Chlorine in nature. Chlorine is a very strong oxidizing agent. What is the most stable form of existence of the element chlorine
| Chlorine | |
|---|---|
| atomic number | 17 |
| Appearance of a simple substance | Yellow-green gas with a pungent odor. Poisonous. |
| Atom properties | |
| Atomic mass (molar mass) |
35.4527 amu (g/mol) |
| Atom radius | 100 pm |
| Ionization energy (first electron) |
1254.9(13.01) kJ/mol (eV) |
| Electronic configuration | 3s 2 3p 5 |
| Chemical properties | |
| covalent radius | 99 pm |
| Ion radius | (+7e)27 (-1e)181 pm |
| Electronegativity (according to Pauling) |
3.16 |
| Electrode potential | 0 |
| Oxidation states | 7, 6, 5, 4, 3, 1, −1 |
| Thermodynamic properties of a simple substance | |
| Density | (at -33.6 °C)1.56 g/cm³ |
| Molar heat capacity | 21.838 J/(K mol) |
| Thermal conductivity | 0.009 W /( K) |
| Melting temperature | 172.2 |
| Melting heat | 6.41 kJ / mol |
| Boiling temperature | 238.6 |
| Heat of evaporation | 20.41 kJ/mol |
| Molar volume | 18.7 cm³/mol |
| The crystal lattice of a simple substance | |
| Lattice structure | orthorhombic |
| Lattice parameters | a=6.29 b=4.50 c=8.21 Å |
| c/a ratio | — |
| Debye temperature | n/a K |
Chlorine (χλωρός - green) - an element of the main subgroup of the seventh group, the third period periodic system chemical elements, with atomic number 17.
The element Chlorine is represented by the symbol Cl(lat. Chlorum). Reactive nonmetal. It belongs to 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 take root, and subsequently became common for the VII group of elements, which includes chlorine).
simple substance chlorine(CAS number: 7782-50-5) Under normal conditions, a yellowish-green poisonous gas with a pungent odor. The chlorine molecule is diatomic (formula Cl 2).
The history of the discovery of chlorine
Chlorine atom diagram
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 \u003d Cl 2 + MnCl 2 + 2H 2 O
Scheele noted the smell of chlorine, similar to the smell of aqua regia, its ability to interact with gold and cinnabar, as well as its bleaching properties.
Scheele, in accordance with the phlogiston theory prevailing in chemistry of that time, suggested that chlorine is a dephlogistic hydrochloric acid, i.e. 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 by electrolysis into sodium And chlorine.
Distribution in nature
In nature, there are two isotopes of chlorine 35 Cl and 37 Cl. Chlorine is the most abundant halogen in the earth's crust. Chlorine is very active - it combines directly with almost all elements of the periodic table.
In nature, it occurs only in the form of compounds in the composition of minerals: halite NaCI, sylvin KCl, sylvinite KCl NaCl, bischofite MgCl 2 6H2O, carnallite KCl MgCl 2 6H 2 O, kainite KCl MgSO 4 3H 2 O. Most large reserves of chlorine are contained in the salts of the waters of the seas and oceans.
Chlorine accounts for 0.025% of the total number of atoms in the earth's crust, the Clarke number of chlorine is 0.19%, and the human body contains 0.25% of chlorine ions by mass. In humans and animals, 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.
Isotopic composition
In nature, there are 2 stable isotopes of chlorine: with a mass number of 35 and 37. The proportions of their content are respectively 75.78% and 24.22%.
| Isotope | Relative mass, a.m.u. | Half life | Decay type | nuclear spin |
|---|---|---|---|---|
| 35Cl | 34.968852721 | stable | — | 3/2 |
| 36Cl | 35.9683069 | 301000 years | β-decay in 36 Ar | 0 |
| 37Cl | 36.96590262 | stable | — | 3/2 |
| 38Cl | 37.9680106 | 37.2 minutes | β-decay in 38 Ar | 2 |
| 39Cl | 38.968009 | 55.6 minutes | β-decay in 39 Ar | 3/2 |
| 40Cl | 39.97042 | 1.38 minutes | β-decay in 40 Ar | 2 |
| 41Cl | 40.9707 | 34 c | β-decay in 41 Ar | |
| 42Cl | 41.9732 | 46.8 s | β-decay in 42 Ar | |
| 43Cl | 42.9742 | 3.3 s | β-decay in 43 Ar |
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.
| Property | Meaning |
|---|---|
| Boiling temperature | -34°C |
| Melting temperature | -101°C |
| Decomposition temperature (dissociations into atoms) |
~1400°С |
| Density (gas, n.o.s.) | 3.214 g/l |
| Affinity for the electron 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) |
| Enthalpy of fusion | 6.406 (kJ/mol) |
| Boiling enthalpy | 20.41 (kJ/mol) |
When cooled, chlorine turns into a liquid at a temperature of about 239 K, and then below 113 K it crystallizes into an orthorhombic lattice with a space group cmca and parameters a=6.29 b=4.50 , c=8.21 . Below 100 K, the orthorhombic modification of crystalline chlorine transforms into the tetragonal one, which has a space group P4 2 /ncm and lattice parameters a=8.56 and c=6.12 .
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 0.909%.
The odor perception threshold in the air is 0.003 (mg/l).
In the CAS registry - number 7782-50-5.
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 about one and a half times less than in air.
Chemical properties
The structure of the electron shell
The valence level of the chlorine atom contains 1 unpaired electron: 1S² 2S² 2p 6 3S² 3p 5, so the valency of 1 for the chlorine atom is very stable. Due to the presence of an unoccupied orbital of the d-sublevel in the chlorine atom, the chlorine atom can also exhibit other valences. Scheme of the formation of excited states of the atom:
Chlorine compounds are also known in which the chlorine atom formally exhibits valency 4 and 6, such as 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
In the light or when heated, it actively reacts (sometimes with an explosion) with hydrogen by a radical mechanism. Mixtures of chlorine with hydrogen, containing from 5.8 to 88.3% hydrogen, explode when irradiated with the formation of hydrogen chloride. A mixture of chlorine and hydrogen in small concentrations burns with a colorless or yellow-green flame. The maximum temperature of the hydrogen-chlorine flame is 2200 °C.:
Cl 2 + H 2 → 2HCl 5Cl 2 + 2P → 2PCl 5 2S + Cl 2 → S 2 Cl 2 Cl 2 + 3F 2 (ex.) → 2ClF 3
Other properties
Cl 2 + CO → COCl 2When 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 Cl 2 + Ca(OH) 2 → CaCl(OCl) + H 2 O 4NH 3 + 3Cl 2 → NCl 3 + 3NH 4Cl
Oxidizing properties of chlorine
Cl 2 + H 2 S → 2HCl + SReactions with organic substances
CH 3 -CH 3 + Cl 2 → C 2 H 6-x Cl x + HClAttaches to unsaturated compounds by multiple bonds:
CH 2 \u003d 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
How to get
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 by-product of 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 sodium chloride solution:
2NaCl + 2H 2 O → H 2 + Cl 2 + 2NaOH Anode: 2Cl - - 2e - → Cl 2 0 Cathode: 2H 2 O + 2e - → H 2 + 2OH -
Since the electrolysis of water takes place in parallel with the electrolysis of sodium chloride, the total 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, mercury cathode electrolysis is the easiest and most convenient method, but this method causes significant environmental damage due to evaporation and leakage of metallic mercury.
Diaphragm method with solid cathode
The cavity of the cell is divided by a porous asbestos partition - diaphragm - into the cathode and anode space, where the cathode and anode of the cell are respectively located. Therefore, such an electrolyzer is often called diaphragm electrolysis, and the production method is diaphragm electrolysis. A stream of saturated anolyte (NaCl solution) continuously enters the anode space of the diaphragm cell. 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 it is 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, under the action of a mercury pump, mercury circulates, passing through the electrolyzer and the decomposer. The cathode of the cell is a stream 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 the released sodium dissolves in mercury at the cathode, forming an amalgam.
Laboratory methods
In laboratories, to obtain 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 produced chlorine is stored in special “tanks” or pumped into high-pressure steel cylinders. Cylinders with liquid chlorine under pressure have a special color - marsh color. It should be noted that during long-term use of chlorine cylinders, extremely explosive nitrogen trichloride accumulates in them, and therefore, from time to time, chlorine cylinders must be routinely flushed and cleaned from nitrogen chloride.
Chlorine quality standards
According to GOST 6718-93 “Liquid chlorine. Specifications» the following grades of chlorine are produced
Application
Chlorine is used in many industries, science and domestic needs:
The main ingredient in bleach is chlorine water.
- In the production of polyvinyl chloride, plastic compounds, synthetic rubber, which are used to make: insulation for wires, window profiles, packaging materials, clothing and footwear, linoleum and gramophone records, varnishes, equipment and foam plastics, toys, instrument parts, Construction Materials. Polyvinyl chloride is produced by polymerizing vinyl chloride, which today is most often obtained from ethylene in a chlorine-balanced method through an intermediate 1,2-dichloroethane.
- The bleaching properties of chlorine have been known since ancient times, although it is not chlorine itself that “bleaches”, but atomic oxygen, which is formed during the decomposition of hypochlorous acid: Cl 2 + H 2 O → HCl + HClO → 2HCl + O .. This method of bleaching fabrics, paper, Cardboard has been used for centuries.
- Production of organochlorine insecticides - substances that kill insects harmful to crops, but are safe for plants. A significant part of the produced chlorine is spent on obtaining plant protection products. One of the most important insecticides is hexachlorocyclohexane (often referred to as hexachlorane). This substance was first synthesized back in 1825 by Faraday, but found practical application only after more than 100 years - in the 30s of our century.
- It was used as a chemical warfare agent, as well as for the production of other chemical warfare agents: tap water, but they cannot offer an alternative to the disinfectant 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 life of pipelines based on polyolefins: polyethylene pipes of various types, including cross-linked polyethylene, more commonly known as PEX (PEX, PE-X). In the USA, to control the admission of pipelines from polymer materials 3 standards were forced to be adopted for use in water supply systems with chlorinated water: ASTM F2023 in relation to pipes made of cross-linked polyethylene (PEX) and hot chlorinated water, ASTM F2263 in relation to all polyethylene pipes and chlorinated water and ASTM F2330 in relation to multilayer (metal polymer) pipes and hot chlorinated water. A positive reaction in terms of durability when interacting with chlorinated water is demonstrated by copper combustion (intestines. Absorption and excretion of chlorine are closely related to sodium ions and bicarbonates, to a lesser extent with mineralocorticoids and the activity of Na + / K + - ATP-ase. 10- 15% of all chlorine, of this amount, from 1/3 to 1/2 - in erythrocytes... About 85% of chlorine is in the extracellular space.Chlorine is excreted from the body mainly with urine (90-95%), feces (4-8% ) and through the skin (up to 2%) Excretion of chlorine is associated with sodium and potassium ions, and reciprocally with HCO 3 - (acid-base balance).
A person consumes 5-10 g of NaCl per day. The minimum human need for chlorine is about 800 mg per day. The infant receives the necessary amount of chlorine through the 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 the destruction of pathogenic bacteria. At present, the role of chlorine in the occurrence of certain diseases in humans is not well understood, 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 - 0.09%; in the blood - 2.89 g / l. In the body of an average person (body weight 70 kg) 95 g of chlorine. Every day with food, a person receives 3-6 g of chlorine, which in excess covers the need for this element.
Chlorine ions are vital for plants. Chlorine is involved in energy metabolism in plants by activating oxidative phosphorylation. It is necessary for the formation of oxygen in the process of photosynthesis by isolated chloroplasts, stimulates auxiliary processes of photosynthesis, primarily those associated with the accumulation of energy. Chlorine has a positive effect on the absorption of oxygen, potassium, calcium, and magnesium compounds by the roots. An excessive concentration of chloride ions in plants can also have a negative side, for example, reduce the content of chlorophyll, 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 in saline soils are called halophytes, they accumulate chloride during the growing season and then get rid of the excess through leaf fall or release chloride on the surface of leaves and branches and receive the double benefit of shading the surface from sunlight. In Russia, halophytes grow on salt domes, outcrops of salt deposits and saline depressions around the Baskunchak and Elton salt lakes.
Among microorganisms, halophiles are also known - halobacteria - which live in highly saline waters or soils.
Features of operation and precautions
Chlorine is a toxic suffocating gas that, if it enters the lungs, causes burns to the lung tissue, suffocation. It has an irritant effect on the respiratory tract at a concentration in the air of about 0.006 mg / l (i.e. twice the chlorine odor threshold). Chlorine was one of the first chemical warfare agents used by Germany in World War I. When working with chlorine, protective clothing, gas masks, and gloves should be used. For a short time, it is possible to protect the respiratory organs from the ingress of chlorine with a rag bandage moistened with a solution of sodium sulfite Na 2 SO 3 or sodium thiosulfate Na 2 S 2 O 3.
MPC of chlorine in atmospheric air the following: average daily - 0.03 mg / m³; maximum one-time - 0.1 mg / m³; in the working premises of an industrial enterprise - 1 mg / m³.
Additional Information
Chlorine production in Russia
gold chloride
Chlorine water
Bleaching powder
Reize's first base chloride
Reize's second base chlorideChlorine compounds
Hypochlorites
Perchlorates
Acid chlorides
Chlorates
chlorides
Organochlorine compoundsAnalyzed
— With the help of reference electrodes ESr-10101 analyzing the content of Cl- and K+.
Chlorine
CHLORINE-A; m.[from Greek. chlōros - pale green] A chemical element (Cl), a greenish-yellow asphyxiating gas with a pungent odor (used as a poison and disinfectant). Chlorine compounds. Chlorine poisoning.
◁ Chlorine (see).
chlorine(lat. Chlorum), a chemical element of group VII of the periodic system, refers to halogens. The name is from the Greek chlōros, yellow-green. Free chlorine consists of diatomic molecules (Cl 2); yellow-green gas with a pungent odor; density 3.214 g/l; t pl -101°C; t kip -33.97°C; at ordinary temperature, it is easily liquefied under a pressure of 0.6 MPa. Chemically very active (oxidizing agent). The main minerals are halite (rock salt), sylvin, bischofite; sea water contains chlorides of sodium, potassium, magnesium and other elements. Used in the production of chlorine-containing organic compounds (60-75%), not organic matter(10-20%), for bleaching cellulose and fabrics (5-15%), for sanitary needs and disinfection (chlorination) of water. Toxic.
CHLORINECHLORINE (lat. Chlorum), Cl (read "chlorine"), a chemical element with atomic number 17, atomic mass 35.453. In its free form, it is a yellow-green heavy gas with a sharp, suffocating odor (hence the name: Greek chloros - yellow-green).
Natural chlorine is a mixture of two nuclides (cm. NUCLIDE) with mass numbers 35 (in a mixture of 75.77% by mass) and 37 (24.23%). Outer electron layer configuration 3 s 2
p 5
. In compounds, it mainly exhibits oxidation states –1, +1, +3, +5 and +7 (valences I, III, V and VII). Located in the third period in group VIIA of the periodic system of elements of Mendeleev, refers to halogens (cm. HALOGENS).
The radius of the neutral chlorine atom is 0.099 nm, the ionic radii are equal, respectively (in parentheses are the values of the coordination number): Cl - 0.167 nm (6), Cl 5+ 0.026 nm (3) and Clr 7+ 0.022 nm (3) and 0.041 nm ( 6). The successive ionization energies of the neutral chlorine atom are 12.97, 23.80, 35.9, 53.5, 67.8, 96.7, and 114.3 eV, respectively. Electron affinity 3.614 eV. On the Pauling scale, the electronegativity of chlorine is 3.16.
Discovery history
The most important chemical compound of chlorine - table salt (chemical formula NaCl, chemical name sodium chloride) - has been known to man since ancient times. There is evidence that the extraction of table salt was carried out as early as 3-4 thousand years BC in Libya. It is possible that, using table salt for various manipulations, alchemists also encountered gaseous chlorine. To dissolve the "king of metals" - gold - they used "aqua regia" - a mixture of hydrochloric and nitric acids, the interaction of which releases chlorine.
For the first time, chlorine gas was obtained and described in detail by the Swedish chemist K. Scheele (cm. SCHEELE Karl Wilhelm) in 1774. He heated hydrochloric acid with the mineral pyrolusite (cm. PYROLUSITE) MnO 2 and observed the evolution of a yellow-green gas with a pungent odor. Since in those days the theory of phlogiston dominated (cm. PHLOGISTON), Scheele considered the new gas as "dephlogistinated hydrochloric acid", i.e., as an oxide (oxide) of hydrochloric acid. A. Lavoisier (cm. Lavoisier Antoine Laurent) considered gas as an oxide of the element "muria" (hydrochloric acid was called muriic acid, from Latin muria - brine). The same point of view was first shared by the English scientist G. Davy (cm. DEVI Humphrey), who spent a lot of time decomposing "murium oxide" into simple substances. He did not succeed, and by 1811 Davy came to the conclusion that this gas is a simple substance, and a chemical element corresponds to it. Davy was the first to propose, in accordance with the yellow-green color of the gas, to call it chlorine (chlorine). The name "chlorine" was given to the element in 1812 by the French chemist J. L. Gay-Lussac (cm. GAY LUSSAC Joseph Louis); it is accepted in all countries except Great Britain and the USA, where the name introduced by Davy has been preserved. It has been suggested that this element should be called "halogen" (i.e., giving birth to salts), but over time it became common name all elements of group VIIA.
Being in nature
The content of chlorine in the earth's crust is 0.013% by mass, in a noticeable concentration it is in the form of Cl ion - present in sea water (on average, about 18.8 g / l). Chemically, chlorine is highly active and therefore does not occur in free form in nature. It is part of such minerals that form large deposits, such as table or rock salt (halite (cm. HALITE)) NaCl, carnallite (cm. CARNALLITE) KCl MgCl 2 6H 21 O, sylvite (cm. SILVIN) KCl, sylvinite (Na, K)Cl, kainite (cm. Cainite) KCl MgSO 4 3H 2 O, bischofite (cm. BISHOPHIT) MgCl 2 6H 2 O and many others. Chlorine can be found in most different breeds, in the soil.
Receipt
To obtain gaseous chlorine, electrolysis of a strong aqueous solution of NaCl is used (sometimes KCl is used). The electrolysis is carried out using a cation exchange membrane separating the cathode and anode spaces. At the same time, through the process
2NaCl + 2H 2 O \u003d 2NaOH + H 2 + Cl 2
three valuable chemical products are obtained at once: at the anode - chlorine, at the cathode - hydrogen (cm. HYDROGEN), and alkali accumulates in the cell (1.13 tons of NaOH for every ton of chlorine produced). The production of chlorine by electrolysis requires large amounts of electricity: 2.3 to 3.7 MW are consumed to produce 1 ton of chlorine.
To obtain chlorine in the laboratory, the reaction of concentrated hydrochloric acid with some strong oxidizing agent (potassium permanganate KMnO 4, potassium dichromate K 2 Cr 2 O 7, potassium chlorate KClO 3 , bleach CaClOCl, manganese oxide (IV) MnO 2) is used. It is most convenient to use potassium permanganate for these purposes: in this case, the reaction proceeds without heating:
2KMnO 4 + 16HCl \u003d 2KCl + 2MnCl 2 + 5Cl 2 + 8H 2 O.
If necessary, chlorine in a liquefied (under pressure) form is transported in railway tanks or in steel cylinders. Chlorine cylinders have a special marking, but even in the absence of such a chlorine cylinder, it is easy to distinguish it from cylinders with other non-toxic gases. The bottom of chlorine cylinders has the shape of a hemisphere, and a cylinder with liquid chlorine cannot be placed vertically without support.
Physical and chemical properties
At normal conditions chlorine is a yellow-green gas, the gas density at 25 ° C is 3.214 g / dm 3 (about 2.5 times the density of air). The melting point of solid chlorine is -100.98°C, the boiling point is -33.97°C. The standard electrode potential Cl 2 /Cl - in an aqueous solution is +1.3583 V.
In the free state, it exists in the form of diatomic Cl 2 molecules. The internuclear distance in this molecule is 0.1987 nm. The electron affinity of the Cl 2 molecule is 2.45 eV, the ionization potential is 11.48 eV. The dissociation energy of Cl 2 molecules into atoms is relatively low and amounts to 239.23 kJ/mol.
Chlorine is slightly soluble in water. At a temperature of 0°C, the solubility is 1.44 wt.%, at 20°C - 0.711°C wt.%, at 60°C - 0.323 wt. %. A solution of chlorine in water is called chlorine water. Equilibrium is established in chlorine water:
Cl 2 + H 2 O H + = Cl - + HOCl.
In order to shift this equilibrium to the left, i.e., to reduce the solubility of chlorine in water, either sodium chloride NaCl or some non-volatile strong acid (for example, sulfuric) should be added to the water.
Chlorine is highly soluble in many non-polar liquids. Liquid chlorine itself serves as a solvent for substances such as Bcl 3 , SiCl 4 , TiCl 4 .
Due to the low energy of dissociation of Cl 2 molecules into atoms and the high electron affinity of the chlorine atom, chlorine is chemically highly active. It enters into direct interaction with most metals (including, for example, gold) and many non-metals. So, without heating, chlorine reacts with alkaline (cm. ALKALI METALS) and alkaline earth metals (cm. ALKALINE EARTH METALS), with antimony:
2Sb + 3Cl 2 = 2SbCl 3
When heated, chlorine reacts with aluminum:
3Cl 2 + 2Al = 2A1Cl 3
and iron:
2Fe + 3Cl 2 \u003d 2FeCl 3.
Chlorine reacts with hydrogen H 2 either when ignited (chlorine burns quietly in a hydrogen atmosphere), or when a mixture of chlorine and hydrogen is irradiated with ultraviolet light. In this case, hydrogen chloride gas HCl is formed:
H 2 + Cl 2 \u003d 2HCl.
A solution of hydrogen chloride in water is called hydrochloric (cm. HYDROCHLORIC ACID)(hydrochloric) acid. The maximum mass concentration of hydrochloric acid is about 38%. Salts of hydrochloric acid - chlorides (cm. Chlorides), for example, ammonium chloride NH 4 Cl, calcium chloride CaCl 2 , barium chloride BaCl 2 and others. Many chlorides are highly soluble in water. Practically insoluble in water and in acidic aqueous solutions of silver chloride AgCl. A qualitative reaction to the presence of chloride ions in a solution is the formation of a white AgCl precipitate with Ag + ions, which is practically insoluble in a nitric acid medium:
CaCl 2 + 2AgNO 3 \u003d Ca (NO 3) 2 + 2AgCl.
At room temperature, chlorine reacts with sulfur (the so-called sulfur monochloride S 2 Cl 2 is formed) and fluorine (the compounds ClF and ClF 3 are formed). When heated, chlorine interacts with phosphorus (depending on the reaction conditions, PCl 3 or PCl 5 compounds are formed), arsenic, boron and other non-metals. Chlorine does not directly react with oxygen, nitrogen, carbon (numerous compounds of chlorine with these elements are obtained indirectly) and inert gases (recently, scientists have found ways to activate such reactions and carry them out “directly”). With other halogens, chlorine forms interhalogen compounds, for example, very strong oxidizing agents - fluorides ClF, ClF 3, ClF 5. The oxidizing power of chlorine is higher than that of bromine, so chlorine displaces the bromide ion from bromide solutions, for example:
Cl 2 + 2NaBr \u003d Br 2 + 2NaCl
Chlorine enters into substitution reactions with many organic compounds, for example, with methane CH 4 and benzene C 6 H 6:
CH 4 + Cl 2 = CH 3 Cl + Hcl or C 6 H 6 + Cl 2 = C 6 H 5 Cl + Hcl.
The chlorine molecule is capable of adding multiple bonds (double and triple) to organic compounds, for example, to ethylene C 2 H 4:
C 2 H 4 + Cl 2 = CH 2 ClCH 2 Cl.
Chlorine interacts with aqueous solutions of alkalis. If the reaction proceeds at room temperature, then chloride (for example, potassium chloride KCl) and hypochlorite are formed. (cm. HYPOCHLORITES)(for example, potassium hypochlorite KClO):
Cl 2 + 2KOH \u003d KClO + KCl + H 2 O.
When chlorine interacts with a hot (temperature of about 70-80 ° C) alkali solution, the corresponding chloride and chlorate are formed (cm. CHLORATES), For example:
3Cl 2 + 6KOH \u003d 5KSl + KClO 3 + 3H 2 O.
When chlorine interacts with a wet slurry of calcium hydroxide Ca (OH) 2, bleach is formed (cm. BLEACHING POWDER)("bleach") CaClOCl.
The oxidation state of chlorine +1 corresponds to a weak, unstable hypochlorous acid (cm. hypochlorous acid) HClO. Its salts are hypochlorites, for example, NaClO is sodium hypochlorite. Hypochlorites are the strongest oxidizers and are widely used as bleaching and disinfecting agents. When hypochlorites, in particular bleach, interact with carbon dioxide CO 2, volatile hypochlorous acid is formed among other products (cm. hypochlorous acid), which can decompose with the release of chlorine oxide (I) Cl 2 O:
2HClO \u003d Cl 2 O + H 2 O.
It is the smell of this gas, Cl 2 O, that is the characteristic smell of bleach.
The oxidation state of chlorine +3 corresponds to a low-stable acid of medium strength HclO 2. This acid is called chloride, its salts are chlorites. (cm. CHLORITES (salts)), for example, NaClO 2 - sodium chlorite.
The oxidation state of chlorine +4 corresponds to only one compound - chlorine dioxide СlО 2.
The oxidation state of chlorine +5 corresponds to strong, stable only in aqueous solutions at a concentration below 40%, chloric acid (cm. hypochlorous acid) HClO 3 . Its salts are chlorates, for example, potassium chlorate KClO 3 .
The oxidation state of chlorine +6 corresponds to only one compound - chlorine trioxide СlО 3 (exists in the form of a dimer Сl 2 О 6).
The oxidation state of chlorine +7 corresponds to a very strong and fairly stable perchloric acid (cm. PERCHLORIC ACID) HClO 4 . Its salts are perchlorates (cm. PERCHLORATES), for example, ammonium perchlorate NH 4 ClO 4 or potassium perchlorate KClO 4 . It should be noted that perchlorates of heavy alkali metals - potassium, and especially rubidium and cesium are slightly soluble in water. Oxide corresponding to the oxidation state of chlorine +7 - Cl 2 O 7.
Among compounds containing chlorine in positive oxidation states, hypochlorites have the strongest oxidizing properties. For perchlorates, oxidizing properties are uncharacteristic.
Application
Chlorine is one of the most important products of the chemical industry. Its world production is tens of millions of tons per year. Chlorine is used to produce disinfectants and bleaches (sodium hypochlorite, bleach and others), hydrochloric acid, chlorides of many metals and non-metals, many plastics (polyvinyl chloride (cm. polyvinyl chloride) and others), chlorine-containing solvents (dichloroethane CH 2 ClCH 2 Cl, carbon tetrachloride CCl 4, etc.), for opening ores, separation and purification of metals, etc. Chlorine is used to disinfect water (cm. CHLORINATION)) and for many other purposes.
Biological role
Chlorine is one of the most important biogenic elements (cm. BIOGENIC ELEMENTS) and is found in all living organisms. Some plants, the so-called halophytes, are not only able to grow on highly saline soils, but also accumulate chlorides in large quantities. Microorganisms (halobacteria, etc.) and animals living in conditions of high salinity of the environment are known. Chlorine is one of the main elements of the water-salt metabolism of animals and humans, which determines the physicochemical processes in the tissues of the body. It is involved in maintaining the acid-base balance in tissues, osmoregulation (cm. OSMO-REGULATION)(chlorine is the main osmotically active substance of blood, lymph, and other body fluids), being mainly outside the cells. In plants, chlorine is involved in oxidative reactions and photosynthesis.
Human muscle tissue contains 0.20-0.52% chlorine, bone - 0.09%; in the blood - 2.89 g / l. In the body of an average person (body weight 70 kg) 95 g of chlorine. Every day with food, a person receives 3-6 g of chlorine, which in excess covers the need for this element.
Features of working with chlorine
Chlorine is a poisonous suffocating gas that, if it enters the lungs, causes burns of lung tissue, suffocation. It has an irritating effect on the respiratory tract at a concentration in the air of about 0.006 mg / l. Chlorine was one of the first chemical poisons (cm. POISONING SUBSTANCES) used by Germany in World War I. When working with chlorine, protective clothing, gas masks, and gloves should be used. For a short time, it is possible to protect the respiratory organs from the ingress of chlorine with a rag bandage moistened with a solution of sodium sulfite Na 2 SO 3 or sodium thiosulfate Na 2 S 2 O 3. MPC of chlorine in the air of working premises is 1 mg/m 3 , in the air of settlements 0.03 mg/m 3 .
encyclopedic Dictionary. 2009 .
Synonyms:See what "chlorine" is in other dictionaries:
Chlorine and... Russian word stress
chlorine- chlorine, and ... Russian spelling dictionary
chlorine- chlorine / ... Morphemic spelling dictionary
- (Greek chloros greenish yellow). Chemically simple, gaseous body, greenish-yellow color, pungent, irritating odor, having the ability to discolor plant matter. Dictionary of foreign words included in the Russian language ... Dictionary of foreign words of the Russian language
- (symbol C1), a widespread non-metallic element, one of the HALOGENS (elements of the seventh group of the periodic table), first discovered in 1774. It is part of sodium chloride (NaCl). Chlorine is a greenish yellow ... ... Scientific and technical encyclopedic dictionary
CHLORINE- CHLORINE, C12, chem. element, atomic number 17, atomic weight 35.457. Being in the VII group of the III period, the chlorine atoms have 7 outer electrons, due to which X. behaves like a typical monovalent metalloid. X. is divided into isotopes with atomic ... ... Big Medical Encyclopedia
Chlorine- usually obtained by electrolysis of alkali metal chlorides, in particular sodium chloride. Chlorine is a greenish-yellow suffocating, corrosive gas that is 2.5 times denser than air, sparingly soluble in water and easily liquefied. Usually transported... Official terminology
Chlorine- (Chlorum), Cl, a chemical element of group VII of the periodic system, atomic number 17, atomic mass 35.453; refers to halogens; yellow-green gas, bp 33.97°C. Used in the production of polyvinyl chloride, chloroprene rubber, ... ... Illustrated Encyclopedic Dictionary
CHLORINE, chlorine, pl. no, husband. (from Greek chloros green) (chem.). Chemical element, suffocating gas, use. in technology, in sanitation as a disinfectant, and in military affairs as a poisonous substance. Explanatory Dictionary of Ushakov. D.N. Ushakov. 1935 1940 ... Explanatory Dictionary of Ushakov
Chlorine ... The initial part of compound words, introducing the meanings of the words: chlorine, chloride (organochlorine, chloroacetone, chlorobenzene, chloromethane, etc.). Explanatory Dictionary of Ephraim. T. F. Efremova. 2000... Modern Dictionary Russian language Efremova
Books
- Russian theater or Complete collection of all Russian theatrical works. Ch 24. Operas: Guardian Professor. - I. Knyazhnin. Trouble from the carriage. - The joy of Dushinka. - Sailor jokes. - . Chlor prince, , . The book is a reprint edition of 1786. Although serious work has been done to restore the original quality of the edition, some pages may…
In nature, chlorine occurs in a gaseous state and only in the form of compounds with other gases. Under conditions close to normal, it is a greenish, poisonous, caustic gas. It has more weight than air. Has a sweet smell. The chlorine molecule contains two atoms. In a calm state does not burn, but when high temperatures enters into interaction with hydrogen, after which an explosion is possible. As a result, phosgene gas is released. Very poisonous. So, even at a low concentration in the air (0.001 mg per 1 dm 3) it 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. Schelee 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.
Chemical characterization 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). Reactive nonmetal. It is denoted by the letters Cl.
It is a typical representative of gases that do not have color, but have a sharp pungent odor. Usually toxic. All halogens are highly soluble in water. Upon contact with moist air, they begin to smoke.
The external electronic configuration of the Cl atom is 3s23p5. Therefore, in compounds, the 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 mentioned above, chlorine is a fairly active non-metal, which allows you to create compounds with almost any metal (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 under the influence of 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 randomly, while chlorates explode only when exposed to any initiators.
Characteristics of chlorine by position in the periodic system:
Simple substance;
. element of the seventeenth group of the periodic table;
. the 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 halogen group;
. under conditions close to normal, it is a yellowish-green poisonous gas with a pungent odor;
. the 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;
. the density of liquid chlorine (during the boiling period) - 1.537 g / cm 3;
. 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. It has very high corrosion properties. 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 -101 ° C).
Chlorine in nature
The earth's crust contains only 0.017% chlorine. The bulk is 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. That is why its highest 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 are mined annually in the world given substance. Which, however, is not surprising, because there are many deposits containing chlorine. Its characteristics, however, largely depend on its geographical location.
Methods for obtaining chlorine
Today, there are a number of methods for obtaining chlorine, of which the following are the most common:
1. Aperture. It is the simplest and least expensive. Salt solution in diaphragm electrolysis enters the anode space. Further on the steel cathode grid flows into the diaphragm. It contains a small amount of polymer fibers. An important feature this device is countercurrent. It is directed from the anode to the cathode space, which makes it possible to obtain chlorine and lye 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 should be noted that the characteristics of the chem. element (chlorine) obtained by these methods will be different. More "clean" is considered to be the membrane method.
3. Mercury method with liquid cathode. Compared to other technologies, this option allows you to get the purest chlorine.
The basic scheme of the installation consists of an electrolyser and interconnected pump and amalgam decomposer. The mercury pumped by the pump together with a solution of common salt serves as the cathode, and carbon or graphite electrodes serve 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 again.
The requirements of industrial safety and the unprofitability of production led to the replacement of the liquid cathode with a solid one.
The 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 biggest 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, besides, chlorinated water destroys pipelines. This is due to the fact that in the free state Cl adversely affects 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 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 bleaching process occurs due to which it is formed after the breakdown of chlorine: Cl 2 + H 2 O → HCl + HClO → 2HCl + O. This method was used 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 preparations kill harmful organisms, leaving 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, stationery, equipment, shells of household appliances, etc. are made. There is an opinion that rubbers obtained in this way harm a person, but this has not been 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, a characteristic of a non-metal will be given 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 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. Kills only living organisms, which makes it indispensable in agriculture and medicine.
Use as a poison
The characteristic of the chlorine atom allows it to be used as a poisonous agent. For the first time, 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 a suffocating agent. Affects the human body through suffocation. First, it irritates the upper respiratory tract and mucous membranes of the eyes. A strong 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, the symptoms are different. 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 thrills 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 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 present not in its pure form, but in the form of compounds.
In organisms of animals and humans, chloride 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 provided in many cells of 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 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 actively takes part in the 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 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 chloride 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 rinsed 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.
The study of chlorine
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 order of work is as follows: you need to take a flask with chlorine and pour small metal shavings into it. In flight, the chips will flare up with bright bright sparks and at the same time a light white smoke of SbCl 3 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, SnCl 4 , is formed. When iron shavings are placed in the vessel, red “drops” are formed and red smoke of FeCl 3 will appear.
Along with practical work the theory is repeated. In particular, such a question as the characterization of chlorine by position in the periodic system (described at the beginning of the article).
As a result of the experiments, it turns out that the element actively reacts to organic compounds. If you place cotton wool soaked in turpentine in a jar of chlorine, it will instantly ignite, and soot will fall sharply from the flask. Sodium effectively smolders with a yellowish flame, and salt crystals appear on the walls of chemical dishes. Students will be interested to know that, while still a young chemist, N. N. Semenov (later Nobel Prize winner), after conducting such an experiment, collected salt from the walls of the flask and, sprinkling bread with it, 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 really turned out!
The physical properties of chlorine are considered: the density of chlorine, its thermal conductivity, specific heat capacity 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 state of this halogen.
Basic physical properties of chlorine
Chlorine is included in group VII of the third period of the periodic system of elements at number 17. It belongs to the halogen subgroup, has 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 liquefies easily under ordinary 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 reactivity, free chlorine does not occur in nature, but exists only in the form of compounds. It is found mainly in the mineral halite (), it is also part of such minerals as: sylvin (KCl), carnallite (KCl MgCl 2 6H 2 O) and sylvinite (KCl NaCl). The content of chlorine 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 of 75.77% 35 Cl and 24.23% 37 Cl.
| Property | Meaning |
|---|---|
| Melting point, °С | -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°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°С (for water at 4°С) | 1,468 |
| Specific volume of gas (at 0°С 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 |
| Melting heat of solid chlorine (at the 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 |
| Saturated steam enthalpy, kJ/kg | 1,306 |
| Enthalpy of liquid chlorine, kJ/kg | 0,879 |
| Refractive index at 14°C | 1,367 |
| Specific conductivity at -70°C, Sm/m | 10 -18 |
| Electron affinity, kJ/mol | 357 |
| Ionization energy, kJ/mol | 1260 |
Density of chlorine
Under normal conditions, chlorine is a heavy gas with a density approximately 2.5 times greater than . Density of gaseous and liquid chlorine under normal conditions (at 0 ° C) is equal to 3.214 and 1468 kg / m 3, 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 (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 example, 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 gaseous chlorine 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 pressure of chlorine 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, °C | 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, °C | 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 go 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 capacity of chlorine
The specific heat capacity of gaseous chlorine C p in 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 capacity of chlorine is 471 J/(kg K) and increases upon heating. The increase in heat capacity at temperatures above 500°C becomes insignificant, and at high temperatures the specific heat capacity of chlorine remains virtually unchanged.
The table shows the results of calculating the specific heat capacity 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 a temperature 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 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 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 gaseous chlorine 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 |
Viscosity of chlorine
The coefficient of dynamic viscosity 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 set temperature T, K;
η T 0 is the coefficient of dynamic viscosity of chlorine at a temperature T 0 =273 K (at n.a.);
C is Sutherland's constant (for chlorine C=351).
Under normal conditions, the dynamic viscosity of chlorine is 0.0123·10 -3 Pa·s. When heated, such a physical property of chlorine 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 a subgroup of manganese. Elements of group VII of the periodic system of D. I. Mendeleev. Student aid. M .: Education, 1976 - 112 p.
- Tables of physical quantities. Directory. Ed. acad. I. K. Kikoina. Moscow: Atomizdat, 1976 - 1008 p.
- Yakimenko L. M., Pasmanik M. I. Reference book on the production of chlorine, caustic soda and basic chlorine products. Ed. 2nd, trans. etc. M.: Chemistry, 1976 - 440 p.
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 is Ypres. Crecy - Ypres - Hiroshima - milestones on the way to turning war into a giant machine of destruction.
At the beginning of 1915, the so-called Ypres ledge formed on the western front line. The allied Anglo-French troops northeast of Ypres wedged into 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, when a flat northeast blew, the Germans began an unusual preparation for the offensive - they carried out the first gas attack in the history of wars. On the Ypres sector of the front, 6,000 cylinders of chlorine were simultaneously opened. Within five minutes, a huge, weighing 180 tons, poisonous yellow-green cloud formed, which slowly moved towards the enemy's trenches.
Nobody expected this. The troops of the French and British were preparing for an attack, for artillery shelling, the soldiers dug in securely, but in front of the destructive chlorine cloud they were absolutely unarmed. The deadly gas penetrated into all the cracks, into all the shelters. The results of the first chemical attack (and the first violation of the 1907 Hague Convention on the Non-Use of Poisonous Substances!) were stunning - chlorine struck about 15 thousand people, and about 5 thousand - to death. And all this - in order to level the front line 6 km long! Two months later, the Germans launched a chlorine attack on the eastern front as well. And two years later, Ypres increased its notoriety. During a heavy battle on July 12, 1917, a poisonous substance, later called mustard gas, was used for the first time in the area of \u200b\u200bthis city. Mustard is a derivative of chlorine, dichlorodiethyl sulfide.
We recalled these episodes of history, connected 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 page in the history of chlorine. But it would be completely wrong to see in chlorine only a poisonous substance and a raw material for the production of other poisonous substances...
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 recall 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 the use of salt by man date back to about 3-4 millennium BC. But the most ancient description of the extraction of rock salt is found in the writings of the Greek historian Herodotus (V century BC). Herodotus describes the mining of rock salt in Libya. In the oasis of Sinah in the center of the Libyan desert was the famous temple of the god Ammon-Ra. That is why Libya was called "Ammonia", and the first name of rock salt was "sal ammoniacum". Later, starting around the thirteenth 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 calcining with salt and clay. And one of the first descriptions of the purification of sodium chloride is found in the writings 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, and in Europe in the 13th century. "royal vodka" was known - a mixture of hydrochloric and nitric acids. The book Hortus Medicinae by the Dutchman Van Helmont, published in 1668, says that when ammonium chloride and nitric acid are heated together, a certain gas is obtained. Based on the description, this gas is very similar to chlorine.
in detail chlorine was first described by the Swedish chemist Scheele in his treatise on pyrolusite. By heating the mineral pyrolusite with hydrochloric acid, Scheele noticed the smell characteristic of aqua regia, collected and studied the yellow-green gas that gave rise to this smell, 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 "dephlogistinated hydrochloric acid". In modern terms, Scheele, and after him other scientists of that time, believed that the new gas was hydrochloric acid oxide.
Somewhat later, Bertholet and Lavoisier suggested that this gas be considered an oxide of some new element, murium. For three and a half decades, chemists have unsuccessfully tried to isolate the unknown murium.
A supporter of "murium oxide" was at first Davy, who in 1807 decomposed electric shock table salt to 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 Greek - yellow-green). And three years later, Gay-Lussac gave the new element more short name- chlorine. True, back in 1811, the German chemist Schweiger proposed another name for chlorine - “halogen” (literally it translates as salt), but this name did not take root 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. First, it is a halogen; secondly, one of the strongest oxidizing agents; thirdly, an extremely poisonous gas; fourthly, the most important product of the main chemical industry; fifthly, raw materials for the production of plastics and pesticides, rubber and artificial fibers, dyes and medicines; sixth, the substance with which titanium and silicon are obtained, glycerin and fluoroplast; seventh, a means for purifying drinking water and bleaching fabrics ...
This listing could be continued.
Under normal conditions, elemental chlorine is a rather heavy yellow-green gas with a sharp 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 gaseous chlorine under normal conditions (temperature 0 ° C and pressure 760 mmHg) 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 hardens. Under increased pressure, chlorine can be turned into a liquid and at higher temperatures up to +144°C. Chlorine is highly soluble in dichloroethane and some other chlorine-containing organic solvents.
Element number 17 is very active - it connects directly with almost all elements of the periodic system. Therefore, in nature, it occurs only in the form of compounds. The most common minerals containing chlorine, 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 their first "wine" (or "credit") that the chlorine content of the earth's crust is 0.20% by weight. For non-ferrous metallurgy, some relatively rare chlorine-containing minerals are very important, for example, horn silver AgCl.
In terms of electrical conductivity, liquid chlorine ranks among the strongest insulators: it conducts current almost a billion times worse than distilled water, and 1022 times worse than silver.
The speed of sound in chlorine is about one and a half times less than in air.
And finally - about the isotopes of chlorine.
Now ten isotopes of this element are known, but only two are found in nature - chlorine-35 and chlorine-37. The first is about three times more than the second.
The remaining eight isotopes were 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.
ELEMENTARY CALCULATION. When chlorine is obtained by electrolysis of a sodium chloride solution, hydrogen and sodium hydroxide are simultaneously obtained: 2NaCl + 2H 2 O \u003d H 2 + Cl 2 + 2NaOH. Of course, hydrogen is 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 obtained almost exclusively by electrolysis of sodium chloride solutions - other methods account for less than 10%. Since the production of chlorine and NaOH are completely interconnected (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) in terms of alkali , you can easily calculate how much chlorine it produces. Each ton of NaOH is "accompanied" by 890 kg of chlorine.
OH AND LUBRICANT! Concentrated sulfuric acid is practically the only liquid that does not interact with chlorine. Therefore, for compressing and pumping chlorine, factories use pumps in which sulfuric acid plays the role of a working fluid and at the same time a lubricant.
Pseudonym of Friedrich Wöhler. Investigating the interaction of organic substances with chlorine, the French chemist of the XIX century. Jean Dumas made an amazing discovery: chlorine is able to replace hydrogen in the molecules of organic compounds. For example, when chlorinating acetic acid, first one hydrogen of the methyl group is replaced by chlorine, then another, third. But the most striking thing was that chemical properties chloroacetic acids differed little from acetic acid itself. The class of reactions discovered by Dumas was completely inexplicable by the then dominant electrochemical hypothesis and the theory of Berzelius radicals. Berzelius, his students and followers vigorously disputed the correctness of Dumas' work. In the German journal Annalen der Chemie und Pharmacie, a mocking letter appeared from the famous German chemist Friedrich Wöhler under the pseudonym S. C. H. Windier (in German, “Schwindler” means “liar”, “deceiver”). It reported that the author managed to replace in fiber (C 6 H 10 O 5), all carbon, hydrogen and oxygen atoms by chlorine, and the properties of the fiber did not change. And that now in London they make warm girdles from cotton wool, consisting of pure chlorine.
CHLORINE AND WATER. Chlorine is visibly 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 the light, they gradually discolor. This is explained by the fact that dissolved chlorine partially interacts with water, hydrochloric and hypochlorous acids are formed: Cl 2 + H 2 O → HCl + HOCl. The latter is unstable and gradually decomposes into HCl and oxygen. Therefore, a solution of chlorine in water gradually turns into a solution of hydrochloric acid.
But at low temperatures, chlorine and iodine form a crystalline hydrate of an 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, and it is determined primarily by the structure of ice. In the crystal lattice of ice, H 2 O molecules can be located in such a way that regularly spaced voids appear between them. The elementary cubic cell contains 46 water molecules, between which there are eight microscopic voids. In these voids, chlorine molecules settle. The exact formula of chlorine hydrate should therefore be written as follows: 8Cl 2 * 46H 2 O.
POISONING WITH CHLORINE. 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%, then acute poisoning, the first sign of which is bouts of severe coughing. In case of chlorine poisoning, absolute rest is necessary; it is useful to inhale oxygen or ammonia (smelling ammonia), or vapors of alcohol with ether. According to existing sanitary standards, the content of chlorine in the air industrial premises should not exceed 0.001 mg / l, i.e. 0.00003%.
HE 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. So, victims of hydrogen sulfide are given to sniff unstable bleach. By interacting, the two poisons are mutually neutralized.
ANALYSIS FOR CHLORINE. To determine the chlorine content, an air sample is passed through absorbers with an acidified solution of potassium iodide. (Chlorine displaces pod, the amount of the latter is easily determined by filtration with a solution of Na 2 S 2 O 3.) To determine the microquantities of chlorine in the air, a colorimetric method is often used, based on a sharp change in the color of some compounds (benzidine, orthotoluidine, methyl orange) during their oxidation with chlorine . For example, a colorless acidified solution of benzidine acquires yellow, and the neutral is blue. The color intensity is proportional to the amount of chlorine.
