Chlorine was probably 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 Hahn), molybdenum, tungsten, chlorine, and independently of other chemists (albeit later) - three more: oxygen, hydrogen and nitrogen. This achievement could not be repeated by any chemist subsequently. At the same time, Scheele, already elected as 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 the post of 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 eat.”
Numerous chlorine compounds were known, of course, long before Scheele. This element is part of many salts, including the most famous - table salt. In 1774, Scheele isolated chlorine in free form by heating the black mineral pyrolusite with concentrated hydrochloric acid: MnO 2 + 4HCl ® Cl 2 + MnCl 2 + 2H 2 O.
At first, chemists considered chlorine not as an element, but as a chemical compound of the unknown element muria (from the Latin muria - brine) with oxygen. It was believed that hydrochloric acid (it was called muric acid) contains chemically bound oxygen. This was “testified”, in particular, by the following fact: when a chlorine solution stood in the light, oxygen was released from it, and hydrochloric acid remained in the solution. However, numerous attempts to “tear” oxygen from chlorine led nowhere. So, no one managed to get carbon dioxide, 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 Humphry Davy, Joseph Louis Gay-Lussac and Louis Jacques Thenard, it became clear that chlorine does not contain oxygen and is a simple substance. The experiments of Gay-Lussac, who analyzed the quantitative ratio of gases in the reaction of chlorine with hydrogen, led to the same conclusion.
In 1811, Davy proposed the name “chlorin” for the new element - from the Greek. "chloros" - yellow-green. This is exactly the color of chlorine. 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 still the British (and Americans) call this element “chlorine”, while the French call it chlore. The Germans, the “legislators” of chemistry throughout almost the entire 19th century, also adopted the abbreviated name. (in German chlorine is Chlor). In 1811, the German physicist Johann Schweiger proposed the name “halogen” for chlorine (from the Greek “hals” - salt, and “gennao” - 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.
The demonstration of hydrogen combustion in a chlorine atmosphere is interesting: sometimes during the experiment an unusual phenomenon occurs by-effect: There is a buzzing sound. Most often, the flame hums when a thin tube through which hydrogen is supplied is lowered into a cone-shaped vessel filled with chlorine; the same is true for spherical flasks, but in cylinders the flame usually does not hum. This phenomenon was called the “singing flame.”
In an aqueous solution, chlorine reacts partially and rather slowly with water; at 25° C, equilibrium: Cl 2 + H 2 O HClO + HCl is established within two days. Hypochlorous acid decomposes in light: HClO ® HCl + O. It is atomic oxygen that is credited with the bleaching effect (absolutely dry chlorine does not have this 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 - yellow-orange gas, ClO 2 - yellow gas (below 9.7 o C - 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 – colorless, very explosive liquid. At low temperatures, unstable oxides Cl 2 O 3 and ClO 3 were obtained. ClO 2 oxide is produced on an industrial scale and is used instead of chlorine for pulp bleaching and disinfection drinking water and wastewater. 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 obtained red salt from yellow blood salt by oxidation with chlorine: 2K 4 + Cl 2 ® K 3 + 2KCl. Chlorine easily oxidizes bromides and chlorides, releasing bromine and iodine in free form.
Chlorine in different oxidation states forms a number of acids: HCl - hydrochloric (hydrochloric, salts - chlorides), HClO - hypochlorous (salts - hypochlorites), HClO 2 - chlorous (salts - chlorites), HClO 3 - hypochlorous (salts - chlorates), HClO 4 – chlorine (salts – perchlorates). Of the oxygen acids, only perchloric acid is stable in its pure form. From salts of oxygen acids practical use have hypochlorites, sodium chlorite NaClO 2 - for bleaching fabrics, for the manufacture of compact pyrotechnic oxygen sources (“oxygen candles”), potassium chlorates (Bertholometa salt), calcium and magnesium (for pest control Agriculture, 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 fuels.
Chlorine reacts with many organic compounds. It quickly attaches to unsaturated compounds with double and triple carbon-carbon bonds (the reaction with acetylene proceeds explosively), 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 played a significant role in the history of organic chemistry. In the 1840s, the French chemist Jean Baptiste Dumas discovered that when chlorine reacts with acetic acid, the reaction occurs with amazing ease
CH 3 COOH + Cl 2 ® CH 2 ClCOOH + HCl. With an excess of chlorine, trichloroacetic acid CCl 3 COOH is formed. However, many chemists were distrustful of Dumas' work. 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 outstanding chemists, among whom were Friedrich Wöhler, Justus Liebig and, of course, Berzelius himself.
To ridicule Dumas, Wöhler handed over to his friend Liebig an article on behalf of a certain S. Windler (Schwindler - in German a fraudster) about a new successful application of the reaction allegedly discovered by Dumas. In the article, Wöhler wrote with obvious mockery about how in manganese acetate Mn(CH 3 COO) 2 it was possible to replace all the elements, according to their valence, with chlorine, resulting in a yellow crystalline substance consisting of only chlorine. 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 at the same time things retain their appearance. In a footnote it was stated that London shops were selling a brisk trade in material consisting of chlorine alone, as this material was 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 the 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 and many dyes. This was used back in the 18th century. for bleaching fabrics.
Chlorine as a poisonous gas.
Scheele, who received chlorine, noted a very unpleasant strong odor, difficulty breathing and coughing. As we 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 has an irritating effect on the respiratory tract, destroying the cells of the mucous membrane of the respiratory tract and lungs. A 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 becomes 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.
St. Petersburg academician Toviy Egorovich 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 suffered excruciating chest pain for eight days. Fortunately, he recovered. The famous English chemist Davy almost died from chlorine poisoning. Experiments with even small amounts of chlorine are dangerous, as they can cause severe lung damage. They say 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 the next demonstration, please take me out to Fresh air. But, unfortunately, the lecture will have to be interrupted.” If you release a lot of chlorine into the air, it becomes a real disaster. This was experienced by the Anglo-French troops during the First World War. 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, on a small six-kilometer section of the front near the Belgian town of Ypres, the valves of 5,730 cylinders were simultaneously opened, each containing 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 thousand people were poisoned, 5 thousand of them to death. A month later, on May 31, the Germans repeated the gas attack on the eastern front - against Russian troops. This happened in Poland near the city of Bolimova. At the 12 km front, out of 12 thousand cylinders, 264 tons of a mixture of chlorine and much more toxic phosgene (acid chloride) were released carbonic acid COCl 2). The tsarist command knew about what happened at Ypres, and yet the Russian soldiers had no means of defense! As a result of the gas attack, the losses amounted to 9,146 people, of which only 108 were as a result of rifle and artillery shelling, the rest were poisoned. At the same time, 1,183 people died almost immediately.
Soon, chemists showed 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 thiosulfate solution, 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 diluted aqueous solution is much less dangerous than poisonous chlorine. Therefore, in those years, thiosulfate had another name - “antichlor”, but the first thiosulfate gas masks were not very effective.
In 1916, the Russian chemist and future academician Nikolai Dmitrievich Zelinsky invented a truly effective gas mask, in which toxic substances were retained by a layer of activated carbon. Such coal with a very developed surface could retain significantly more chlorine than gauze soaked in hyposulfite. Fortunately, the “chlorine attacks” remained only a tragic episode in history. After the World War, chlorine had only peaceful professions left.
Use of chlorine.
Every year, huge amounts of chlorine are produced worldwide – tens of millions of tons. Only in the USA by the end of the 20th century. About 12 million tons of chlorine were produced annually by electrolysis (10th place among chemical production). The bulk of it (up to 50%) is spent on the chlorination of organic compounds - to produce solvents, synthetic rubber, polyvinyl chloride and other plastics, chloroprene rubber, pesticides, medicines, many other necessary and healthy products. The rest is consumed for the synthesis of inorganic chlorides, in the pulp and paper industry for bleaching wood pulp, and for water purification. Chlorine is used in relatively small quantities 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 is obtained. Chlorine is also used for the production of bleaching agents (hypochlorites, bleach) and water disinfection by chlorination.
Ilya Leenson
· Isotopic composition · Physical and chemical properties · Chemical properties · Preparation methods · Chlorine storage · Chlorine quality standards · Application · Biological role · Toxicity · Literature · Related articles · Comments · Notes · Official website ·
Chlorine is used in many industries, science and household needs:
The main component of bleaches is Labarraco water (sodium hypochlorite)
- In the production of polyvinyl chloride, plastic compounds, synthetic rubber, from which they are made: insulation for wires, window profiles, packaging materials, clothes and shoes, linoleum and records, varnishes, equipment and foam plastics, toys, instrument parts, Construction Materials. Polyvinyl chloride is produced by the polymerization of vinyl chloride, which today is 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, despite the fact that it is not chlorine itself that “bleaches,” but atomic oxygen, which is formed during the decomposition of hypochlorous acid: Cl 2 + H 2 O → HCl + HClO → 2HCl + O. This method of bleaching fabrics, paper, and 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, and in addition 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 tap water. An alternative is ozonation. Materials from which they are made water pipes, interact differently with chlorinated tap water. Free chlorine in tap water significantly reduces the service life of pipelines based on polyolefins: polyethylene pipes various types, including cross-linked polyethylene, 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 pipes made of cross-linked polyethylene (PEX) and hot chlorinated water, ASTM F2263 in relation to polyethylene pipes all and chlorinated water and ASTM F2330 as 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, berthollet salt, metal chlorides, poisons, drugs, fertilizers.
- In metallurgy for the production of pure metals: titanium, tin, tantalum, niobium.
- As an indicator of solar neutrinos in chlorine-argon detectors.
Many the developed countries strive to limit the use of chlorine in everyday life, including because when burning chlorine-containing waste, a significant amount of dioxins is formed.
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) at normal conditions- 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 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 (content in sea water 19 g/l). Chlorine accounts for 0.025% of total number atoms of the earth's crust, the clarke number of chlorine is 0.017%, and human body contains 0.25% chlorine ions by weight. In the human and animal bodies, chlorine is found mainly in intercellular fluids (including blood) and plays important role in the regulation of osmotic processes, as well as in processes associated with the work of nerve cells.
Physical and physico-chemical properties
Under normal conditions, chlorine is a yellow-green gas with a suffocating odor. Some of it 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 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. 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 during the First World War. world war. When working with chlorine, you should use protective clothing, a gas mask, and gloves. On a short time You can protect your respiratory organs from chlorine getting into them with a cloth bandage moistened with a solution of sodium sulfite Na 2 SO 3 or sodium thiosulfate Na 2 S 2 O 3 .
The maximum permissible concentrations of chlorine in atmospheric air are as follows: average daily - 0.03 mg/m³; maximum single dose - 0.1 mg/m³; in work areas industrial enterprise— 1 mg/m³.
| are present in sea water, but in such small quantities that their direct isolation from water is very difficult. However, there are some algae that accumulate iodine in their tissues, such as kelp. The ash of these algae serves as a raw material for the production of iodine. A significant amount of iodine (from 10 to 50 mg/l.) is contained in underground drilling waters. The iodine content in the earth's crust is 4*10-6% atoms. There are minor deposits of iodine salts - KIO 3 and KIO 4 - in Chile and Bolivia. | total weight | astata | on the globe, according to estimates, does not exceed 30 g. Table. Electronic structure and some properties of halogen atoms and molecules | Element symbol | F |
| Cl | |||||
| Br | I | At | Serial number | Structure of the outer electronic layer | 2s 2 2p 5 |
| 3s 2 3p 5 | 4,0 | 3,0 | 2,8 | 2,5 | ~2,2 |
| 4s 2 4p 5 | 0,064 | 0,099 | 0,114 | 0,133 | – |
| 5s 2 5p 5 | -1 | -1, +1, +3, +5, +7 | – | ||
| 6s 2 6p 5 | Relative electronegativity (RE) | Atomic radius, nm | Oxidation states | State of aggregation | Pale green gas |
| Green-yellow. gas | -219 | -101 | -8 | ||
| Brown liquid | -183 | -34 | |||
| Dark violet crystals | 1,51 | 1,57 | 3,14 | 4,93 | – |
| Black crystals | t°pl.(°C) | boiling temperature (°C) | 3,5 | 0,02 | – |
ρ (g/cm3)
Solubility in water (g/100 g water)
reacts with water
(Chlorum; from Greek - yellow-green), Cl - chemical. element of group VII of the periodic system of elements; at. n. 17, at. m. 35.453. Yellow-green gas with a pungent odor. In compounds it exhibits oxidation states - 1, + 1, +3, + 5 and + 7. The most stable compounds are X. with extreme oxidation states: - 1 and + 7. Natural X. consists of the isotopes 35Cl (75.53%) and 37Сl (24.47%). There are seven known radioactive isotopes with mass numbers 32-40 and two isomers; the longest-lived isotope 36Cl with a half-life of 3.08 x 10 5 years (beta decay, electron capture). X. was discovered in 1774 by the Swede, chemist K. Scheele, and isolated in 1810 by the English. chemist G. Davy.
The chlorine content in the earth's crust is 4.5 x 10-2%. There is ch. arr. in sea water (up to 2% chlorides), in the form of deposits of rock salt NaCl, sylvite, carnallite, bischofite MgCl2x6H20 and kainite KMg 3H20. Basic physical constants of elemental X. melting point -101.6° C; boiling point - 34.6° C; density of liquid X. (at boiling point) 1.56 g/cm3; heat of fusion 1.62 kcal/mol; heat of evaporation (at boiling point) 4.42 kcal/mol. X. combines directly with most non-metals (except carbon)
The dependence of the stress of the onset and propagation of brittle fracture on temperature, characterizing the cold resistance of structural steels according to critical temperatures: 1 - yield strength; 2 - occurrence of destruction; h - propagation of destruction; t > t1 - area of ductile destruction; t2< t < t1, - область квазихрупких разрушений; t < t2-область хрупких разрушений. да, азота и кислорода)и с подавляющим большинством металлов.
Sometimes chlorine reacts with metals in the presence of traces of moisture. Dry chlorine does not interact with iron, which allows it to be stored in steel cylinders. Above the temperature of 540° C in relation to X., not a single metal is resistant (at this temperature, the most resistant to gaseous X. high-nickel alloys such as Inconel begin to corrode). Soluble in water (2 volumes per 1 volume of water at a temperature of 25 ° C), partially hydrolyzing to form a solution of hypochlorous and hydrochloric acid. Of the compounds of X. with non-metals, the most important is HCl chloride, which is formed through direct interaction (in the light) of Chlorine with hydrogen or under the influence of strong minerals, acids (for example, H2SO4) on metal compounds with chlorine (for example, NaCl), and is also a by-product when obtaining plural. organochlorine compounds. Chloride is a colorless gas, in a dry state it does not interact with most metals and their oxides. It dissolves very well in water (426 volumes of HCl in 1 volume of water at a temperature of 25° C), forming a hydrochloric acid.
Hydrochloric acid, being very strong, interacts with all electronegative metals (standing in the electrochemical series of voltages higher than hydrogen). In non-aqueous solutions of hydrogen chloride (for example, in acetonitrile), certain electropositive substances (for example, ) can also corrode. Chlorine does not interact directly with oxygen. Cl20, ClO2, Cl206 and Cl207 can be obtained indirectly, which correspond to the acids HClO - hypochlorous (salts - hypochlorites), HClO2 - chloride (salts -), HClO3 - hypochlorous (salts - chlorates) and HClO4 - perchloric (salts - perchlorates). Hypochlorous and chloride compounds are unstable and exist only in dilute aqueous solutions. All chlorines are strong oxidizing agents.
Oxidative ability to do and their salts decrease, and their strength increases from hypochlorous to chloric. The most commonly used oxidizing agents are calcium chlorite Ca(OCl)2, bertholite salt KClO3 and bleach Ca2OCl2 - double salt of hydrochloric and hypochlorous acid. Chlorine combines with other halogens to form interhalogen compounds: ClF, ClF3, BrCl, IСl and IC3. According to chemistry Holy compounds of elements with chlorine () are divided into salt-like, acid chlorides and non-salt-like neutral. Salt-like chlorides include compounds with chlorine of metals I, II and IIIa of subgroups of the periodic system of elements, as well as compounds with X. metals of other groups in lower oxidation states. Most salt-like chlorides melt at tall tits and are highly soluble in water with few exceptions (eg AgCl).
Salt-like substances in the molten state conduct current relatively well (their conductivity at a temperature of 800 ° C is LiCl - 2.17; NaCl - 3.57; KCl - 2.20 ohm -1 cb -1). Acid chlorides include chlorides of non-metals (for example, boron, silicon, phosphorus) and chlorides of metals of subgroup IIIb and groups IV-VIII of the periodic system in higher degrees oxidation. Acid chlorides, when interacting with water, form the corresponding acid and release chloride. A non-salt neutral chloride is, for example, CCl4 tetrachloride. Basic prom. method of obtaining X.-solutions of NaCl or HCl (graphite or titanium anodes). Chlorine is very toxic, the maximum permissible content of free X. in the air is 0.001 mg/l. Chlorine is the most practically important of the halogens; it is used for bleaching fabrics and paper, disinfecting drinking water, for producing hydrochloric acid, in organic synthesis, in the production and purification of many metals using chlorine metallurgy methods. Hypochlorites are also used as bleaching and disinfectants, in pyrotechnics and match production, and perchlorates are used as a component of solid rocket fuels.
Chlorine is
Chlorine gas is yellow-green in color. It is poisonous, has a sharp, suffocating, unpleasant odor. Chlorine is heavier than air and dissolves relatively well in water (for 1 volume of water, 2 volumes of chlorine), forming chlorine water; Cl 2 aqi turns into liquid at a temperature of -34 °C, and hardens at -101 °C. Density 1.568 g/cm³
Cl - as a substance was used during the First World War as a chemical warfare agent, because it is heavier than air and is well retained above the surface of the earth. The maximum permissible concentration of free chlorine in the air is 0.001 mg/l.
Chronic chlorine poisoning causes changes in complexion, pulmonary and bronchial diseases. In case of chlorine poisoning, a mixture of alcohol vapor with ether or water vapor mixed with ammonia should be used as an antidote.
In small quantities, chlorine can cure diseases of the upper respiratory tract, as it has a detrimental effect on bacteria. Due to its disinfectant effect, chlorine is used to disinfect hydrogen water.
As salts they are vital elements. Chlorine in the form of table salt is constantly used in food and is also included in green plants- chlorophyll.
The interaction of chlorine with hydrogen occurs explosively only in the light:
Cl 2 + H 2 = 2HCl
2Na + Cl2 = 2NaCl
This is the basis for increasing the percentage of noble metals in low-grade alloys; for this, pre-crushed material is heated in the presence of freely passing chlorine.
If metals can have different oxidation states, when reacting with chlorine they exhibit the highest:
2Fe + 3Cl 2 = 2FeCl 3
Cu + Cl 2 = CuCl 2
Interaction of chlorine with complex substances
When chlorine interacts with complex substances, it behaves like, for example, when interacting with water. At first, the halogen dissolves in water to form chlorine water (Claq), and then gradually a reaction begins between water and chlorine:
Cl2 + H 2 O = 2HCl + [O]
However, this reaction does not proceed immediately to the formation of the final products. At the first stage of the process, two acids are formed - hydrochloric HCl and hypochlorous (this mixture of acids is dissolved)
Cl 2 + H 2 O = HCl + HClO
Hypochlorous acid then decomposes:
HClO = HCl + [O]
Atomic formationoxygen largely explains the oxidizing effect of chlorine. Organic dyes placed in chlorine water become discolored. Testing for litmus does not acquire its characteristic color in acid, but completely loses it. This is explained by the presence of atomic oxygen, which has an oxidizing effect on litmus.
Halogens also react with organic substances
If you introduce a piece of paper soaked in turpentine (an organic substance consisting of hydrogen and carbon) into a chlorine atmosphere, you will notice the release of a large amount of soot and the smell of hydrogen chloride, sometimes the reaction proceeds with ignition. This is explained by the fact that chlorine displaces from compounds with hydrogen and forms hydrogen chloride, and is released in the form of soot in a free state. This is why rubber products are not used.