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 it for the first time in Europe firearms.) Ypres Hiroshima milestones on the path of turning the 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 rock salt mining 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.” Speaking 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 “muria oxide,” and in 1807 he decomposed electric shock table salt 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 is the main one 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 not delivered by railway, but on barges 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 cold water V high towers, lined with ceramic tiles on the inside and filled with a ceramic nozzle (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.
Hexachloran, like many other insecticides, is used in the form of dusts with fillers (talc, kaolin), or in the form of suspensions and emulsions, or, finally, in the form of aerosols. 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 when 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 pairs of alcohol 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 neutral 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 1960s by DuPont, has 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).
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 a dephlogisticated hydrochloric acid, that is, hydrochloric acid oxide. 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 (content in sea water 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 a temperature of −34 °C, chlorine also becomes liquid at normal temperatures. 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, for the production of chlorine, processes based on the oxidation of hydrogen chloride with strong oxidizing agents (for example, manganese (IV) oxide, potassium permanganate, potassium dichromate) are usually used:
2KMnO 4 + 16HCl → 2KCl + 2MnCl 2 + 5Cl 2 +8H 2 O K 2 Cr 2 O 7 + 14HCl → 3Cl 2 + 2KCl + 2CrCl 3 + 7H 2 O
Chlorine storage
The chlorine produced is stored in special “tanks” or pumped into high-pressure steel cylinders. Cylinders with liquid chlorine under pressure have a special color - swamp color. It should be noted that during prolonged use of chlorine cylinders, extremely explosive nitrogen trichloride accumulates in them, and therefore, from time to time, chlorine cylinders must undergo routine washing and cleaning of nitrogen chloride.
Chlorine Quality Standards
According to GOST 6718-93 “Liquid chlorine. Technical specifications" the following grades of chlorine are produced
Application
Chlorine is used in many industries, science and household needs:
- In the production of polyvinyl chloride, plastic compounds, synthetic rubber, from which they make: wire insulation, window profiles, packaging materials, clothing and shoes, linoleum and gramophone records, varnishes, equipment and foam plastics, toys, instrument parts, building materials. Polyvinyl chloride is produced by the polymerization of vinyl chloride, which today is most often produced from ethylene by the chlorine-balanced method through the intermediate 1,2-dichloroethane.
- The bleaching properties of chlorine have been known for a long time, although it is not chlorine itself that “bleaches,” but atomic oxygen, which is formed during the breakdown of hypochlorous acid: Cl 2 + H 2 O → HCl + HClO → 2HCl + O.. This method of bleaching fabrics, paper, cardboard has been used for several centuries.
- Production of organochlorine insecticides - substances that kill insects harmful to crops, but are safe for plants. A significant portion of the chlorine produced is consumed to obtain plant protection products. One of the most important insecticides is hexachlorocyclohexane (often called hexachlorane). This substance was first synthesized back in 1825 by Faraday, but it found practical application only more than 100 years later - in the 30s of the twentieth century.
- It was used as a chemical warfare agent, as well as for the production of other chemical warfare agents: mustard gas, phosgene.
- To disinfect water - “chlorination”. The most common method of disinfecting drinking water; is based on the ability of free chlorine and its compounds to inhibit the enzyme systems of microorganisms that catalyze redox processes. To disinfect drinking water, the following are used: chlorine, chlorine dioxide, chloramine and bleach. SanPiN 2.1.4.1074-01 establishes the following limits (corridor) of the permissible content of free residual chlorine in drinking water centralized water supply 0.3 - 0.5 mg/l. A number of scientists and even politicians in Russia criticize the very concept of chlorination of tap water, but cannot offer an alternative to the disinfecting aftereffect of chlorine compounds. The materials from which water pipes are made interact differently with chlorinated tap water. Free chlorine in tap water significantly reduces the service life of polyolefin-based pipelines: various types of polyethylene pipes, including cross-linked polyethylene, also known as PEX (PE-X). In the USA, to control the admission of pipelines made of polymer materials for use in water supply systems with chlorinated water, they were forced to adopt 3 standards: ASTM F2023 in relation to cross-linked polyethylene (PEX) pipes and hot chlorinated water, ASTM F2263 in relation to all polyethylene pipes and chlorinated water, and ASTM F2330 applied to multilayer (metal-polymer) pipes and hot chlorinated water. In terms of durability when interacting with chlorinated water, copper water pipes demonstrate positive results.
- Registered in the food industry as food additives 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. Baby receives required amount 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 have 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. For a short time, you can protect the respiratory organs from chlorine entering them with a cloth bandage moistened with a solution of sodium sulfite Na 2 SO 3 or sodium thiosulfate Na 2 S 2 O 3.
MPC of chlorine atmospheric air the following: average daily - 0.03 mg/m³; maximum single dose - 0.1 mg/m³; in the working premises of an industrial enterprise - 1 mg/m³.
DEFINITION
Chlorine– 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. Easily soluble in water, in to a large extent undergoes 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. |
The physical properties of chlorine are considered: the density of chlorine, its thermal conductivity, specific heat and dynamic viscosity at various temperatures. The physical properties of Cl 2 are presented in the form of tables for the liquid, solid and gaseous states of this halogen.
Basic physical properties of chlorine
Chlorine is included in group VII of the third period of the periodic table of elements at number 17. It belongs to the subgroup of halogens, has relative atomic and molecular masses of 35.453 and 70.906, respectively. At temperatures above -30°C, chlorine is a greenish-yellow gas with a characteristic strong, irritating odor. It liquefies easily under normal pressure (1.013·10 5 Pa) when cooled to -34°C, and forms a clear amber liquid that solidifies at -101°C.
Due to its high chemical activity, free chlorine does not occur in nature, but exists only in the form of compounds. It is found mainly in the mineral halite (), and is also part of such minerals as sylvite (KCl), carnallite (KCl MgCl 2 6H 2 O) and sylvinite (KCl NaCl). The chlorine content in the earth's crust approaches 0.02% of the total number of atoms of the earth's crust, where it is found in the form of two isotopes 35 Cl and 37 Cl in a percentage ratio of 75.77% 35 Cl and 24.23% 37 Cl.
| Property | Meaning |
|---|---|
| Melting point, °C | -100,5 |
| Boiling point, °C | -30,04 |
| Critical temperature, °C | 144 |
| Critical pressure, Pa | 77.1 10 5 |
| Critical density, kg/m 3 | 573 |
| Gas density (at 0°C and 1.013 10 5 Pa), kg/m 3 | 3,214 |
| Saturated steam density (at 0°C and 3.664 10 5 Pa), kg/m 3 | 12,08 |
| Density of liquid chlorine (at 0°C and 3.664 10 5 Pa), kg/m 3 | 1468 |
| Density of liquid chlorine (at 15.6°C and 6.08 10 5 Pa), kg/m 3 | 1422 |
| Density of solid chlorine (at -102°C), kg/m 3 | 1900 |
| Relative density of gas in air (at 0°C and 1.013 10 5 Pa) | 2,482 |
| Relative density of saturated steam in air (at 0°C and 3.664 10 5 Pa) | 9,337 |
| Relative density of liquid chlorine at 0°C (relative to water at 4°C) | 1,468 |
| Specific volume of gas (at 0°C and 1.013 10 5 Pa), m 3 /kg | 0,3116 |
| Specific volume of saturated steam (at 0°C and 3.664 10 5 Pa), m 3 /kg | 0,0828 |
| Specific volume of liquid chlorine (at 0°C and 3.664 10 5 Pa), m 3 /kg | 0,00068 |
| Chlorine vapor pressure at 0°C, Pa | 3.664 10 5 |
| Dynamic viscosity of gas at 20°C, 10 -3 Pa s | 0,013 |
| Dynamic viscosity of liquid chlorine at 20°C, 10 -3 Pa s | 0,345 |
| Heat of fusion of solid chlorine (at melting point), kJ/kg | 90,3 |
| Heat of vaporization (at boiling point), kJ/kg | 288 |
| Heat of sublimation (at melting point), kJ/mol | 29,16 |
| Molar heat capacity C p of gas (at -73…5727°C), J/(mol K) | 31,7…40,6 |
| Molar heat capacity C p of liquid chlorine (at -101…-34°C), J/(mol K) | 67,1…65,7 |
| Gas thermal conductivity coefficient at 0°C, W/(m K) | 0,008 |
| Thermal conductivity coefficient of liquid chlorine at 30°C, W/(m K) | 0,62 |
| Gas enthalpy, kJ/kg | 1,377 |
| Enthalpy of saturated steam, kJ/kg | 1,306 |
| Enthalpy of liquid chlorine, kJ/kg | 0,879 |
| Refractive index at 14°C | 1,367 |
| Specific electrical conductivity at -70°С, S/m | 10 -18 |
| Electron affinity, kJ/mol | 357 |
| Ionization energy, kJ/mol | 1260 |
Chlorine Density
Under normal conditions, chlorine is a heavy gas with a density approximately 2.5 times higher. Density of gaseous and liquid chlorine under normal conditions (at 0°C) is equal to 3.214 and 1468 kg/m3, respectively. When liquid or gaseous chlorine is heated, its density decreases due to an increase in volume due to thermal expansion.
Density of chlorine gas
The table shows the density of chlorine in the gaseous state at various temperatures (ranging from -30 to 140°C) and normal atmospheric pressure (1.013·10 5 Pa). The density of chlorine changes with temperature - it decreases when heated. For example, at 20°C the density of chlorine is 2.985 kg/m3, and when the temperature of this gas increases to 100°C, the density value decreases to a value of 2.328 kg/m 3.
| t, °С | ρ, kg/m 3 | t, °С | ρ, kg/m 3 |
|---|---|---|---|
| -30 | 3,722 | 60 | 2,616 |
| -20 | 3,502 | 70 | 2,538 |
| -10 | 3,347 | 80 | 2,464 |
| 0 | 3,214 | 90 | 2,394 |
| 10 | 3,095 | 100 | 2,328 |
| 20 | 2,985 | 110 | 2,266 |
| 30 | 2,884 | 120 | 2,207 |
| 40 | 2,789 | 130 | 2,15 |
| 50 | 2,7 | 140 | 2,097 |
As pressure increases, the density of chlorine increases. The tables below show the density of chlorine gas in the temperature range from -40 to 140°C and pressure from 26.6·10 5 to 213·10 5 Pa. With increasing pressure, the density of chlorine in the gaseous state increases proportionally. For example, an increase in chlorine pressure from 53.2·10 5 to 106.4·10 5 Pa at a temperature of 10°C leads to a twofold increase in the density of this gas.
| ↓ t, °С | P, kPa → | 26,6 | 53,2 | 79,8 | 101,3 |
|---|---|---|---|---|
| -40 | 0,9819 | 1,996 | — | — |
| -30 | 0,9402 | 1,896 | 2,885 | 3,722 |
| -20 | 0,9024 | 1,815 | 2,743 | 3,502 |
| -10 | 0,8678 | 1,743 | 2,629 | 3,347 |
| 0 | 0,8358 | 1,678 | 2,528 | 3,214 |
| 10 | 0,8061 | 1,618 | 2,435 | 3,095 |
| 20 | 0,7783 | 1,563 | 2,35 | 2,985 |
| 30 | 0,7524 | 1,509 | 2,271 | 2,884 |
| 40 | 0,7282 | 1,46 | 2,197 | 2,789 |
| 50 | 0,7055 | 1,415 | 2,127 | 2,7 |
| 60 | 0,6842 | 1,371 | 2,062 | 2,616 |
| 70 | 0,6641 | 1,331 | 2 | 2,538 |
| 80 | 0,6451 | 1,292 | 1,942 | 2,464 |
| 90 | 0,6272 | 1,256 | 1,888 | 2,394 |
| 100 | 0,6103 | 1,222 | 1,836 | 2,328 |
| 110 | 0,5943 | 1,19 | 1,787 | 2,266 |
| 120 | 0,579 | 1,159 | 1,741 | 2,207 |
| 130 | 0,5646 | 1,13 | 1,697 | 2,15 |
| 140 | 0,5508 | 1,102 | 1,655 | 2,097 |
| ↓ t, °С | P, kPa → | 133 | 160 | 186 | 213 |
|---|---|---|---|---|
| -20 | 4,695 | 5,768 | — | — |
| -10 | 4,446 | 5,389 | 6,366 | 7,389 |
| 0 | 4,255 | 5,138 | 6,036 | 6,954 |
| 10 | 4,092 | 4,933 | 5,783 | 6,645 |
| 20 | 3,945 | 4,751 | 5,565 | 6,385 |
| 30 | 3,809 | 4,585 | 5,367 | 6,154 |
| 40 | 3,682 | 4,431 | 5,184 | 5,942 |
| 50 | 3,563 | 4,287 | 5,014 | 5,745 |
| 60 | 3,452 | 4,151 | 4,855 | 5,561 |
| 70 | 3,347 | 4,025 | 4,705 | 5,388 |
| 80 | 3,248 | 3,905 | 4,564 | 5,225 |
| 90 | 3,156 | 3,793 | 4,432 | 5,073 |
| 100 | 3,068 | 3,687 | 4,307 | 4,929 |
| 110 | 2,985 | 3,587 | 4,189 | 4,793 |
| 120 | 2,907 | 3,492 | 4,078 | 4,665 |
| 130 | 2,832 | 3,397 | 3,972 | 4,543 |
| 140 | 2,761 | 3,319 | 3,87 | 4,426 |
Density of liquid chlorine
Liquid chlorine can exist in a relatively narrow temperature range, the boundaries of which lie from minus 100.5 to plus 144 ° C (that is, from the melting point to the critical temperature). Above a temperature of 144°C, chlorine will not turn into a liquid state under any pressure. The density of liquid chlorine in this temperature range varies from 1717 to 573 kg/m3.
| t, °С | ρ, kg/m 3 | t, °С | ρ, kg/m 3 |
|---|---|---|---|
| -100 | 1717 | 30 | 1377 |
| -90 | 1694 | 40 | 1344 |
| -80 | 1673 | 50 | 1310 |
| -70 | 1646 | 60 | 1275 |
| -60 | 1622 | 70 | 1240 |
| -50 | 1598 | 80 | 1199 |
| -40 | 1574 | 90 | 1156 |
| -30 | 1550 | 100 | 1109 |
| -20 | 1524 | 110 | 1059 |
| -10 | 1496 | 120 | 998 |
| 0 | 1468 | 130 | 920 |
| 10 | 1438 | 140 | 750 |
| 20 | 1408 | 144 | 573 |
Specific heat capacity of chlorine
Specific heat chlorine gas C p in kJ/(kg K) in the temperature range from 0 to 1200°C and normal atmospheric pressure can be calculated using the formula:
where T is the absolute temperature of chlorine in degrees Kelvin.
It should be noted that under normal conditions the specific heat capacity of chlorine is 471 J/(kg K) and increases when heated. The increase in heat capacity at temperatures above 500°C becomes insignificant, and at high temperatures the specific heat of chlorine remains virtually unchanged.
The table shows the results of calculating the specific heat of chlorine using the above formula (the calculation error is about 1%).
| t, °С | C p , J/(kg K) | t, °С | C p , J/(kg K) |
|---|---|---|---|
| 0 | 471 | 250 | 506 |
| 10 | 474 | 300 | 508 |
| 20 | 477 | 350 | 510 |
| 30 | 480 | 400 | 511 |
| 40 | 482 | 450 | 512 |
| 50 | 485 | 500 | 513 |
| 60 | 487 | 550 | 514 |
| 70 | 488 | 600 | 514 |
| 80 | 490 | 650 | 515 |
| 90 | 492 | 700 | 515 |
| 100 | 493 | 750 | 515 |
| 110 | 494 | 800 | 516 |
| 120 | 496 | 850 | 516 |
| 130 | 497 | 900 | 516 |
| 140 | 498 | 950 | 516 |
| 150 | 499 | 1000 | 517 |
| 200 | 503 | 1100 | 517 |
At temperatures close to absolute zero, chlorine is in a solid state and has a low specific heat capacity (19 J/(kg K)). As the temperature of solid Cl 2 increases, its heat capacity increases and reaches a value of 720 J/(kg K) at minus 143°C.
Liquid chlorine has a specific heat capacity of 918...949 J/(kg K) in the range from 0 to -90 degrees Celsius. According to the table, it can be seen that the specific heat capacity of liquid chlorine is higher than that of gaseous chlorine and decreases with increasing temperature.
Thermal conductivity of chlorine
The table shows the values of the thermal conductivity coefficients of chlorine gas at normal atmospheric pressure in the temperature range from -70 to 400°C.
The thermal conductivity coefficient of chlorine under normal conditions is 0.0079 W/(m deg), which is 3 times less than at the same temperature and pressure. Heating chlorine leads to an increase in its thermal conductivity. Thus, at a temperature of 100°C, the value of this physical property of chlorine increases to 0.0114 W/(m deg).
| t, °С | λ, W/(m deg) | t, °С | λ, W/(m deg) |
|---|---|---|---|
| -70 | 0,0054 | 50 | 0,0096 |
| -60 | 0,0058 | 60 | 0,01 |
| -50 | 0,0062 | 70 | 0,0104 |
| -40 | 0,0065 | 80 | 0,0107 |
| -30 | 0,0068 | 90 | 0,0111 |
| -20 | 0,0072 | 100 | 0,0114 |
| -10 | 0,0076 | 150 | 0,0133 |
| 0 | 0,0079 | 200 | 0,0149 |
| 10 | 0,0082 | 250 | 0,0165 |
| 20 | 0,0086 | 300 | 0,018 |
| 30 | 0,009 | 350 | 0,0195 |
| 40 | 0,0093 | 400 | 0,0207 |
Chlorine viscosity
The coefficient of dynamic viscosity of gaseous chlorine in the temperature range 20...500°C can be approximately calculated using the formula:
where η T is the coefficient of dynamic viscosity of chlorine at a given temperature T, K;
η T 0 - coefficient of dynamic viscosity of chlorine at temperature T 0 = 273 K (at normal conditions);
C is the Sutherland constant (for chlorine C = 351).
Under normal conditions, the dynamic viscosity of chlorine is 0.0123·10 -3 Pa·s. When heated, this physical property chlorine, as a viscosity, takes on higher values.
Liquid chlorine has a viscosity an order of magnitude higher than gaseous chlorine. For example, at a temperature of 20°C, the dynamic viscosity of liquid chlorine has a value of 0.345·10 -3 Pa·s and decreases with increasing temperature.
Sources:
- Barkov S. A. Halogens and the manganese subgroup. Elements of group VII of the periodic table of D. I. Mendeleev. A manual for students. M.: Education, 1976 - 112 p.
- Tables of physical quantities. Directory. Ed. acad. I. K. Kikoina. M.: Atomizdat, 1976 - 1008 p.
- Yakimenko L. M., Pasmanik M. I. Handbook on the production of chlorine, caustic soda and basic chlorine products. Ed. 2nd, per. and others. M.: Chemistry, 1976 - 440 p.
Chlorine 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. Thus, no one has been able to obtain carbon dioxide by heating chlorine with coal (which, at high temperatures, “takes away” oxygen from many compounds containing it). As a result of similar experiments carried out by 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 side effect occurs: a buzzing sound is heard. 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 to bleach pulp and disinfect 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 – 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. Of the salts of oxygen acids, hypochlorites are used in practical use, 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. Maximum permissible in air industrial enterprises the concentration is considered to be 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 into the 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, 264 tons of a mixture of chlorine and much more toxic phosgene (carbonic acid chloride COCl 2) were released from 12 thousand cylinders. 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
