melting point of calcium. Calcium (chemical element)

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physical properties. Calcium is a silvery-white malleable metal that melts at 850°C. C and boils at 1482 degrees. C. It is much harder than the alkali metals.

Chemical properties. Calcium is an active metal. So under normal conditions, it easily interacts with atmospheric oxygen and halogens:

2 Ca + O2 \u003d 2 CaO (calcium oxide);

Ca + Br2 = CaBr2 (calcium bromide).

With hydrogen, nitrogen, sulfur, phosphorus, carbon and other non-metals, calcium reacts when heated:

Ca + H2 = CaH2 (calcium hydride);

3 Ca + N2 = Ca3N2 (calcium nitride);

Ca + S = CaS (calcium sulfide);

3 Ca + 2 P = Ca3P2 (calcium phosphide);

Ca + 2 C \u003d CaC2 (calcium carbide).

Calcium interacts slowly with cold water, and very vigorously with hot water:

Ca + 2 H2O \u003d Ca (OH) 2 + H2.

Calcium can take away oxygen or halogens from oxides and halides of less active metals, i.e. it has reducing properties:

5 Ca + Nb2O5 = CaO + 2 Nb;

• 1. Being in nature
• 3. Receipt
• 4. Application

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Calcium | guide Pesticides.ru

For many people, the knowledge about calcium is limited to the fact that this element is necessary for healthy bones and teeth. Where else it is contained, why it is needed and how necessary, not everyone has an idea. However, calcium is found in many compounds that are familiar to us, both natural and man-made. Chalk and lime, stalactites and stalagmites of caves, ancient fossils and cement, gypsum and alabaster, dairy products and anti-osteoporosis drugs - all this and more is high in calcium.

This element was first obtained by G. Davy in 1808, and at first it was not used very actively. Nevertheless, now this metal is the fifth in the world in terms of production, and the need for it is increasing year by year. The main area of ​​​​calcium use is the production of building materials and mixtures. However, it is necessary for building not only houses, but also living cells. In the human body, calcium is part of the skeleton, makes muscle contractions possible, ensures blood clotting, regulates the activity of a number of digestive enzymes, and performs other rather numerous functions. It is no less important for other living objects: animals, plants, fungi and even bacteria. At the same time, the need for calcium is quite high, which makes it possible to classify it as a macronutrient.

Calcium (Calcium), Ca is a chemical element of the main subgroup of group II of the periodic system of Mendeleev. Atomic number - 20. Atomic mass - 40.08.

Calcium is an alkaline earth metal. In the free state malleable, rather hard, white. Density refers to light metals.

• Density - 1.54 g / cm3,
• Melting point - +842 ° C,
• Boiling point - +1495 ° C.

Calcium has pronounced metallic properties. In all compounds, the oxidation state is +2.

In air, it is covered with a layer of oxide; when heated, it burns with a reddish, bright flame. It reacts slowly with cold water, and quickly displaces hydrogen from hot water and forms hydroxide. When reacted with hydrogen, it forms hydrides. At room temperature, it reacts with nitrogen to form nitrides. It also easily combines with halogens and sulfur, restores metal oxides when heated.

Calcium is one of the most abundant elements in nature. In the earth's crust, its content is 3% by weight. It occurs in the form of deposits of chalk, limestone, marble (a natural variety of calcium carbonate CaCO3). In large quantities there are deposits of gypsum (CaSO4 x 2h3O), phosphorite (Ca3 (PO4) 2 and various calcium-containing silicates.

Water

. Calcium salts are almost always present in natural water. Of these, only gypsum is slightly soluble in it. With the content of carbon dioxide in water, calcium carbonate goes into solution in the form of bicarbonate Ca(HCO3)2.

hard water

. Natural water with a large amount of calcium or magnesium salts is called hard.

soft water

. With a low content of these salts or their absence, water is called soft.

Soils

. As a rule, soils are adequately provided with calcium. And, since calcium is contained in a larger mass in the vegetative part of plants, its removal with the crop is negligible.

Losses of calcium from the soil occur as a result of its leaching by precipitation. This process depends on the granulometric composition of soils, rainfall, plant species, forms and doses of lime and mineral fertilizers. Depending on these factors, calcium losses from the arable layer range from several tens to 200–400 kg/ha or more.

Calcium content in different soil types

Podzolic soils contain 0.73% (of the dry matter of the soil) calcium.

Gray forest - 0.90% calcium.

Chernozems - 1.44% calcium.

Serozems - 6.04% calcium.

In the plant, calcium is in the form of phosphates, sulfates, carbonates, in the form of salts of pectin and oxalic acids. Almost 65% of calcium in plants can be extracted with water. The rest is treated with weak acetic and hydrochloric acids. Most calcium is found in aging cells.

Calcium deficiency symptoms according to:
culture	deficiency symptoms
General symptoms	Whitening of the apical bud; Whitening of young leaves; The tips of the leaves are bent down; The edges of the leaves curl up;
Potato	Upper leaves are poorly blooming; The growing point of the stem dies; There is a light stripe on the edges of the leaves, later it darkens; The edges of the leaves are twisted up;
Cabbage white and cauliflower	On the leaves of young plants, chlorotic spotting (marbling) or white stripes along the edges; In older plants, the leaves curl and burns appear on them; Growth point dies
	Leaf terminal lobes die Flowers fall; A dark spot appears on the fruit at the apex, which increases as the fruit grows (tomato apex rot)
	The apical buds die; The edges of young leaves are wrapped up, torn, then die off; The upper parts of the shoots die off; Damage to the tips of the roots; In the pulp of the fruit - brown spots (bitter pitting); The taste of the fruit deteriorates; Decreased marketability of fruits

Functions of calcium

The effect of this element on plants is multilateral and, as a rule, positive. Calcium:

• Enhances metabolism;
• Plays an important role in the movement of carbohydrates;
• Influences the metamorphoses of nitrogenous substances;
• Accelerates the consumption of seed reserve proteins during germination;
• Plays a role in the process of photosynthesis;
• a strong antagonist of other cations, prevents their excessive entry into plant tissues;
• It affects the physicochemical properties of protoplasm (viscosity, permeability, etc.), and hence the normal course of biochemical processes in the plant;
• Calcium compounds with pectin glue the walls of individual cells together;
• Influences the activity of enzymes.

It should be noted that the effect of calcium compounds (lime) on the activity of enzymes is expressed not only in direct action, but also due to the improvement of the physicochemical properties of the soil and its nutritional regime. In addition, soil liming significantly affects the processes of vitamin biosynthesis.

Lack (deficiency) of calcium in plants

The lack of calcium primarily affects the development of the root system. The formation of root hairs stops on the roots. The outer cells of the root are destroyed.

This symptom manifests itself both with a lack of calcium and with an imbalance in the nutrient solution, that is, the predominance of monovalent sodium, potassium and hydrogen cations in it.

In addition, the presence of nitrate nitrogen in the soil solution enhances the flow of calcium into plant tissues, while ammonia decreases it.

Signs of calcium starvation are expected when the calcium content is less than 20% of the soil cation exchange capacity.

Symptoms. Visually, calcium deficiency is established by the following signs:

• At the roots of plants, damaged brown tips are observed;
• The growth point is deformed and dies;
• Flowers, ovaries and buds fall off;
• Fruits are damaged by necrosis;
• Leaves are chlorotic;
• The apical bud dies, and the growth of the stem stops.

Cabbage, alfalfa, clover are highly sensitive to the presence of calcium. It has been established that these same plants are also characterized by increased sensitivity to soil acidity.

Mineral calcium poisoning results in interveinal chlorosis with whitish necrotic patches. They can be colored or have concentric rings filled with water. Some plants respond to excess calcium by growing leaf rosettes, dying off shoots and falling leaves. Symptoms are similar in appearance to a lack of iron and magnesium.

The source of replenishment of calcium in the soil is lime fertilizers. They are divided into three groups:

• Hard calcareous rocks;
• Soft calcareous rocks;
• Industrial waste with high lime content.

Hard calcareous rocks according to the content of CaO and MgO are divided into:

• limestones (55–56% CaO and up to 0.9% MgO);
• dolomitic limestones (42–55% CaO and up to 9% MgO);
• dolomites (32–30% CaO and 18–20% MgO).

Limestones

- basic lime fertilizers. Contain 75–100% Ca and Mg oxides in terms of CaCO3.

Dolomitized limestone

. Contains 79-100% active ingredient (a.i.) in terms of CaCO3. It is recommended in crop rotations with potatoes, legumes, flax, root crops, as well as on heavily podzolized soils.

Marl

. Contains up to 25–15% CaCO3 and impurities in the form of clay with sand up to 20–40%. Acts slowly. Recommended for use on light soils.

Chalk

. Contains 90–100% CaCO3. Action is faster than that of limestone. It is a valuable lime fertilizer in finely ground form.

burnt lime

(CaO). The content of CaCO3 is over 70%. It is characterized as a strong and fast acting liming material.

Slaked lime

(Ca(OH)2). The content of CaCO3 is 35% or more. It is also a strong and fast acting lime fertilizer.

Dolomite flour

. The content of CaCO3 and MgCO3 is about 100%. Slower in action than calcareous tuffs. Typically used where magnesium is required.

calcareous tuffs

. The content of CaCO3 is 15–96%, impurities are up to 25% clay and sand, 0.1% P2O5. Action is faster than that of limestone.

Defecation mud (defecation)

. Consists of CaCO3 and Ca(OH)2. The content of lime on CaO is up to 40%. Nitrogen is also present - 0.5% and P2O5 - 1-2%. This is waste from sugar beet factories. It is recommended for use not only to reduce soil acidity, but also in beet-growing areas on chernozem soils.

Shale ash cyclones

. Dry pulverized material. The content of the active substance is 60-70%. Refers to industrial waste.

Dust from kilns and cement plants

. The content of CaCO3 must exceed 60%. In practice, it is used in farms located in the immediate vicinity of cement plants.

Metallurgical slag

. Used in the regions of the Urals and Siberia. Non-hygroscopic, easy to spray. Must contain at least 80% CaCO3, have a moisture content of not more than 2%. The granulometric composition is important: 70% - less than 0.25 mm, 90% - less than 0.5 mm.

organic fertilizers. The content of Ca in terms of CaCO3 is 0.32–0.40%.

Phosphate flour. The calcium content is 22% CaCO3.

Lime fertilizers are used not only to provide soil and plants with calcium. The main purpose of their use is soil liming. This is a method of chemical reclamation. It is aimed at neutralizing excess soil acidity, improving its agrophysical, agrochemical and biological properties, supplying plants with magnesium and calcium, mobilizing and immobilizing macroelements and microelements, creating optimal water-physical, physical, and air conditions for the life of cultivated plants.

Soil liming efficiency

Simultaneously with meeting the need of plants for calcium as an element of mineral nutrition, liming leads to multiple positive changes in soils.

Effect of liming on the properties of some soils

Calcium promotes coagulation of soil colloids and prevents their leaching. This leads to easier soil cultivation and improved aeration.

As a result of liming:

• sandy humus soils increase their water absorption capacity;
• on heavy clay soils, soil aggregates and clods are formed that improve water permeability.

In particular, organic acids are neutralized and H-ions are displaced from the absorbing complex. This leads to the elimination of exchange and reduction of hydrolytic acidity of the soil. At the same time, there is an improvement in the cationic composition of the soil absorbing complex, which occurs due to the change of hydrogen and aluminum ions to calcium and magnesium cations. This increases the degree of saturation of soils with bases and increases the uptake capacity.

The effect of liming on the supply of plants with nitrogen

After liming, the positive agrochemical properties of the soil and its structure can be preserved for several years. This contributes to the creation of favorable conditions for enhancing beneficial microbiological processes to mobilize nutrients. The activity of ammonifiers, nitrifiers, nitrogen-fixing bacteria that live freely in the soil is enhanced.

Liming helps to increase the reproduction of nodule bacteria and improve the supply of nitrogen to the host plant. It has been established that bacterial fertilizers lose their effectiveness on acidic soils.

The effect of liming on the supply of plants with ash elements

Liming contributes to the supply of ash elements to the plant, since the activity of bacteria that decompose organic phosphorus compounds in the soil and promote the transition of iron and aluminum phosphates into calcium phosphate salts available to plants is enhanced. Liming of acidic soils enhances microbiological and biochemical processes, which, in turn, increases the amount of nitrates, as well as assimilable forms of phosphorus and potassium.

The effect of liming on the forms and availability of macronutrients and trace elements

Liming increases the amount of calcium, and when using dolomite flour - magnesium. Simultaneously, the toxic forms of manganese and aluminum become insoluble and pass into the precipitated form. The availability of elements such as iron, copper, zinc, manganese is declining. Nitrogen, sulfur, potassium, calcium, magnesium, phosphorus and molybdenum are becoming more available.

Effect of liming on the action of physiologically acidic fertilizers

Liming increases the effectiveness of physiologically acidic mineral fertilizers, especially ammonia and potash.

The positive effect of physiologically acidic fertilizers fades without lime, and over time can turn into a negative one. So on the fertilized sites, the yields are even less than on the unfertilized ones. The combination of liming with the use of fertilizers increases their effectiveness by 25–50%.

Liming activates enzymatic processes in the soil, which indirectly judge its fertility.

Compiled by: Grigorovskaya P.I.

Page added: 05.12.13 00:40

Last update: 05/22/14 16:25

Literary sources:

Glinka N.L. General chemistry. Textbook for universities. Publisher: L: Chemistry, 1985, p. 731

Mineev V.G. Agrochemistry: Textbook. - 2nd edition, revised and supplemented. - M .: MGU Publishing House, KolosS Publishing House, 2004. - 720 p., L. ill.: ill. – (Classic university textbook).

Petrov B.A., Seliverstov N.F. Mineral nutrition of plants. Reference manual for students and gardeners. Yekaterinburg, 1998. 79 p.

Encyclopedia for children. Volume 17. Chemistry. / Head. ed. V.A. Volodin. - M.: Avanta +, 2000. - 640 p., ill.

Yagodin B.A., Zhukov Yu.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodina. - M.: Kolos, 2002. - 584 p.: silt (Textbooks and teaching aids for students of higher educational institutions).

Images (remastered):

20 Ca Calcium, under license CC BY

Calcium deficiency in wheat, by CIMMYT, licensed under CC BY-NC-SA

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Calcium and its role for humanity - Chemistry

Calcium and its role for mankind

Introduction

Being in nature

Receipt

Physical Properties

Chemical properties

The use of calcium compounds

Biological role

Conclusion

Bibliography

Introduction

Calcium is an element of the main subgroup of the second group, the fourth period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 20. It is denoted by the symbol Ca (lat. Calcium). The simple substance calcium (CAS number: 7440-70-2) is a soft, reactive, silvery-white alkaline earth metal.

Despite the ubiquity of element #20, even chemists have not seen elemental calcium. But this metal, both externally and in behavior, is completely different from alkali metals, contact with which is fraught with the danger of fires and burns. It can be safely stored in air, it does not ignite from water. The mechanical properties of elemental calcium do not make it a "black sheep" in the family of metals: calcium surpasses many of them in strength and hardness; it can be turned on a lathe, drawn into a wire, forged, pressed.

And yet, elemental calcium is almost never used as a structural material. He's too active for that. Calcium easily reacts with oxygen, sulfur, halogens. Even with nitrogen and hydrogen, under certain conditions, it reacts. The environment of carbon oxides, inert for most metals, is aggressive for calcium. It burns in an atmosphere of CO and CO2.

History and origin of the name

The name of the element comes from lat. calx (in the genitive case calcis) -- "lime", "soft stone". It was proposed by the English chemist Humphrey Davy, who in 1808 isolated calcium metal by the electrolytic method. Davy electrolyzed a mixture of wet slaked lime with mercury oxide HgO on a platinum plate, which was the anode. A platinum wire immersed in liquid mercury served as the cathode. As a result of electrolysis, calcium amalgam was obtained. Having driven away mercury from it, Davy received a metal called calcium.

Calcium compounds - limestone, marble, gypsum (as well as lime - a product of burning limestone) have been used in construction for several millennia ago. Until the end of the 18th century, chemists considered lime to be a simple body. In 1789, A. Lavoisier suggested that lime, magnesia, barite, alumina and silica are complex substances.

Being in nature

Due to the high chemical activity of calcium in the free form in nature is not found.

Calcium accounts for 3.38% of the mass of the earth's crust (5th place in abundance after oxygen, silicon, aluminum and iron).

Isotopes. Calcium occurs in nature in the form of a mixture of six isotopes: 40Ca, 42Ca, 43Ca, 44Ca, 46Ca and 48Ca, among which the most common - 40Ca - is 96.97%.

Of the six naturally occurring calcium isotopes, five are stable. The sixth 48Ca isotope, the heaviest of the six and very rare (its isotopic abundance is only 0.187%), was recently discovered to undergo double beta decay with a half-life of 5.3×1019 years.

in rocks and minerals. Most of the calcium is contained in the composition of silicates and aluminosilicates of various rocks (granites, gneisses, etc.), especially in feldspar - anorthite Ca.

In the form of sedimentary rocks, calcium compounds are represented by chalk and limestone, consisting mainly of the mineral calcite (CaCO3). The crystalline form of calcite, marble, is much less common in nature.

Calcium minerals such as calcite CaCO3, anhydrite CaSO4, alabaster CaSO4 0.5h3O and gypsum CaSO4 2h3O, fluorite CaF2, apatites Ca5(PO4)3(F,Cl,OH), dolomite MgCO3 CaCO3 are quite widespread. The presence of calcium and magnesium salts in natural water determines its hardness.

Calcium, which migrates vigorously in the earth's crust and accumulates in various geochemical systems, forms 385 minerals (fourth in terms of the number of minerals).

Migration in the earth's crust. In the natural migration of calcium, a significant role is played by the “carbonate equilibrium”, associated with the reversible reaction of the interaction of calcium carbonate with water and carbon dioxide with the formation of soluble bicarbonate:

CaCO3 + h3O + CO2 - Ca (HCO3) 2 - Ca2+ + 2HCO3-

(the equilibrium shifts to the left or right depending on the concentration of carbon dioxide).

biogenic migration. In the biosphere, calcium compounds are found in almost all animal and plant tissues (see also below). A significant amount of calcium is part of living organisms. So, hydroxyapatite Ca5 (PO4) 3OH, or, in another way, 3Ca3 (PO4) 2 Ca (OH) 2 is the basis of the bone tissue of vertebrates, including humans; shells and shells of many invertebrates, egg shells, etc. are composed of calcium carbonate CaCO3. In living tissues of humans and animals, 1.4-2% Ca (by mass fraction); in a human body weighing 70 kg, the calcium content is about 1.7 kg (mainly in the composition of the intercellular substance of bone tissue).

Receipt

Free metallic calcium is obtained by electrolysis of a melt consisting of CaCl2 (75-80%) and KCl or from CaCl2 and CaF2, as well as by aluminothermic reduction of CaO at 1170-1200 °C:

4CaO + 2Al = CaAl2O4 + 3Ca.

Physical Properties

Calcium metal exists in two allotropic modifications. Up to 443 °C, stable?-Ca with a cubic face-centered lattice (parameter a = 0.558 nm), above stable?-Ca with a cubic body-centered lattice of the type?-Fe (parameter a = 0.448 nm). Standard enthalpy? H0 transition? > ? is 0.93 kJ/mol.

Chemical properties

Calcium is a typical alkaline earth metal. The chemical activity of calcium is high, but lower than that of all other alkaline earth metals. It readily reacts with oxygen, carbon dioxide and moisture in the air, due to which the surface of calcium metal is usually dull gray, so calcium is usually stored in the laboratory, like other alkaline earth metals, in a tightly closed jar under a layer of kerosene or liquid paraffin.

In the series of standard potentials, calcium is located to the left of hydrogen. The standard electrode potential of the Ca2+/Ca0 pair is ?2.84 V, so that calcium actively reacts with water, but without ignition:

Ca + 2H2O \u003d Ca (OH) 2 + H2 ^ + Q.

With active non-metals (oxygen, chlorine, bromine), calcium reacts under normal conditions:

2Ca + O2 = 2CaO, Ca + Br2 = CaBr2.

When heated in air or oxygen, calcium ignites. With less active non-metals (hydrogen, boron, carbon, silicon, nitrogen, phosphorus and others), calcium interacts when heated, for example:

Ca + H2 = CaH2, Ca + 6B = CaB6,

3Ca + N2 = Ca3N2, Ca + 2C = CaC2,

3Ca + 2P = Ca3P2 (

calcium phosphide), calcium phosphides of CaP and CaP5 compositions are also known;

2Ca + Si = Ca2Si

(calcium silicide), calcium silicides of compositions CaSi, Ca3Si4 and CaSi2 are also known.

The course of the above reactions, as a rule, is accompanied by the release of a large amount of heat (that is, these reactions are exothermic). In all compounds with non-metals, the oxidation state of calcium is +2. Most of the calcium compounds with non-metals are easily decomposed by water, for example:

CaH2 + 2H2O \u003d Ca (OH) 2 + 2H2 ^,

Ca3N2 + 3H2O = 3Ca(OH)2 + 2Nh4^.

The Ca2+ ion is colorless. When soluble calcium salts are added to the flame, the flame turns brick red.

Calcium salts such as CaCl2 chloride, CaBr2 bromide, CaI2 iodide and Ca(NO3)2 nitrate are highly soluble in water. CaF2 fluoride, CaCO3 carbonate, CaSO4 sulfate, Ca3(PO4)2 orthophosphate, CaC2O4 oxalate and some others are insoluble in water.

Of great importance is the fact that, unlike calcium carbonate CaCO3, acidic calcium carbonate (hydrocarbonate) Ca(HCO3)2 is soluble in water. In nature, this leads to the following processes. When cold rain or river water, saturated with carbon dioxide, penetrates underground and falls on limestones, their dissolution is observed:

CaCO3 + CO2 + H2O \u003d Ca (HCO3) 2.

In the same places where water saturated with calcium bicarbonate comes to the surface of the earth and is heated by the sun's rays, the reverse reaction occurs:

Ca(HCO3)2 = CaCO3 + CO2^ + H2O.

So in nature there is a transfer of large masses of substances. As a result, huge gaps can form underground, and beautiful stone "icicles" - stalactites and stalagmites - form in the caves.

The presence of dissolved calcium bicarbonate in water largely determines the temporary hardness of water. It is called temporary because when water is boiled, the bicarbonate decomposes, and CaCO3 precipitates. This phenomenon leads, for example, to the fact that scale forms in the kettle over time.

Applications of metallic calcium

The main use of calcium metal is as a reducing agent in the production of metals, especially nickel, copper and stainless steel. Calcium and its hydride are also used to obtain hard-to-recover metals such as chromium, thorium and uranium. Alloys of calcium with lead are used in batteries and bearing alloys. Calcium granules are also used to remove traces of air from electrovacuum devices.

Metalthermy

Pure metallic calcium is widely used in metallothermy to obtain rare metals.

Alloying

Pure calcium is used to alloy lead, which is used for the manufacture of battery plates, maintenance-free starter lead-acid batteries with low self-discharge. Also, metallic calcium is used for the production of high-quality calcium babbits BKA.

Nuclear fusion

The 48Ca isotope is the most effective and widely used material for the production of superheavy elements and the discovery of new elements in the periodic table. For example, in the case of using 48Ca ions to produce superheavy elements in accelerators, the nuclei of these elements are formed hundreds and thousands of times more efficiently than when using other "projectiles" (ions).

The use of calcium compounds

calcium hydride. By heating calcium in a hydrogen atmosphere, Cah3 (calcium hydride) is obtained, which is used in metallurgy (metallothermy) and in the production of hydrogen in the field.

Optical and laser materials. Calcium fluoride (fluorite) is used in the form of single crystals in optics (astronomical objectives, lenses, prisms) and as a laser material. Calcium tungstate (scheelite) in the form of single crystals is used in laser technology, and also as a scintillator.

calcium carbide. Calcium carbide CaC2 is widely used to obtain acetylene and to reduce metals, as well as in the production of calcium cyanamide (by heating calcium carbide in nitrogen at 1200 ° C, the reaction is exothermic, carried out in cyanamide furnaces).

Chemical current sources. Calcium, as well as its alloys with aluminum and magnesium, are used in reserve thermal electric batteries as an anode (for example, a calcium-chromate element). Calcium chromate is used in such batteries as the cathode. A feature of such batteries is an extremely long shelf life (decades) in a usable condition, the ability to operate in any conditions (space, high pressures), high specific energy by weight and volume. The disadvantage is the short duration. Such batteries are used where it is necessary to create colossal electric power for a short time (ballistic missiles, some spacecraft, etc.).

Refractory materials. Calcium oxide, both in free form and as part of ceramic mixtures, is used in the production of refractory materials.

Medicines. Calcium compounds are widely used as an antihistamine.

Calcium chloride

Calcium gluconate

calcium glycerophosphate

In addition, calcium compounds are introduced into preparations for the prevention of osteoporosis, into vitamin complexes for pregnant women and the elderly.

Biological role

Calcium is a common macronutrient in plants, animals and humans. In humans and other vertebrates, most of it is found in the skeleton and teeth in the form of phosphates. The skeletons of most groups of invertebrates (sponges, coral polyps, mollusks, etc.) are composed of various forms of calcium carbonate (lime). Calcium ions are involved in the processes of blood coagulation, as well as in maintaining a constant osmotic pressure of the blood. Calcium ions also serve as one of the universal second messengers and regulate a variety of intracellular processes - muscle contraction, exocytosis, including the secretion of hormones and neurotransmitters, etc. The calcium concentration in the cytoplasm of human cells is about 10–7 mol, in intercellular fluids about 10 ?3 mol.

The need for calcium depends on age. For adults, the required daily allowance is from 800 to 1000 milligrams (mg), and for children from 600 to 900 mg, which is very important for children due to the intensive growth of the skeleton. Most of the calcium that enters the human body with food is found in dairy products, the remaining calcium is found in meat, fish, and some plant foods (legumes are especially rich). Absorption occurs both in the large and small intestines and is facilitated by an acidic environment, vitamin D and vitamin C, lactose, and unsaturated fatty acids. The role of magnesium in calcium metabolism is also important, with its deficiency, calcium is “washed out” of the bones and deposited in the kidneys (kidney stones) and muscles.

Assimilation of calcium is prevented by aspirin, oxalic acid, estrogen derivatives. Combining with oxalic acid, calcium gives water-insoluble compounds that are components of kidney stones.

Due to the large number of processes associated with calcium, the content of calcium in the blood is precisely regulated, and with proper nutrition, deficiency does not occur. Prolonged absence from the diet can cause cramps, joint pain, drowsiness, growth defects, and constipation. A deeper deficiency leads to permanent muscle cramps and osteoporosis. Abuse of coffee and alcohol can be the causes of calcium deficiency, as part of it is excreted in the urine.

Excessive doses of calcium and vitamin D can cause hypercalcemia, followed by intense calcification of bones and tissues (mainly affecting the urinary system). A prolonged excess disrupts the functioning of muscle and nerve tissues, increases blood clotting and reduces the absorption of zinc by bone cells. The maximum daily safe dose for an adult is 1500 to 1800 milligrams.

Products Calcium, mg/100 g

Sesame 783

Nettle 713

Mallow forest 505

Plantain big 412

Galinsoga 372

Sardines in oil 330

Budra ivy 289

Dog rosehip 257

Almond 252

Plantain lanceolate. 248

Hazelnut 226

Amaranth seed 214

Watercress 214

Soy beans dry 201

Children under 3 years - 600 mg.

Children 4 to 10 years old - 800 mg.

Children 10 to 13 years old - 1000 mg.

Adolescents 13 to 16 years old - 1200 mg.

Youth 16 and older - 1000 mg.

Adults 25 to 50 years old - 800 to 1200 mg.

Pregnant and breastfeeding women - 1500 to 2000 mg.

Conclusion

Calcium is one of the most abundant elements on earth. There is a lot of it in nature: mountain ranges and clay rocks are formed from calcium salts, it is found in sea and river water, and is part of plant and animal organisms.

Calcium constantly surrounds the townspeople: almost all the main building materials - concrete, glass, brick, cement, lime - contain this element in significant quantities.

Naturally, having such chemical properties, calcium cannot be found in nature in a free state. But calcium compounds - both natural and artificial - have become of paramount importance.

Bibliography

1. Editorial board: Knunyants I. L. (editor-in-chief) Chemical Encyclopedia: in 5 volumes - Moscow: Soviet Encyclopedia, 1990. - T. 2. - S. 293. - 671 p.

2. Doronin. N. A. Kaltsy, Goshimizdat, 1962. 191 pages with illustrations.

3. Dotsenko VA. - Therapeutic and preventive nutrition. - Q. nutrition, 2001 - N1-p.21-25

4. Bilezikian J. P. Calcium and bone metabolism // In: K. L. Becker, ed.

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Calcium is a metal element of the main subgroup II of group 4 of the period of the periodic system of chemical elements. It belongs to the family of alkaline earth metals. The outer energy level of the calcium atom contains 2 paired s-electrons

Which he is able to give energetically during chemical interactions. Thus, Calcium is a reducing agent and in its compounds has an oxidation state of +2. In nature, calcium occurs only in the form of salts. The mass fraction of calcium in the earth's crust is 3.6%. The main natural calcium mineral is calcite CaCO3 and its varieties - limestone, chalk, marble. There are also living organisms (for example, corals), the backbone of which consists mainly of calcium carbonate. Also important calcium minerals are dolomite CaCO3 MgCO3, fluorite CaF2, gypsum CaSO4 2h3O, apatite, feldspar, etc. Calcium plays an important role in the life of living organisms. The mass fraction of calcium in the human body is 1.4-2%. It is part of the teeth, bones, other tissues and organs, participates in the process of blood coagulation, stimulates cardiac activity. To provide the body with a sufficient amount of calcium, it is imperative to consume milk and dairy products, green vegetables, fish. The simple substance calcium is a typical silver-white metal. It is quite hard, plastic, has a density of 1.54 g/cm3 and a melting point of 842? C. Chemically, calcium is very active. Under normal conditions, it easily interacts with oxygen and moisture in the air, so it is stored in hermetically sealed vessels. When heated in air, calcium ignites and forms an oxide: 2Ca + O2 = 2CaO. Calcium reacts with chlorine and bromine when heated, and with fluorine even in the cold. The products of these reactions are the corresponding halides, for example: Ca + Cl2 = CaCl2. When calcium is heated with sulfur, calcium sulfide is formed: Ca + S = CaS. Calcium can also react with other non-metals. Interaction with water leads to the formation of poorly soluble calcium hydroxide and the evolution of gaseous hydrogen : Ca + 2h3O = Ca (OH) 2 + h3. Calcium metal is widely used. It is used as a rozkisnik in the manufacture of steels and alloys, as a reducing agent for the production of some refractory metals.

Calcium is obtained by electrolysis of a calcium chloride melt. Thus, calcium was first obtained in 1808 by Humphry Davy.

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History of calcium

Calcium was discovered in 1808 by Humphry Davy, who, by electrolysis of slaked lime and mercury oxide, obtained calcium amalgam, as a result of the process of distillation of mercury from which the metal remained, which received the name calcium. in latin lime sounds like calx, it was this name that was chosen by the English chemist for the discovered substance.

Calcium is an element of the main subgroup II of group IV of the period of the periodic system of chemical elements D.I. Mendeleev, has an atomic number of 20 and an atomic mass of 40.08. The accepted designation is Ca (from Latin - Calcium).

Physical and chemical properties

Calcium is a reactive, soft, silver-white alkali metal. Due to the interaction with oxygen and carbon dioxide, the surface of the metal tarnishes, so calcium needs a special storage regime - a tightly closed container in which the metal is poured with a layer of liquid paraffin or kerosene.

Calcium is the most well-known of the trace elements necessary for a person, the daily requirement for it is from 700 to 1500 mg for a healthy adult, but it increases during pregnancy and lactation, this must be taken into account and calcium should be taken in the form of drugs.

Being in nature

Calcium has a very high chemical activity, therefore, in a free (pure) form, it does not occur in nature. Nevertheless, it is the fifth most common in the earth's crust, in the form of compounds it is found in sedimentary (limestone, chalk) and rocks (granite), anorite feldspar contains a lot of calcium.

It is widely distributed in living organisms, its presence is found in plants, animal and human organisms, where it is present mainly in the composition of teeth and bone tissue.

Calcium absorption

An obstacle to the normal absorption of calcium from foods is the consumption of carbohydrates in the form of sweets and alkalis, which neutralize the hydrochloric acid of the stomach, which is necessary to dissolve calcium. The process of calcium absorption is quite complicated, so sometimes it is not enough to get it only with food, an additional intake of the microelement is necessary.

Interaction with others

To improve calcium absorption in the intestine, it is necessary, which tends to facilitate the process of calcium absorption. When taking calcium (in the form of supplements) in the process of eating, absorption is blocked, but taking calcium supplements separately from food does not affect this process in any way.

Almost all of the body's calcium (1 to 1.5 kg) is found in the bones and teeth. Calcium is involved in the processes of nervous tissue excitability, muscle contractility, blood clotting processes, is part of the nucleus and membranes of cells, cell and tissue fluids, has anti-allergic and anti-inflammatory effects, prevents acidosis, activates a number of enzymes and hormones. Calcium is also involved in the regulation of cell membrane permeability and has the opposite effect.

Signs of calcium deficiency

Signs of a lack of calcium in the body are such, at first glance, unrelated symptoms:

• nervousness, mood deterioration;
• cardiopalmus;
• convulsions, numbness of the limbs;
• growth retardation and children;
• high blood pressure;
• delamination and fragility of nails;
• pain in the joints, lowering the "pain threshold";
• profuse menstruation.

Causes of calcium deficiency

The causes of calcium deficiency can be unbalanced diets (especially starvation), low calcium content in food, smoking and addiction to coffee and caffeinated drinks, dysbacteriosis, kidney disease, thyroid gland, pregnancy, lactation periods and menopause.

Excess calcium, which can occur with excessive consumption of dairy products or uncontrolled intake of drugs, is characterized by severe thirst, nausea, vomiting, loss of appetite, weakness, and increased urination.

The use of calcium in life

Calcium has found application in the metallothermic production of uranium, in the form of natural compounds it is used as a raw material for the production of gypsum and cement, as a means of disinfection (everyone knows bleach).

Calcium is an element of the main subgroup of the second group, the fourth period of the periodic system of chemical elements, with atomic number 20. It is denoted by the symbol Ca (lat. Calcium). The simple substance calcium (CAS number: 7440-70-2) is a soft, reactive, silver-white alkaline earth metal.

History and origin of the name

The name of the element comes from lat. calx (in the genitive case calcis) - "lime", "soft stone". It was proposed by the English chemist Humphrey Davy, who in 1808 isolated calcium metal by the electrolytic method. Davy electrolyzed a mixture of wet slaked lime with mercury oxide HgO on a platinum plate, which was the anode. A platinum wire immersed in liquid mercury served as the cathode. As a result of electrolysis, calcium amalgam was obtained. Having driven away mercury from it, Davy received a metal called calcium.
Calcium compounds - limestone, marble, gypsum (as well as lime - a product of burning limestone) have been used in construction for several millennia ago. Until the end of the 18th century, chemists considered lime to be a simple body. In 1789, A. Lavoisier suggested that lime, magnesia, barite, alumina and silica are complex substances.

Receipt

Free metallic calcium is obtained by electrolysis of a melt consisting of CaCl 2 (75-80%) and KCl or from CaCl 2 and CaF 2, as well as aluminothermic reduction of CaO at 1170-1200 ° C:
4CaO + 2Al → CaAl 2 O 4 + 3Ca.

Physical Properties

Calcium metal exists in two allotropic modifications. Up to 443 °C, α-Ca with a cubic face-centered lattice is stable (parameter a = 0.558 nm), above β-Ca is stable with a cubic body-centered lattice of the α-Fe type (parameter a = 0.448 nm). The standard enthalpy ΔH 0 of the α → β transition is 0.93 kJ/mol.
With a gradual increase in pressure, it begins to show the properties of a semiconductor, but does not become a semiconductor in the full sense of the word (it is no longer a metal either). With a further increase in pressure, it returns to the metallic state and begins to exhibit superconducting properties (the superconductivity temperature is six times higher than that of mercury, and far exceeds all other elements in conductivity). The unique behavior of calcium is similar in many ways to strontium (i.e., the parallels in the periodic table are preserved).

Chemical properties

Calcium is a typical alkaline earth metal. The chemical activity of calcium is high, but lower than that of all other alkaline earth metals. It readily reacts with oxygen, carbon dioxide and moisture in the air, due to which the surface of calcium metal is usually dull gray, so calcium is usually stored in the laboratory, like other alkaline earth metals, in a tightly closed jar under a layer of kerosene or liquid paraffin.

Calcium

CALCIUM-I; m.[from lat. calx (calcis) - lime] A chemical element (Ca), a silver-white metal that is part of limestone, marble, etc.

◁ Calcium, th, th. K salts.

calcium

(lat. Calcium), a chemical element of group II of the periodic system, belongs to the alkaline earth metals. Name from lat. calx, genitive calcis - lime. Silver-white metal, density 1.54 g / cm 3, t pl 842ºC. At normal temperatures, it easily oxidizes in air. In terms of prevalence in the earth's crust, it occupies the 5th place (minerals calcite, gypsum, fluorite, etc.). As an active reducing agent, it is used to obtain U, Th, V, Cr, Zn, Be and other metals from their compounds, to deoxidize steels, bronzes, etc. It is included in the composition of antifriction materials. Calcium compounds are used in construction (lime, cement), calcium preparations - in medicine.

CALCIUM

CALCIUM (lat. Calcium), Ca (read "calcium"), a chemical element with atomic number 20, is located in the fourth period in group IIA of the periodic system of Mendeleev's elements; atomic mass 40.08. Belongs to the number of alkaline earth elements (cm. ALKALINE EARTH METALS).
Natural calcium consists of a mixture of nuclides (cm. NUCLIDE) with mass numbers 40 (in a mixture by mass 96.94%), 44 (2.09%), 42 (0.667%), 48 (0.187%), 43 (0.135%) and 46 (0.003%). Outer electron layer configuration 4 s 2 . In almost all compounds, the oxidation state of calcium is +2 (valency II).
The radius of the neutral calcium atom is 0.1974 nm, the radius of the Ca 2+ ion is from 0.114 nm (for the coordination number 6) to 0.148 nm (for the coordination number 12). The sequential ionization energies of a neutral calcium atom are 6.133, 11.872, 50.91, 67.27, and 84.5 eV, respectively. On the Pauling scale, the electronegativity of calcium is about 1.0. In its free form, calcium is a silvery-white metal.
Discovery history
Calcium compounds are found everywhere in nature, so mankind has been familiar with them since ancient times. Lime has been used in the construction industry for a long time. (cm. LIME)(quicklime and slaked), which for a long time was considered a simple substance, "earth". However, in 1808 the English scientist G. Davy (cm. DEVI Humphrey) managed to get a new metal from lime. To do this, Davy subjected to electrolysis a mixture of slightly moistened slaked lime with mercury oxide and isolated a new metal from the amalgam formed on the mercury cathode, which he called calcium (from Latin calx, genus case calcis - lime). In Russia, for some time this metal was called "limestone".
Being in nature
Calcium is one of the most abundant elements on Earth. It accounts for 3.38% of the mass of the earth's crust (5th place in abundance after oxygen, silicon, aluminum and iron). Due to the high chemical activity of calcium in the free form in nature is not found. Most of the calcium is found in silicates. (cm. SILICATES) and aluminosilicates (cm. ALUMOSILICATES) various rocks (granites (cm. GRANITE), gneisses (cm. GNEISS) and so on.). In the form of sedimentary rocks, calcium compounds are represented by chalk and limestone, consisting mainly of the mineral calcite. (cm. CALCITE)(CaCO3). The crystalline form of calcite - marble - is found in nature much less frequently.
Calcium minerals such as limestone are quite widespread. (cm. LIMESTONE)СaCO 3 , anhydrite (cm. ANHYDRITE) CaSO 4 and gypsum (cm. GYPSUM) CaSO 4 2H 2 O, fluorite (cm. FLUORITE) CaF 2 , apatite (cm. APATITE) Ca 5 (PO 4) 3 (F, Cl, OH), dolomite (cm. DOLOMITE) MgCO 3 CaCO 3. The presence of calcium and magnesium salts in natural water determines its hardness. (cm. HARDNESS OF WATER). A significant amount of calcium is part of living organisms. So, hydroxylapatite Ca 5 (PO 4) 3 (OH), or, in another entry, 3Ca 3 (PO 4) 2 Ca (OH) 2 - the basis of the bone tissue of vertebrates, including humans; shells and shells of many invertebrates, egg shells, etc. are made of calcium carbonate CaCO 3.
Receipt
Calcium metal is obtained by electrolysis of a melt consisting of CaCl 2 (75-80%) and KCl or from CaCl 2 and CaF 2, as well as aluminothermic reduction of CaO at 1170-1200 ° C:
4CaO + 2Al = CaAl 2 O 4 + 3Ca.
Physical and chemical properties
Calcium metal exists in two allotropic modifications (see Allotropy (cm. ALLOTROPY)). Up to 443 °C, a-Ca with a cubic face-centered lattice is stable (parameter a = 0.558 nm), higher b-Ca is stable with a cubic body-centered lattice of the a-Fe type (parameter a = 0.448 nm). The melting point of calcium is 839 ° C, the boiling point is 1484 ° C, the density is 1.55 g / cm 3.
The chemical activity of calcium is high, but lower than that of all other alkaline earth metals. It easily reacts with oxygen, carbon dioxide and moisture in the air, due to which the surface of calcium metal is usually dull gray, so in the laboratory calcium is usually stored, like other alkaline earth metals, in a tightly closed jar under a layer of kerosene.
In the series of standard potentials, calcium is located to the left of hydrogen. The standard electrode potential of the Ca 2+ /Ca 0 pair is -2.84 V, so that calcium actively reacts with water:
Ca + 2H 2 O \u003d Ca (OH) 2 + H 2.
With active non-metals (oxygen, chlorine, bromine), calcium reacts under normal conditions:
2Ca + O 2 \u003d 2CaO; Ca + Br 2 \u003d CaBr 2.
When heated in air or oxygen, calcium ignites. With less active non-metals (hydrogen, boron, carbon, silicon, nitrogen, phosphorus and others), calcium interacts when heated, for example:
Ca + H 2 \u003d CaH 2 (calcium hydride),
Ca + 6B = CaB 6 (calcium boride),
3Ca + N 2 = Ca 3 N 2 (calcium nitride)
Ca + 2C \u003d CaC 2 (calcium carbide)
3Ca + 2P = Ca 3 P 2 (calcium phosphide), calcium phosphides of CaP and CaP 5 compositions are also known;
2Ca + Si \u003d Ca 2 Si (calcium silicide), calcium silicides of the compositions CaSi, Ca 3 Si 4 and CaSi 2 are also known.
The course of the above reactions, as a rule, is accompanied by the release of a large amount of heat (i.e., these reactions are exothermic). In all compounds with non-metals, the oxidation state of calcium is +2. Most of the calcium compounds with non-metals are easily decomposed by water, for example:
CaH 2 + 2H 2 O \u003d Ca (OH) 2 + 2H 2,
Ca 3 N 2 + 3H 2 O \u003d 3Ca (OH) 2 + 2NH 3.
Calcium oxide is typically basic. In the laboratory and technology, it is obtained by thermal decomposition of carbonates:
CaCO 3 \u003d CaO + CO 2.
Technical calcium oxide CaO is called quicklime.
It reacts with water to form Ca (OH) 2 and release a large amount of heat:
CaO + H 2 O \u003d Ca (OH) 2.
Ca (OH) 2 obtained in this way is usually called slaked lime or lime milk (cm. LIME MILK) due to the fact that the solubility of calcium hydroxide in water is low (0.02 mol / l at 20 ° C), and when it is added to water, a white suspension is formed.
When interacting with acid oxides, CaO forms salts, for example:
CaO + CO 2 \u003d CaCO 3; CaO + SO 3 \u003d CaSO 4.
The Ca 2+ ion is colorless. When calcium salts are added to the flame, the flame turns brick red.
Calcium salts such as CaCl 2 chloride, CaBr 2 bromide, CaI 2 iodide and Ca(NO 3) 2 nitrate are highly soluble in water. CaF 2 fluoride, CaCO 3 carbonate, CaSO 4 sulfate, Ca 3 (PO 4) 2 average orthophosphate, CaC 2 O 4 oxalate and some others are insoluble in water.
Important is the fact that, unlike the average calcium carbonate CaCO 3, acidic calcium carbonate (hydrocarbonate) Ca (HCO 3) 2 is soluble in water. In nature, this leads to the following processes. When cold rain or river water, saturated with carbon dioxide, penetrates underground and falls on limestones, their dissolution is observed:
CaCO 3 + CO 2 + H 2 O \u003d Ca (HCO 3) 2.
In the same places where water saturated with calcium bicarbonate comes to the surface of the earth and is heated by the sun's rays, the reverse reaction occurs:
Ca (HCO 3) 2 \u003d CaCO 3 + CO 2 + H 2 O.
So in nature there is a transfer of large masses of substances. As a result, huge dips can form underground (see Karst (cm. Karst (natural phenomenon))), and beautiful stone "icicles" - stalactites are formed in the caves (cm. STALAPTITES (mineral formations)) and stalagmites (cm. STALAGMITES).
The presence of dissolved calcium bicarbonate in water largely determines the temporary hardness of water. (cm. HARDNESS OF WATER). It is called temporary because when water is boiled, the bicarbonate decomposes, and CaCO 3 precipitates. This phenomenon leads, for example, to the fact that scale forms in the kettle over time.
The use of calcium and its compounds
Metallic calcium is used for metallothermic production of uranium (cm. Uranium (chemical element)), thorium (cm. THORIUM), titanium (cm. TITANIUM (chemical element)), zirconium (cm. ZIRCONIUM), cesium (cm. CESIUM) and rubidium (cm. RUBIDIUM).
Natural calcium compounds are widely used in the production of binders (cement (cm. CEMENT), gypsum (cm. GYPSUM), lime, etc.). The binding effect of slaked lime is based on the fact that over time, calcium hydroxide reacts with carbon dioxide in the air. As a result of the ongoing reaction, needle-like crystals of CaCO3 calcite are formed, which grow into nearby stones, bricks, and other building materials and, as it were, weld them into a single whole. Crystalline calcium carbonate - marble - fine finishing material. Chalk is used for whitewashing. Large quantities of limestone are consumed in the production of pig iron, as they make it possible to transfer refractory impurities of iron ore (for example, quartz SiO 2) into relatively low-melting slags.
Bleach is very effective as a disinfectant. (cm. BLEACHING POWDER)- “chlorine” Ca(OCl)Cl - mixed chloride and calcium hypochlorite (cm. CALCIUM HYPOCHLORITE) with high oxidizing power.
Calcium sulfate is also widely used, existing both in the form of an anhydrous compound and in the form of crystalline hydrates - the so-called "semi-aqueous" sulfate - alabaster (cm. ALEVIZ FRYAZIN (Milanese)) CaSO 4 0.5H 2 O and two-water sulfate - gypsum CaSO 4 2H 2 O. Gypsum is widely used in construction, sculpture, for the manufacture of stucco and various art products. Gypsum is also used in medicine to fix bones in case of fractures.
Calcium chloride CaCl 2 is used along with table salt to combat icing of road surfaces. Calcium fluoride CaF 2 is an excellent optical material.
calcium in the body
Calcium is a biogenic element (cm. BIOGENIC ELEMENTS), constantly present in the tissues of plants and animals. An important component of the mineral metabolism of animals and humans and the mineral nutrition of plants, calcium performs a variety of functions in the body. Contains apatite (cm. APATITE), as well as calcium sulfate and carbonate forms the mineral component of bone tissue. The human body weighing 70 kg contains about 1 kg of calcium. Calcium is involved in the work of ion channels (cm. ION CHANNELS), carrying out the transport of substances through biological membranes, in the transmission of a nerve impulse (cm. NERVE IMPULSE), in the process of blood coagulation (cm. BLOOD COAGULATION) and fertilization. Calciferols regulate calcium metabolism in the body (cm. CALCIFEROLS)(vitamin D). Lack or excess of calcium leads to various diseases - rickets (cm. RICKETS), calcification (cm. CALCINOSIS) etc. Therefore, human food should contain calcium compounds in the right quantities (800-1500 mg of calcium per day). Calcium content is high in dairy products (such as cottage cheese, cheese, milk), some vegetables and other foods. Calcium preparations are widely used in medicine.

encyclopedic Dictionary. 2009 .

Synonyms:

See what "calcium" is in other dictionaries:

- (Ca) yellow shiny and malleable metal. Specific gravity 1.6. Dictionary of foreign words included in the Russian language. Pavlenkov F., 1907. CALCIUM (new lat. calcium, from lat. calx lime). Silver colored metal. Dictionary of foreign words, ... ... Dictionary of foreign words of the Russian language

CALCIUM- CALCIUM, Calcium, chem. element, char. Ca, shiny, silvery white metal with crystalline. fracture, belonging to the group of alkaline earth metals. Oud. weight 1.53; at. V. 40.07; melting point 808°. Sa is one of the very ... ... Big Medical Encyclopedia

- (Calcium), Ca, a chemical element of group II of the periodic system, atomic number 20, atomic mass 40.08; refers to alkaline earth metals; mp 842shC. Contained in the bone tissue of vertebrates, mollusk shells, eggshells. Calcium ... ... Modern Encyclopedia

The metal is silvery white, viscous, malleable, rapidly oxidizing in air. Melting rate pa 800 810°. In nature, it occurs in the form of various salts, which form deposits of chalk, limestone, marble, phosphorites, apatites, gypsum, etc. On the yellow. dor… … Technical railway dictionary

- (lat. Calcium) Ca, a chemical element of group II of the periodic system, atomic number 20, atomic mass 40.078, belongs to the alkaline earth metals. The name is from the Latin calx, genitive calcis lime. Silvery white metal, ... ... Big Encyclopedic Dictionary

Calcium is an element of the main subgroup of the second group, the fourth period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 20. It is designated by the symbol Ca (lat. Calcium). The simple substance calcium is a soft, reactive, silver-white alkaline earth metal.

Calcium in the environment

There is a lot of it in nature: mountain ranges and clay rocks are formed from calcium salts, it is found in sea and river water, and is part of plant and animal organisms. Calcium accounts for 3.38% of the mass of the earth's crust (5th place in abundance after oxygen, silicon, aluminum and iron).

Isotopes of calcium

Calcium occurs in nature as a mixture of six isotopes: 40 Ca, 42 Ca, 43 Ca, 44 Ca, 46 Ca and 48 Ca, among which the most common - 40 Ca - is 96.97%.

Of the six naturally occurring calcium isotopes, five are stable. The sixth isotope 48Ca, the heaviest of the six and very rare (its isotopic abundance is only 0.187%), was recently discovered to undergo double beta decay with a half-life of 5.3×10 19 years.

The content of calcium in rocks and minerals

Most of the calcium is contained in the composition of silicates and aluminosilicates of various rocks (granites, gneisses, etc.), especially in feldspar - anorthite Ca.

In the form of sedimentary rocks, calcium compounds are represented by chalk and limestone, consisting mainly of the mineral calcite (CaCO 3). The crystalline form of calcite - marble - is found in nature much less frequently.

Calcium minerals such as calcite CaCO 3 , anhydrite CaSO 4 , alabaster CaSO 4 0.5H 2 O and gypsum CaSO 4 2H 2 O, fluorite CaF 2 , apatites Ca 5 (PO 4) 3 (F, Cl, OH), dolomite MgCO 3 CaCO 3 . The presence of calcium and magnesium salts in natural water determines its hardness.

Calcium, which migrates vigorously in the earth's crust and accumulates in various geochemical systems, forms 385 minerals (fourth in terms of the number of minerals).

Migration of calcium in the earth's crust

In the natural migration of calcium, a significant role is played by the “carbonate equilibrium”, associated with the reversible reaction of the interaction of calcium carbonate with water and carbon dioxide with the formation of soluble bicarbonate:

CaCO 3 + H 2 O + CO 2 ↔ Ca (HCO 3) 2 ↔ Ca 2+ + 2HCO 3 -

(the equilibrium shifts to the left or right depending on the concentration of carbon dioxide).

Biogenic migration plays an important role.

The content of calcium in the biosphere

Calcium compounds are found in almost all animal and plant tissues (see also below). A significant amount of calcium is part of living organisms. So, hydroxyapatite Ca 5 (PO 4) 3 OH, or, in another entry, 3Ca 3 (PO 4) 2 Ca (OH) 2 - the basis of the bone tissue of vertebrates, including humans; shells and shells of many invertebrates, egg shells, etc. are made of calcium carbonate CaCO 3. In living tissues of humans and animals, 1.4-2% Ca (by mass fraction); in a human body weighing 70 kg, the calcium content is about 1.7 kg (mainly in the composition of the intercellular substance of bone tissue).

Getting calcium

Calcium was first obtained by Davy in 1808 by electrolysis. But, like other alkali and alkaline earth metals, element No. 20 cannot be obtained by electrolysis from aqueous solutions. Calcium is obtained by electrolysis of its molten salts.

This is a complex and energy intensive process. Calcium chloride is melted in the electrolyzer with the addition of other salts (they are needed in order to lower the melting point of CaCl 2).

The steel cathode only touches the electrolyte surface; the released calcium sticks and freezes on it. As calcium is released, the cathode is gradually raised and, ultimately, a calcium "rod" 50 ... 60 cm long is obtained. Then it is removed, beaten off from the steel cathode and the process starts all over again. The “touch method” is used to obtain calcium heavily contaminated with calcium chloride, iron, aluminum, and sodium. It is purified by remelting in an argon atmosphere.

If the steel cathode is replaced by a metal cathode capable of alloying with calcium, then the corresponding alloy will be obtained during electrolysis. Depending on the purpose, it can be used as an alloy, or pure calcium can be obtained by distillation in a vacuum. This is how calcium alloys with zinc, lead and copper are obtained.

Another method for obtaining calcium - metallothermic - was theoretically substantiated as early as 1865 by the famous Russian chemist N.N. Beketov. Calcium is reduced with aluminum at a pressure of only 0.01 mmHg. Process temperature 1100...1200°C. Calcium is thus obtained in the form of vapor, which is then condensed.

In recent years, another method for obtaining the element has been developed. It is based on the thermal dissociation of calcium carbide: heated in a vacuum to 1750°C, the carbide decomposes with the formation of calcium vapor and solid graphite.

Physical properties of calcium

Calcium metal exists in two allotropic modifications. Up to 443 °C, α-Ca with a cubic face-centered lattice is stable (parameter a = 0.558 nm), above β-Ca is stable with a cubic body-centered lattice of the α-Fe type (parameter a = 0.448 nm). Standard enthalpy Δ H 0 of the α → β transition is 0.93 kJ/mol.

With a gradual increase in pressure, it begins to show the properties of a semiconductor, does not become a semiconductor in the full sense of the word (it is no longer a metal either). With a further increase in pressure, it returns to the metallic state and begins to exhibit superconducting properties (the superconductivity temperature is six times higher than that of mercury, and far exceeds all other elements in conductivity). The unique behavior of calcium is similar in many ways to strontium.

Despite the ubiquity of the element, even chemists have not all seen elemental calcium. But this metal, both externally and in behavior, is completely different from alkali metals, contact with which is fraught with the danger of fires and burns. It can be safely stored in air, it does not ignite from water. The mechanical properties of elemental calcium do not make it a "black sheep" in the family of metals: calcium surpasses many of them in strength and hardness; it can be turned on a lathe, drawn into a wire, forged, pressed.

And yet, elemental calcium is almost never used as a structural material. He's too active for that. Calcium easily reacts with oxygen, sulfur, halogens. Even with nitrogen and hydrogen, under certain conditions, it reacts. The environment of carbon oxides, inert for most metals, is aggressive for calcium. It burns in an atmosphere of CO and CO 2 .

Naturally, having such chemical properties, calcium cannot be found in nature in a free state. But calcium compounds - both natural and artificial - have become of paramount importance.

Chemical properties of calcium

Calcium is a typical alkaline earth metal. The chemical activity of calcium is high, but lower than that of all other alkaline earth metals. It readily reacts with oxygen, carbon dioxide and moisture in the air, due to which the surface of calcium metal is usually dull gray, so calcium is usually stored in the laboratory, like other alkaline earth metals, in a tightly closed jar under a layer of kerosene or liquid paraffin.

In the series of standard potentials, calcium is located to the left of hydrogen. The standard electrode potential of the Ca 2+ / Ca 0 pair is −2.84 V, so that calcium actively reacts with water, but without ignition:

Ca + 2H 2 O \u003d Ca (OH) 2 + H 2 + Q.

With active non-metals (oxygen, chlorine, bromine), calcium reacts under normal conditions:

2Ca + O 2 \u003d 2CaO, Ca + Br 2 \u003d CaBr 2.

When heated in air or oxygen, calcium ignites. With less active non-metals (hydrogen, boron, carbon, silicon, nitrogen, phosphorus and others), calcium interacts when heated, for example:

Ca + H 2 \u003d CaH 2, Ca + 6B \u003d CaB 6,

3Ca + N 2 \u003d Ca 3 N 2, Ca + 2C \u003d CaC 2,

3Ca + 2P = Ca 3 P 2 (calcium phosphide), calcium phosphides of CaP and CaP 5 compositions are also known;

2Ca + Si \u003d Ca 2 Si (calcium silicide), calcium silicides of the compositions CaSi, Ca 3 Si 4 and CaSi 2 are also known.

The course of the above reactions, as a rule, is accompanied by the release of a large amount of heat (that is, these reactions are exothermic). In all compounds with non-metals, the oxidation state of calcium is +2. Most of the calcium compounds with non-metals are easily decomposed by water, for example:

CaH 2 + 2H 2 O \u003d Ca (OH) 2 + 2H 2,

Ca 3 N 2 + 3H 2 O \u003d 3Ca (OH) 2 + 2NH 3.

The Ca 2+ ion is colorless. When soluble calcium salts are added to the flame, the flame turns brick red.

Calcium salts such as CaCl 2 chloride, CaBr 2 bromide, CaI 2 iodide and Ca(NO 3) 2 nitrate are highly soluble in water. CaF 2 fluoride, CaCO 3 carbonate, CaSO 4 sulfate, Ca 3 (PO 4) 2 orthophosphate, CaC 2 O 4 oxalate and some others are insoluble in water.

Important is the fact that, unlike calcium carbonate CaCO 3, acidic calcium carbonate (hydrocarbonate) Ca (HCO 3) 2 is soluble in water. In nature, this leads to the following processes. When cold rain or river water, saturated with carbon dioxide, penetrates underground and falls on limestones, their dissolution is observed:

CaCO 3 + CO 2 + H 2 O \u003d Ca (HCO 3) 2.

In the same places where water saturated with calcium bicarbonate comes to the surface of the earth and is heated by the sun's rays, the reverse reaction occurs:

Ca (HCO 3) 2 \u003d CaCO 3 + CO 2 + H 2 O.

So in nature there is a transfer of large masses of substances. As a result, huge gaps can form underground, and beautiful stone "icicles" - stalactites and stalagmites - form in the caves.

The presence of dissolved calcium bicarbonate in water largely determines the temporary hardness of water. It is called temporary because when boiling water, the bicarbonate decomposes, and CaCO 3 precipitates. This phenomenon leads, for example, to the fact that scale forms in the kettle over time.

Application calcium

Until recently, metallic calcium has almost never been used. The United States, for example, before the Second World War consumed only 10...25 tons of calcium per year, Germany - 5...10 tons. But for the development of new areas of technology, many rare and refractory metals are needed. It turned out that calcium is a very convenient and active reducing agent for many of them, and the element began to be used in the production of thorium, vanadium, zirconium, beryllium, niobium, uranium, tantalum and other refractory metals. Pure metallic calcium is widely used in metallothermy to obtain rare metals.

Pure calcium is used to alloy lead, which is used for the manufacture of battery plates, maintenance-free starter lead-acid batteries with low self-discharge. Also, metallic calcium is used for the production of high-quality calcium babbits BKA.

Applications of metallic calcium

The main use of calcium metal is as a reducing agent in the production of metals, especially nickel, copper and stainless steel. Calcium and its hydride are also used to obtain hard-to-recover metals such as chromium, thorium and uranium. Alloys of calcium with lead are used in batteries and bearing alloys. Calcium granules are also used to remove traces of air from electrovacuum devices.

Natural chalk in the form of a powder is included in the compositions for polishing metals. But it is impossible to brush your teeth with natural chalk powder, as it contains the remains of shells and shells of the smallest animals, which have increased hardness and destroy tooth enamel.

Usagecalciumin nuclear fusion

The 48 Ca isotope is the most effective and widely used material for the production of superheavy elements and the discovery of new elements in the periodic table. For example, in the case of using 48 Ca ions to produce superheavy elements in accelerators, the nuclei of these elements are formed hundreds and thousands of times more efficiently than when using other "projectiles" (ions). Radioactive calcium is widely used in biology and medicine as an isotope tracer in the study of mineral metabolism processes in a living organism. With its help, it was found that in the body there is a continuous exchange of calcium ions between plasma, soft tissues and even bone tissue. 45 Ca also played an important role in the study of the metabolic processes occurring in soils and in the study of the processes of calcium assimilation by plants. Using the same isotope, it was possible to detect sources of contamination of steel and ultrapure iron with calcium compounds during the smelting process.

The ability of calcium to bind oxygen and nitrogen made it possible to use it for cleaning inert gases and as a getter (A getter is a substance that serves to absorb gases and create a deep vacuum in electronic devices.) in vacuum radio equipment.

The use of calcium compounds

Some artificial calcium compounds have become even more famous and familiar than limestone or gypsum. Thus, slaked Ca(OH) 2 and quicklime CaO lime was used by the builders of antiquity.

Cement is also a calcium compound obtained artificially. First, a mixture of clay or sand with limestone is fired and clinker is obtained, which is then ground into a fine gray powder. You can talk a lot about cement (or rather, about cements), this is the topic of an independent article.

The same applies to glass, which also usually contains an element.

calcium hydride

By heating calcium in a hydrogen atmosphere, CaH 2 (calcium hydride) is obtained, which is used in metallurgy (metallothermy) and in the production of hydrogen in the field.

Optical and laser materials

Calcium fluoride (fluorite) is used in the form of single crystals in optics (astronomical objectives, lenses, prisms) and as a laser material. Calcium tungstate (scheelite) in the form of single crystals is used in laser technology, and also as a scintillator.

calcium carbide

Calcium carbide is a substance discovered by chance when testing a new furnace design. More recently, calcium carbide CaCl 2 was used mainly for oxy-fuel welding and cutting of metals. When carbide interacts with water, acetylene is formed, and the combustion of acetylene in an oxygen jet makes it possible to obtain a temperature of almost 3000°C. Recently, acetylene, and with it carbide, is used less and less for welding and more and more - in the chemical industry.

calcium aschemical current source

Calcium, as well as its alloys with aluminum and magnesium, are used in reserve thermal electric batteries as an anode (for example, a calcium-chromate element). Calcium chromate is used in such batteries as the cathode. A feature of such batteries is an extremely long shelf life (decades) in a usable condition, the ability to operate in any conditions (space, high pressures), high specific energy by weight and volume. The disadvantage is the short duration. Such batteries are used where it is necessary to create colossal electric power for a short time (ballistic missiles, some spacecraft, etc.).

Refractory materials fromcalcium

Calcium oxide, both in free form and as part of ceramic mixtures, is used in the production of refractory materials.

Medicines

Calcium compounds are widely used as an antihistamine.

• Calcium chloride
• Calcium gluconate
• calcium glycerophosphate

In addition, calcium compounds are introduced into preparations for the prevention of osteoporosis, into vitamin complexes for pregnant women and the elderly.

calcium in the human body

Calcium is a common macronutrient in plants, animals and humans. In humans and other vertebrates, most of it is found in the skeleton and teeth in the form of phosphates. The skeletons of most groups of invertebrates (sponges, coral polyps, mollusks, etc.) are composed of various forms of calcium carbonate (lime). The need for calcium depends on age. For adults, the required daily allowance is from 800 to 1000 milligrams (mg), and for children from 600 to 900 mg, which is very important for children due to the intensive growth of the skeleton. Most of the calcium that enters the human body with food is found in dairy products, the remaining calcium is found in meat, fish, and some plant foods (legumes are especially rich).

Assimilation of calcium is prevented by aspirin, oxalic acid, estrogen derivatives. Combining with oxalic acid, calcium gives water-insoluble compounds that are components of kidney stones.

Excessive doses of calcium and vitamin D can cause hypercalcemia, followed by intense calcification of bones and tissues (mainly affecting the urinary system). The maximum daily safe dose for an adult is 1500 to 1800 milligrams.

calcium in hard water

The complex of properties defined by one word "hardness" is given to water by calcium and magnesium salts dissolved in it. Hard water is unsuitable in many cases of life. It forms a layer of scale in steam boilers and boiler plants, makes it difficult to dye and wash fabrics, but is suitable for making soap and emulsifying in perfumery. Therefore, in the past, when water softening methods were imperfect, textile and perfume enterprises were usually located near sources of “soft” water.

Distinguish between temporary and permanent hardness. Temporary (or carbonate) hardness is given to water by soluble bicarbonates Ca (HCO 3) 2 and Mg (HCO 3) 2. It can be eliminated by simple boiling, in which bicarbonates are converted into water-insoluble calcium and magnesium carbonates.

Permanent hardness is created by sulfates and chlorides of the same metals. And it can be eliminated, but it is much more difficult to do it.

The sum of both hardnesses is the total hardness of the water. It is valued differently in different countries. It is customary to express the hardness of water as the number of milligram equivalents of calcium and magnesium in one liter of water. If there is less than 4 mEq in a liter of water, then the water is considered soft; as their concentration increases, more and more rigid and, if the content exceeds 12 units, very rigid.

Water hardness is usually determined using a soap solution. Such a solution (of a certain concentration) is added dropwise to a measured amount of water. As long as there are Ca 2+ or Mg 2+ ions in the water, they will interfere with the formation of foam. According to the costs of the soap solution before the appearance of foam, the content of Ca 2+ and Mg 2+ ions is calculated.

Interestingly, the hardness of water was determined in a similar way back in ancient Rome. Only red wine served as a reagent - its coloring substances also form a precipitate with calcium and magnesium ions.

Calcium storage

Metallic calcium can be stored for a long time in pieces weighing from 0.5 to 60 kg. Such pieces are stored in paper bags enclosed in galvanized iron drums with soldered and painted seams. Tightly closed drums are placed in wooden boxes. Pieces weighing less than 0.5 kg cannot be stored for a long time - they quickly turn into oxide, hydroxide and calcium carbonate.