Calcium compounds- limestone, marble, gypsum (as well as lime - a product of limestone) have been used in construction since ancient times. Until the end of the 18th century, chemists considered lime to be a simple substance. In 1789, A. Lavoisier suggested that lime, magnesia, barite, alumina and silica are complex substances. In 1808, Davy, subjecting a mixture of wet slaked lime with mercury oxide to electrolysis with a mercury cathode, prepared a calcium amalgam, and after driving mercury out of it, he obtained a metal called "calcium" (from lat. Calx, genus. case calcis - lime).

Arrangement of electrons in orbits.

+20Ca… |3s 3p 3d | 4s

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

The crystal lattices of metals can be of various types, however, calcium is characterized by a face-centered cubic lattice.

The sizes, shape and mutual arrangement of crystals in metals are emitted by metallographic methods. The most complete assessment of the metal structure in this respect is given by microscopic analysis of its thin section. A sample is cut out of the metal under test, and its plane is ground, polished and etched with a special solution (etchant). As a result of etching, the structure of the sample is highlighted, which is examined or photographed using a metallographic microscope.

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

Calcium is highly reactive with metals, especially with oxygen. In air, it oxidizes more slowly than alkali metals, since the oxide film on it is less permeable to oxygen. When heated, calcium burns with the release of huge amounts of heat:

Calcium reacts with water, displacing hydrogen from it and forming a base:

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

Owing to its great reactivity with oxygen, calcium finds some use in obtaining rare metals from their oxides. Metal oxides are heated together with calcium chips; as a result of the reactions, calcium oxide and a metal are obtained. The use of calcium and some of its alloys for the so-called deoxidation of metals is based on the same property. Calcium is added to molten metal and it removes traces of dissolved oxygen; the resulting calcium oxide floats to the surface of the metal. Calcium is part of some alloys.

Calcium is obtained by electrolysis of molten calcium chloride or by the aluminothermic method. Calcium oxide, or slaked lime, is a white powder that melts at 2570°C. It is obtained by calcining limestone:

CaCO3 \u003d CaO + CO2 ^

Calcium oxide is a basic oxide, so it reacts with acids and acid anhydrides. With water, it gives a base - calcium hydroxide:

CaO + H2O = Ca(OH)2

The addition of water to calcium oxide, called lime slaking, proceeds with the release of a large amount of heat. Part of the water is converted into steam. Calcium hydroxide, or slaked lime, is a white substance, slightly soluble in water. An aqueous solution of calcium hydroxide is called lime water. Such a solution has rather strong alkaline properties, since calcium hydroxide dissociates well:

Ca (OH) 2 \u003d Ca + 2OH

Compared to hydrates of alkali metal oxides, calcium hydroxide is a weaker base. This is explained by the fact that the calcium ion is doubly charged and more strongly attracts hydroxyl groups.

Hydrated lime and its solution, called lime water, react with acids and acid anhydrides, including carbon dioxide. Lime water is used in laboratories to discover carbon dioxide, since the resulting insoluble calcium carbonate causes the water to become cloudy:

Ca + 2OH + CO2 = CaCO3v + H2O

However, when carbon dioxide is passed for a long time, the solution becomes transparent again. This is due to the fact that calcium carbonate is converted into a soluble salt - calcium bicarbonate:

CaCO3 + CO2 + H2O = Ca(HCO3)2

In industry, calcium is obtained in two ways:

By heating a briquetted mixture of CaO and Al powder at 1200 ° C in a vacuum of 0.01 - 0.02 mm. rt. Art.; released by the reaction:

6CaO + 2Al = 3CaO Al2O3 + 3Ca

Calcium vapor condenses on a cold surface.

By electrolysis of a melt of CaCl2 and KCl with a liquid copper-calcium cathode, an alloy of Cu - Ca (65% Ca) is prepared, from which calcium is distilled off at a temperature of 950 - 1000 ° C in a vacuum of 0.1 - 0.001 mm Hg.

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

Calcium is one of the most abundant elements in nature. It contains approximately 3% (mass) in the earth's crust. Calcium salts form in nature large accumulations in the form of carbonates (chalk, marble), sulfates (gypsum), phosphates (phosphorites). Under the influence of water and carbon dioxide, carbonates pass into solution in the form of hydrocarbons and are transported by underground and river waters over long distances. When calcium salts are washed out, caves can form. Due to the evaporation of water or an increase in temperature, deposits of calcium carbonate can form in a new place. So, for example, stalactites and stalagmites are formed in caves.

Soluble calcium and magnesium salts determine the overall hardness of water. If they are present in water in small quantities, then the water is called soft. With a high content of these salts (100 - 200 mg of calcium salts - in 1 liter in terms of ions), water is considered hard. In such water, soap foams poorly, since calcium and magnesium salts form insoluble compounds with it. In hard water, food products are poorly boiled, and when boiled, it gives scale on the walls of steam boilers. Scale does not conduct heat well, causes an increase in fuel consumption and accelerates the wear of the boiler walls. Scale formation is a complex process. When heated, the acid salts of calcium and magnesium carbonic acid decompose and turn into insoluble carbonates:

Ca + 2HCO3 = H2O + CO2 + CaCO3v

The solubility of calcium sulfate CaSO4 also decreases when heated, so it is part of the scale.

The hardness caused by the presence of calcium and magnesium bicarbonates in water is called carbonate or temporary, since it is eliminated by boiling. In addition to carbonate hardness, non-carbonate hardness is also distinguished, which depends on the content of sulfates and chlorides of calcium and magnesium in the water. These salts are not removed by boiling, and therefore non-carbonate hardness is also called constant hardness. Carbonate and non-carbonate hardness add up to total hardness.

To completely eliminate hardness, water is sometimes distilled. Boil water to remove carbonate hardness. General hardness is eliminated either by adding chemicals or by using so-called cation exchangers. When using the chemical method, soluble calcium and magnesium salts are converted into insoluble carbonates, for example, milk of lime and soda are added:

Ca + 2HCO3 + Ca + 2OH = 2H2O + 2CaCO3v

Ca + SO4 + 2Na + CO3 = 2Na + SO4 + CaCO3v

Removing stiffness with cation exchangers is a more advanced process. Cation exchangers are complex substances (natural compounds of silicon and aluminum, high molecular weight organic compounds), the composition of which can be expressed by the formula Na2R, where R is a complex acid residue. When water is filtered through a layer of cation exchanger, Na ions (cations) are exchanged for Ca and Mg ions:

Ca + Na2R = 2Na + CaR

Consequently, Ca ions from the solution pass into the cation exchanger, and Na ions pass from the cation exchanger into the solution. To restore the used cation exchanger, it is washed with a solution of common salt. In this case, the reverse process occurs: Ca ions in the cation exchanger are replaced by Na ions:

2Na + 2Cl + CaR = Na2R + Ca + 2Cl

The regenerated cation exchanger can be used again for water purification.

In the form of a pure metal, Ca is used as a reducing agent for U, Th, Cr, V, Zr, Cs, Rb and some rare earth metals and their compounds. It is also used for the deoxidation of steels, bronzes and other alloys, for the removal of sulfur from petroleum products, for the dehydration of organic liquids, for the purification of argon from nitrogen impurities, and as a gas absorber in electric vacuum devices. Antifiction materials of the Pb - Na - Ca system, as well as Pb - Ca alloys, which are used to make the sheath of electric cables, have received great use in technology. Alloy Ca - Si - Ca (silicocalcium) is used as a deoxidizer and degasser in the production of quality steels.

Calcium is one of the biogenic elements necessary for the normal course of life processes. It is present in all tissues and fluids of animals and plants. Only rare organisms can develop in an environment devoid of Ca. In some organisms, the content of Ca reaches 38%: in humans - 1.4 - 2%. Cells of plant and animal organisms need strictly defined ratios of Ca, Na and K ions in extracellular media. Plants get Ca from the soil. According to their relation to Ca, plants are divided into calcephiles and calcephobes. Animals get Ca from food and water. Ca is necessary for the formation of a number of cellular structures, maintaining the normal permeability of outer cell membranes, for fertilizing the eggs of fish and other animals, and activating a number of enzymes. Ca ions transmit excitation to the muscle fiber, causing its contraction, increase the strength of heart contractions, increase the phagocytic function of leukocytes, activate the system of protective blood proteins, and participate in its coagulation. In cells, almost all Ca is in the form of compounds with proteins, nucleic acids, phospholipids, in complexes with inorganic phosphates and organic acids. In the blood plasma of humans and higher animals, only 20-40% Ca can be associated with proteins. In animals with a skeleton, up to 97 - 99% of all Ca is used as a building material: in invertebrates, mainly in the form of CaCO3 (mollusc shells, corals), in vertebrates, in the form of phosphates. Many invertebrates store Ca before molting to build a new skeleton or to provide vital functions in adverse conditions. The content of Ca in the blood of humans and higher animals is regulated by the hormones of the parathyroid and thyroid glands. Vitamin D plays the most important role in these processes. Ca absorption occurs in the anterior part of the small intestine. Assimilation of Ca worsens with a decrease in acidity in the intestine and depends on the ratio of Ca, phosphorus and fat in food. The optimal Ca/P ratios in cow's milk are about 1.3 (in potatoes 0.15, in beans 0.13, in meat 0.016). With an excess of P and oxalic acid in food, the absorption of Ca worsens. Bile acids accelerate its absorption. The optimal ratio of Ca/fat in human food is 0.04 - 0.08 g of Ca per 1 g. fat. Excretion of Ca occurs mainly through the intestines. Mammals during lactation lose a lot of Ca with milk. With violations of phosphorus-calcium metabolism in young animals and children, rickets develop, in adult animals - a change in the composition and structure of the skeleton (osteomalacia).

In medicine, Ca drugs eliminate disorders associated with a lack of Ca ions in the body (with tetany, spasmophilia, rickets). Ca preparations reduce hypersensitivity to allergens and are used to treat allergic diseases (serum sickness, sleeping 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. It is 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 by mouth and intravenously. Ossocalcinol (15% sterile suspension of specially prepared bone powder in peach oil) has been proposed for tissue therapy.

Ca preparations also include gypsum (CaSO4), used in surgery for plaster casts, and chalk (CaCO3), administered orally with increased acidity of gastric juice and for the preparation of tooth powder.

Home / Lectures 1st year / General and organic chemistry / Question 23. Calcium / 2. Physical and chemical properties

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 reacting 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 soil types.

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).

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Calcium and its role for humanity - Chemistry

Calcium and its role for humanity

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 easily reacts with oxygen, carbon dioxide and moisture in the air, which is why 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 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 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.

www.e-ng.ru

world of science

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.

worldofscience.ru

The bone skeleton is composed of it, but the body is not able to produce the element on its own. It's about calcium. Adult women and men need to get at least 800 milligrams of alkaline earth metal per day. It is possible to extract it from oatmeal, hazelnuts, milk, barley groats, sour cream, beans, almonds.

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

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 an element, since it has become one of the most important for living beings, and is there a use for the substance outside their organisms?

Chemical and physical properties of calcium

In the periodic table, the element occupies the 20th place. 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 matter has 4 electronic levels. They have 20 electrons, which is indicated by the atomic number of the element. It also testifies to 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 silver-white, shiny and light. The hardness of alkaline earth metals is higher than that of alkali metals.

The calcium index is about 3 points according to. Gypsum, for example, has the same hardness. The 20th element is cut with a knife, but much more difficult than any of the simple alkali metals.

What is the meaning of the name "alkaline earth"? So calcium and other metals of his group were dubbed by alchemists. They called the oxides of the elements earths. Oxides of substances calcium groups make the water alkaline.

However, , radium, barium, as well as 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 carbonic form of the metal is the notorious 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. In order for calcium to react with oxygen, normal conditions are sufficient. Only in nature, the element does not occur in its pure form, only in compounds.

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

At the same time, the precipitate calcium hydroxide. Remains 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 gets to 842 degrees, calcium can melt. At 1484 on the Celsius scale, the metal boils.

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

In the human body, the element is represented by both solid and liquid states of aggregation. Softened calcium water, which is present in, transfers more easily. Outside the bones is only 1% of the 20th substance.

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

Application 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 the 20th element. One of the alloys is called bearing.

Pictured are calcium-rich foods.

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

What kind of calcium used in ferrous metallurgy? All the same pure. The difference is in the purpose of the element. Now, he's playing the part. It is an additive to alloys that reduces the temperature of their formation and facilitates the separation of slags. calcium granules fall asleep in electrovacuum 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. Disperse them with the help of ions - a kind of projectiles. If Ca48 acts in their role, the efficiency of synthesis increases hundreds of times in comparison with the use of ions of other substances.

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

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

In medicine, they also prescribe not pure metal, 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"prescribed to adolescents, pregnant women and the elderly.

They need dietary supplements to provide the increased need of the body for the 20th element, 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 full absorption calcium.

Instruction to "Calcium nycomed3" indicates that the drug belongs to pharmaceutical formulations 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.

In pharmacies, the drug " Calcium is an acid ascorbic". Such a duet is prescribed during pregnancy, during breastfeeding. Teenagers also need a supplement.

Extraction of calcium

calcium in foods, minerals, compounds, known to mankind since ancient times. In its pure form, the metal was isolated only in 1808. Luck favored Humphrey Davy. An English physicist extracted calcium by electrolysis of the element's molten salts. 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. For the first time, calcium was isolated in this way in the middle of the last century, in the USA.

The price of calcium

There are few manufacturers of metallic calcium. So, in Russia, the Chapetsky Mechanical Plant is mainly engaged in deliveries. It is located in Udmurtia. The company trades in granules, shavings and lumps of metal. The price tag for a ton of raw materials is around $1,500.

The product is also offered by some chemical laboratories, for example, the Russian Chemist society. Last, offers a 100-gram calcium. Reviews testify that it is a 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 lost their relevance yet.

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 easily reacts with oxygen, carbon dioxide and moisture in the air, which is why 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 is very common in nature in the form of various compounds. In the earth's crust, it ranks fifth, accounting for 3.25%, and is most often found in the form of limestone CaCO3, dolomite CaCO3 * MgCO3, gypsum CaSO4 * 2H2O, phosphorite Ca3 (PO4) 2 and fluorspar CaF2, not counting a significant proportion of calcium in composition of silicate rocks. Seawater contains an average of 0.04% (w/w) calcium

Physical and chemical properties of calcium

Calcium is in the subgroup of alkaline earth metals of group II of the periodic system of elements; serial number 20, atomic weight 40.08, valence 2, atomic volume 25.9. Calcium isotopes: 40 (97%), 42 (0.64%), 43 (0.15%), 44 (2.06%), 46 (0.003%), 48 (0.185%). Electronic structure of the calcium atom: 1s2, 2s2p6, 3s2p6, 4s2. The radius of the atom is 1.97 A, the radius of the ion is 1.06 A. Up to 300 ° calcium crystals have the shape of a cube with centered faces and a side size of 5.53 A, above 450 ° - a hexagonal shape. The specific gravity of calcium is 1.542, the melting point is 851°, the boiling point is 1487°, the heat of fusion is 2.23 kcal/mol, the heat of vaporization is 36.58 kcal/mol. Atomic heat capacity of solid calcium Cp = 5.24 + 3.50*10v-3 T for 298-673°K and Cp = 6.29+1.40*10v-3T for 673-1124°K; for liquid calcium Cp = 7.63. Entropy of solid calcium 9.95 ± 1, gaseous at 25° 37.00 ± 0.01.
The vapor pressure of solid calcium was studied by Yu.A. Priselkov and A.N. Nesmeyanov, P. Douglas and D. Tomlin. The values ​​of elasticity of saturated calcium vapor are given in table. one.

In terms of thermal conductivity, calcium approaches sodium and potassium, at temperatures of 20-100 ° the coefficient of linear expansion is 25 * 10v-6, at 20 ° the electrical resistivity is 3.43 μ ohm / cm3, from 0 to 100 ° the temperature coefficient of electrical resistance is 0.0036. Electrochemical equivalent 0.74745 g/a*h. Tensile strength of calcium 4.4 kg/mm2, Brinell hardness 13, elongation 53%, reduction ratio 62%.
Calcium has a silvery-white color, glistens when broken. In air, the metal is covered with a thin bluish-gray film of nitride, oxide, and partially calcium peroxide. Calcium is flexible and malleable; it can be processed on a lathe, drilled, cut, sawed, pressed, drawn, etc. The purer the metal, the greater its ductility.
In a series of voltages, calcium is located among the most electronegative metals, which explains its high chemical activity. At room temperature, calcium does not react with dry air, at 300 ° and above it is intensively oxidized, and with strong heating it burns with a bright orange-reddish flame. In humid air, calcium is gradually oxidized, turning into hydroxide; it reacts relatively slowly with cold water, but vigorously displaces hydrogen from hot water, forming hydroxide.
Nitrogen reacts markedly with calcium at 300° and very intensely at 900° to form the nitride Ca3N2. With hydrogen at a temperature of 400°, calcium forms the hydride CaH2. With dry halogens, with the exception of fluorine, calcium does not bind at room temperature; intensive formation of halides occurs at 400° and above.
Strong sulfuric (65-60 ° Be) and nitric acids act weakly on pure calcium. Of the aqueous solutions of mineral acids, hydrochloric acid, strongly nitric acid, and weakly sulfuric acid act very strongly. In concentrated NaOH solutions and in soda solutions, calcium is almost not destroyed.

Application

Calcium is increasingly used in various industries. Recently, it has gained great importance as a reducing agent in the production of a number of metals. Pure uranium metal is obtained by reducing uranium fluoride with calcium metal. Titanium oxides, as well as oxides of zirconium, thorium, tantalum, niobium and other rare metals, can be reduced with calcium or its hydrides. Calcium is a good deoxidizer and degasser in the production of copper, nickel, chromium-nickel alloys, special steels, nickel and tin bronzes; it removes sulfur, phosphorus, and carbon from metals and alloys.
Calcium forms refractory compounds with bismuth, so it is used to purify lead from bismuth.
Calcium is added to various light alloys. It contributes to the improvement of the surface of the ingots, fineness and reduction of oxidizability. Bearing alloys containing calcium are widely used. Lead alloys (0.04% Ca) can be used to make cable sheaths.
Calcium is used for the dehydration of alcohols and solvents for the desulfurization of petroleum products. Calcium-zinc alloys or zinc-magnesium alloys (70% Ca) are used to produce high-quality porous concrete. Calcium is a part of antifriction alloys (lead-calcium babbits).
Due to the ability to bind oxygen and nitrogen, calcium or calcium alloys with sodium and other metals are used to purify noble gases and as a getter in vacuum radio equipment. Calcium is also used to produce hydride, which is a source of hydrogen in the field. With carbon, calcium forms calcium carbide CaC2, which is used in large quantities to produce acetylene C2H2.

History of development

Devi first obtained calcium in the form of an amalgam in 1808 using the electrolysis of wet lime with a mercury cathode. Bunsen in 1852 obtained an amalgam with a high calcium content by electrolysis of a hydrochloric acid solution of calcium chloride. Bunsen and Mathyssen in 1855 obtained pure calcium by electrolysis of CaCl2 and Moissan by electrolysis of CaF2. In 1893, Borchers significantly improved the electrolysis of calcium chloride by applying cathode cooling; Arndt in 1902 obtained by electrolysis a metal containing 91.3% Ca. Ruff and Plata used a mixture of CaCl2 and CaF2 to lower the electrolysis temperature; Borchers and Stockem obtained a sponge at a temperature below the melting point of calcium.
Rathenau and Süter solved the problem of electrolytic production of calcium by proposing a method of electrolysis with a touch cathode, which soon became industrial. There have been many proposals and attempts to obtain calcium alloys by electrolysis, especially on a liquid cathode. According to F.O. Banzel, it is possible to obtain calcium alloys by electrolysis of CaF2 with the addition of salts or fluoroxides of other metals. Poulenet and Melan obtained a Ca-Al alloy on a liquid aluminum cathode; Kugelgen and Seward produced a Ca-Zn alloy on a zinc cathode. The preparation of Ca-Zn alloys was studied in 1913 by V. Moldengauer and J. Andersen, who also obtained Pb-Ca alloys on a lead cathode. Koba, Simkins, and Gire used a 2000 A lead cathode cell and produced an alloy with 2% Ca at a current efficiency of 20%. I. Tselikov and V. Wazinger added NaCl to the electrolyte to obtain an alloy with sodium; R.R. Syromyatnikov stirred the alloy and achieved 40-68% current efficiency. Calcium alloys with lead, zinc and copper are produced by electrolysis on an industrial scale.
The thermal method of obtaining calcium has aroused considerable interest. Aluminothermic reduction of oxides was discovered in 1865 by H.H. Beketov. In 1877, Malet discovered the interaction of a mixture of calcium, barium, and strontium oxides with aluminum when heated. Winkler tried to reduce these same oxides with magnesium; Biltz and Wagner, reducing calcium oxide with aluminum in a vacuum, obtained a low yield of the metal. Gunz in 1929 achieved the best results. A.I. Voinitsky in 1938 reduced calcium oxide with aluminum and silico alloys in the laboratory. The method was patented in 1938. At the end of the Second World War, the thermal method received industrial application.
In 1859, Caron proposed a method for obtaining alloys of sodium with alkaline earth metals by the action of metallic sodium on their chlorides. According to this method, calcium (and barine) is obtained in an alloy with lead. Until the Second World War, the industrial production of calcium by electrolysis was carried out in Germany and Fraction. In Biterfeld (Germany) in the period from 1934 to 1939, 5-10 tons of calcium were produced annually. The US demand for calcium was covered by imports, which amounted to 10-25 g per year in the period 1920-1940. Since 1940, when imports from France ceased, the United States began to produce calcium itself in significant quantities by electrolysis; at the end of the war they began to receive calcium by vacuum thermal method; according to S. Loomis, its output reached 4.5 tons per day. According to Minerale Yarbuk, Dominium Magnesium in Canada produced calcium per year:

There is no information on the scale of calcium production in recent years.

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Metal tile - metal material for roofing. The surface of the sheets is coated with polymeric materials and zinc. Natural tiles are imitated by the material...

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Testing equipment has been widely used in various fields. Its quality must be impeccable. To achieve this goal, the devices are equipped with...