Interaction of magnesium with simple substances. Getting magnesium. Chemical properties of magnesium

Magnesium is an element of the main subgroup of the second group, the third period of the periodic system of chemical elements, 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. Moderately common in nature. During combustion, a large amount of light and heat is released.

origin of name

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 MgSO 4 7H 2 O. 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.
It was first isolated in its pure form by Sir Humphry Davy in 1808.

Receipt

The usual industrial method for obtaining metallic magnesium is the electrolysis of a mixture of anhydrous magnesium chlorides MgCl 2 (bischofite), sodium NaCl and potassium KCl. Magnesium chloride undergoes electrochemical reduction in the melt:
MgCl 2 (electrolysis) \u003d Mg + Cl 2.

The molten metal is periodically taken from the electrolysis bath, and new portions of magnesium-containing raw materials are added to it. Since the magnesium obtained in this way contains a relatively large amount (about 0.1%) of impurities, if necessary, "raw" magnesium is subjected to additional purification. For this purpose, electrolytic refining, vacuum remelting with the use of special additives - fluxes, which “take away” impurities from magnesium or distillation (sublimation) of the metal in vacuum are used. The purity of refined magnesium reaches 99.999% and higher.
Another method for obtaining magnesium has also been developed - thermal. In this case, silicon or coke is used to reduce magnesium oxide at high temperature:
MgO + C = Mg + CO

The use of silicon makes it possible to obtain magnesium from raw materials such as CaCO 3 ·MgCO 3 dolomite without preliminary separation of magnesium and calcium. With the participation of dolomite, reactions occur:
CaCO 3 MgCO 3 \u003d CaO + MgO + 2CO 2,
2MgO + CaO + Si = CaSiO 3 + 2Mg.

The advantage of the thermal process is that it makes it possible to obtain higher purity magnesium. To obtain magnesium, not only mineral raw materials are used, but also sea water.

Physical Properties

Magnesium is a silver-white metal with a hexagonal lattice, space group P 6 3 /mmc. Under normal conditions, the surface of magnesium is covered with a strong protective film of magnesium oxide MgO, which is destroyed when heated in air to about 600 ° C, after which the metal burns with a dazzling white flame to form magnesium oxide and nitride Mg 3 N 2 . The density of magnesium at 20 ° C is 1.737 g / cm³, the melting point of the metal is t melt = 651 ° C, the boiling point is t bp = 1103 ° C, the thermal conductivity at 20 ° C is 156 W / (m K). Magnesium of high purity is ductile, well pressed, rolled and machinable.

Chemical properties

A mixture of powdered magnesium with potassium permanganate KMnO 4 is an explosive.
Hot magnesium reacts with water:
Mg (decay) + H 2 O \u003d MgO + H 2;

Alkalis do not act on magnesium, it dissolves easily in acids with the release of hydrogen:
Mg + 2HCl \u003d MgCl 2 + H 2;

When heated in air, magnesium burns to form an oxide; a small amount of nitride can also form with nitrogen:
2Mg + O 2 \u003d 2MgO;
3Mg + N 2 \u003d Mg 3 N 2

Magnesium is an element of the main subgroup of the second group, the third period with atomic number 12.

The structure of the atom:

1) E-cloud configuration 1s 2 | 2s 2 2p 6 3s 2

2) The radius of the atom is 145 10 -12 (Meter)

3) Atomic mass 24.305 (g/mol)

Physical properties:

1) silver-white metal, has a metallic luster

2) plastic and malleable metal, well pressed, rolled and amenable to cutting.

3) thermal conductivity at 20°C - 156 W/(m*K)

4) soft (magnesium hardness 2 on the Mohs scale)

5) boiling point tboil = 1103°C

6) metal melting point tmelt = 651°C

7) density of magnesium at 20°C - 1.737 g/cm

8) non-ferrous metal

9) conducts electricity (specific electrical resistance of conductors (at 20°C) - 4.400 10 -8 (Ohm Meter)

10) according to the magnetic properties of a paramagnet

Distribution in nature

Magnesium is one of the most abundant elements in the earth's crust. The main types of finding magnesian raw materials are:

sea water - (Mg 0.12-0.13%),

carnallite - MgCl 2 * KCl * 6H 2 O (Mg 8.7%),

bischofite - MgCl 2 * 6H 2 O (Mg 11.9%),

kieserite - MgSO 4 * H 2 O (Mg 17.6%),

epsomite - MgSO 4 * 7H 2 O (Mg 16.3%),

kainite - KCl * MgSO 4 * 3H 2 O (Mg 9.8%),

magnesite - MgCO 3 (Mg 28.7%),

dolomite - CaCO 3 * MgCO 3 (Mg 13.1%),

brucite - Mg (OH) 2 (Mg 41.6%).

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 are composed predominantly of the mineral dolomite. There are also sedimentary minerals - magnesite, epsomite, carnallite, langbeinite.

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, soapstone (talc), asbestos (chrysotile), and mica. Spinel belongs to precious stones.

A large amount of magnesium is found in the waters of the seas and oceans and in natural brines. 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.

Chemical properties:

1) the configuration of the outer electrons of the magnesium atom 3s 2

2) in all stable compounds, magnesium is bivalent

3) active metal

4) atomic radius 145 * 10 -12 (Meter)

5) hexagonal crystal lattice

6) metal crystal lattice

7) metal chemical bond

The most important magnesium compounds and their uses.

Magnesium hydride MgH 2 . Solid white non-volatile substance. Slightly soluble in water. Decomposes water and alcohols. Breaks down into elements when heated. Formed by the interaction of magnesium with hydrogen when heated. It is one of the most capacious hydrogen accumulators used for its storage.

Oxide (white magnesia, burnt magnesia) magnesium MgO. Occurs naturally in the form of grayish-green transparent octahedral crystals. Slightly soluble in water, soluble in alcohol, dilute acids. It can be obtained by burning magnesium in oxygen, by calcining magnesium hydroxide or carbonate.

It is used for the manufacture of laboratory products (crucibles, boats, baguettes, combustion tubes), refractory bricks, magnesia cement.

Magnesium hydroxide Mg(OH) 2 . It occurs naturally as a white, fibrous substance called brucite. Colorless trigonal crystals with a layered lattice. Weak base. Soluble in dilute acids and ammonium salts. Slightly soluble in water. Dehydrates when heated. In industry, it is extracted from sea water by precipitation with lime or dolomite milk. It can be obtained by the action of alkali metal hydroxides on magnesium salts.

Used as a food additive, to bind sulfur dioxide, as a flocculant in waste water treatment, as a flame retardant in thermoplastic polymers (polyolefins, PVC), as an additive in detergents, for the production of magnesium oxide, sugar refining, as a component of toothpastes . In medicine, it is used as a medicine to neutralize stomach acid, and also as a very strong laxative. In the European Union, magnesium hydroxide is registered as a food additive E528.

Magnesium fluoride MgF 2 . Colorless diamagnetic tetrahedral crystals. Slightly soluble in water and acetone, soluble in solutions of fluorides and sulfates of alkali metals. It can be obtained by burning magnesium in a fluorine atmosphere or by treating magnesium oxide with hydrofluoric acid.

It is used to protect metals from corrosion and the manufacture of frosted glass and ceramics.

Magnesium chloride MgCl 2 . Colorless hexagonal crystals with a layered structure, very hygroscopic. Let's well dissolve in water, alcohol, pyridine, we will dissolve a little in acetone. It can be obtained by burning magnesium in chlorine, by acting with hydrochloric acid on metallic magnesium.

It is used for the electrolytic production of metallic magnesium, for the impregnation of fabrics and wood, for the production of magnesian cements, as well as in medicine.

Magnesium bromide MgBr 2 . Colorless hexagonal diamagnetic crystals. Soluble in water, alcohol. Easily attaches ammonia, pyridine and ethylenediamine. Obtained by the interaction of magnesium and bromine when heated.

It is used to obtain elemental bromine, silver bromide and other bromides that are slightly soluble in water.

Magnesium iodide MgI 2 . Colorless crystals, very hygroscopic. Easily soluble in water, alcohol, ether. Obtained by direct interaction of magnesium and iodine or by the reaction between magnesium chloride and ammonium iodide.

Used in some homeopathic preparations.

Magnesium sulfide MgS. Colorless cubic crystals. Slightly soluble in water. Reacts with halogens. Decomposes with dilute acids to form salts and release hydrogen sulfide. Obtained by the interaction of magnesium with sulfur or hydrogen sulfide.

Magnesium sulfate MgSO 4 . Colorless rhombohedral diamagnetic crystals. Soluble in water, alcohol and ether. It can be obtained in the laboratory by reacting magnesium oxide or carbonate with sulfuric acid. In industry, it is obtained from sea water or from natural minerals - carnallite and kieserite.

It is used for finishing fabrics, the production of fire-resistant fabrics and paper, in leather tanning, as a mordant in the dyeing industry.

Magnesium nitrate Mg(NO 3 ) 2 . Colorless crystals. Soluble in water, alcohol and concentrated nitric acid. In industry, it is obtained from the natural mineral nitromagnesite. Obtained in the laboratory by the interaction of magnesium, magnesium oxide or magnesium hydroxide with dilute nitric acid.

DEFINITION

Magnesium- the twelfth element of the Periodic table. Designation - Mg from the Latin "magnesium". Located in the third period, group IIA. Refers to metals. The nuclear charge is 12.

Magnesium is very common in nature. It occurs in large quantities as magnesium carbonate, forming the minerals magnesite MgCO 3 and dolomite MgCO 3 × CaCO 3 . Sulfate and magnesium chloride are part of the minerals kainite KCl × MgSO 4 × 3H 2 O and carnallite KCl × MgCl 2 × 6H 2 O. The Mg 2+ ion is found in sea water, giving it a bitter taste. The total amount of magnesium in the earth's crust is about 2% (wt.).

In the form of a simple substance, magnesium is a silvery white (Fig. 1), a very light metal. In air, it changes little, as it is quickly covered with a thin layer of oxide, which protects it from further oxidation.

Rice. 1. Magnesium. Appearance.

Atomic and molecular weight of magnesium

The relative molecular weight of a substance (M r) is a number showing how many times the mass of a given molecule is greater than 1/12 of the mass of a carbon atom, and the relative atomic mass of an element (Ar r) is how many times the average mass of atoms of a chemical element is greater than 1/12 the mass of a carbon atom.

Since in the free state magnesium exists in the form of monatomic Mg molecules, the values of its atomic and molecular masses are the same. They are equal to 24.304.

Isotopes of magnesium

It is known that magnesium can occur in nature in the form of three stable isotopes 24 Mg (23.99%), 25 Mg (24.99%) and 26 Mg (25.98%). Their mass numbers are 24, 25 and 26, respectively. The nucleus of the atom of the magnesium isotope 24 Mg contains twelve protons and twelve neutrons, and the isotopes 25 Mg and 26 Mg contain the same number of protons, thirteen and fourteen neutrons, respectively.

There are artificial isotopes of magnesium with mass numbers from 5 to 23 and from 27 to 40.

Magnesium ions

At the external energy level of the magnesium atom, there are two electrons that are valence:

1s 2 2s 2 2p 6 3s 2 .

As a result of the chemical interaction, manium gives up its valence electrons, i.e. is their donor, and turns into a positively charged ion:

Mg 0 -2e → Mg 2+.

Magnesium molecule and atom

In the free state, magnesium exists in the form of monatomic Mg molecules. Here are some properties that characterize the magnesium atom and molecule:

magnesium alloys

Alloys called electrons have especially valuable properties. They belong to three systems: Mg-Al-Zn, Mg-Mn and Mg-Zn-Zr. The most widely used are alloys of the Mg-Al-Zn system, containing from 3 to 10% aluminum and from 0.2 to 3% zinc. The advantage of magnesium alloys is their low density (about 1.8 g/cm3).

Examples of problem solving

EXAMPLE 1

Magnesium is a metal widely distributed in nature, which is of great biogenic importance for humans. It is an integral part of a large number of different minerals, sea water, hydrothermal waters.

Properties

Silvery shiny metal, very light and ductile. Non-magnetic, high thermal conductivity. Under normal conditions in air, it is covered with an oxide film. When heated above 600 ° C, the metal burns with the release of a large amount of heat and light. It burns in carbon dioxide and actively reacts with water, so it is useless to extinguish it by traditional methods.

Magnesium does not interact with alkalis, it reacts with acids with the release of hydrogen. Resistant to halogens and their compounds; for example, does not interact with fluorine, hydrofluoric acid, dry chlorine, iodine, bromine. Does not collapse under the influence of oil products. Magnesium is not resistant to corrosion, this deficiency is corrected by adding small amounts of titanium, manganese, zinc, and zirconium to the alloy.

Magnesium is necessary for the health of the cardiovascular and nervous systems, for the synthesis of proteins and the absorption of glucose, fats and amino acids by the body. Magnesium orotate (vitamin B13) plays an important role in metabolism, normalizes cardiac activity, prevents the deposition of cholesterol on the walls of blood vessels, increases the efficiency of the body of athletes, not inferior in effectiveness to steroid drugs.

Magnesium is obtained in various ways, from natural minerals and sea water.

Application

Most of the extracted magnesium is used for the production of magnesium structural alloys that are in demand in the aviation, automotive, nuclear, chemical, oil refining industries, and in instrument making. Magnesium alloys are characterized by lightness, strength, high specific rigidity, and good machinability. They are non-magnetic, excellent heat dissipation, and 20 times more resistant to vibration than alloy steel. Magnesium alloys are used for the manufacture of tanks for the storage of gasoline and petroleum products, parts of nuclear reactors, jackhammers, pneumatic tubes, wagons; tanks and pumps for working with hydrofluoric acid, for storing bromine and iodine; cases of laptops and cameras.
- Magnesium is widely used to obtain some metals by reduction (vanadium, zirconium, titanium, beryllium, chromium, etc.); to give steel and cast iron better mechanical characteristics, to clean aluminium.
- In its pure form, it is part of many semiconductors.
- In the chemical industry, magnesium powder is used to dry organic substances, such as alcohol, aniline. Magnesium compounds are used in complex chemical synthesis (for example, to obtain vitamin A).
- Magnesium powder is in demand in rocket technology as a high-calorie fuel. In military affairs - in the production of lighting rockets, tracer ammunition, incendiary bombs.
- Pure magnesium and its compounds are used to manufacture powerful chemical current sources.
- Magnesium oxide is used for the manufacture of crucibles and metallurgical furnaces, refractory bricks, in the manufacture of synthetic rubber.
- Magnesium fluoride crystals are in demand in optics.
- Magnesium hydride is a solid powder containing a large percentage of hydrogen, which is easily obtained by heating. The substance is used as a "storage" of hydrogen.
- Now less often, but earlier, magnesium powder was widely used in chemical flashlights.
- Magnesium compounds are used for bleaching and etching fabrics, for the manufacture of heat-insulating materials, special types of bricks.
- Magnesium is part of many medicines, both internal and external (bischofite) use. It is used as an anticonvulsant, laxative, sedative, cardiac, antispasmodic, to regulate the acidity of gastric juice, as an antidote for acid poisoning, as a gastric disinfectant, to treat injuries and joints.
- Magnesium stearate is used in the pharmaceutical and cosmetic industries as a filler for tablets, powders, creams, shadows; in the food industry it is used as a food additive E470, which prevents caking of products.

In the chemical store "PrimeChemicalsGroup" you can buy chemical magnesium and its various compounds - magnesium stearate, bischofite, magnesium chloride, magnesium carbonate and others, as well as a wide range of chemical reagents, laboratory glassware and other goods for laboratories and production. You will love the prices and service!

Interaction with hydrogen at elevated temperature leads to the solid hydride MgH:

Mg + H = MgH (4.1)

In air, in a compact state, it is stable, but finely crushed, it is capable of spontaneous combustion. With cold water, due to the low solubility of Mg (OH), magnesium reacts slowly, but heating significantly speeds up the reaction:

Mg + 2HO \u003d Mg (OH) + H (4.2)

The low solubilities of magnesium oxide and hydroxide are associated with the covalence of the bond in them. This also explains the refractoriness of MgO, which is a polymer (MgO)x. Being a base of medium strength, magnesium hydroxide forms salts that are weakly hydrolyzed in concentrated solutions. If you increase the concentration of OH- ions in solution, then their hydrolysis is markedly enhanced.

Magnesium readily dissolves in acids with the release of hydrogen:

Mg + HCl = MgCl + H (4.3)

Alkalis do not work on him. Therefore, there is no amphotericity in magnesium compounds.

Magnesium nitride is obtained by direct interaction of nitrogen with metals at high temperature:

3Mg + N = MgN (4.4)

When in contact with water, many nitrides are completely hydrolyzed to form ammonia and metal hydroxide. For example:

MgN + 6HO = 3Mg(OH) + 2NH (4.5).

When silicon dioxide is heated with an excess of metallic magnesium, reducing silicon combines with magnesium, forming magnesium silicide MgSi:

4Mg + SiO = MgSi + 2MgO (4.6) .

Although magnesium is far ahead of hydrogen in the series of stresses, but, as we have already said, it decomposes water very slowly due to the formation of poorly soluble magnesium hydroxide. When heated in air, magnesium burns to form magnesium oxide MgO:

2Mg + O = 2MgO (4.7)

and a small amount of magnesium nitride MgN.

The use of magnesium and its compounds

Green plants were the first to "found" the use of magnesium. In fact, magnesium is part of chlorophyll, which converts solar energy, making it available to other living beings. Organic substances formed with the help of chlorophyll (sugar, starch) are necessary for human and animal nutrition. This means that magnesium is the element of life.

Plant needs for magnesium vary. All root crops - potatoes, table and fodder beets and other vegetables - are important consumers of magnesium, as well as legumes - clover, alfalfa, lupine. But cereals - rye, oats, wheat - need less magnesium. Chlorophyll contains from 2 to 3% magnesium, and the total amount of magnesium in the chlorophyll of all plants on the Earth is close to 100,000,000,000 tons.

Therefore, magnesium salts have long been successfully used as fertilizers: after all, magnesium is involved in the processes of photosynthesis. The increase in potato yield due to magnesium fertilizers is 27--28 centners per 1 ha, and this is in the Moscow region! In other areas (with different soil composition) the increase in yield can be even greater!

Magnesium is also part of the human body. So, magnesium is found in the blood (overwork is most often caused by a decrease in the amount of magnesium in human blood), in the teeth and in the brain. It has been established that the enzyme that promotes the transfer of phosphorus in our body contains magnesium. Enzyme molecules are gradually destroyed. Therefore, new molecules must be created in the body all the time. Hence the constant need of the body for magnesium.

The human body contains about 80 g of iron, 150 g of sodium, 1000 g of calcium and about 60 g of magnesium. Doctors have long paid attention to the medicinal properties of magnesium preparations. So, magnesium sulfate already familiar to us, when taken orally, has a laxative effect. To combat convulsive conditions (for example, with tetanus or poisoning), intramuscular injections of magnesium sulfate are used. Another magnesium medicine - magnesium carbonate MgCO - is recommended for oral administration with increased acidity of gastric juice, as well as heartburn. This substance is used as a powder, it is also part of the tooth powder.

The need for magnesium in an adult is approximately 10 mg per 1 kg of body weight per day. In a rapidly growing child's body, with an increase in weight by 1 kg, 25 mg of magnesium is retained.

But many of the mysteries of magnesium in a living organism have not yet been solved by scientists. To resolve them, scientists conduct experiments. It turned out, for example, that dogs whose food lacks magnesium developed myocardial infarction. An excess of calcium and magnesium in the diet of cows leads to the appearance of female offspring. It has long been found out that the shell of chicken eggs is the stronger, the more magnesium is in the food of laying hens.

The main field of application of metallic magnesium is the production of various light alloys on its basis. The addition of small amounts of other metals to magnesium dramatically changes its mechanical properties, giving the alloy significant hardness, strength, and corrosion resistance. Alloys called electrons have especially valuable properties. They belong to three systems: Mg--Al--Zn, Mg--Mn and Mg--Zn--Zr. The most widely used are alloys of the Mg - Al - Zn system, containing from 3 to 10% Al and from 0.2 to 3% Zn. The advantage of magnesium alloys is their low density (about 1.8 g/cm). They are used primarily in rocket technology and in the aircraft industry, as well as in auto, motorcycle, and instrument making. The disadvantage of magnesium alloys is their low resistance to corrosion in a humid atmosphere and in water, especially sea water.

Pure magnesium finds application in metallurgy. Some metals, in particular titanium, are obtained by the magnesium thermal method. In the production of some steels and non-ferrous alloys, magnesium is used to remove oxygen and sulfur from them. Magnesium is widely used in the organic synthesis industry. With its help, numerous substances belonging to various classes of organic compounds, as well as organoelement compounds, are obtained. Mixtures of magnesium powder with oxidizing agents are used in the manufacture of lighting and incendiary rockets.

Magnesium oxide MgO is usually obtained by calcining natural magnesite MgCO. It is a white loose powder known as burnt magnesia. Due to its high melting point (about 3000°C), magnesium oxide is used for the preparation of refractory crucibles, pipes, and bricks.

Magnesium hydroxide Mg(OH) is obtained as a slightly soluble white precipitate by the action of alkalis on soluble magnesium salts. Unlike beryllium hydroxide, magnesium hydroxide has only basic properties, being a base of medium strength.

Magnesium sulfate MgSO * 7HO, or bitter salt, is found in sea water. Unlike sulfates of alkaline earth metals, it is highly soluble in water.

Magnesium chloride MgCl * 6HO forms colorless, highly soluble crystals that deliquesce in air. The hygroscopicity of crude table salt is due to the admixture of small amounts of magnesium chloride in it.

Under the action of soda on soluble magnesium salts, not an average salt is obtained, but a mixture of basic carbonates. This mixture is used in medicine under the name of white magnesia.

Magnesium hydroxochloride MgOHCl is of great industrial importance. The technical product is obtained by mixing magnesium oxide with a concentrated aqueous solution of magnesium chloride and is called magnesia cement. Such a mixture after a while hardens, turning into a dense white, easily polished mass. Solidification can be explained by the fact that the hydroxochloride, initially formed according to the equation:

MgO + MgCl + HO = 2MgOHCl (5.1)

then it polymerizes in --Mg--O--Mg--O--Mg-- type chains, at the ends of which there are chlorine atoms or hydroxyl groups.

Magnesia cement as a binder is used in the manufacture of millstones, grindstones, and various plates. A mixture of it with sawdust called xylolite is used to cover floors.

Natural magnesium silicates are widely used: talc 3MgO * 4SiO * HO and especially asbestos CaO * 3MgO * 4SiO. The latter, due to its fire resistance, low thermal conductivity and fibrous structure, is an excellent heat-insulating material.