Calcium is included. Atomic and molecular mass of calcium

Ufa State Petroleum Technical University

Department of General and Analytical Chemistry

on the topic: “The element calcium. Properties, production, application"

Prepared by student of group BTS-11-01 Prokaev G.L.

Associate Professor Krasko S.A.

Introduction

History and origin of the name

Being in nature

Receipt

Physical properties

Chemical properties

Applications of calcium metal

Application 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 designated by the symbol Ca (lat. Calcium). The simple substance calcium (CAS number: 7440-70-2) is a soft, reactive alkaline earth metal of a silvery-white color.

Calcium is called an alkaline earth metal and is classified as an S element. At the outer electronic level, calcium has two electrons, so it gives compounds: CaO, Ca(OH)2, CaCl2, CaSO4, CaCO3, etc. Calcium is a typical metal - it has a high affinity for oxygen, reduces almost all metals from their oxides, and forms a fairly strong base Ca(OH)2.

Despite the ubiquity of element No. 20, even chemists have not all seen elemental calcium. But this metal, both in appearance and in behavior, is not at all similar to 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.

Elemental calcium is almost never used as a structural material. He's too active for that. Calcium easily reacts with oxygen, sulfur, and 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 Humphry Davy, who isolated calcium metal by the electrolytic method in 1808. Davy electrolyzed a mixture of wet slaked lime and mercuric oxide HgO on a platinum plate, which served as the anode. The cathode was a platinum wire immersed in liquid mercury. As a result of electrolysis, calcium amalgam was obtained. Having distilled mercury from it, Davy obtained a metal called calcium.

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

Being in nature

Due to its high chemical activity, calcium does not occur in free form in nature.

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

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

Of the six natural isotopes of calcium, five are stable. A 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 ×1019 years.

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

In the form of sedimentary rocks, calcium compounds are represented by chalk and limestones, 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 0.5H2O and gypsum CaSO4 2H2O, fluorite CaF2, apatite 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, vigorously migrating in the earth's crust and accumulating in various geochemical systems, forms 385 minerals (the fourth largest number of minerals).

Migration in the earth's crust. In the natural migration of calcium, a significant role is played by “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 + H2O + CO2 ↔ Ca (HCO3)2 ↔ Ca2+ + 2HCO3ˉ

(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 found in living organisms. Thus, hydroxyapatite Ca5(PO4)3OH, or, in another entry, 3Ca3(PO4)2·Ca(OH)2, is the basis of the bone tissue of vertebrates, including humans; The shells and shells of many invertebrates, eggshells, etc. are made of calcium carbonate CaCO3. In living tissues of humans and animals there is 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 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 aluminothermic reduction of CaO at 1170-1200 °C:

CaO + 2Al = CaAl2O4 + 3Ca.

A method has also been developed for producing calcium by thermal dissociation of calcium carbide CaC2

Physical properties

Calcium metal exists in two allotropic modifications. Stable up to 443°C α -Ca with cubic lattice, higher stability β-Ca with cubic body-centered lattice type α -Fe. Standard enthalpy ΔH0 transition α → β is 0.93 kJ/mol.

Calcium is a light metal (d = 1.55), silvery-white in color. It is harder and melts at a higher temperature (851 ° C) compared to sodium, which is located next to it in the periodic table. This is explained by the fact that there are two electrons per calcium ion in the metal. Therefore, the chemical bond between the ions and the electron gas is stronger than that of sodium. During chemical reactions, calcium valence electrons are transferred to atoms of other elements. In this case, doubly charged ions are formed.

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 easily reacts with oxygen, carbon dioxide and moisture in the air, which is why 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 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 calcium reacts actively with water, but without ignition:

2H2O = Ca(OH)2 + H2 + Q.

Calcium reacts with active non-metals (oxygen, chlorine, bromine) under normal conditions:

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

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

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

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

Ca + 2P = Ca3P2 (calcium phosphide),

calcium phosphides of the compositions CaP and CaP5 are also known;

Ca + Si = Ca2Si (calcium silicide),

Calcium silicides of the compositions CaSi, Ca3Si4 and CaSi2 are also known.

The occurrence 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 = Ca(OH)2 + 2H2,N2 + 3H2O = 3Ca(OH)2 + 2NH3.

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. Insoluble in water are fluoride CaF2, carbonate CaCO3, sulfate CaSO4, orthophosphate Ca3(PO4)2, oxalate CaC2O4 and some others.

It is important that, unlike calcium carbonate CaCO3, acidic calcium carbonate (bicarbonate) 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 limestone, their dissolution is observed:

CaCO3 + CO2 + H2O = 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, a reverse reaction occurs:

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

This is how large masses of substances are transferred in nature. As a result, huge gaps can form underground, and beautiful stone “icicles” - stalactites and stalagmites - form in caves.

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

calcium metal chemical physical

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 produce difficult-to-reduce metals such as chromium, thorium and uranium. Calcium-lead alloys are used in batteries and bearing alloys. Calcium granules are also used to remove traces of air from vacuum devices. Soluble calcium and magnesium salts cause overall water hardness. If they are present in water in small quantities, then the water is called soft. If the content of these salts is high, water is considered hard. Hardness is eliminated by boiling; to completely eliminate the water, it is sometimes distilled.

Metallothermy

Pure metallic calcium is widely used in metallothermy for the production of rare metals.

Alloying of alloys

Pure calcium is used to alloy lead used for the production of battery plates and 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 commonly used material for the production of superheavy elements and the discovery of new elements on 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).

Application of calcium compounds

Calcium hydride. By heating calcium in a hydrogen atmosphere, CaH2 (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 for the production of acetylene and for the reduction of 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 backup thermal electric batteries as an anode (for example, calcium-chromate element). Calcium chromate is used in such batteries as a cathode. The peculiarity of such batteries is an extremely long shelf life (decades) in a suitable condition, the ability to operate in any conditions (space, high pressures), high specific energy in terms of weight and volume. Disadvantage: short lifespan. Such batteries are used where it is necessary to create colossal electrical power for a short period of time (ballistic missiles, some spacecraft, etc.).

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

Medicines. In medicine, Ca drugs eliminate disorders associated with a lack of Ca ions in the body (tetany, spasmophilia, rickets). Ca preparations reduce hypersensitivity to allergens and are used to treat allergic diseases (serum sickness, sleepy fever, etc.). Ca preparations reduce increased vascular permeability and have an anti-inflammatory effect. They are used for hemorrhagic vasculitis, radiation sickness, inflammatory processes (pneumonia, pleurisy, etc.) and some skin diseases. Prescribed as a hemostatic agent, to improve the activity of the heart muscle and enhance the effect of digitalis preparations, as an antidote for poisoning with magnesium salts. Together with other drugs, Ca preparations are used to stimulate labor. Ca chloride is administered orally and intravenously.

Ca preparations also include gypsum (CaSO4), used in surgery for plaster bandages, and chalk (CaCO3), prescribed internally for increased acidity of gastric juice and for the preparation of tooth powder.

Biological role

Calcium is a common macronutrient in the body of plants, animals and humans. In humans and other vertebrates, most of it is contained in the skeleton and teeth in the form of phosphates. The skeletons of most groups of invertebrates (sponges, coral polyps, mollusks, etc.) consist of various forms of calcium carbonate (lime). Calcium ions are involved in blood clotting processes, as well as in ensuring 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.

Most of the calcium that enters the human body with food is found in dairy products; the remaining calcium comes from meat, fish, and some plant products (especially legumes). Absorption occurs in both 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 important; with its deficiency, calcium is “washed out” from the bones and deposited in the kidneys (kidney stones) and muscles.

Aspirin, oxalic acid, and estrogen derivatives interfere with the absorption of calcium. When combined with oxalic acid, calcium produces water-insoluble compounds that are components of kidney stones.

Due to the large number of processes associated with it, the calcium content in the blood is precisely regulated, and with proper nutrition, a deficiency does not occur. Prolonged absence from the diet can cause cramps, joint pain, drowsiness, growth defects, and constipation. Deeper deficiency leads to constant muscle cramps and osteoporosis. Abuse of coffee and alcohol can cause calcium deficiency, since some 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). Long-term 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

Large plantain 412

Sardines in oil 330

Ivy budra 289

Dog rose 257

Almond 252

Plantain lanceolist. 248

Hazelnut 226

Watercress 214

Soybeans dry 201

Children under 3 years old - 600 mg.

Children from 4 to 10 years old - 800 mg.

Children from 10 to 13 years old - 1000 mg.

Adolescents from 13 to 16 years old - 1200 mg.

Youth 16 and older - 1000 mg.

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

Pregnant and breastfeeding women - from 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 city dwellers: almost all main building materials - concrete, glass, brick, cement, lime - contain this element in significant quantities.

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

Bibliography

1.Editorial Board: Knunyants I. L. (chief editor) Chemical encyclopedia: in 5 volumes - Moscow: Soviet Encyclopedia, 1990. - T. 2. - P. 293. - 671 pp.

2.Doronin. N.A. Calcium, Goskhimizdat, 1962. 191 pp. with illustrations.

.Dotsenko V.A. - Therapeutic and preventive nutrition. - Question. nutrition, 2001 - N1-p.21-25

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

5.M.H. Karapetyants, S.I. Drakin - General and inorganic chemistry, 2000. 592 pp. with illustrations.

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, chemically active alkaline earth metal of a silvery-white color.

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 most abundant 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 natural isotopes of calcium, five are stable. The sixth isotope 48 Ca, 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 x 10 19 years.

Calcium content in rocks and minerals

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

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

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, vigorously migrating in the earth's crust and accumulating in various geochemical systems, forms 385 minerals (the fourth largest number of minerals).

Calcium migration in the earth's crust

In the natural migration of calcium, a significant role is played by “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 -

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

Biogenic migration plays a huge role.

Calcium content in the biosphere

Calcium compounds are found in almost all animal and plant tissues (see also below). A significant amount of calcium is found in living organisms. Thus, hydroxyapatite Ca 5 (PO 4) 3 OH, or, in another entry, 3Ca 3 (PO 4) 2 ·Ca(OH) 2, is the basis of the bone tissue of vertebrates, including humans; The shells and shells of many invertebrates, eggshells, etc. are made of calcium carbonate CaCO 3. In living tissues of humans and animals there is 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 intercellular substance of bone tissue).

Getting calcium

Calcium was first obtained by Davy in 1808 using 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 an electrolyzer with the addition of other salts (they are needed to lower the melting point of CaCl 2).

The steel cathode only touches the surface of the electrolyte; the released calcium sticks and hardens 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 taken out, beaten off the steel cathode and the process begins all over again. The “touch method” produces calcium heavily contaminated with calcium chloride, iron, aluminum, and sodium. It is purified by melting it in an argon atmosphere.

If the steel cathode is replaced by a cathode made of a metal that can be alloyed 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 producing calcium - metallothermic - was theoretically justified back in 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 obtained in the form of steam, which is then condensed.

In recent years, another method of obtaining the element has been developed. It is based on the thermal dissociation of calcium carbide: carbide heated in a vacuum to 1750°C decomposes to form 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 (parameter a = 0.558 nm) is stable; β-Ca with a cubic body-centered lattice of the α-Fe type (parameter a = 0.448 nm) is more stable. Standard enthalpy Δ H 0 transition α → β is 0.93 kJ/mol.

With a gradual increase in pressure, it begins to exhibit 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 temperature of superconductivity 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 in appearance 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 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, and 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 exist in nature in a free state. But calcium compounds - both natural and artificial - have acquired paramount importance.

Chemical properties of calcium

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 = Ca(OH) 2 + H 2 + Q.

Calcium reacts with active non-metals (oxygen, chlorine, bromine) under normal conditions:

2Ca + O 2 = 2CaO, Ca + Br 2 = CaBr 2.

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

Ca + H 2 = CaH 2, Ca + 6B = CaB 6,

3Ca + N 2 = Ca 3 N 2, Ca + 2C = CaC 2,

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

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

CaH 2 + 2H 2 O = Ca(OH) 2 + 2H 2,

Ca 3 N 2 + 3H 2 O = 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. Insoluble in water are CaF 2 fluoride, CaCO 3 carbonate, CaSO 4 sulfate, Ca 3 (PO 4) 2 orthophosphate, CaC 2 O 4 oxalate and some others.

It is important that, unlike calcium carbonate CaCO 3, acid calcium carbonate (bicarbonate) 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 limestone, their dissolution is observed:

CaCO 3 + CO 2 + H 2 O = 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, a reverse reaction occurs:

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

This is how large masses of substances are transferred in nature. As a result, huge gaps can form underground, and beautiful stone “icicles” - stalactites and stalagmites - form in caves.

The presence of dissolved calcium bicarbonate in water largely determines the temporary hardness of water. It is called temporary because when water boils, 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, calcium metal found almost no use. The USA, 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 for the production of rare metals.

Applications of calcium metal

Natural chalk in powder form is included in compositions for polishing metals. But you cannot brush your teeth with natural chalk powder, since it contains the remains of shells and shells of small animals, which are extremely hard and destroy tooth enamel.

Usagecalciumin nuclear fusion

The isotope 48 Ca is the most effective and commonly used material for the production of superheavy elements and the discovery of new elements of 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 indicator in the study of mineral metabolism processes in a living organism. With its help, it was established that in the body there is a continuous exchange of calcium ions between plasma, soft tissues and even bone tissue. 45Ca also played a major role in the study of metabolic processes occurring in soils and in the study of the processes of calcium absorption by plants. Using the same isotope, it was possible to detect sources of contamination of steel and ultra-pure iron with calcium compounds during the smelting process.

The ability of calcium to bind oxygen and nitrogen has made it possible to use it for the purification of inert gases and as a getter (Getter is a substance used to absorb gases and create a deep vacuum in electronic devices.) in vacuum radio equipment.

Application of calcium compounds

Some artificially produced calcium compounds have become even more well-known and common than limestone or gypsum. Thus, slaked Ca(OH)2 and quicklime CaO were used by ancient builders.

Cement is also a calcium compound obtained artificially. First, a mixture of clay or sand and limestone is fired to produce clinker, 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 the 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 while testing a new furnace design. Until recently, calcium carbide CaCl 2 was used mainly for autogenous welding and cutting of metals. When carbide interacts with water, acetylene is formed, and the combustion of acetylene in a stream of oxygen allows one to obtain a temperature of almost 3000°C. Recently, acetylene, and along with it carbide, are being used less and less for welding and more and more in the chemical industry.

Calcium likechemical current source

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

Fireproof 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 included in drugs for the prevention of osteoporosis, in vitamin complexes for pregnant women and the elderly.

Calcium in the human body

Calcium is a common macronutrient in the body of plants, animals and humans. In humans and other vertebrates, most of it is contained in the skeleton and teeth in the form of phosphates. The skeletons of most groups of invertebrates (sponges, coral polyps, mollusks, etc.) consist of various forms of calcium carbonate (lime). Calcium requirements depend on age. For adults, the required daily intake 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 comes from meat, fish, and some plant products (especially legumes).

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

A set of properties, defined by one word “hardness,” is imparted to water by calcium and magnesium salts dissolved in it. Hard water is unsuitable for many life situations. It forms a layer of scale in steam boilers and boiler installations, makes it difficult to dye and wash fabrics, but is suitable for making soap and preparing emulsions in perfume production. Therefore, earlier, when methods of softening water were imperfect, textile and perfume factories were usually located near sources of “soft” water.

A distinction is made between temporary and permanent rigidity. Temporary (or carbonate) hardness is imparted to water by soluble hydrocarbonates Ca(HCO 3) 2 and Mg(HCO 3) 2. It can be eliminated by simple boiling, during which bicarbonates are converted into water-insoluble calcium and magnesium carbonates.

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

The sum of both hardnesses makes up the total water hardness. It is valued differently in different countries. It is customary to express water hardness by 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, it becomes increasingly harsh and, if the content exceeds 12 units, very harsh.

Water hardness is usually determined using a soap solution. This 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. Based on the consumption of the soap solution before foam appears, the content of Ca 2+ and Mg 2+ ions is calculated.

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

Calcium storage

Calcium metal can be stored for a long time in pieces weighing from 0.5 to 60 kg. Such pieces are stored in paper bags placed 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.

Among all the elements of the periodic table, several can be identified, without which not only do various diseases develop in living organisms, but it is generally impossible to live and grow normally. One of these is calcium.

It is interesting that when we talk about this metal as a simple substance, it has no benefit for humans, even harm. However, as soon as you mention Ca 2+ ions, a lot of points immediately arise that characterize their importance.

Position of calcium in the periodic table

The characterization of calcium, like any other element, begins with indicating its location in the periodic table. After all, it makes it possible to learn a lot about a given atom:

nuclear charge;
number of electrons and protons, neutrons;
oxidation state, highest and lowest;
electronic configuration and other important things.

The element we are considering is located in the fourth major period of the second group, the main subgroup, and has a serial number of 20. Also, the periodic chemical table shows the atomic weight of calcium - 40.08, which is the average value of the existing isotopes of a given atom.

The oxidation state is one, always constant, equal to +2. Formula CaO. The Latin name for the element is calcium, hence the symbol for the Ca atom.

Characteristics of calcium as a simple substance

Under normal conditions, this element is a metal, silvery-white in color. The formula of calcium as a simple substance is Ca. Due to its high chemical activity, it is capable of forming many compounds belonging to different classes.

In a solid state of aggregation, it is not part of the human body, therefore it is important for industrial and technical needs (mainly chemical syntheses).

It is one of the most common metals in the earth’s crust, about 1.5%. It belongs to the alkaline earth group, since when dissolved in water it produces alkalis, but in nature it is found in the form of multiple minerals and salts. A lot of calcium (400 mg/l) is included in sea water.

Crystal cell

The characteristics of calcium are explained by the structure of the crystal lattice, which can be of two types (since there is an alpha and beta form):

cubic face-centric;
volume-centric.

The type of bond in the molecule is metallic; at lattice sites, like all metals, there are atom ions.

Being in nature

There are several main substances in nature that contain this element.

Sea water.
Rocks and minerals.
Living organisms (shells and shells, bone tissue, etc.).
Groundwater in the earth's crust.

The following types of rocks and minerals can be identified as natural sources of calcium.

Dolomite is a mixture of calcium and magnesium carbonate.
Fluorite is calcium fluoride.
Gypsum - CaSO 4 2H 2 O.
Calcite - chalk, limestone, marble - calcium carbonate.
Alabaster - CaSO 4 ·0.5H 2 O.
Apatity.

In total, there are about 350 different minerals and rocks that contain calcium.

Methods of obtaining

For a long time it was not possible to isolate the metal in its free form, since its chemical activity is high and cannot be found in nature in its pure form. Therefore, until the 19th century (1808), the element in question was another mystery posed by the periodic table.

The English chemist Humphry Davy managed to synthesize calcium as a metal. It was he who first discovered the peculiarities of the interaction of melts of solid minerals and salts with electric current. Today, the most relevant way to obtain this metal is the electrolysis of its salts, such as:

a mixture of calcium and potassium chlorides;
a mixture of fluoride and calcium chloride.

It is also possible to extract calcium from its oxide using aluminothermy, a common method in metallurgy.

Physical properties

The characteristics of calcium according to physical parameters can be described in several points.

The state of aggregation is solid under normal conditions.
Melting point - 842 0 C.
The metal is soft and can be cut with a knife.
Color - silver-white, shiny.
It has good conductive and heat-conducting properties.
When heated for a long time, it turns into a liquid, then a vapor state, losing its metallic properties. Boiling point 1484 0 C.

The physical properties of calcium have one peculiarity. When pressure is applied to a metal, at some point in time it loses its metallic properties and ability to conduct electrically. However, with a further increase in exposure, it is restored again and manifests itself as a superconductor, several times higher in these indicators than other elements.

Chemical properties

The activity of this metal is very high. Therefore, there are many interactions that calcium enters into. Reactions with all non-metals are common for him, because as a reducing agent he is very strong.

Under normal conditions, it easily reacts to form the corresponding binary compounds with: halogens, oxygen.
When heated: hydrogen, nitrogen, carbon, silicon, phosphorus, boron, sulfur and others.
In the open air it immediately interacts with carbon dioxide and oxygen, and therefore becomes covered with a gray coating.
Reacts violently with acids, sometimes causing inflammation.

Interesting properties of calcium appear when it comes to salts. So, beautiful caves growing on the ceiling and walls are nothing more than formed over time from water, carbon dioxide and bicarbonate under the influence of processes within underground waters.

Considering how active the metal is in its normal state, it is stored in laboratories, just like alkaline metals. In a dark glass container, with a tightly closed lid and under a layer of kerosene or paraffin.

A qualitative reaction to calcium ion is the coloring of the flame in a beautiful, rich brick-red color. You can also identify the metal in the composition of the compounds by the insoluble precipitates of some of its salts (calcium carbonate, fluoride, sulfate, phosphate, silicate, sulfite).

Metal connections

The types of metal compounds are as follows:

oxide;
hydroxide;
calcium salts (medium, acidic, basic, double, complex).

Calcium oxide known as CaO is used to create a building material (lime). If you quench the oxide with water, you get the corresponding hydroxide, which exhibits the properties of an alkali.

Various calcium salts, which are used in different sectors of the economy, are of great practical importance. We have already mentioned above what kind of salts exist. Let us give examples of the types of these connections.

Medium salts - carbonate CaCO 3, phosphate Ca 3 (PO 4) 2 and others.
Acidic - hydrogen sulfate CaHSO 4.
The main ones are bicarbonate (CaOH) 3 PO 4.
Complex - Cl 2.
Double - 5Ca(NO 3) 2 *NH 4 NO 3 *10H 2 O.

It is in the form of compounds of this class that calcium is important for biological systems, since salts are the source of ions for the body.

Biological role

Why is calcium important for the human body? There are several reasons.

It is the ions of this element that are part of the intercellular substance and tissue fluid, participating in the regulation of excitation mechanisms, the production of hormones and neurotransmitters.
Calcium accumulates in bones and tooth enamel in an amount of about 2.5% of the total body weight. This is quite a lot and plays an important role in strengthening these structures, maintaining their strength and stability. The growth of the body without this is impossible.
Blood clotting also depends on the ions in question.
It is part of the heart muscle, participating in its excitation and contraction.
It is a participant in the processes of exocytosis and other intracellular changes.

If the amount of calcium consumed is not enough, then diseases such as:

rickets;
osteoporosis;
blood diseases.

The daily intake for an adult is 1000 mg, and for children over 9 years old 1300 mg. In order to prevent an excess of this element in the body, you should not exceed the specified dose. Otherwise, intestinal diseases may develop.

For all other living beings, calcium is no less important. For example, although many do not have a skeleton, their external means of strengthening are also formations of this metal. Among them:

shellfish;
mussels and oysters;
sponges;
coral polyps.

They all carry on their backs or, in principle, form in the process of life a certain external skeleton that protects them from external influences and predators. Its main component is calcium salts.

Vertebrates, like humans, need these ions for normal growth and development and receive them from food.

There are many options with which it is possible to replenish the missing element in the body. The best, of course, are natural methods - products containing the desired atom. However, if for some reason this is insufficient or impossible, the medical route is also acceptable.

So, the list of foods containing calcium is something like this:

dairy and fermented milk products;
fish;
greenery;
grains (buckwheat, rice, baked goods made from whole grain flour);
some citrus fruits (oranges, tangerines);
legumes;
all nuts (especially almonds and walnuts).

If you are allergic to some foods or cannot eat them for another reason, then calcium-containing preparations will help replenish the level of the necessary element in the body.

All of them are salts of this metal, which have the ability to be easily absorbed by the body, quickly absorbed into the blood and intestines. Among them, the most popular and used are the following.

Calcium chloride - solution for injection or for oral administration to adults and children. It differs in the concentration of salt in the composition; it is used for “hot injections”, since it causes exactly this sensation when injected. There are forms with fruit juice for easier oral administration.
Available in both tablets (0.25 or 0.5 g) and solutions for intravenous injection. Often in tablet form it contains various fruit additives.
Calcium lactate - available in tablets of 0.5 g.

It makes up a bone skeleton, but the body is not able to produce the element on its own. We're talking about calcium. Adult women and men need to receive at least 800 milligrams of alkaline earth metal per day. It can be extracted from oatmeal, hazelnuts, milk, barley, sour cream, beans, and almonds.

Calcium also found in peas, mustard, and cottage cheese. True, if you combine them with sweets, coffee, cola and foods rich in oxalic acid, the digestibility of the element decreases.

The gastric environment becomes alkaline, calcium is captured in insoluble and excreted from the body. Bones and teeth begin to break down. What is it about the element, since it has become one of the most important for living beings, and is there any use for the substance outside their organisms?

Chemical and physical properties of calcium

The element occupies 20th place in the periodic table. It is in the main subgroup of the 2nd group. The period to which calcium belongs is the 4th. This means that an atom of a substance has 4 electronic levels. They contain 20 electrons, as indicated by the element's atomic number. It also indicates its charge - +20.

Calcium in the body, as in nature, is an alkaline earth metal. This means that in its pure form the element is silvery-white, shiny and light. The hardness of alkaline earth metals is higher than that of alkali metals.

The calcium indicator is about 3 points according to. For example, gypsum has the same hardness. The 20th element can be cut with a knife, but it is much more difficult than any of the simple alkali metals.

What is the meaning of the name “alkaline earth”? This is how alchemists dubbed calcium and other metals of his group. They called the oxides of elements earths. Oxides of substances calcium groups impart an alkaline environment to the water.

However, radium, barium, like the 20th element, are found not only in combination with oxygen. There are many calcium salts in nature. The most famous of them is the mineral calcite. The carbon dioxide form of the metal is the well-known chalk, limestone and gypsum. Each of them is calcium carbonate.

The 20th element also has volatile compounds. They color the flame orange-red, which becomes one of the markers for identifying substances.

All alkaline earth metals burn easily. For calcium to react with oxygen, normal conditions are sufficient. Only in nature the element is not found in its pure form, only in compounds.

Calcium oxy- a film that covers metal when it is exposed to air. The coating is yellowish. It contains not only standard oxides, but also peroxides and nitrides. If calcium is in water rather than in air, it will displace hydrogen from it.

In this case, a precipitate forms - calcium hydroxide. Residues of pure metal float to the surface, pushed by hydrogen bubbles. The same scheme works with acids. With hydrochloric acid, for example, it precipitates calcium chloride and hydrogen is released.

Some reactions require elevated temperatures. If it reaches 842 degrees, calcium is possible melt. At 1,484 Celsius, the metal boils.

Calcium solution, like a pure element, conducts heat and electric current well. But, if the substance is very heated, the metallic properties are lost. That is, neither molten nor gaseous calcium has them.

In the human body, the element is presented in both solid and liquid aggregate states. Softened calcium water, which is present in, is easier to tolerate. Only 1% of the 20th substance is found outside the bones.

However, its transport through tissues plays an important role. Blood calcium regulates muscle contraction, including the heart, and maintains normal blood pressure.

Uses of calcium

In its pure form, the metal is used in. They go to battery grids. The presence of calcium in the alloy reduces the self-discharge of batteries by 10-13%. This is especially important for stationary models. Bearings are also made from a mixture of lead and element 20. One of the alloys is called bearing alloys.

Pictured are products containing calcium

Alkaline earth metal is added to steel to remove sulfur impurities from the alloy. The reducing properties of calcium are also useful in the production of uranium, chromium, cesium, rubidium, etc.

What calcium used in ferrous metallurgy? Still the same clean. The difference is in the purpose of the element. Now, he plays the role. This is an additive to alloys that reduces the temperature of their formation and facilitates the separation of slags. Calcium granules poured into electric vacuum devices to remove traces of air from them.

The 48th isotope of calcium is in demand at nuclear enterprises. Superheavy elements are produced there. Raw materials are obtained at nuclear accelerators. They are accelerated with the help of ions - a kind of projectiles. If Ca48 plays their role, the efficiency of synthesis increases hundreds of times compared to the use of ions of other substances.

In optics, the 20th element is valued as compounds. Calcium fluoride and tungstate become lenses, objectives and prisms of astronomical instruments. Minerals are also found in laser technology.

Geologists call calcium fluoride fluorite, and tungsten - scheelite. For the optical industry, their single crystals are selected, that is, individual, large units with a continuous lattice and a clear shape.

In medicine, it is also not pure metal that is prescribed, but substances based on it. They are more easily absorbed by the body. Calcium gluconate– the cheapest remedy, used for osteoporosis. A drug " Calcium Magnesium» is prescribed for adolescents, pregnant women and senior citizens.

They need dietary supplements to meet the body’s increased need for the 20th element and to avoid developmental pathologies. Calcium-phosphorus metabolism regulates "Calcium D3". “D3” in the name of the product indicates the presence of vitamin D in it. It is rare, but necessary for complete absorption calcium.

Instructions To "Calcium nikomed3" indicates that the drug belongs to pharmaceutical compositions of combined action. The same is said about calcium chloride. It not only replenishes the deficiency of the 20th element, but also saves from intoxication, and is also able to replace blood plasma. In some pathological conditions this may be necessary.

The drug is also available in pharmacies Calcium is an acid ascorbic." This duet is prescribed during pregnancy and breastfeeding. Teenagers also need supplements.

Calcium mining

Calcium in foods, minerals, compounds, has been known to mankind since ancient times. The metal was isolated in its pure form only in 1808. Fortune smiled on Humphry Davy. An English physicist extracted calcium by electrolysis of molten salts of the element. This method is still used today.

However, industrialists more often resort to the second method, discovered after Humphrey’s research. Calcium is reduced from its oxide. The reaction is started with powder, sometimes. The interaction takes place under vacuum conditions at elevated temperatures. Calcium was first isolated in this way in the middle of the last century, in the USA.

Calcium price

There are few producers of calcium metal. Thus, in Russia, supplies are mainly carried out by the Chapetsk Mechanical Plant. It is located in Udmurtia. The company sells granules, shavings and lump metal. The price tag per ton of raw materials is around $1,500.

The product is also offered by some chemical laboratories, for example, the Russian Chemist society. Latest, offers 100 gram calcium. Reviews indicate that it is powder under oil. The cost of one package is 320 rubles.

In addition to offers to buy real calcium, business plans for its production are also sold on the Internet. For about 70 pages of theoretical calculations they ask for about 200 rubles. Most of the plans were drawn up in 2015, that is, they have not yet lost their relevance.

History of calcium

Calcium was discovered in 1808 by Humphry Davy, who, by electrolysis of slaked lime and mercuric oxide, obtained calcium amalgam, as a result of the process of distilling mercury from which the metal remained, called 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 periodic table 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 the Latin - Calcium).

Physical and chemical properties

Calcium is a reactive soft alkali metal with a silvery-white color. Due to interaction with oxygen and carbon dioxide, the surface of the metal becomes dull, so calcium requires a special storage regime - a tightly closed container, in which the metal is filled with a layer of liquid paraffin or kerosene.

Calcium is the most well-known of the microelements necessary for humans; the daily requirement for it ranges from 700 to 1500 mg for a healthy adult, but it increases during pregnancy and lactation; this must be taken into account and calcium must be obtained in the form of preparations.

Being in nature

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

It is quite widespread in living organisms; its presence has been found in plants, animals and humans, where it is present mainly in teeth and bone tissue.

Calcium absorption

An obstacle to the normal absorption of calcium from food 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 complex, so sometimes it is not enough to get it only from food; additional intake of the microelement is necessary.

Interaction with others

To improve the absorption of calcium in the intestine, it is necessary, which tends to facilitate the process of calcium absorption. When taking calcium (in the form of supplements) while 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 bones and teeth. Calcium is involved in the processes of excitability of nervous tissue, muscle contractility, blood clotting processes, is part of the nucleus and membranes of cells, cellular and tissue fluids, has anti-allergic and anti-inflammatory effects, prevents acidosis, and 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 calcium deficiency in the body are the following, at first glance, unrelated symptoms:

nervousness, worsening mood;
cardiopalmus;
convulsions, numbness of extremities;
slowing of growth and children;
high blood pressure;
splitting and brittleness of nails;
joint pain, lowering the “pain threshold”;
heavy menstruation.

Causes of calcium deficiency

Causes of calcium deficiency may include unbalanced diets (especially fasting), low calcium content in food, smoking and addiction to coffee and caffeine-containing drinks, dysbacteriosis, kidney disease, thyroid disease, pregnancy, lactation and menopause.

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

Uses 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 (well-known bleach).