Chlorine in nature. Physical and chemical properties of chlorine. Chlorine methods for producing chlorine
In 1774, Karl Scheele, a chemist from Sweden, first obtained chlorine, but it was believed that it was not a separate element, but a type of hydrochloric acid (calorizator). Elemental chlorine was obtained at the beginning of the 19th century by G. Davy, who decomposed table salt into chlorine and sodium by electrolysis.
Chlorine (from the Greek χλωρός - green) is an element of group XVII of the periodic table of chemical elements D.I. Mendeleev, has atomic number 17 and atomic mass 35.452. The accepted designation Cl (from the Latin Chlorum).
Being in nature
Chlorine is the most abundant halogen in the earth's crust, most often in the form of two isotopes. Due to chemical activity, it is found only in the form of compounds of many minerals.
Chlorine is a poisonous yellow-green gas that has a strong, unpleasant odor and a sweetish taste. It was chlorine after its discovery that was proposed to be called halogen, it is included in the group of the same name as one of the most chemically active non-metals.
Daily chlorine requirement
Normally, a healthy adult should receive 4-6 g of chlorine per day; the need for it increases with active physical activity or hot weather (with increased sweating). Typically, the body receives its daily requirement from food with a balanced diet.
The main supplier of chlorine to the body is table salt - especially if it is not heat-treated, so it is better to salt ready-made dishes. Also contain chlorine, seafood, meat, and, and,.
Interaction with others
The acid-base and water balance of the body is regulated by chlorine.
Signs of a lack of chlorine
A lack of chlorine is caused by processes that lead to dehydration of the body - heavy sweating in the heat or during physical exertion, vomiting, diarrhea and some diseases of the urinary system. Signs of chlorine deficiency are lethargy and drowsiness, muscle weakness, obvious dry mouth, loss of taste, and lack of appetite.
Signs of excess chlorine
Signs of excess chlorine in the body are: increased blood pressure, dry cough, pain in the head and chest, pain in the eyes, lacrimation, disorders of the gastrointestinal tract. As a rule, an excess of chlorine can be caused by drinking ordinary tap water that undergoes a chlorine disinfection process and occurs in workers in industries that are directly related to the use of chlorine.
Chlorine in the human body:
- regulates water and acid-base balance,
- removes fluid and salts from the body through the process of osmoregulation,
- stimulates normal digestion,
- normalizes the condition of red blood cells,
- cleanses the liver of fat.
The main use of chlorine is in the chemical industry, where it is used to produce polyvinyl chloride, polystyrene foam, packaging materials, as well as chemical warfare agents and plant fertilizers. Disinfecting drinking water with chlorine is practically the only available method of water purification.
In nature, chlorine occurs in a gaseous state and only in the form of compounds with other gases. In conditions close to normal, it is a poisonous, caustic gas of a greenish color. Has more weight than air. Has a sweet smell. A chlorine molecule contains two atoms. In a calm state it does not burn, but at high temperatures it interacts with hydrogen, after which an explosion is possible. As a result, phosgene gas is released. Very poisonous. Thus, even at low concentrations in the air (0.001 mg per 1 dm 3) it can cause death. chlorine states that it is heavier than air, therefore, it will always be located near the floor in the form of a yellowish-green haze.
Historical facts
For the first time in practice, this substance was obtained by K. Scheeley in 1774 by combining hydrochloric acid and pyrolusite. However, only in 1810 P. Davy was able to characterize chlorine and establish that it is a separate chemical element.
It is worth noting that in 1772 he was able to obtain hydrogen chloride, a compound of chlorine and hydrogen, but the chemist was unable to separate these two elements.
Chemical characteristics of chlorine
Chlorine is a chemical element of the main subgroup of group VII of the periodic table. It is in the third period and has atomic number 17 (17 protons in the atomic nucleus). Chemically active non-metal. Denoted by the letters Cl.
It is a typical representative of gases that have no color, but have a pungent, pungent odor. Typically toxic. All halogens are well diluted in water. When exposed to humid air, they begin to smoke.
The external electronic configuration of the Cl atom is 3s2Зр5. Therefore, in compounds, a chemical element exhibits oxidation levels of -1, +1, +3, +4, +5, +6 and +7. The covalent radius of the atom is 0.96 Å, the ionic radius of Cl- is 1.83 Å, the atomic electron affinity is 3.65 eV, the ionization level is 12.87 eV.
As stated above, chlorine is a fairly active non-metal, which makes it possible to create compounds with almost any metals (in some cases using heat or moisture, displacing bromine) and non-metals. In powder form, it reacts with metals only when exposed to high temperatures.
The maximum combustion temperature is 2250 °C. With oxygen it can form oxides, hypochlorites, chlorites and chlorates. All compounds containing oxygen become explosive when interacting with oxidizing substances. It is worth noting that they can explode arbitrarily, while chlorates explode only when exposed to any initiators.
Characteristics of chlorine by position in the periodic table:
Simple substance;
. element of the seventeenth group of the periodic table;
. third period of the third row;
. seventh group of the main subgroup;
. atomic number 17;
. denoted by the symbol Cl;
. reactive non-metal;
. is in the halogen group;
. in conditions close to normal, it is a poisonous gas of a yellowish-green color with a pungent odor;
. a chlorine molecule has 2 atoms (formula Cl 2).
Physical properties of chlorine:
Boiling point: -34.04 °C;
. melting point: -101.5 °C;
. density in the gaseous state - 3.214 g/l;
. density of liquid chlorine (during the boiling period) - 1.537 g/cm3;
. density of solid chlorine - 1.9 g/cm 3 ;
. specific volume - 1.745 x 10 -3 l/g.
Chlorine: characteristics of temperature changes
In the gaseous state it tends to liquefy easily. At a pressure of 8 atmospheres and a temperature of 20 ° C, it looks like a greenish-yellow liquid. Has very high corrosive properties. As practice shows, this chemical element can maintain a liquid state up to a critical temperature (143 ° C), subject to increased pressure.
If it is cooled to a temperature of -32 ° C, it will change to liquid regardless of atmospheric pressure. With a further decrease in temperature, crystallization occurs (at -101 ° C).
Chlorine in nature
The earth's crust contains only 0.017% chlorine. The bulk is found in volcanic gases. As stated above, the substance has great chemical activity, as a result of which it is found in nature in compounds with other elements. However, many minerals contain chlorine. The characteristics of the element allow the formation of about a hundred different minerals. As a rule, these are metal chlorides.
Also, a large amount of it is found in the World Ocean - almost 2%. This is due to the fact that chlorides dissolve very actively and are carried by rivers and seas. The reverse process is also possible. The chlorine is washed back onto the shore, and then the wind carries it around the surrounding area. That is why its greatest concentration is observed in coastal zones. In the arid regions of the planet, the gas we are considering is formed through the evaporation of water, as a result of which salt marshes appear. About 100 million tons of this substance are mined annually in the world. Which, however, is not surprising, because there are many deposits containing chlorine. Its characteristics, however, largely depend on its geographical location.
Methods for producing chlorine
Today there are a number of methods for producing chlorine, of which the most common are the following:
1. Diaphragm. It is the simplest and least expensive. The brine solution in diaphragm electrolysis enters the anode space. Then it flows through the steel cathode grid into the diaphragm. It contains a small amount of polymer fibers. An important feature of this device is counterflow. It is directed from the anode space to the cathode space, which makes it possible to obtain chlorine and alkalis separately.
2. Membrane. The most energy efficient, but difficult to implement in an organization. Similar to diaphragm. The difference is that the anode and cathode spaces are completely separated by a membrane. Therefore, the output is two separate streams.
It is worth noting that the characteristics of the chemical element (chlorine) obtained by these methods will be different. The membrane method is considered to be more “clean”.
3. Mercury method with a liquid cathode. Compared to other technologies, this option allows you to obtain the purest chlorine.
The basic diagram of the installation consists of an electrolyzer and an interconnected pump and amalgam decomposer. The mercury pumped along with a solution of table salt serves as the cathode, and carbon or graphite electrodes serve as the anode. The operating principle of the installation is as follows: chlorine is released from the electrolyte, which is removed from the electrolyzer along with the anolyte. Impurities and residual chlorine are removed from the latter, re-saturated with halite and returned to electrolysis.
Industrial safety requirements and unprofitable production led to the replacement of the liquid cathode with a solid one.
Use of chlorine for industrial purposes
The properties of chlorine allow it to be actively used in industry. With the help of this chemical element, various (vinyl chloride, chloro-rubber, etc.), drugs, disinfectants are obtained. But the largest niche occupied in the industry is the production of hydrochloric acid and lime.
Methods for purifying drinking water are widely used. Today they are trying to move away from this method, replacing it with ozonation, since the substance we are considering negatively affects the human body, and chlorinated water destroys pipelines. This is due to the fact that in the free state Cl has a detrimental effect on pipes made from polyolefins. However, most countries prefer the chlorination method.
Chlorine is also used in metallurgy. With its help, a number of rare metals (niobium, tantalum, titanium) are obtained. In the chemical industry, various organochlorine compounds are actively used to control weeds and for other agricultural purposes; the element is also used as a bleach.
Due to its chemical structure, chlorine destroys most organic and inorganic dyes. This is achieved by completely discoloring them. This result is possible only in the presence of water, because the process of discoloration occurs due to which is formed after the breakdown of chlorine: Cl 2 + H 2 O → HCl + HClO → 2HCl + O. This method found application a couple of centuries ago and is still popular today.
The use of this substance for the production of organochlorine insecticides is very popular. These agricultural products kill harmful organisms while leaving the plants intact. A significant portion of all chlorine produced on the planet is used for agricultural needs.
It is also used in the production of plastic compounds and rubber. They are used to make wire insulation, office supplies, equipment, housings for household appliances, etc. There is an opinion that rubbers obtained in this way are harmful to humans, but this has not been confirmed by science.
It is worth noting that chlorine (the characteristics of the substance were described in detail by us earlier) and its derivatives, such as mustard gas and phosgene, are also used for military purposes to produce chemical warfare agents.
Chlorine as a bright representative of non-metals
Nonmetals are simple substances that include gases and liquids. In most cases, they conduct electricity worse than metals and have significant differences in physical and mechanical characteristics. With the help of a high level of ionization they are able to form covalent chemical compounds. Below we will give a description of a non-metal using chlorine as an example.
As mentioned above, this chemical element is a gas. Under normal conditions, it completely lacks properties similar to those of metals. Without outside help, it cannot interact with oxygen, nitrogen, carbon, etc. It exhibits its oxidizing properties in connections with simple substances and some complex ones. It is a halogen, which is clearly reflected in its chemical properties. In combination with other representatives of halogens (bromine, astatine, iodine), it displaces them. In the gaseous state, chlorine (its characteristics are direct confirmation of this) is highly soluble. Is an excellent disinfectant. It kills only living organisms, which makes it indispensable in agriculture and medicine.
Use as a poisonous substance
The characteristics of the chlorine atom make it possible to use it as a poisonous agent. Gas was first used by Germany on April 22, 1915, during the First World War, as a result of which about 15 thousand people died. At the moment it is not applicable.
Let us give a brief description of the chemical element as an asphyxiant. Affects the human body through suffocation. First it irritates the upper respiratory tract and the mucous membrane of the eyes. A severe cough begins with attacks of suffocation. Further, penetrating into the lungs, the gas corrodes the lung tissue, which leads to edema. Important! Chlorine is a fast-acting substance.
Depending on the concentration in the air, symptoms vary. At low levels, a person experiences redness of the mucous membrane of the eyes and mild shortness of breath. A content of 1.5-2 g/m 3 in the atmosphere causes heaviness and sharp sensations in the chest, sharp pain in the upper respiratory tract. The condition may also be accompanied by severe lacrimation. After 10-15 minutes of being in a room with such a concentration of chlorine, severe lung burns and death occur. At denser concentrations, death is possible within a minute from paralysis of the upper respiratory tract.
Chlorine in the life of organisms and plants
Chlorine is found in almost all living organisms. The peculiarity is that it is not present in pure form, but in the form of compounds.
In animal and human organisms, chlorine ions maintain osmotic equality. This is due to the fact that they have the most suitable radius for penetration into membrane cells. Along with potassium ions, Cl regulates the water-salt balance. In the intestine, chloride ions create a favorable environment for the action of proteolytic enzymes of gastric juice. Chlorine channels are found in many cells in our body. Through them, intercellular fluid exchange occurs and the pH of the cell is maintained. About 85% of the total volume of this element in the body resides in the intercellular space. It is eliminated from the body through the urethra. Produced by the female body during breastfeeding.
At this stage of development, it is difficult to say unequivocally which diseases are provoked by chlorine and its compounds. This is due to the lack of research in this area.
Chlorine ions are also present in plant cells. He actively takes part in energy metabolism. Without this element, the process of photosynthesis is impossible. With its help, the roots actively absorb the necessary substances. But a high concentration of chlorine in plants can have a detrimental effect (slowing down the process of photosynthesis, stopping development and growth).
However, there are such representatives of the flora who were able to "make friends" or at least get along with this element. The characteristic of a non-metal (chlorine) contains such an item as the ability of a substance to oxidize soils. In the process of evolution, the plants mentioned above, called halophytes, occupied empty salt marshes, which were empty due to an overabundance of this element. They absorb chlorine ions, and then get rid of them with the help of leaf fall.
Transportation and storage of chlorine
There are several ways to move and store chlorine. The characteristic of the element implies the need for special high-pressure cylinders. Such containers have an identification marking - a vertical green line. Cylinders must be thoroughly washed monthly. With prolonged storage of chlorine, a very explosive precipitate is formed in them - nitrogen trichloride. If all safety rules are not observed, spontaneous ignition and explosion are possible.
Chlorine study
Future chemists should know the characteristics of chlorine. According to the plan, 9th graders can even make laboratory experiments with this substance based on basic knowledge of the discipline. Naturally, the teacher is obliged to conduct a safety briefing.
The work procedure is as follows: you need to take a flask with chlorine and pour small metal shavings into it. In flight, the shavings will flare up with bright light sparks and at the same time light white SbCl 3 smoke will form. When tin foil is immersed in a vessel with chlorine, it will also spontaneously ignite, and fiery snowflakes will slowly fall to the bottom of the flask. During this reaction, a smoky liquid is formed - SnCl 4. When iron filings are placed in a vessel, red “drops” will form and red FeCl 3 smoke will appear.
Along with practical work, theory is repeated. In particular, such a question as the characteristics of chlorine by position in the periodic table (described at the beginning of the article).
As a result of experiments, it turns out that the element actively reacts to organic compounds. If you place cotton wool, previously soaked in turpentine, in a jar of chlorine, it will instantly ignite and soot will suddenly fall out of the flask. Sodium smolders spectacularly with a yellowish flame, and salt crystals appear on the walls of the chemical container. It will be interesting for students to know that, while still a young chemist, N. N. Semenov (later a Nobel Prize winner), after conducting such an experiment, collected salt from the walls of the flask and, sprinkling it on bread, ate it. Chemistry turned out to be right and did not let the scientist down. As a result of the experiment carried out by the chemist, ordinary table salt actually turned out!
Chlorine(lat. chlorum), cl, chemical element of group VII of the periodic system of Mendeleev, atomic number 17, atomic mass 35.453; belongs to the family halogens. Under normal conditions (0°C, 0.1 Mn/m 2 or 1 kgf/cm 2) yellow-green gas with a pungent irritating odor. Natural chromium consists of two stable isotopes: 35 cl (75.77%) and 37 cl (24.23%). Radioactive isotopes with mass numbers of 32, 33, 34, 36, 38, 39, 40 and half-lives ( t 1/2) respectively 0.31; 2.5; 1.56 sec; 3 , 1 ? 10 5 years; 37.3, 55.5 and 1.4 min. 36 cl and 38 cl are used as isotope tracers.
Historical reference. X. was first obtained in 1774 K. Scheele interaction of hydrochloric acid with pyrolusite mno 2. However, only in 1810 Davy established that chlorine is an element and named it chlorine (from the Greek chloro s - yellow-green). In 1813 J. L. Gay Lussac proposed the name X for this element.
Distribution in nature. Chromium occurs in nature only in the form of compounds. The average content of chromium in the earth's crust (clarke) is 1.7? 10 -2% by weight, in acidic igneous rocks - granites, etc. 2.4 ? 10-2 , in basic and ultrabasic 5 ? 10 -3. Water migration plays the main role in the history of chemistry in the earth's crust. It is found in the form of cl ion in the World Ocean (1.93%), underground brines and salt lakes. Number of own minerals (mainly natural chlorides) 97, the main one is halite naci . Large deposits of potassium and magnesium chlorides and mixed chlorides are also known: sylvin kcl, sylvinite(na, k) ci, carnallite kci? mgcl2? 6h2o, Cainite kci? mgso 4? 3h 2 o, bischofite mgci 2 ? 6h 2 o. In the history of the Earth, the supply of hcl contained in volcanic gases to the upper parts of the earth's crust was of great importance.
Physical and chemical properties. H. has t kip -34.05°С, t nл - 101°C. The density of gaseous chromium under normal conditions is 3.214 g/l; saturated steam at 0°C 12.21 g/l; liquid chlorine at a boiling point of 1.557 g/cm 3 ; solid chemical at - 102°c 1.9 g/cm 3 . The saturated vapor pressure of chemicals at 0°C is 0.369; at 25°c 0.772; at 100°c 3.814 Mn/m 2 or respectively 3.69; 7.72; 38.14 kgf/cm 2 . Heat of fusion 90.3 kJ/kg (21,5 cal/g); heat of vaporization 288 kJ/kg (68,8 cal/g); heat capacity of gas at constant pressure 0.48 kJ/(kg? TO) . Critical constants of chemicals: temperature 144°c, pressure 7.72 Mn/m 2 (77,2 kgf/cm 2) , density 573 g/l, specific volume 1.745? 10 -3 l/g. Solubility (in g/l) X. at a partial pressure of 0.1 Mn/m 2 , or 1 kgf/cm 2 , in water 14.8 (0°C), 5.8 (30°c), 2.8 (70°c); in solution 300 g/l naci 1.42 (30°c), 0.64 (70°c). Below 9.6°C, chlorine hydrates form in aqueous solutions. Variable composition cl ? n h 2 o (where n = 6 ? 8); These are yellow cubic crystals that decompose into chemicals and water when the temperature rises. Chromium dissolves well in ticl 4, sic1 4, sncl 4 and some organic solvents (especially in hexane c 6 h 14 and carbon tetrachloride ccl 4). The X. molecule is diatomic (cl 2). Thermal dissociation degree cl 2 + 243 kj u 2cl at 1000 K is equal to 2.07? 10 -40%, at 2500 K 0.909%. External electronic configuration of the cl 3 atom s 2 3 p 5 . In accordance with this, chromium in compounds exhibits oxidation states of -1, +1, +3, +4, +5, +6 and +7. The covalent radius of the atom is 0.99 å, the ionic radius cl is 1.82 å, the electron affinity of the X atom is 3.65 ev, ionization energy 12.97 ev.
Chemically, chromium is very active; it combines directly with almost all metals (with some only in the presence of moisture or upon heating) and with nonmetals (except carbon, nitrogen, oxygen, and inert gases), forming the corresponding chlorides, reacts with many compounds, replaces hydrogen in saturated hydrocarbons and adds to unsaturated compounds. Chromium displaces bromine and iodine from their compounds with hydrogen and metals; Of the compounds of chromium with these elements, it is replaced by fluorine. Alkali metals, in the presence of traces of moisture, react with chemicals with ignition; most metals react with dry chemicals only when heated. Steel, as well as some metals, are resistant in a dry chemical atmosphere at low temperatures, so they are used for the manufacture of equipment and storage facilities for dry chemicals. Phosphorus ignites in a chemical atmosphere, forming pcl 3, and with further chlorination - pcl 5; sulfur with chromium when heated gives s 2 cl 2, scl 2, etc. s n cl m. Arsenic, antimony, bismuth, strontium, and tellurium energetically interact with chlorine. A mixture of chlorine with hydrogen burns with a colorless or yellow-green flame to form hydrogen chloride(it's a chain reaction)
The maximum temperature of the hydrogen-chlorine flame is 2200°c. Mixtures of chlorine with hydrogen containing from 5.8 to 88.5% h 2 are explosive.
With oxygen, chromium forms oxides: cl 2 o, clo 2, cl 2 o 6, cl 2 o 7, cl 2 o 8 , as well as hypochlorites (salts hypochlorous acid) , chlorites, chlorates and perchlorates. All oxygen compounds of chlorine form explosive mixtures with easily oxidized substances. Chromium oxides are weakly stable and can explode spontaneously; hypochlorites slowly decompose during storage; chlorates and perchlorates can explode under the influence of initiators.
Chromium hydrolyzes in water, forming hypochlorous and hydrochloric acids: cl 2 + h 2 o u hclo + hcl. When aqueous solutions of alkalis are chlorinated in the cold, hypochlorites and chlorides are formed: 2naoh + cl 2 = nacio + naci + h 2 o, and when heated, chlorates are formed. Chlorination of dry calcium hydroxide is obtained bleach.
When ammonia reacts with chemicals, nitrogen trichloride is formed . When chlorinating organic compounds, chromium either replaces hydrogen: r-h + ci 2 = rcl + hci, or joins multiple bonds to form various chlorine-containing organic compounds .
X. forms with other halogens interhalogen compounds. Fluorides clf, clf 3, clf 5 are very reactive; For example, in a clp 3 atmosphere, glass wool spontaneously ignites. Known compounds of chlorine with oxygen and fluorine are X. oxyfluorides: clo 3 f, clo 2 f 3, clof, clof 3 and fluorine perchlorate fclo 4.
Receipt. Chromium began to be produced industrially in 1785 by reacting hydrochloric acid with manganese dioxide or pyrolusite. In 1867, the English chemist G. Deacon developed a method for producing chromium by oxidizing hcl with atmospheric oxygen in the presence of a catalyst. From the end of the 19th to the beginning of the 20th centuries. Chlorine is obtained by electrolysis of aqueous solutions of alkali metal chlorides. Using these methods in the 70s. 20th century 90-95% of chemicals are produced in the world. Small amounts of chromium are obtained as a by-product in the production of magnesium, calcium, sodium, and lithium by electrolysis of molten chlorides. In 1975, world production of chlorine was about 25 million tons. T. Two main methods of electrolysis of aqueous solutions of naci are used: 1) in electrolyzers with a solid cathode and a porous filter diaphragm; 2) in electrolyzers with a mercury cathode. According to both methods, gaseous X is released at a graphite or oxide titanium-ruthenium anode. According to the first method, hydrogen is released at the cathode and a solution of naoh and nacl is formed, from which commercial caustic soda is separated by subsequent processing. According to the second method, sodium amalgam is formed at the cathode; when it is decomposed with pure water in a separate apparatus, a solution of naoh, hydrogen and pure mercury is obtained, which again goes into production. Both methods give 1 T X. 1.125 T naoh.
Diaphragm electrolysis requires less capital investment for the organization of chemical production and produces cheaper naoh. The mercury cathode method produces very pure naoh, but the loss of mercury pollutes the environment. In 1970, 62.2% of the world's chemical output was produced using the mercury cathode method, 33.6% with a solid cathode, and 4.2% using other methods. After 1970, electrolysis with a solid cathode and an ion exchange membrane began to be used, making it possible to obtain pure naoh without the use of mercury.
Application. One of the important branches of the chemical industry is the chlorine industry. The main quantities of chlorine are processed at the site of its production into chlorine-containing compounds. Chromium is stored and transported in liquid form in cylinders, barrels, and railways. tanks or in specially equipped vessels. Industrial countries are characterized by the following approximate consumption of chemicals: for the production of chlorine-containing organic compounds - 60-75%; inorganic compounds containing chemicals - 10-20%; for bleaching pulp and fabrics - 5-15%; for sanitary needs and water chlorination - 2-6% of total production.
Chromium is also used for the chlorination of certain ores in order to extract titanium, niobium, zirconium, and others.
L. M. Yakimenko.
X. in the body. H. - one of biogenic elements, a permanent component of plant and animal tissues. The content of ch. in plants (a lot of ch. in halophytes) - from thousandths of a percent to whole percent, in animals - tenths and hundredths of a percent. The daily requirement of an adult for H. (2-4 G) is covered by food products. Chromium is usually supplied with food in excess in the form of sodium chloride and potassium chloride. Bread, meat and dairy products are especially rich in X. In the animal body, chromium is the main osmotically active substance in blood plasma, lymph, cerebrospinal fluid, and some tissues. Plays a role in water-salt metabolism, promoting tissue retention of water. Regulation of acid-base balance in tissues is carried out along with other processes by changing the distribution of chemicals between the blood and other tissues. X. participates in energy metabolism in plants, activating both oxidative phosphorylation, and photophosphorylation. X. has a positive effect on the absorption of oxygen by roots. Chromium is necessary for the formation of oxygen during photosynthesis in isolated chloroplasts. Chromium is not included in most nutrient media for the artificial cultivation of plants. It is possible that very low concentrations of X are sufficient for plant development.
M. Ya. Shkolnik.
Poisoning X . possible in the chemical, pulp and paper, textile, pharmaceutical industries, etc. X. irritates the mucous membranes of the eyes and respiratory tract. Primary inflammatory changes are usually accompanied by a secondary infection. Acute poisoning develops almost immediately. When medium and low concentrations of chromium are inhaled, chest tightness and pain, dry cough, rapid breathing, pain in the eyes, lacrimation, increased levels of leukocytes in the blood, increased body temperature, etc. are noted. Bronchopneumonia, toxic pulmonary edema, depressive states, and convulsions are possible. In mild cases, recovery occurs within 3-7 days As long-term consequences, catarrh of the upper respiratory tract, recurrent bronchitis, pneumosclerosis, etc. are observed; possible activation of pulmonary tuberculosis. With prolonged inhalation of small concentrations of chromium, similar but slowly developing forms of the disease are observed. Prevention of poisoning: sealing production equipment, effective ventilation, using a gas mask if necessary. Maximum permissible concentration of chemicals in the air of industrial premises 1 mg/m 3 . The production of chemicals, bleach and other chlorine-containing compounds is classified as production with hazardous working conditions, where according to Sov. Legislation restricts the use of labor of women and minors.
A. A. Kasparov.
Lit.: Yakimenko L. M., Production of chlorine, caustic soda and inorganic chlorine products, M., 1974; Nekrasov B.V., Fundamentals of General Chemistry, 3rd ed., [vol.] 1, M., 1973; Harmful substances in industry, ed. N. V. Lazareva, 6th ed., vol. 2, L., 1971; comprehensive inorganic chemistry, ed. j. c. bailar, v. 1-5, oxf. - , 1973.
download abstract
Chlorine was first obtained in 1772 by Scheele, who described its release during the interaction of pyrolusite with hydrochloric acid in his treatise on pyrolusite: 4HCl + MnO 2 = Cl 2 + MnCl 2 + 2H 2 O
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, but attempts to isolate it remained unsuccessful until the work of Davy, who managed to decompose table salt into sodium and chlorine by electrolysis.
The name of the element comes from the Greek clwroz- "green".
Being in nature, receiving:
Natural chlorine is a mixture of two isotopes 35 Cl and 37 Cl. In the earth's crust, chlorine is the most common halogen. Since chlorine is very active, in nature it is found only in the form of compounds in the minerals: halite NaCl, sylvite KCl, sylvinite KCl NaCl, bischofite MgCl 2 6H 2 O, 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.
On an industrial scale, chlorine is produced together with sodium hydroxide and hydrogen by electrolysis of a solution of table salt:
2NaCl + 2H 2 O => H 2 + Cl 2 + 2NaOH
To recover chlorine from hydrogen chloride, which is a by-product during the industrial chlorination of organic compounds, the Deacon process is used (catalytic oxidation of hydrogen chloride with atmospheric oxygen):
4HCl + O 2 \u003d 2H 2 O + 2Cl 2
Processes usually used in laboratories are based on the oxidation of hydrogen chloride with strong oxidizing agents (for example, manganese (IV) oxide, potassium permanganate, potassium dichromate):
2KMnO 4 + 16HCl \u003d 5Cl 2 + 2MnCl 2 + 2KCl + 8H 2 O
K 2 Cr 2 O 7 + 14HCl = 3Cl 2 + 2CrCl 3 + 2KCl + 7H 2 O
Physical properties:
Under normal conditions, chlorine is a yellow-green gas with a suffocating odor. Chlorine is noticeably soluble in water ("chlorine water"). At 20°C, 2.3 volumes of chlorine dissolve in one volume of water. Boiling point = -34°C; melting point = -101°C, density (gas, n.s.) = 3.214 g/l.
Chemical properties:
Chlorine is very active - it combines directly with almost all elements of the periodic system, metals and non-metals (except carbon, nitrogen, oxygen and inert gases). Chlorine is a very strong oxidizing agent, displacing less active non-metals (bromine, iodine) from their compounds with hydrogen and metals:
Cl 2 + 2HBr = Br 2 + 2HCl; Cl 2 + 2NaI \u003d I 2 + 2NaCl
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 HClO + HCl;
Chlorine interacts with many organic compounds, entering into substitution or addition reactions:
CH 3 -CH 3 + xCl 2 => C 2 H 6-x Cl x + xHCl
CH 2 \u003d CH 2 + Cl 2 \u003d\u003e Cl-CH 2 -CH 2 -Cl
C 6 H 6 + Cl 2 => C 6 H 6 Cl + HCl
Chlorine has seven oxidation states: -1, 0, +1, +3, +4, +5, +7.
The most important connections:
Hydrogen chloride HCl- a colorless gas that smokes in air due to the formation of fog droplets with water vapor. It has a pungent odor and severely irritates the respiratory tract. Contained in volcanic gases and waters, in gastric juice. Chemical properties depend on what state it is in (can be in a gaseous, liquid or solution state). The HCl solution is called hydrochloric acid. It is a strong acid and displaces weaker acids from their salts. Salts - chlorides- solid crystalline substances with high melting points.
Covalent chlorides- chlorine compounds with non-metals, gases, liquids or fusible solids that have characteristic acidic properties, usually easily hydrolyzed by water to form hydrochloric acid:
PCl 5 + 4H 2 O = H 3 PO 4 + 5HCl;
Chlorine(I) oxide Cl 2 O., a gas of brownish-yellow color with a pungent odor. Affects the respiratory organs. Easily dissolves in water, forming hypochlorous acid.
Hypochlorous acid HClO. Exists only in solutions. It is a weak and unstable acid. Easily decomposes into hydrochloric acid and oxygen. Strong oxidizing agent. Formed when chlorine is dissolved in water. Salts - hypochlorites, unstable (NaClO*H 2 O decomposes with an explosion at 70 °C), strong oxidizers. Widely used for bleaching and disinfection bleaching powder, mixed salt Ca(Cl)OCl
Chlorous acid HClO 2, in its free form is unstable, even in a dilute aqueous solution it quickly decomposes. Acid of medium strength, salts - chlorites are generally colorless and highly soluble in water. Unlike hypochlorites, chlorites exhibit pronounced oxidizing properties only in an acidic environment. The greatest use (for bleaching fabrics and paper pulp) is sodium chlorite NaClO 2.
Chlorine(IV) oxide ClO 2, - greenish-yellow gas with an unpleasant (pungent) smell, ...
Chloric acid, HClO 3 - in the free form is unstable: disproportionate to ClO 2 and HClO 4 . Salts - chlorates; of these, sodium, potassium, calcium and magnesium chlorates are the most important. These are strong oxidizing agents, explosive when mixed with reducing agents. Potassium chlorate ( Berthollet's salt) - KClO 3, was used to produce oxygen in the laboratory, but due to its high danger it was no longer used. Solutions of potassium chlorate were used as a weak antiseptic and external medicinal gargle.
Perchloric acid HClO 4, in aqueous solutions, perchloric acid is the most stable of all oxygen-containing chlorine acids. Anhydrous perchloric acid, which is obtained using concentrated sulfuric acid from 72% HClO 4, is not very stable. It is the strongest monoprotic acid (in aqueous solution). Salts - perchlorates, are used as oxidizers (solid rocket engines).
Application:
Chlorine is used in many industries, science and domestic needs:
- In the production of polyvinyl chloride, plastic compounds, synthetic rubber;
- For bleaching fabric and paper;
- Production of organochlorine insecticides - substances that kill insects harmful to crops, but are safe for plants;
- For water disinfection - "chlorination";
- 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.
Biological role and toxicity:
Chlorine is one of the most important biogenic elements and is part of all living organisms. In animals and humans, chlorine ions are involved in maintaining osmotic balance; the chloride ion has an optimal radius for penetration through the cell membrane. Chlorine ions are vital for plants, participating in energy metabolism in plants, activating oxidative phosphorylation.
Chlorine in the form of a simple substance is poisonous; if it enters the lungs, it causes burns of lung tissue and suffocation. It has an irritating effect on the respiratory tract at a concentration in the air of about 0.006 mg/l (i.e., twice the threshold for the perception of the smell of chlorine). Chlorine was one of the first chemical agents used by Germany in World War I.
Korotkova Yu., Shvetsova I.
HF Tyumen State University, 571 group.
Sources: Wikipedia: http://ru.wikipedia.org/wiki/Cl, etc.,
Website of the Russian Chemical Technical University named after. D.I. Mendeleev:
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, °С | -100,5 |
| Boiling point, °С | -30,04 |
| Critical temperature, °C | 144 |
| Critical pressure, Pa | 77.1 10 5 |
| Critical density, kg/m 3 | 573 |
| Gas density (at 0°С and 1.013 10 5 Pa), kg/m 3 | 3,214 |
| Density of saturated steam (at 0°С 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°С), kg/m 3 | 1900 |
| Relative density in air of gas (at 0°C and 1.013 10 5 Pa) | 2,482 |
| Relative air density of saturated steam (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
The specific heat capacity of 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, the physical property of chlorine, such as 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.
