver.

The speed of sound in chlorine is approximately one and a half times less than in air.

And finally, about chlorine isotopes.

Nine isotopes of this element are now known, but only two are found in nature: chlorine-35 and chlorine-37. The first is about three times larger than the second.

The remaining seven isotopes are 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 produced?

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

Naturally, the main chlorine raw material is rock salt. If a chlorine plant is located near a river, then salt is delivered not by rail, but by barge - it’s 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 arrives at warehouses. Three six-month supplies of raw materials chlorine production, usually large-scale, are stored here.

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

In an aqueous solution, table 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 remove this extra electron. This happens in an electrolyzer on a positively charged electrode (anode). It is as if electrons are “sucked” 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 breaks down.

There are two types of technological design for the production of chlorine: diaphragm and mercury. In the first case, the cathode is a perforated iron sheet, and the cathode and anode spaces of the electrolyzer are separated by an asbestos diaphragm. At the iron cathode, hydrogen ions are discharged and an aqueous solution of sodium hydroxide is formed. If mercury is used as a cathode, then sodium ions are discharged on it and a 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 electrolysers.

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 especially aggressive. Subsequently, it is first cooled with cold water in high towers, lined with ceramic tiles on the inside and filled with ceramic packing (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 react.

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

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

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

One of many

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

The limited space of our article does not allow us to talk about all chlorine compounds, but without talking about at least some substances that require chlorine to be produced, 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 portion of the chlorine produced is consumed to obtain plant protection products.

One of the most important insecticides is hexachlorocyclohexane (often called hexachlorane). This substance was first synthesized back in 1825 by Faraday, but it found practical application only more than 100 years later in the 30s of our century.

Hexachlorane is now produced 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 chlorination reaction of benzene (C 6 H 6 + 3 Cl 2 → C 6 H 6 Cl 6) proceeds quite quickly.

Hexachlorane, 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. Hexachlorane is especially effective in treating seeds and in controlling pests 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 greater than the costs. Unfortunately, hexachlorane is not harmless to humans...

Polyvinyl chloride

If you ask any schoolchild to list the plastics known to him, he will be one of the first to name polyvinyl chloride (otherwise known as 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” onto 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 by 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 produce vinyl chloride - thermal cracking of dichloroethane.

CH 2 Cl CH 2 Cl → CH 2 = CHCl + HCl. The combination of these two methods is of interest when HCl, released during cracking of dichloroethane, is used in the production of vinyl chloride using the acetylene method.

Vinyl chloride is a colorless gas with a pleasant, somewhat intoxicating ethereal odor; it polymerizes easily. To obtain the polymer, liquid vinyl chloride is pumped under pressure into warm water, where it is crushed into tiny droplets. To prevent them from merging, a little gelatin or polyvinyl alcohol is added to the water, and in order for the polymerization reaction to begin to develop, a polymerization initiator - benzoyl peroxide - is added there. After a few hours, the droplets harden and a suspension of the polymer in water is formed. The polymer powder is separated using a filter or centrifuge.

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

We only talked about two substances that require element No. 17 to obtain. Just two out of many hundreds. There are many similar examples that can be given. And they all say that chlorine is not only a poisonous and dangerous gas, but a very important, very useful element.

Elementary calculation

When producing chlorine by electrolysis of a solution of table salt, hydrogen and sodium hydroxide are simultaneously obtained: 2NACl + 2H 2 O = 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, for example the conversion of natural gas... But caustic soda is produced almost exclusively by electrolysis of solutions of table salt; other methods account for less than 10%. Since the production of chlorine and NaOH is completely interrelated (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) for alkali , you can easily calculate how much chlorine it produces. Each ton of NaOH is “accompanied” by 890 kg of chlorine.

Well, lube!

Concentrated sulfuric acid is practically the only liquid that does not react with chlorine. Therefore, to compress and pump chlorine, factories use pumps in which sulfuric acid acts as a working fluid and at the same time as a lubricant.

Pseudonym of Friedrich Wöhler

Investigating the interaction of organic substances with chlorine, a French chemist of the 19th century. Jean Dumas made an amazing discovery: chlorine is able to replace hydrogen in the molecules of organic compounds. For example, when acetic acid is chlorinated, first one hydrogen of the methyl group is replaced by chlorine, then another, 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 electrochemical hypothesis and the Berzelius theory of radicals that were dominant at that time (in the words of the French chemist Laurent, the discovery of chloroacetic acid was like a meteor that destroyed the entire old school). Berzelius and his students and followers vigorously disputed the correctness of Dumas's work. A mocking letter from the famous German chemist Friedrich Wöhler under the pseudonym S.S.N. appeared in the German magazine Annalen der Chemie und Pharmacie. Windier (in German “Schwindler” means “liar”, “deceiver”). It reported that the author managed to replace all carbon atoms in fiber (C 6 H 10 O 5). hydrogen and oxygen into chlorine, and the properties of the fiber did not change. And now in London they make warm belly pads from cotton wool consisting... of pure chlorine.

Chlorine and water

Chlorine is noticeably 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 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, which is determined primarily by the structure of ice. In the crystal lattice of ice, H2O molecules can be arranged in such a way that regularly spaced voids appear between them. A cubic unit cell contains 46 water molecules, between which there are eight microscopic voids. It is in these voids that chlorine molecules settle. The exact formula of chlorine crystalline 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 severe coughing attacks. In case of chlorine poisoning, absolute rest is necessary; It is useful to inhale oxygen, or ammonia (sniffing ammonia), or alcohol vapor with ether. According to existing sanitary standards, the chlorine content 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. Thus, victims of hydrogen sulfide are given unstable bleach to smell. By interacting, the two poisons are mutually neutralized.

Chlorine test

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 using a solution of Na 2 S 2 O 3). To determine trace amounts 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) when oxidized with chlorine. For example, a colorless acidified solution of benzidine becomes yellow, and a neutral solution turns blue. The color intensity is proportional to the amount of chlorine.

_____________________________________

Currently, the “gold standard” of anodes for chlorine production are considered to be anodes made of titanium dioxide modified with oxides of platinum metals, primarily ruthenium dioxide RuO 2 . Ruthenium-titanium oxide anodes (ORTA) are known in 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 base. Despite the high cost, ORTA have undeniable advantages over graphite anodes:

Several times higher permissible current density makes it possible to reduce the size of the equipment;
- there are practically no anode corrosion products, which greatly simplifies the cleaning of the electrolyte;
- anodes have excellent corrosion resistance and can operate in industrial conditions for more than a year without replacement (repair).

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

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

The material for the manufacture of membranes for chlorine production is Nafion, an ionomer based on polytetrafluoroethylene with grafted perfluorovinyl sulfonic ether groups. This material, developed in the 60s of the last century by DuPont, is characterized by excellent chemical, thermal and mechanical resistance and satisfactory conductivity. To this day, it remains the material of choice when constructing many electrochemical installations (- editor's note).

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

How was this element discovered?

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

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

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

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

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

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

What is chlorine (Cl)

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

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

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

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

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

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

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

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

Characteristics of chlorine in the periodic system

Chlorine as a halogen

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

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

Properties of Cl as a non-metal

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

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

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

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

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

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

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

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

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

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

Effect of temperature on the state of aggregation of Cl

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

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

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

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

Where does Cl exist in nature?

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

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

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

Effect on the body

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

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

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

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

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

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

Human uses of Cl

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

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

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

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

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

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

How is chlorine produced?

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

• Chemical.
• Electrochemical.

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

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

Chlorine(from the Greek χλωρ?ς - “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. Indicated by the symbol Cl(lat. Chlorum). Chemically active non-metal. It is part of the group of halogens (originally the name “halogen” was used by the German chemist Schweiger for chlorine [literally, “halogen” is translated as salt), but it did not catch on, and subsequently became common for group VII of elements, which includes chlorine).

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

History of the discovery of chlorine

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

4HCl + MnO2 = Cl2 + MnCl2 + 2H2O

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

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

Distribution in nature

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

Physical and physico-chemical properties

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

Some physical properties of chlorine

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

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

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

Solubility

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

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

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

Chemical properties

Structure of the electron shell

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

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

Interaction with metals

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

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

Interaction with non-metals

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

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

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

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

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

Cl 2 + 3F 2 (ex.) → 2ClF 3

Other properties

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

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

When reacting with carbon monoxide, phosgene is formed:

Cl 2 + CO → COCl 2

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

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

Chlorination of dry calcium hydroxide produces bleach:

Cl 2 + Ca(OH) 2 → CaCl(OCl) + H 2 O

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

4NH 3 + 3Cl 2 → NCl 3 + 3NH 4 Cl

Oxidizing properties of chlorine

Chlorine is a very strong oxidizing agent.

Cl 2 + H 2 S → 2HCl + S

Reactions with organic substances

With saturated compounds:

CH 3 -CH 3 + Cl 2 → C 2 H 5 Cl + HCl

Attaches to unsaturated compounds via multiple bonds:

CH 2 =CH 2 + Cl 2 → Cl-CH 2 -CH 2 -Cl

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

C 6 H 6 + Cl 2 → C 6 H 5 Cl + HCl

Methods of obtaining

Industrial methods

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

MnO 2 + 4HCl → MnCl 2 + Cl 2 + 2H 2 O

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

4HCl + O 2 → 2H 2 O + 2Cl 2

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

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

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

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

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

Diaphragm method with solid cathode

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

Membrane method with solid cathode

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

Mercury method with liquid cathode

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

Laboratory methods

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

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

Chlorine storage

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

Chlorine Quality Standards

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

Application

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

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

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

Biological role

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

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

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

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

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

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

Features of operation and precautions

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

The maximum permissible concentrations of chlorine in atmospheric air are as follows: average daily - 0.03 mg/m³; maximum single dose - 0.1 mg/m³; in the working premises of an industrial enterprise - 1 mg/m³.