Chlorine in a gaseous state. Chlorine is a very strong oxidizing agent. The electronic structure of the chlorine atom
DEFINITION
Chlorine is in the third period of the VII group of the main (A) subgroup of the Periodic table.
Refers to elements of the p-family. Non-metal. Non-metallic elements in this group are collectively called halogens. Designation - Cl. Serial number - 17. Relative atomic mass - 35.453 amu.
The electronic structure of the chlorine atom
The chlorine atom consists of a positively charged nucleus (+17), consisting of 17 protons and 18 neutrons, around which 17 electrons move in 3 orbits.
Fig. 1. Schematic structure of the chlorine atom.
The orbital distribution of electrons is as follows:
17Cl) 2) 8) 7;
1s 2 2s 2 2p 6 3s 2 3p 5 .
At the outer energy level of the chlorine atom there are seven electrons, all of them are considered valence. The energy diagram of the ground state takes the following form:
The presence of one unpaired electron indicates that chlorine is capable of exhibiting an oxidation state of +1. Several excited states are also possible due to the presence of a vacant 3 d-orbital. First, electrons are vaporized 3 p-sub-level and are occupied by free d-orbitals, and after - electrons 3 s-sublevel:
This explains the presence of three more oxidation states in chlorine: +3, +5 and +7.
Examples of problem solving
EXAMPLE 1
| Exercise | Two elements with nuclear charges Z = 17 and Z = 18 are given. The simple substance formed by the first element is a poisonous gas with a pungent odor, and the second is a non-poisonous, odorless gas that does not support breathing. Write down the electronic formulas of the atoms of both elements. Which one forms a poisonous gas? |
| Solution | Electronic formulas of the given elements will be written as follows: 17 Z 1 s 2 2s 2 2p 6 3s 2 3p 5 ; 18 Z 1 s 2 2s 2 2p 6 3s 2 3p 6 . The charge of the nucleus of an atom of a chemical element is equal to its ordinal number in the Periodic Table. Therefore, it is chlorine and argon. Two chlorine atoms form a molecule of a simple substance - Cl 2, which is a poisonous gas with a pungent odor |
| Answer | Chlorine and argon. |
Chlorine(lat. Chlorum), Cl, chemical element VII of group of the periodic system of Mendeleev, atomic number 17, atomic mass 35.453; belongs to the halogen family. Under normal conditions (0 ° C, 0.1 MN / m 2, or 1 kgf / cm 2) yellow-green gas with a sharp irritating odor. Natural Chlorine consists of two stable isotopes: 35 Cl (75.77%) and 37 Cl (24.23%). Artificially obtained radioactive isotopes with mass numbers 31-47, in particular: 32, 33, 34, 36, 38, 39, 40 with half-lives (T ½), respectively, 0.31; 2.5; 1.56 sec; 3.1 · 10 5 years; 37.3, 55.5 and 1.4 minutes. 36 Cl and 38 Cl are used as isotopic indicators.
History reference. Chlorine was obtained for the first time in 1774 by K. Scheele by the interaction of hydrochloric acid with pyrolusite MnO 2. However, only in 1810 G. Davy established that chlorine is an element and named it chlorine (from the Greek chloros - yellow-green). In 1813 J.L. Gay-Lussac proposed the name Chlorine for this element.
Distribution of Chlorine in nature. Chlorine is found in nature only in the form of compounds. The average content of Chlorine in the earth's crust (clarke) is 1.7 · 10 -2% by weight, in acid igneous rocks - granites and others 2.4 · 10 -2, in basic and ultrabasic 5 · 10 -3. Water migration plays a major role in the history of Chlorine in the earth's crust. In the form of the Cl ion - it is contained in the World Ocean (1.93%), underground brines and salt lakes. The number of its own minerals (mainly natural chlorides) is 97, the main of which is halite NaCl (rock salt). Large deposits of potassium and magnesium chlorides and mixed chlorides are also known: sylvinite KCl, sylvinite (Na, K) Cl, carnalite KCl MgCl 2 6H 2 O, kainite KCl MgSO 4 3H 2 O, bischofite MgCl 2 6H 2 O In the history of the Earth, the influx of HCl contained in volcanic gases into the upper parts of the earth's crust was of great importance.
Physical properties of Chlorine. Chlorine has a boiling point of -34.05 ° C, a melting point of -101 ° C. The density of gaseous Chlorine under normal conditions is 3.214 g / l; saturated steam at 0 ° C 12.21 g / l; liquid Chlorine at a boiling point of 1.557 g / cm 3; solid Chlorine at - 102 ° C 1.9 g / cm 3. The saturated vapor pressure of Chlorine at 0 ° C is 0.369; at 25 ° C 0.772; at 100 ° C 3.814 MN / m 2 or 3.69, respectively; 7.72; 38.14 kgf / cm 2. Heat of fusion 90.3 kJ / kg (21.5 cal / g); heat of vaporization 288 kJ / kg (68.8 cal / g); heat capacity of gas at constant pressure 0.48 kJ / (kg · K). Chlorine critical constants: 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) of Chlorine 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 a solution of 300 g / l NaCl 1.42 (30 ° C), 0.64 (70 ° C). Below 9.6 ° C, chlorine hydrates of variable composition Cl 2 · nH 2 O (where n = 6-8) are formed in aqueous solutions; these are yellow crystals of a cubic system, decomposing with increasing temperature into Chlorine and water. Chlorine is readily soluble in TiCl 4, SiCl 4, SnCl 4 and some organic solvents (especially in hexane C 6 H 14 and carbon tetrachloride CCl 4). Chlorine molecule is diatomic (Cl 2). The degree of thermal dissociation Cl 2 + 243 kJ = 2Cl at 1000 K is 2.07 · 10 -4%, at 2500 K 0.909%.
Chlorine chemical properties. The outer electronic configuration of the Cl 3s 2 Зр 5 atom. In accordance with this, Chlorine in compounds exhibits oxidation states -1, + 1, +3, +4, +5, +6 and +7. The covalent radius of the atom is 0.99 Å, the ionic radius of Cl is 1.82 Å, the affinity of the Chlorine atom to the electron is 3.65 eV, and the ionization energy is 12.97 eV.
Chemically, chlorine is very active, it combines directly with almost all metals (with some only in the presence of moisture or when heated) and with non-metals (except carbon, nitrogen, oxygen, inert gases), forming the corresponding chlorides, reacts with many compounds, replaces hydrogen in saturated hydrocarbons and attaches to unsaturated compounds. Chlorine displaces bromine and iodine from their compounds with hydrogen and metals; it is displaced by fluorine from chlorine compounds with these elements. Alkali metals in the presence of traces of moisture interact with Chlorine with ignition, most metals react with dry Chlorine only when heated. Steel, as well as some metals, are resistant in an atmosphere of dry Chlorine at low temperatures, therefore they are used for the manufacture of equipment and storage facilities for dry Chlorine. Phosphorus ignites in an atmosphere of Chlorine, forming РCl 3, and upon further chlorination - РСl 5; sulfur with Chlorine when heated gives S 2 Cl 2, SCl 2 and other S n Cl m. Arsenic, antimony, bismuth, strontium, tellurium interact vigorously with Chlorine. A mixture of chlorine with hydrogen burns with a colorless or yellow-green flame with the formation of hydrogen chloride (this is a chain reaction).
The maximum temperature of the hydrogen-chlorine flame is 2200 ° C. Chlorine-hydrogen mixtures containing from 5.8 to 88.5% H 2 are explosive.
Chlorine forms oxides with oxygen: Cl 2 O, ClO 2, Cl 2 O 6, Cl 2 O 7, Cl 2 O 8, as well as hypochlorites (hypochlorous acid salts), chlorites, chlorates and perchlorates. All oxygenated chlorine compounds form explosive mixtures with easily oxidizable substances. Chlorine oxides are unstable and can explode spontaneously, hypochlorites decompose slowly during storage, chlorates and perchlorates can explode under the influence of initiators.
Chlorine in water is hydrolyzed, forming hypochlorous and hydrochloric acids: Cl 2 + H 2 O = HClO + HCl. When chlorinating aqueous solutions of alkalis in the cold, hypochlorites and chlorides are formed: 2NaOH + Cl 2 = NaClO + NaCl + H 2 O, and when heated, chlorates. Chlorinated lime is obtained by chlorination of dry calcium hydroxide.
When ammonia interacts with Chlorine, nitrogen trichloride is formed. In the chlorination of organic compounds, Chlorine either replaces hydrogen or binds at multiple bonds, forming various chlorine-containing organic compounds.
Chlorine forms interhalogen compounds with other halogens. Fluorides ClF, ClF 3, ClF 3 are very reactive; for example, glass wool ignites spontaneously in a ClF 3 atmosphere. Known compounds of chlorine with oxygen and fluorine - Chlorine oxyfluorides: ClO 3 F, ClO 2 F 3, ClOF, ClOF 3 and fluorine perchlorate FClO 4.
Chlorine production. Chlorine began to be produced industrially in 1785 by the interaction of hydrochloric acid with manganese (II) oxide or pyrolusite. In 1867, the English chemist G. Deacon developed a method for producing Chlorine by oxidizing HCl with atmospheric oxygen in the presence of a catalyst. Since the late 19th - early 20th century, Chlorine is produced by electrolysis of aqueous solutions of alkali metal chlorides. These methods produce 90-95% of Chlorine in the world. Small amounts of Chlorine are produced along the way during the production of magnesium, calcium, sodium and lithium by electrolysis of molten chlorides. There are two main methods of electrolysis of aqueous NaCl solutions: 1) in electrolyzers with a solid cathode and a porous filtering diaphragm; 2) in electrolyzers with a mercury cathode. Both methods produce chlorine gas at the graphite or titanium-ruthenium oxide anode. According to the first method, hydrogen is released at the cathode and a solution of NaOH and NaCl is formed, from which commercial caustic soda is isolated by subsequent processing. According to the second method, sodium amalgam is formed at the cathode, when it is decomposed with pure water in a separate apparatus, a NaOH solution, hydrogen and pure mercury are obtained, which again goes into production. Both methods give 1.125 tons of NaOH per ton of Chlorine.
Diaphragm electrolysis requires less capital investment to organize the production of Chlorine, and gives cheaper NaOH. The mercury cathode method produces very pure NaOH, but the loss of mercury pollutes the environment.
Chlorine application. One of the important branches of the chemical industry is the chlorine industry. The main quantities of Chlorine are processed at the place of its production into chlorine-containing compounds. Chlorine is stored and transported in liquid form in cylinders, barrels, railway tanks or in specially equipped ships. For industrialized countries, the following approximate consumption of Chlorine is typical: for the production of chlorine-containing organic compounds - 60-75%; inorganic compounds containing Chlorine, -10-20%; for bleaching of cellulose and fabrics - 5-15%; for sanitary needs and water chlorination - 2-6% of the total output.
Chlorine is also used for the chlorination of some ores in order to extract titanium, niobium, zirconium and others.
Chlorine in the body. Chlorine is one of the biogenic elements, a constant component of plant and animal tissues. Chlorine content in plants (a lot of Chlorine in halophytes) is from thousandths of a percent to whole percent, in animals - tenths and hundredths of a percent. The daily requirement of an adult for Chlorine (2-4 g) is covered by food. Chlorine 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 Chlorine. In animals, Chlorine is the main osmotically active substance in blood plasma, lymph, cerebrospinal fluid and some tissues. Plays a role in water-salt metabolism, contributing to the retention of water by tissues. The regulation of acid-base balance in tissues is carried out along with other processes by changing the distribution of Chlorine between blood and other tissues. Chlorine is involved in energy metabolism in plants, activating both oxidative phosphorylation and photophosphorylation. Chlorine has a positive effect on the uptake of oxygen by the roots. Chlorine is required for the formation of oxygen during photosynthesis by isolated chloroplasts. Chlorine is not included in the majority of nutrient media for artificial cultivation of plants. It is possible that very low concentrations of Chlorine are sufficient for the development of plants.
Chlorine poisoning is possible in the chemical, pulp and paper, textile, pharmaceutical industries and others. Chlorine irritates the mucous membranes of the eyes and respiratory tract. Secondary infection usually joins the primary inflammatory changes. Acute poisoning develops almost immediately. When medium and low concentrations of Chlorine are inhaled, chest tightness and pain, dry cough, rapid breathing, pain in the eyes, lacrimation, an increase in the content of leukocytes in the blood, body temperature, etc. are noted. ... In mild cases, recovery occurs within 3-7 days. As long-term consequences, catarrh of the upper respiratory tract, recurrent bronchitis, pneumosclerosis and others are observed; possible activation of pulmonary tuberculosis. With prolonged inhalation of small concentrations of Chlorine, similar, but slowly developing forms of the disease are observed. Prevention of poisoning: sealing of production facilities, equipment, effective ventilation, if necessary, use of a gas mask. The production of Chlorine, bleach and other chlorine-containing compounds refers to industries with hazardous working conditions.
The physical properties of chlorine are considered: the density of chlorine, its thermal conductivity, specific heat and dynamic viscosity at different temperatures. The physical properties of Cl 2 are tabulated for the liquid, solid and gaseous state of this halogen.
Basic physical properties of chlorine
Chlorine is included in the VII group of the third period of the periodic system of elements at number 17. It belongs to the subgroup of halogens, has a relative atomic and molecular weights of 35.453 and 70.906, respectively. At temperatures above -30 ° C, chlorine is a greenish-yellow gas with a characteristic pungent irritating odor. It easily liquefies under ordinary pressure (1.013 · 10 5 Pa), when cooled to -34 ° C, and forms a clear amber liquid that solidifies at a temperature of -101 ° C.
Due to its high chemical activity, free chlorine does not occur in nature, but only exists in the form of compounds. It is found mainly in the mineral halite (), and is also a 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 in the earth's crust, where it is 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, ° С | 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 ° С 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 air density of gas (at 0 ° С and 1.013 · 10 5 Pa) | 2,482 |
| Relative air density of saturated vapor (at 0 ° C and 3.66410 5 Pa) | 9,337 |
| Relative density of liquid chlorine at 0 ° С (by water at 4 ° С) | 1,468 |
| Specific gas volume (at 0 ° С and 1.013 · 10 5 Pa), m 3 / kg | 0,3116 |
| Specific volume of saturated steam (at 0 ° С and 3.664 · 10 5 Pa), m 3 / kg | 0,0828 |
| Specific volume of liquid chlorine (at 0 ° С and 3.664 · 10 5 Pa), m 3 / kg | 0,00068 |
| Chlorine vapor pressure at 0 ° С, Pa | 3.664 · 10 5 |
| Dynamic viscosity of gas at 20 ° С, 10 -3 Pa · s | 0,013 |
| Dynamic viscosity of liquid chlorine at 20 ° С, 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 ° С), J / (mol · K) | 67,1…65,7 |
| Gas thermal conductivity coefficient at 0 ° С, W / (m K) | 0,008 |
| Thermal conductivity coefficient of liquid chlorine at 30 ° С, W / (m K) | 0,62 |
| Enthalpy of gas, kJ / kg | 1,377 |
| Saturated steam enthalpy, kJ / kg | 1,306 |
| Enthalpy of liquid chlorine, kJ / kg | 0,879 |
| Refractive index at 14 ° С | 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, respectively, 3.214 and 1468 kg / m 3... When liquid or gaseous chlorine is heated, its density decreases due to the increase in volume due to thermal expansion.
Density of chlorine gas
The table shows the density values of chlorine in the gaseous state at various temperatures (in the range from -30 to 140 ° C) and normal atmospheric pressure (1.013 · 10 5 Pa). The density of chlorine changes with temperature - when heated, it decreases. For instance, at 20 ° C the density of chlorine is 2.985 kg / m 3, and when the temperature of this gas rises 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 |
With increasing pressure, 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 the 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 at any pressure. The density of liquid chlorine in this temperature range varies from 1717 to 573 kg / m 3.
| 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 of chlorine
The specific heat capacity of gaseous chlorine C p in terms of kJ / (kg K) in the temperature range from 0 to 1200 ° C and normal atmospheric pressure can be calculated by the formula:
where T is the absolute temperature of chlorine in degrees Kelvin.
It should be noted that under normal conditions the specific heat of chlorine has a value of 471 J / (kg · K) and increases with heating. The increase in heat capacity at temperatures above 500 ° С becomes insignificant, and at high temperatures the specific heat capacity of chlorine practically does not change.
The table shows the results of calculating the specific heat of chlorine according to 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 (19 J / (kg · K)). As the temperature of solid Cl 2 increases, its heat capacity increases and reaches 720 J / (kg · K) at minus 143 ° C.
Liquid chlorine has a specific heat 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 and decreases with increasing temperature.
Chlorine thermal conductivity
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 of chlorine under normal conditions is 0.0079 W / (m · deg), which is 3 times less than that at the same temperature and pressure. Heating chlorine increases its thermal conductivity. So, 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 dynamic viscosity coefficient of gaseous chlorine in the temperature range of 20 ... 500 ° C can be approximately calculated by 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);
С - Suzherland's constant (for chlorine С = 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 an order of magnitude higher viscosity 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 subgroup of manganese. Elements of the VII group of the periodic system of D. I. Mendeleev. A student manual. 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 of the production of chlorine, caustic soda and basic chlorine products. Ed. 2nd, lane. et al. M .: Chemistry, 1976 - 440 p.
Element VII of subgroup of D.I. Mendeleev's Periodic Table. At the external level, there are 7 electrons, therefore, when interacting with reducing agents, chlorine shows its oxidizing properties, attracting an electron of the metal.
Physical properties of chlorine.
Chlorine is a yellow gas. Has a pungent odor.
Chlorine chemical properties.
Free chlorine very active. It reacts with all simple substances except oxygen, nitrogen and noble gases:
Si + 2 Cl 2 = SiCl 4 + Q.
When interacting with hydrogen at room temperature, there is practically no reaction, but as soon as illumination acts as an external influence, a chain reaction arises, which has found its application in organic chemistry.
When heated, chlorine is able to displace iodine or bromine from their acids:
Cl 2 + 2 HBr = 2 HCl + Br 2 .
Chlorine reacts with water, partially dissolving in it. This mixture is called chlorine water.
Reacts with alkalis:
Cl 2 + 2NaOH = NaCl + NaClO + H 2 O (cold),
Cl 2 + 6KOH = 5KCl + KClO 3 + 3 H 2 O (heat).
Chlorine production.
1. Electrolysis of sodium chloride melt, which proceeds according to the following scheme:
2. Laboratory method for chlorine production:
MnO 2 + 4HCl = MnCl 2 + Cl 2 + 2H 2 O.
Chlorine occurs naturally in a gaseous state and only in the form of compounds with other gases. Under normal conditions, it is a greenish poisonous corrosive gas. It is heavier than air. Has a sweet scent. The 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. The result is phosgene gas. Very poisonous. So, even at a low concentration in the air (0.001 mg per 1 dm 3) can cause death. chlorine says that it is heavier than air, therefore, it will always be 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. Schele 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 with hydrogen, but the chemist could not separate these two elements.
Chlorine chemical characteristics
Chlorine is a chemical element of the main subgroup of the VII group of the periodic table. It is in the third period and has atomic number 17 (17 protons in the atomic nucleus). Reactive non-metal. It is designated by the letters Cl.
Gases that are colorless, but have a pungent, pungent odor are typical. Generally toxic. All halogens are readily diluted in water. Smoke on contact with moist air.
The outer electronic configuration of the Cl atom is 3s23p5. 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 affinity of the atom to the electron is 3.65 eV, the ionization level is 12.87 eV.
As indicated above, chlorine is a fairly active non-metal, which allows you to create compounds with almost any metals (in some cases by heating or with the help of moisture, while 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 is capable of forming oxides, hypochlorites, chlorites and chlorates. All compounds containing oxygen become explosive when interacting with oxidizing substances. It should be noted that they can explode arbitrarily, while chlorates explode only when exposed to any initiators.
Chlorine characteristic by position in the periodic system:
Simple substance;
... element of the seventeenth group of the periodic table;
... third period of the third row;
... the seventh group of the main subgroup;
... atomic number 17;
... denoted by the symbol Cl;
... reactive non-metal;
... is in the group of halogens;
... under conditions close to normal, it is a poisonous gas of yellowish-green color with a pungent odor;
... the chlorine molecule has 2 atoms (formula Cl 2).
Chlorine physical properties:
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 / cm 3;
... solid chlorine density - 1.9 g / cm 3;
... specific volume - 1.745 x 10 -3 l / g.
Chlorine: characteristic of temperature changes
In a 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. Very highly corrosive. As practice shows, this chemical element can maintain a liquid state up to a critical temperature (143 ° C), subject to an increase in 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 an indicator of -101 ° C).
Chlorine in nature
The earth's crust contains only 0.017% chlorine. The bulk is found in volcanic gases. As indicated above, the substance has a high chemical activity, as a result of which it occurs in nature in compounds with other elements. However, many minerals contain chlorine. The characteristic of the element allows the formation of about a hundred different minerals. As a rule, these are metal chlorides.
Also, a large amount of it is in the oceans - almost 2%. This is due to the fact that chlorides are very actively dissolved and carried by rivers and seas. The reverse process is also possible. Chlorine is washed back to the shore, and then the wind carries it around the neighborhood. 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 by 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.
Chlorine production methods
Today there are a number of methods for producing chlorine, of which the following are the most common:
1. Diaphragm. It is the simplest and least expensive. The saline solution in diaphragm electrolysis enters the anode space. Further along the steel cathode grid flows 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 one, which makes it possible to separately obtain chlorine and lye.
2. Membrane. 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 should be noted that the characteristics of the chemical. the element (chlorine) obtained by these methods will be different. The membrane method is considered to be "cleaner".
3. Mercury method with a liquid cathode. Compared to other technologies, this option allows you to get the most pure chlorine.
The basic diagram of the installation consists of an electrolyzer and an interconnected pump and amalgam decomposer. The mercury pumped by the pump together with a solution of sodium chloride serves as the cathode, and carbon or graphite electrodes are used as the anode. The principle of operation of the installation is as follows: chlorine is released from the electrolyte, which is removed from the electrolyzer together with the anolyte. Impurities and chlorine residues are removed from the latter, saturated with halite and returned to electrolysis.
Industrial safety requirements and unprofitable production led to the replacement of a liquid cathode with a solid one.
Industrial chlorine applications
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 biggest niche in the industry is the production of hydrochloric acid and lime.
Methods of purification of drinking water are widely used. Today, they are trying to move away from this method, replacing it with ozonization, since the substance we are considering negatively affects the human body, moreover, chlorinated water destroys pipelines. This is due to the fact that in the free state, Cl has a detrimental effect on pipes made of 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 for weed control 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. Such a result is possible only if water is present, because the discoloration process occurs due to which is formed after the decomposition of chlorine: Cl 2 + H 2 O → HCl + HClO → 2HCl + O. This method was used a couple of centuries ago and is popular to this day.
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 part of all chlorine produced on the planet goes to agricultural needs.
It is also used in the production of plastic compounds and rubber. With their help, wire insulation, office supplies, equipment, casings of household appliances, etc. are made. There is an opinion that rubbers obtained in this way harm a person, but this is not confirmed by science.
It is worth noting that chlorine (the characteristics of the substance were disclosed in detail by us earlier) and its derivatives, such as mustard gas and phosgene, are also used for military purposes to obtain chemical warfare agents.
Chlorine as a bright representative of non-metals
Non-metals are simple substances that include gases and liquids. In most cases, they conduct electric current 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 will be given the characteristics of a non-metal using the example of chlorine.
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 bonds with simple substances and some complex ones. Refers to halogens, which is clearly reflected in its chemical characteristics. In compounds with other representatives of halogens (bromine, astatine, iodine), it displaces them. In the gaseous state, chlorine (its characteristic is a direct confirmation of this) dissolves well. It is an excellent disinfectant. It kills only living organisms, which makes it indispensable in agriculture and medicine.
Use as a poisonous substance
The characteristic of the chlorine atom makes it possible to use it as a poisonous agent. For the first time, the gas was 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 does not apply.
Let us give a brief description of the chemical element as an asphyxiant. Affects the human body through strangulation. 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 eats away at the lung tissue, which leads to edema. Important! Chlorine is a fast-acting substance.
Symptoms vary depending on the concentration in the air. With a low content in a person, redness of the mucous membrane of the eyes, slight shortness of breath is observed. The content in the atmosphere of 1.5-2 g / m 3 causes heaviness and acute sensations in the chest, sharp pain in the upper respiratory tract. Also, the condition may be accompanied by severe lacrimation. After 10-15 minutes of being in a room with such a concentration of chlorine, a severe burn of the lungs and death occurs. At higher 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 present not in pure form, but in the form of compounds.
In organisms of animals and humans, 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, chlorine ions create a favorable environment for the action of proteolytic enzymes in gastric juice. Chlorine channels are provided in many cells of our body. Through them, intercellular fluid exchange takes place 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 excreted 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 takes an active part in energy exchange. 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 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 a point as the ability of a substance to oxidize soil. 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.
Transport and storage of chlorine
There are several ways to move and store chlorine. The characteristic of the element suggests the need for special high-pressure cylinders. Such containers are identified by a vertical green line. The cylinders must be thoroughly flushed monthly. With long-term storage of chlorine, a very explosive precipitate is formed in them - nitrogen trichloride. Failure to comply with all safety rules may spontaneous ignition and explosion.
Chlorine study
The characteristics of chlorine should be known to future chemists. According to the plan, 9th graders can even conduct laboratory experiments with this substance based on basic knowledge of the discipline. Naturally, the teacher is obliged to conduct a safety briefing.
The order of work 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 is formed. When tin foil is immersed in a vessel with chlorine, it will also self-ignite, and fiery snowflakes will slowly descend to the bottom of the flask. During this reaction, a smoky liquid is formed - SnCl 4. When the iron shavings are placed in the vessel, red "drops" are formed and the red smoke of FeCl 3 appears.
Along with practical work, theory is repeated. In particular, such a question as the characteristic of chlorine by position in the periodic system (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 put cotton wool soaked in turpentine in a jar of chlorine, it will instantly ignite, and soot will suddenly fall out of the flask. Sodium effectively smolders with a yellowish flame, and salt crystals appear on the walls of the chemical vessel. Students will be interested in learning that, while still a young chemist, N.N.Semenov (later a Nobel Prize winner), having carried out such an experiment, collected salt from the walls of the flask and, sprinkling it on the bread, ate it. Chemistry turned out to be right and did not disappoint the scientist. As a result of the experiment carried out by the chemist, ordinary table salt really turned out!
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