Magnesium. Description and properties of magnesium
In our country, rich deposits of magnesite are located in the Middle Urals (Satkinskoye) and in the Orenburg region (Khalilovskoye). And in the area of the city of Solikamsk, the world's largest deposit of carnallite is being developed. Dolomite - the most common of magnesium-containing minerals - is found in the Donbass, Moscow and Leningrad regions and many other places.
Metallic magnesium is obtained in two ways - electrothermal (or metallothermic) and electrolytic. As the names suggest, both processes involve electricity. But in the first case, its role is reduced to heating the reaction apparatus, and magnesium oxide obtained from minerals is reduced with some kind of reducing agent, for example, coal, silicon, aluminum. This method is quite promising, in recent years it has been increasingly used. However, the main industrial method for obtaining Mg is the second, electrolytic.
The electrolyte is a melt of anhydrous chlorides of magnesium, potassium and sodium; metallic magnesium is released on the iron cathode, and chloride ions are discharged on the graphite anode. The process takes place in special electrolytic baths. Molten magnesium floats to the surface of the bath, from where it is occasionally removed by a vacuum ladle and then poured into moulds. But the process does not end there: there are still too many impurities in such magnesium. Therefore, the second stage is inevitable - purification of Mg. Magnesium can be refined in two ways - by remelting and fluxing or by vacuum sublimation. The meaning of the first method is well known: special additives - fluxes - interact with impurities and turn them into compounds that are easy to separate from the metal with a mechanical nut. The second method - vacuum sublimation - requires more sophisticated equipment, but it produces more pure magnesium. Sublimation is carried out in special vacuum apparatus - steel cylindrical retorts. The "draft" metal is placed at the bottom of the retort, it is closed and the air is pumped out. Then the lower part of the retort is heated, while the upper part is constantly cooled by outside air. Under the action of high temperature, magnesium sublimates - it passes into a gaseous state, bypassing the liquid state. Its vapor rises and condenses on the cold walls of the upper part of the retort. In this way, a very pure metal containing over 99.99% magnesium can be obtained.
From the realm of Neptune
But not only the earth's crust is rich in magnesium - its almost inexhaustible and constantly replenished reserves are stored in the blue pantries of the oceans and seas. Each cubic meter of sea water contains about 4 kg of magnesium. In total, more than 64016 tons of this element are dissolved in the waters of the world ocean.
Magnesium mining
How is magnesium extracted from the sea? Sea water is mixed in huge tanks with milk of lime made from ground sea shells. This produces the so-called milk of magnesia, which is dried and converted into magnesium chloride. Well, then electrolytic processes come into play.
The source of magnesium can be not only sea water, but also the water of salt lakes containing magnesium chloride. We have such lakes in our country: in the Crimea - Saki and Sasyk-Sivash, in the Volga region - Lake Elton and many others.
For what purpose is element No. 12 and its compounds used?
Magnesium is extremely light, and this property could make it an excellent structural material, but, alas, pure magnesium is soft and fragile. Therefore, designers use magnesium in the form of its alloys with other metals. Magnesium alloys with aluminum, zinc and manganese are especially widely used. Each of the components contributes its own "share" to the general properties: aluminum and zinc increase the strength of the alloy, manganese increases its anti-corrosion resistance. Well, what about magnesium? Magnesium gives the alloy lightness - magnesium alloy parts are 20-30% lighter than aluminum and 50-75% lighter than cast iron and steel ... There are many elements that improve magnesium alloys, increase their heat resistance and ductility, make them more resistant to oxidation. These are lithium, beryllium, calcium, cerium, cadmium, titanium and others.
The magnesium rocket won't take off, but...
But there are, unfortunately, "enemies" - iron, silicon, nickel; they worsen the mechanical properties of alloys, reduce their resistance to corrosion.
Magnesium alloys are widely used. Aviation and jet technology, nuclear reactors, engine parts, tanks for gasoline and oil, instruments, car bodies, buses, cars, wheels, oil pumps, jackhammers, pneumatic drills, photo and movie cameras, binoculars - this is not a complete list of applications magnesium alloys.
Magnesium plays an important role in metallurgy. It is used as a reducing agent in the production of some valuable metals - vanadium, chromium, titanium, zirconium. Magnesium introduced into molten cast iron modifies it, i.e., improves its structure and improves its mechanical properties. Modified cast iron castings successfully replace steel forgings. In addition, metallurgists use magnesium to deoxidize steel and alloys.
The property of magnesium (in the form of powder, wire or tape) - to burn with a blinding white flame - is widely used in military technology for the manufacture of lighting and signal rockets, tracer bullets and projectiles, and incendiary bombs. Photographers are well acquainted with magnesium: “Calm down! I'm filming!" - and a bright flash of magnesium blinds you for a moment. However, magnesium plays this role less and less - the electric lamp "blitz" has replaced it almost everywhere.
The use of magnesium
And in another grandiose work - the accumulation of solar energy - magnesium is involved. It is part of chlorophyll, which absorbs solar energy and with its help turns carbon dioxide and water into complex organic substances (sugar, starch, etc.) necessary for human and animal nutrition. Without chlorophyll there would be no life, and without magnesium there would be no chlorophyll - it contains 2% of this element. Is it a lot? Judge for yourself: the total amount of magnesium in the chlorophyll of all plants on the Earth is about 100 billion tons! Element number 12 is also part of almost all living organisms.
If you weigh 60 kg, then approximately 25 g of them are magnesium. Magnesium services are widely used by medicine: everyone is familiar with the “epsom salt” MgSO 4 -7H 2 O. When taken orally, it serves as a reliable and fast-acting laxative, and when administered intramuscularly or intravenously, it relieves convulsions, reduces vascular spasms. Pure magnesium oxide (burnt magnesia) is used for hyperacidity of gastric juice, heartburn, acid poisoning. Magnesium peroxide serves as a disinfectant for stomach disorders.
But medicine is not limited to the scope of magnesium compounds. So, magnesium oxide is used in the production of cements, refractory bricks, and in the rubber industry. Magnesium peroxide ("novozon") is used for bleaching fabrics. Magnesium sulphate is used in the textile and paper industries, as a mordant for dyeing, an aqueous solution of magnesium chloride is used for the preparation of magnesia cement, xylolite and other synthetic materials. Magnesium carbonate MgCO 3 is used in the production of thermal insulation materials.
And, finally, another vast field of activity of magnesium is organic chemistry. Magnesium powder is used for dehydration of such important organic substances as alcohol and aniline. Magnesium compounds are widely used in the synthesis of many organic substances.
So, the activity of magnesium in nature and the national economy is very multifaceted. But those who think: "he has already done everything he could" are hardly right. There is every reason to believe that the best role of magnesium is ahead.
Products containing magnesium - RAW ON THE BRIDGE. If desired, magnesium can be extracted even from ... a simple cobblestone: after all, each kilogram of stone used for paving roads contains about 20 g of magnesium. True, there is no need for such a process yet - magnesium from a road stone would be too expensive.
- MAGNESIUM, SECOND AND ERA. How much magnesium is in the ocean? Imagine that from the first days of our era, people began to evenly and intensively extract magnesium from sea water and by now have exhausted all the water reserves of this element. What do you think the "intensity" of production should be? It turns out that every second for almost 2,000 years would have to be mined. million tons! But even during the Second World War, when the production of this metal was at its maximum, only 80 thousand tons of magnesium were obtained from sea water annually (!)
- DELICIOUS MEDICINES. Statistics say that residents of areas with a warmer climate experience spasms of blood vessels less often than northerners. Medicine explains this by the nutritional characteristics of both. After all, it is known that intravenous and intramuscular infusions of solutions of certain magnesium salts relieve spasms and convulsions. Fruits and vegetables help to accumulate in the body the necessary supply of these salts. Apricots, peaches and cauliflower are especially rich in magnesium. There is it in ordinary cabbage, potatoes, tomatoes.
- CAUTION DO NOT DAMAGE. Working with magnesium alloys sometimes causes a lot of trouble - magnesium is easily oxidized. Melting and casting of these alloys have to be carried out under a layer of slag - otherwise the molten metal may catch fire from contact with air.
When grinding or polishing magnesium products, a dust extraction device must be installed above the machine, because the smallest particles of magnesium sprayed in the air create an explosive mixture.
However, this does not mean that any work with magnesium is fraught with the danger of fire or explosion. Magnesium can be ignited only by melting it, and it is not so easy to do this under normal conditions - the high thermal conductivity of the alloy will not allow a match or even a torch to turn cast products into white oxide powder. But with shavings or firewood tape made of magnesium, you really need to handle it very carefully.
- DO NOT HAVE TO WAIT. Conventional radio tubes begin to work normally only after their grids are heated to 800 ° C. Every time you turn on the radio or TV, you have to wait a while before the sounds of music begin to play or the blue screen flickers. To eliminate this shortcoming of radio tubes, Polish scientists from the Department of Electrical Engineering at the Wroclaw University of Technology proposed coating the cathodes of lamps with MgO: such lamps start working immediately after switching on.
- THE PROBLEM OF EGGSHELL. A few years ago, scientists at the University of Minnesota in the United States chose eggshells as the object of scientific research. They were able to establish that the shell is stronger, the more magnesium it contains. This means that by changing the composition of the feed for laying hens, it is possible to increase the strength of the shell. How important this conclusion is for agriculture can be judged by at least the following figures: in Minnesota alone, annual losses due to egg breakage exceed a million dollars. No one here will say that this work of scientists "is not worth a damn".
- MAGNESIUM AND... HEART. Experiments conducted by Hungarian scientists on animals have shown that the lack of Mg in the body increases the susceptibility to heart attacks. Some dogs were given food rich in salts of this element, others - poor. By the end of the experiment, those dogs whose diet was low in magnesium “earned” a myocardial infarction.
- SAVE MAGNESIUM! French biologists believe that magnesium will help physicians in the fight against such a serious illness of the 20th century as overwork. Studies show that the blood of tired people contains less magnesium than healthy ones, and even the most insignificant deviations of “magnesium blood” from the norm do not pass without a trace.
It is important to remember that in cases where a person is often and for any reason irritated, the magnesium contained in the body “burns out”. That is why in nervous, easily excitable people, disturbances in the functioning of the heart muscles are observed much more often.
- CARBONATED MAGNESIUM AND LIQUID OXYGEN. Large containers for storing liquid oxygen are usually made in the form of a cylinder or a ball - so that there is less heat loss. But a well-chosen form of storage is not everything. You need good thermal insulation. You can use a deep vacuum for this purpose (as in a Dewar vessel), you can use mineral wool, but often loose powder of magnesium carbonate is poured between the inner and outer walls of the storage. This thermal insulation is both cheap and reliable.
Magnesium is a light silvery-white metal, shiny, but tarnishes in air due to the formation of a protective oxide film on its surface. The chemical formula of magnesium is Mg. 12 - atomic number of magnesium in the periodic system of chemical elements D.I. Mendeleev.
Magnesium is quite common in the earth's crust. Only oxygen, silicon, aluminum, iron and calcium are ahead of magnesium in this regard. In nature, it occurs in the form of compounds. The most important minerals containing magnesium - magnesite MgCO 3 and the double salt dolomite CaMg 2 . Huge reserves of magnesium are found in the seas and oceans in the form of MgCl 2 . About 1500 minerals are known to science. And almost 200 of them contain magnesium.
Getting magnesium
How was magnesium discovered?
In 1695, the English physician Crewe analyzed mineral water from a spring near the city of Epsom. When this water was evaporated, white salt with a bitter taste formed on the walls of the vessel. This salt has medicinal properties. Apothecaries called this salt English or Epson. Later, the salt was called white magnesia because of its resemblance to the white powder that was obtained by calcining the mineral found near the Greek city of Magnesia.
Magnesium metal was first obtained in 1808 by the British chemist Humphrey Davy. Davy electrolyzed a mixture of white magnesia and mercury oxide. As a result, he received an alloy of mercury and an unknown metal. Having isolated the metal, Davy suggested calling it magnesium. But the magnesium received by Davy contained impurities. Pure, without impurities, magnesium was obtained only in 1829 by the French chemist Antoine Bussy.
Chemical properties of magnesium
Magnesium is an active metal. And like all active metals, it burns well. Under normal conditions, its surface is protected by an oxide film. But when heated to 600 degrees, the film is destroyed, and magnesium reacts with oxygen. The combustion product of magnesium is magnesium oxide, a white powder.
2Mg + O 2 \u003d 2MgO
When burning, a lot of heat and light is released. Moreover, according to its spectral analysis, the light during the combustion of magnesium is almost the same as sunlight. This property was used by the first photographers over 100 years ago. The burning of magnesium powder with the addition of potassium permanganate or barium nitrate illuminated the subject, which made it possible to take clear pictures indoors, where lighting was insufficient.
Magnesium reacts with water only when heated. As a result of this reaction, hydrogen is released.
Mg + 2H 2 O \u003d Mg (OH) 2 + H 2
Magnesium also burns in carbon dioxide.
2Mg + CO 2 \u003d 2MgO + C
Magnesium reacts with halogens at room temperature.
Mg + Br 2 = MgBr 2
Magnesium reacts with sulfur only when heated, forming magnesium sulfide.
Mg + S = MgS
Magnesium does not react with alkalis.
Getting magnesium
Magnesium metal is obtained by electrothermal or electrolytic methods.
In the first case, magnesite or dolomite in the reaction apparatus is calcined. The result is magnesium oxide MgO. Magnesium oxide is then reduced with aluminium, silicon or carbon. This is how pure magnesium is obtained.
But the main industrial method for obtaining magnesium is electrolytic. In special baths-electrolyzers there is a melt of magnesium chloride MgCl2. As a result of electrolysis, magnesium is released on the iron cathode, and chloride ions are collected on the graphite anode. Molten magnesium is collected and poured into moulds. Then magnesium is purified from impurities.
The use of magnesium
Magnesium's ability to readily react with oxygen allows it to be used in steelmaking to remove oxygen dissolved in molten metals. Magnesium powder is used in rocketry as a high-calorie fuel. Highly purified magnesium is used in the production of semiconductors.
Magnesium is the lightest of the metals. It is four times lighter than iron and one and a half times lighter than aluminum. In its pure form, magnesium is soft and fragile. It is impossible to make technical structures out of it. But the mechanical strength of magnesium increases significantly if zinc, aluminum or manganese is added to it. Additives are introduced in a small amount so as not to increase the specific gravity of magnesium. Unfortunately, these alloys lose their strength when heated. But if zinc, copper, silver, beryllium, thorium, zirconium, titanium are added to them, then they retain their mechanical strength even when the temperature rises. Magnesium alloy cases can be found in mobile phones, camcorders, laptops. In addition, magnesium alloy parts absorb vibration 100 times better than aluminum and 20 times better than alloy steel. Therefore, they are widely used in aviation, automotive and other fields of technology.
Magnesium compounds have been known to man for a very long time. Magnesite (in Greek Magnhsia oliqV) was a soft white, soapy-to-touch mineral (soapstone or talc) found in the Magnesia region of Thessaly. When this mineral was calcined, a white powder was obtained, which became known as white magnesia.
In 1695, N. Gro, evaporating the mineral water of the Epsom spring (England), obtained a salt that had a bitter taste and a laxative effect (MgSO 4 7H 2 O). A few years later, it turned out that when interacting with soda or potash, this salt forms a white friable powder, the same as that formed when magnesite is calcined.
In 1808, the English chemist and physicist Humphry Davy, by electrolysis of slightly moistened white magnesia with mercury oxide as a cathode, obtained an amalgam of a new metal capable of forming white magnesia. They called it magnesium. Davy received the contaminated metal, and pure magnesium was isolated only in 1829 by the French chemist Bussy Antoine (1794–1882).
Distribution of magnesium in nature and its industrial extraction.
Magnesium is found in crystalline rocks in the form of insoluble carbonates or sulfates, and also (in a less accessible form) in the form of silicates. The estimate of its total content significantly depends on the geochemical model used, in particular, on the weight ratios of volcanic and sedimentary rocks. Now values from 2 to 13.3% are used. Perhaps the most acceptable value is 2.76%, which places magnesium sixth in abundance after calcium (4.66%), ahead of sodium (2.27%) and potassium (1.84%).
Large land areas such as the Dolomites in Italy consist predominantly of the mineral dolomite MgCa(CO 3 ) 2 . Sedimentary minerals magnesite MgCO 3, epsomite MgSO 4 7H 2 O, carnallite K 2 MgCl 4 6H 2 O, langbeinite K 2 Mg 2 (SO 4) 3 are also found there.
There are deposits of dolomite in many other regions, including the Moscow and Leningrad regions. Rich deposits of magnesite are found in the Middle Urals and in the Orenburg region. The largest deposit of carnallite is being developed in the area of Solikamsk. Magnesium silicates are represented by the basalt mineral olivine (Mg,Fe) 2 (SiO 4), soapstone (talc) Mg 3 Si 4 O 10 (OH) 2, asbestos (chrysotile) Mg 3 Si 2 O 5 (OH) 4 and mica. Spinel MgAl 2 O 4 belongs to precious stones.
A large amount of magnesium is found in the waters of the seas and oceans and in natural brines ( cm. CHEMISTRY OF THE HYDROSPHERE). In some countries, they are the raw material for magnesium production. It is second only to sodium in its content in sea water among the metallic elements. Each cubic meter of sea water contains about 4 kg of magnesium. Magnesium is also found in fresh water, which, along with calcium, determines its hardness.
Magnesium is always found in plants, as it is part of the chlorophylls.
Characterization of a simple substance and industrial production of metallic magnesium.
Magnesium is a silvery-white lustrous metal, relatively soft, ductile and malleable. Its strength and hardness are minimal in prevalence for cast samples, higher for pressed samples.
Under normal conditions, magnesium is resistant to oxidation due to the formation of a strong oxide film. However, it actively reacts with most non-metals, especially when heated. Magnesium ignites in the presence of halogens (in the presence of moisture), forming the corresponding halides, and burns with a dazzlingly bright flame in air, turning into MgO oxide and Mg 3 N 2 nitride:
2Mg (c) + O 2 (g) \u003d 2MgO (c); DG° = –1128 kJ/mol
3Mg (c) + N 2 (t) \u003d Mg 3 N 2 (c); DG° = -401 kJ/mol
Despite the low melting point (650 ° C), it is impossible to melt magnesium in air.
Under the action of hydrogen under a pressure of 200 atm at 150 ° C, magnesium forms a hydride MgH 2 . Magnesium does not react with cold water, but it displaces hydrogen from boiling water and forms hydroxide Mg (OH) 2:
Mg + 2H 2 O \u003d Mg (OH) 2 + H 2
At the end of the reaction, the pH value (10.3) of the formed saturated solution of magnesium hydroxide corresponds to the equilibrium:
In the latter case, the forming mixture of carbon monoxide and magnesium vapor must be rapidly cooled with an inert gas to prevent a reverse reaction.
World production of magnesium is approaching 400 thousand tons per year. The main producers are the USA (43%), CIS countries (26%) and Norway (17%). In recent years, China has been sharply increasing magnesium exports. In Russia, one of the largest magnesium producers is the titanium-magnesium plant in Berezniki (Perm region) and the Solikamsk magnesium plant. Magnesium production is also being developed in the city of Asbest.
Magnesium is the lightest structural material used on an industrial scale. Its density (1.7 g cm–3) is less than two thirds that of aluminum. Magnesium alloys weigh four times less than steel. In addition, magnesium is highly machinable and can be cast and reworked by any standard metalworking method (rolling, stamping, drawing, forging, welding, soldering, riveting). Therefore, its main area of application is as a light structural metal.
Magnesium alloys typically contain over 90% magnesium, as well as 2–9% aluminium, 1–3% zinc, and 0.2–1% manganese. Strength retention at high temperatures (up to 450°C) improves markedly when alloyed with rare earth metals (eg praseodymium and neodymium) or thorium. These alloys can be used for automotive engine cases as well as aircraft fuselages and landing gear. Magnesium is used not only in aviation, but also in the manufacture of ladders, walkways in docks, cargo platforms, conveyors and lifts, as well as in the production of photographic and optical equipment.
Up to 5% magnesium is added to industrial aluminum to improve mechanical properties, weldability and corrosion resistance. Magnesium is also used for the cathodic protection of other metals against corrosion, as an oxygen scavenger and a reducing agent in the production of beryllium, titanium, zirconium, hafnium, and uranium. Mixtures of magnesium powder with oxidizing agents are used in pyrotechnics for the preparation of lighting and incendiary compositions.
magnesium compounds.
The predominant oxidation state (+2) for magnesium is due to its electronic configuration, ionization energies, and atomic size. The oxidation state (+3) is impossible, since the third ionization energy for magnesium is 7733 kJ mol -1 . This energy is much higher than can be compensated by the formation of additional bonds, even if they are predominantly covalent. The reasons for the instability of magnesium compounds in the oxidation state (+1) are less obvious. Estimation of the enthalpy of formation of such compounds shows that they must be stable with respect to their constituent elements. The reason that magnesium(I) compounds are not stable is the much higher enthalpy of formation of magnesium(II) compounds, which should lead to rapid and complete disproportionation:
Mg (c) + Cl 2 (g) = MgCl 2 (c);
D H° arr \u003d -642 kJ / (mol MgCl 2)
2Mg(c) + Cl 2 (g) = 2MgCl(c);
D H° arr = –250 kJ/(2 mol MgCl)
2MgCl (c) \u003d Mg (c) + MgCl 2 (c);
D H° disprop = -392 kJ/(2 mol MgCl)
If a synthetic route is found that makes disproportionation difficult, such compounds may be obtained. There is some evidence for the formation of magnesium(I) particles during electrolysis on magnesium electrodes. So, during the electrolysis of NaCl on a magnesium anode, hydrogen is released, and the amount of magnesium lost by the anode corresponds to a charge of +1.3. Similarly, during the electrolysis of an aqueous solution of Na 2 SO 4, the amount of hydrogen released corresponds to the oxidation of water by magnesium ions, the charge of which corresponds to +1.4.
Most magnesium salts are highly soluble in water. The dissolution process is accompanied by slight hydrolysis. The resulting solutions have a slightly acidic environment:
2+ + H 2 O + + H 3 O +
Magnesium compounds with many non-metals, including carbon, nitrogen, phosphorus, and sulfur, are irreversibly hydrolyzed by water.
Magnesium hydride composition MgH 2 is a polymer with bridging hydrogen atoms. The coordination number of magnesium in it is 4. Such a structure leads to a sharp decrease in the thermal stability of the compound. Magnesium hydride is easily oxidized by atmospheric oxygen and water. These reactions are accompanied by a large release of energy.
magnesium nitride Mg3N2. Forms yellowish crystals. Hydrolysis of magnesium nitride produces ammonia hydrate:
Mg 3 N 2 + 8H 2 O \u003d 3Mg (OH) 2 + 2NH 3 H 2 O
If the hydrolysis of magnesium nitride is carried out in an alkaline medium, ammonia hydrate is not formed, but gaseous ammonia is released. Hydrolysis in an acid medium leads to the formation of magnesium and ammonium cations:
Mg 3 N 2 + 8H 3 O + = 3Mg 2+ + 2NH 4 + + 8H 2 O
magnesium oxide MgO is called burnt magnesia. It is obtained by roasting magnesite, dolomite, basic magnesium carbonate, magnesium hydroxide, as well as by calcining bischofite MgCl 2 ·6H 2 O in an atmosphere of water vapor.
The reactivity of magnesium oxide depends on the temperature of its production. Magnesium oxide prepared at 500–700°C is called light magnesia. It easily reacts with dilute acids and water to form the corresponding salts or magnesium hydroxide, and absorbs carbon dioxide and moisture from the air. Magnesium oxide obtained at 1200-1600°C is called heavy magnesia. It is characterized by acid resistance and water resistance.
Magnesium oxide is widely used as a heat resistant material. It is characterized by both high thermal conductivity and good electrical insulating properties. Therefore, this compound is used in insulating radiators for local heating.
Lighter varieties of magnesia are used for the preparation of magnesia cement and building materials based on it, as well as a vulcanizing agent in the rubber industry.
magnesium hydroxide Mg(OH) 2 forms colorless crystals. The solubility of this compound is low (2 10 -4 mol/l at 20°C). It can be converted into a solution by the action of ammonium salts:
Mg(OH) 2 + 2NH 4 Cl \u003d MgCl 2 + 2NH 3 H 2 O
Magnesium hydroxide is thermally unstable and decomposes when heated:
Mg(OH) 2 \u003d MgO + H 2 O
On an industrial scale, magnesium hydroxide is produced by lime precipitation from sea water and natural brines.
Magnesium hydroxide is a mild base, which in the form of an aqueous solution (milk of magnesia) is widely used to reduce the acidity of gastric juice. At the same time, despite the softness, Mg(OH) 2 neutralizes acids 1.37 times more than sodium hydroxide NaOH and 2.85 times more than sodium bicarbonate NaHCO 3 .
It is also used to obtain magnesium oxide, sugar refining, water purification in boiler plants, as a component of toothpastes.
magnesium carbonate MgCO 3 forms colorless crystals. It occurs in nature in an anhydrous form (magnesite). In addition, penta-, tri- and monohydrates of magnesium carbonate are known.
The solubility of magnesium carbonate in the absence of carbon dioxide is about 0.5 mg/L. In the presence of an excess of carbon dioxide and water, magnesium carbonate turns into soluble bicarbonate, and when boiled, the reverse process occurs. Carbonate and bicarbonate interact with acids with the release of carbon dioxide and the formation of the corresponding salts. When heated, magnesium carbonate, without melting, decomposes:
MgCO 3 \u003d MgO + CO 2
This process is used to produce magnesium oxide. In addition, natural magnesium carbonate is a feedstock for the production of metallic magnesium and its compounds. It is also used as fertilizer and to reduce soil acidity.
Loose powder of magnesium carbonate is poured between the double walls of liquid oxygen storage. This thermal insulation is cheap and reliable.
Magnesium sulfate MgSO 4 is known in the anhydrous state, as well as in the form of various hydrates. In nature, kieserite MgSO 4 H 2 O, epsomite MgSO 4 7H 2 O and MgSO 4 6H 2 O hexahydrate are found.
In medicine, magnesium sulfate heptahydrate MgSO 4 7H 2 O, commonly known as Epsom salt or bitter salt, is used. This compound has a laxative effect. With intramuscular or intravenous infusions, magnesium sulfate relieves a convulsive state, reduces vasospasm.
Magnesium sulfate is used in the textile and paper industries as a dye mordant, as well as as a weighting agent for cotton and silk, and as a paper filler. It serves as a raw material for the production of magnesium oxide.
magnesium nitrate Mg(NO 3) 2 are colorless hygroscopic crystals. Solubility in water at 20 ° C is 73.3 g per 100 g. The hexahydrate crystallizes from aqueous solutions. Above 90°C, it dehydrates to a monohydrate. Then there is a splitting of water with partial hydrolysis and decomposition to magnesium oxide. This process is used in the synthesis of high purity magnesium oxide. Nitrates of other metals, as well as various magnesium compounds, are obtained from magnesium nitrate. In addition, magnesium nitrate is part of complex fertilizers and pyrotechnic mixtures.
Magnesium perchlorate Mg(ClO 4) 2 forms very hygroscopic colorless crystals. It is highly soluble in water (99.6 g per 100 g) and organic solvents. The hexahydrate crystallizes from aqueous solutions. Concentrated solutions of magnesium perchlorate in organic solvents and its solvates with reducing agent molecules are explosive.
Partially hydrated magnesium perchlorate containing 2–2.5 water molecules is produced under the commercial name "anhydrone". To obtain anhydrous magnesium perchlorate, it is dried in vacuum at 200–300°C. It is used as a gas dryer. It absorbs not only water vapor, but also ammonia, vapors of alcohols, acetone and other polar substances.
Magnesium perchlorate is used as a Friedel-Crafts acylation catalyst and as an oxidizing agent in microanalysis.
magnesium fluoride MgF 2 is slightly soluble in water (0.013 g per 100 g at 25 ° C). It occurs naturally as the mineral selaite. Magnesium fluoride is obtained by reacting magnesium sulfate or oxide with hydrofluoric acid or magnesium chloride with potassium or ammonium fluoride.
Magnesium fluoride is a component of fluxes, glasses, ceramics, enamels, catalysts, mixtures for the production of artificial mica and asbestos. In addition, it is an optical and laser material.
magnesium chloride MgCl 2 is one of the most industrially important magnesium salts. Its solubility is 54.5 g per 100 g of water at 20°C. Concentrated aqueous solutions of magnesium chloride dissolve magnesium oxide. MgCl 2 ·mMg(OH) 2 ·nH 2 O crystallizes from the resulting solutions. These compounds are part of magnesia cements.
Magnesium chloride forms crystalline hydrates with 1, 2, 4, 6, 8 and 12 water molecules. As the temperature rises, the number of crystallization water molecules decreases.
In nature, magnesium chloride is found in the form of minerals bischofite MgCl 2 6H 2 O, chlormagnesite MgCl 2, and carnallite. It is found in sea water, brine of salt lakes, some underground brines.
Anhydrous magnesium chloride is used in the production of metallic magnesium and magnesium oxide, hexahydrate - for the production of magnesia cements. An aqueous solution of magnesium chloride is used as a refrigerant and antifreeze. It serves as an anti-icing agent for airfields, railway rails and switches, as well as against freezing of coal and ores. Wood is impregnated with a solution of magnesium chloride to make it fire resistant.
magnesium bromide MgBr 2 is highly soluble in water (101.5 g per 100 g at 20 ° C). From aqueous solutions, it crystallizes from -42.7 to 0.83 ° C in the form of a decahydrate, at a higher temperature - in the form of a hexahydrate. It forms numerous crystal solvates, such as MgB 2 6ROH (R = Me, Et, Pr), MgBr 2 6Me 2 CO, MgBr 2 3Et 2 O, as well as ammines MgBr 2 . n NH 3 ( n = 2–6).
Complex compounds of magnesium. In aqueous solutions, the magnesium ion exists as a 2+ aqua complex. In a non-aqueous solvent, such as liquid ammonia, the magnesium ion forms complexes with solvent molecules. Solvates of magnesium salts usually crystallize from such solutions. Several halide complexes of the MX 4 2– type are known, where X is a halide anion.
Among the complex compounds of magnesium, chlorophylls, which are modified porphyrin complexes of magnesium, are of particular importance. They are vital for photosynthesis in green plants.
Magnesium compounds. For magnesium, numerous compounds containing metal-carbon bonds have been obtained. Especially many studies are devoted to Grignard reagents RMgX (X = Cl, Br, I).
Grignard reagents are the most important organometallic compounds of magnesium and probably the most used organometallic reagents. This is due to their ease of production and synthetic versatility. It has been established that in solution these compounds can contain various chemical particles that are in mobile equilibrium.
Grignard reagents are usually prepared by slowly adding an organic halide to a slurry of magnesium turnings in an appropriate solvent with vigorous stirring in the complete absence of air and moisture. The reaction usually starts slowly. It can be initiated by a small crystal of iodine, which destroys the protective layer on the metal surface.
Grignard reagents are widely used for the synthesis of alcohols, aldehydes, ketones, carboxylic acids, esters and amides and are probably the most important reagents for creating carbon-carbon bonds, as well as bonds between carbon atoms and other elements (nitrogen, oxygen, sulfur, etc.). .d.).
Compounds R 2 Mg usually decompose when heated. In the crystalline state, they have the structure of linear polymers with bridged alkyl groups. The MgMe 2 compound is a non-volatile polymer, stable up to ~250°C, insoluble in hydrocarbons and only slightly soluble in ether. The MgEt 2 compound and higher homologues are very similar to MgMe 2 , but they decompose at a lower temperature (175–200°C), forming the corresponding alkene and MgH 2 in the reverse reaction to their preparation. Looks like them and MgPh 2; it is insoluble in benzene, dissolves in ether to form the monomeric complex MgPh 2 ·2Et 2 O, and decomposes at 280°C to form Ph 2 and metallic magnesium.
The biological role of magnesium.
Green leaves of plants contain chlorophylls, which are magnesium-containing porphyrin complexes involved in photosynthesis.
Magnesium is also closely involved in biochemical processes in animal organisms. Magnesium ions are essential for the initiation of enzymes responsible for the conversion of phosphates, for the transmission of nerve impulses and for the metabolism of carbohydrates. They are also involved in muscle contraction, which is initiated by calcium ions.
A few years ago, scientists at the University of Minnesota in the United States found that eggshells are stronger the more magnesium they contain.
The body of an adult weighing 65 kg contains about 20 g of magnesium (mainly in the form of ions). Most of it is concentrated in the bones. The intracellular fluid contains magnesium complexes with ATP and ADP.
The daily requirement for this element is 0.35 g. With a monotonous diet, a lack of green vegetables and fruits, as well as alcoholism, magnesium deficiency often occurs. Apricots, peaches and cauliflower are especially rich in magnesium. There is it in ordinary cabbage, potatoes, tomatoes.
Statistics say that residents of areas with a warmer climate experience spasms of blood vessels less often than northerners. It is believed that the reason for this is the peculiarities of nutrition in cold regions. They eat fewer fruits and vegetables, which means they get less magnesium.
Studies by French biologists have shown that the blood of tired people contains less magnesium than those of rested people. It is believed that a diet rich in magnesium should help doctors in the fight against such a serious illness as overwork.
Elena Savinkina
Magnesium and its compounds have long been known to people. Magnesium salts were first obtained in 1695 by an English physician. The doctor analyzed the water from the nearest source. When the liquid was evaporated, salt with a bitter taste was obtained. Pharmacists and doctors believed that the salt obtained as a result of the reaction could be used for medicinal purposes. Salt became known as white magnesia.
However, relatively pure magnesium was obtained much later. The chemist Davy obtained the metal (as well as other active metals) as a result of the process of electrolysis. However, the magnesium obtained by G. Davy as a result of the reaction could not yet be called pure. Pure magnesium was obtained by Bussy a little later - in 1828.
Characteristics of magnesium
Physical properties
Magnesium is white in color and has a characteristic luster. Magnesium is quite soft, has good ductility and malleability. The element has a relatively low melting point - about 650 ° C. Magnesium tarnishes in the open air. This is because an oxide film forms on the surface of the piece of metal. Magnesium burns well with a bright white flame.
Chemical properties
Magnesium is an active element. As a rule, this explains the chemical properties of the element.
- Magnesium burns great. However, in normal situations, the metal is protected by a special oxide film that prevents magnesium from reacting with oxygen. When heated, the oxide film disappears and magnesium reacts with oxygen. As a result of combustion in oxygen, magnesium oxide is formed. An interesting fact is that the light emitted by the element during combustion is very similar to sunlight. This feature was noticed even by the first photographers. That is why magnesium powder with some impurities was used as a flash to illuminate the photographed object.
- Also, when heated, magnesium reacts with hydrogen, as well as with sulfur.
- Magnesium reacts with halogens at room temperature.
- Magnesium does not react with alkalis.
Magnesium is a fairly common element on Earth. It can be found quite often.
- First, magnesium is part of the Earth's crust. The concentration of magnesium in the Earth's crust is at the level of 1.9%.
- Secondly, a large number of magnesium derivatives are part of crystalline rocks. As a rule, magnesium occurs here in the form of carbonates, sulfates and silicates.
- Also, a fairly large amount of magnesium is found in sea and ocean waters. One cubic meter of salty ocean water contains approximately 4 kg of magnesium. In terms of its content in sea water, magnesium is second only to sodium. It is worth saying that magnesium is not only in salty sea water, but also in fresh water.
- Magnesium is always included in the composition of plants.
Applications of magnesium
Magnesium and its compounds are widely used in industry.
- Most often, magnesium and its alloys are used as a light structural metal. The fact is that the alloys of this metal weigh little (the mass of magnesium alloys is about four times less than the mass of steel), while they are quite strong and durable. Such alloys can be used for automotive parts, aircraft landing gear, stairs, cargo platforms and other structures.
- Magnesium is also used in metallurgy. Some magnesium is added, for example, to aluminum. This improves the corrosion resistance of the alloy.
- A mixture of magnesium with various oxidizing agents is widely used in pyrotechnics, for the preparation of various incendiary and lighting compositions.
Magnesium- an element of the main subgroup of the second group, the third period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 12. It is denoted by the symbol Mg (lat. Magnesium). The simple substance magnesium (CAS number: 7439-95-4) is a light, malleable silver-white metal.
1 element of the periodic table In 1695, salt was isolated from the mineral water of the Epsom spring in England, which had a bitter taste and laxative effect. Apothecaries called it bitter salt, as well as English, or Epsom salt. The mineral epsomite has the composition MgSO4 7H2O. The Latin name of the element comes from the name of the ancient city of Magnesia in Asia Minor, in the vicinity of which there are deposits of the mineral magnesite.
In 1792, Anton von Ruprecht obtained a new metal, which he called austria, by reducing charcoal from white magnesia. Later it was found that "Austrium" is an extremely low purity magnesium, since the original substance was heavily contaminated with iron.
Discovery history
In 1695, salt was isolated from the mineral water of the Epsom Spring in England, which had a bitter taste and laxative effect. Apothecaries called it bitter salt, as well as English, or Epsom salt. The mineral epsomite has the composition MgSO4 7H2O. The Latin name of the element comes from the name of the ancient city of Magnesia in Asia Minor, in the vicinity of which there are deposits of the mineral magnesite.
In 1792, Anton von Ruprecht obtained a new metal, which he called austria, by reducing charcoal from white magnesia. "Austrium" was later found to be extremely low purity magnesium, since the original material was heavily contaminated with iron.
It was first isolated in its pure form by Sir Humphry Davy in 1808 by distilling mercury from magnesium amalgam, which he obtained by electrolysis of a semi-liquid mixture of magnesium oxide and mercury.
Being in nature
Magnesium clarke (wt.) - 1.95% (19.5 kg / t). It is one of the most common elements in the earth's crust. Large amounts of magnesium are found in sea water. The main types of finding magnesian raw materials are:
sea water - (Mg 0.12-0.13%),
carnallite - MgCl2. KCl. 6H2O (Mg 8.7%),
bischofite - MgCl2. 6H2O (Mg 11.9%),
kieserite - MgSO4. H2O (Mg 17.6%),
epsomite - MgSO4. 7H2O (Mg 16.3%),
kainite - KCl. MgSO4. 3H2O (Mg 9.8%),
magnesite - MgCO3 (Mg 28.7%),
dolomite - CaCO3 MgCO3 (Mg 13.1%),
brucite - Mg (OH) 2 (Mg 41.6%).
Magnesian salts are found in large quantities in the salt deposits of self-sustaining lakes. Deposits of fossil salts of carnallite of sedimentary origin are known in many countries.
Magnesite is formed predominantly under hydrothermal conditions and belongs to medium-temperature hydrothermal deposits. Dolomite is also an important magnesium raw material. Dolomite deposits are widespread, their reserves are huge. They are associated with carbonate strata and most of them are of Precambrian or Permian age. Dolomite deposits are formed by sedimentation, but can also occur when limestone is exposed to hydrothermal solutions, groundwater or surface water.
MAGNESIUM RATE TABLE
| Floor | Age | Daily intake of magnesium, mg / day | Upper limit, mg/day |
|---|---|---|---|
| babies | 0 to 6 months | 30 | Not determined |
| babies | 7 to 12 months | 75 | Not determined |
| Children | 1 to 3 years | 80 | 145 |
| Children | 4 to 8 years old | 130 | 240 |
| Children | 9 to 13 years old | 240 | 590 |
| Girls | 14 to 18 years old | 360 | 710 |
| Youths | 14 to 18 years old | 410 | 760 |
| Men | from 19 to 30 years old | 400 | 750 |
| Men | 31 years and older | 420 | 770 |
| Women | from 19 to 30 years old | 310 | 660 |
| Women | 31 years and older | 320 | 670 |
| Pregnant women | 14 to 18 years old | 400 | 750 |
| Pregnant women | from 19 to 30 years old | 350 | 700 |
| Pregnant women | 31 years and older | 360 | 710 |
| breastfeeding women | 14 to 18 years old | 360 | 710 |
| breastfeeding women | from 19 to 30 years old | 310 | 660 |
| breastfeeding women | 31 years and older | 320 | 670 |
Ductile, silvery white metal
Magnesium / Magnesium (Mg), 12
(molar mass)
[comm 1] a. e.m. (g/mol)
1.31 (Pauling scale)
(first electron)
737.3 (7.64) kJ/mol (eV)
1.738 g/cm³
650°C (923K)
1090°C (1363K)
9.20 kJ/mol
131.8 kJ/mol
24.90 J/(K mol)
14.0 cm³/mol
hexagonal
a=0.32029 nm, c=0.52000 nm
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