In nature, chlorine occurs in a gaseous state and only in the form of compounds with other gases. In conditions close to normal, it is a poisonous caustic gas of a greenish color. It has more weight than air. It has a sweet smell. The chlorine molecule contains two atoms. In a calm state it does not burn, but at high temperatures it enters into interaction with hydrogen, after which an explosion is possible. As a result, phosgene gas is released. Very toxic. So, even with a low concentration in the air (0.001 mg per 1 dm 3 ) it can cause death. The main characteristic of non-metal chlorine is 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 C. Schelier 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 Joseph Priestley was able to get hydrogen chloride - a combination 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 located in the third period and has an atomic number 17 (17 protons in the atomic nucleus). Reactive non-metal. It is denoted by the letters Cl.
It is a typical representative of halogens. These are gases that do not have color, but have a pungent pungent odor. Generally toxic. All halogens are well diluted in water. Upon contact with moist air begin to smoke.
External electronic configuration of the Cl 3s25 atom. 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 for the electron is 3.65 eV, and 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 metal (in some cases by heating or using moisture, 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. It can form oxides, hypochlorites, chlorites and chlorates with oxygen. All compounds containing oxygen become explosive under conditions of interaction with oxidizing substances. It is worth noting that chlorine oxides can arbitrarily explode, while chlorates explode only when exposed to any initiators.
Characterization 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;
• is indicated by the symbol Cl;
• chemically active non-metal;
• is in the halogen group;
• in conditions close to normal, it is a poisonous gas of yellowish-green color with a pungent odor;
• The chlorine molecule has 2 atoms (Cl 2 formula).
Physical properties of chlorine:
• boiling point: -34.04 ° C;
• melting point: -101.5 ° C;
• density in the gaseous state - 3, 214 g / l;
• density of liquid chlorine (during boiling) - 1.537 g / cm 3 ;
• density of solid chlorine - 1.9 g / cm 3 ;
• specific volume - 1.745 x 10 -3 l / g.
Chlorine: Characterization of Temperature Changes
In the gaseous state, it tends to be easily liquefied. 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), provided that the pressure increases.
If it is cooled to a temperature of -32 ° C, it will change its state of aggregation to liquid regardless of atmospheric pressure. With a further decrease in temperature, crystallization occurs (at a value of -101 ° C).
Chlorine in nature
In the earth's crust of chlorine contains only 0.017%. The bulk is in volcanic gases. As indicated above, the substance has a high chemical activity, as a result of which it naturally occurs in compounds with other elements. However, many minerals contain chlorine. The characteristic of the element allows the formation of about one hundred different minerals. As a rule, these are metal chlorides.
Also, a large number 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 greatest concentration is observed in coastal zones. In the arid regions of the planet, the gas under consideration 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 characteristic, however, largely depends on its geographical location.
Chlorine production methods
Today, there are a number of methods for producing chlorine, of which the following are most common:
1. Aperture. It is the simplest and less expensive. Salt solution in the diaphragm electrolysis enters the space of the anode. 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 the counterflow. It is directed from the anode space to the cathode, which allows separate production of chlorine and liquors.
2. Membrane. The most energy efficient, but difficult to implement in the organization. Similar to aperture. The difference is that the anode and cathode spaces are completely separated by a membrane. Therefore, the output is two separate streams.
It is worth noting that the characteristic of chem. the element (chlorine) obtained by these methods will be different. The membrane method is considered to be more “pure”.
3. Mercury method with a liquid cathode. Compared to other technologies, this option allows you to get the purest chlorine.
The schematic diagram of the installation consists of an electrolyzer and interconnected pump and amalgam decomposer. Mercury pumped together with sodium chloride solution 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 discharged from the electrolyzer together with the anolyte. Impurities and chlorine residues are removed from the latter, saturated with halite and again returned to electrolysis.
Industrial safety requirements and unprofitable production have led to the replacement of a liquid cathode with a solid one.
Industrial use of chlorine
The properties of chlorine allow it to be actively used in industry. Using this chemical element, various organochlorine compounds (vinyl chloride, chloro-rubber, etc.), medicines, and disinfectants are obtained. But the largest niche employed in industry is the production of hydrochloric acid and lime.
Widely applied methods of purification of drinking water. 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, in addition, chlorinated water destroys pipelines. This is due to the fact that, in the free state, Cl adversely affects pipes made of polyolefins. Nevertheless, most countries prefer the chlorination method.
Also, chlorine is used in metallurgy. With its help, a number of rare metals (niobium, tantalum, titanium) are obtained. In the chemical industry, various organochlorine compounds are actively used to control weeds and for other agricultural purposes, and an element is also used as 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 atomic oxygen, 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 and this day.
The use of this substance for the production of organochlorine insecticides is very popular. These agricultural products kill harmful organisms by 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, insulation of wires, stationery, equipment, shells of household appliances, etc. is 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 was described in detail earlier by us) 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. Using a high level of ionization, they are able to form covalent chemical compounds. Below we will give a description of non-metal using chlorine as an example.
As mentioned above, this chemical element is a gas. Under normal conditions, it completely lacks properties similar to those of metals. Without outside help, it cannot interact with oxygen, nitrogen, carbon, etc. It exhibits its oxidizing properties in bonds with simple substances and some complex ones. It belongs 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 chemical agent
The characteristic of the chlorine atom allows its use as a poisonous agent. The gas was first used by Germany on 04/22/1915, during the First World War, as a result of which about 15 thousand people died. At the moment, as a toxic substance is not used.
We give a brief description of the chemical element as a choking agent. Affects the human body through strangulation. First, it irritates the upper respiratory tract and the mucous membrane of the eyes. A strong cough begins with attacks of suffocation. Further, penetrating into the lungs, 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 severity and thrill in the chest, sharp pain in the upper respiratory tract. Also, the condition may be accompanied by severe lacrimation. After 10-15 minutes 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.
When working with this substance, it is recommended to use protective clothing, gas mask, gloves.
Chlorine in the life of organisms and plants
Chlorine is part of almost all living organisms. The peculiarity is that it is present not in its pure form, but in the form of compounds.
In animals and humans, chlorine ions support 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 intestines, chlorine 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 through the urethra. It is produced by the female body during breastfeeding.
At this stage of development, it is difficult to say unequivocally which diseases are caused by chlorine and its compounds. This is due to a lack of research in this area.
Chlorine ions are also present in plant cells. He is actively involved in energy metabolism. Without this element, the process of photosynthesis is impossible. With its help, the roots actively absorb the necessary substances. But a high concentration of chlorine in plants can have a detrimental effect (slowing down the process of photosynthesis, stopping development and growth).
However, there are such representatives of the flora who were able to "make friends" or at least get along with this element. The characteristic of non-metal (chlorine) contains such an item as the ability of a substance to oxidize the soil. During 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 leaf fall.
Chlorine Transport and Storage
There are several ways to transport and store chlorine. Characterization of the element requires the need for special high-pressure cylinders. Such containers have identification marking - a vertical green line. Each month, the cylinders must be thoroughly washed. During long-term storage of chlorine, a very explosive precipitate is formed in them - nitrogen trichloride. Failure to comply with all safety rules may result in spontaneous ignition and explosion.
Chlorine study
Future chemists should be aware of the characteristics of chlorine. According to the plan, 9th graders can even set up laboratory experiments with this substance on the basis of basic knowledge of the discipline. Naturally, the teacher is obliged to conduct safety training.
The procedure is as follows: you need to take a flask with chlorine and pour small metal shavings into it. In flight, the chips flare up with bright bright sparks and at the same time light white smoke SbCl 3 is formed . When immersed in a vessel with tin foil chlorine, it will also self-ignite, and fire snowflakes will slowly drop to the bottom of the flask. During this reaction, a smoky liquid is formed - SnCl 4 . When iron chips are placed in the vessel, red “drops” form and red smoke FeCl 3 appears.
Along with practical work, the 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 cotton wool soaked previously in turpentine is placed in a jar of chlorine, it will instantly ignite, and soot will suddenly fall out of the flask. Sodium smolders effectively with a yellowish flame, and salt crystals appear on the walls of chemical dishes. Pupils will be interested to learn that, as a young chemist, N. N. Semenov (later a Nobel Prize winner), having conducted such an experiment, collected salt from the walls of the flask and, sprinkling bread on it, ate it. Chemistry turned out to be right and did not fail the scientist. As a result of the chemist's experience, it really turned out to be ordinary table salt!