What can calcium interact with? Chemical and physical properties of calcium, its interaction with water
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 degrees Celsius. 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).
With cold water calcium interacts slowly, and with hot - very vigorously:
Ca + 2 H2O \u003d Ca (OH) 2 + H2.
Calcium can take away oxygen or halogens from oxides and halides less active metals, i.e. it has restorative 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 different high content 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, and 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 - chemical element 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 features:
- At the roots of plants, damaged brown tips are observed;
- The growth point is deformed and dies;
- Flowers, ovaries and buds fall off;
- Fruits are damaged by necrosis;
- Leaves are chlorotic;
- The apical bud dies, and the growth of the stem stops.
Cabbage, alfalfa, clover are highly sensitive to the presence of calcium. It has been established that these same plants are also characterized by increased sensitivity to soil acidity.
Mineral calcium poisoning results in interveinal chlorosis with whitish necrotic patches. They can be colored or have concentric rings filled with water. Some plants respond to excess calcium by growing leaf rosettes, dying off shoots and falling leaves. Symptoms are similar in appearance to a lack of iron and magnesium.
The source of replenishment of calcium in the soil is lime fertilizers. They are divided into three groups:
- Hard calcareous rocks;
- Soft calcareous rocks;
- Industrial waste with high lime content.
Hard calcareous rocks according to the content of CaO and MgO are divided into:
- limestones (55–56% CaO and up to 0.9% MgO);
- dolomitic limestones (42–55% CaO and up to 9% MgO);
- dolomites (32–30% CaO and 18–20% MgO).
Limestones
- basic lime fertilizers. Contain 75–100% Ca and Mg oxides in terms of CaCO3.Dolomitized limestone
. Contains 79-100% active ingredient (a.i.) in terms of CaCO3. It is recommended in crop rotations with potatoes, legumes, flax, root crops, as well as on heavily podzolized soils.Marl
. Contains up to 25–15% CaCO3 and impurities in the form of clay with sand up to 20–40%. Acts slowly. Recommended for use on light soils.Chalk
. Contains 90–100% CaCO3. Action is faster than that of limestone. It is a valuable lime fertilizer in finely ground form.burnt lime
(CaO). The content of CaCO3 is over 70%. It is characterized as a strong and fast acting liming material.Slaked lime
(Ca(OH)2). The content of CaCO3 is 35% or more. It is also a strong and fast acting lime fertilizer.Dolomite flour
. The content of CaCO3 and MgCO3 is about 100%. Slower in action than calcareous tuffs. Typically used where magnesium is required.calcareous tuffs
. The content of CaCO3 is 15–96%, impurities are up to 25% clay and sand, 0.1% P2O5. Action is faster than that of limestone.Defecation mud (defecation)
. Consists of CaCO3 and Ca(OH)2. The content of lime on CaO is up to 40%. Nitrogen is also present - 0.5% and P2O5 - 1-2%. This is waste from sugar beet factories. It is recommended for use not only to reduce soil acidity, but also in beet-growing areas on chernozem soils.Shale ash cyclones
. Dry pulverized material. The content of the active substance is 60-70%. Refers to industrial waste.Dust from kilns and cement plants
. The content of CaCO3 must exceed 60%. In practice, it is used in farms located in the immediate vicinity of cement plants.Metallurgical slag
. Used in the regions of the Urals and Siberia. Non-hygroscopic, easy to spray. Must contain at least 80% CaCO3, have a moisture content of not more than 2%. The granulometric composition is important: 70% - less than 0.25 mm, 90% - less than 0.5 mm.organic fertilizers. The content of Ca in terms of CaCO3 is 0.32–0.40%.
Phosphate flour. The calcium content is 22% CaCO3.
Lime fertilizers are used not only to provide soil and plants with calcium. The main purpose of their use is soil liming. This is a method of chemical reclamation. It is aimed at neutralizing excess soil acidity, improving its agrophysical, agrochemical and biological properties, supplying plants with magnesium and calcium, mobilizing and immobilizing macroelements and microelements, creating optimal water-physical, physical, and air conditions for the life of cultivated plants.
Soil liming efficiency
Simultaneously with meeting the need of plants for calcium as an element of mineral nutrition, liming leads to multiple positive changes in soils.
Effect of liming on the properties of some soils
Calcium promotes coagulation of soil colloids and prevents their leaching. This leads to easier soil cultivation and improved aeration.
As a result of liming:
- sandy humus soils increase their water absorption capacity;
- on heavy clay soils, soil aggregates and clods are formed that improve water permeability.
In particular, organic acids are neutralized and H-ions are displaced from the absorbing complex. This leads to the elimination of exchange and reduction of hydrolytic acidity of the soil. At the same time, there is an improvement in the cationic composition of the soil absorbing complex, which occurs due to the change of hydrogen and aluminum ions to calcium and magnesium cations. This increases the degree of saturation of soils with bases and increases the uptake capacity.
The effect of liming on the supply of plants with nitrogen
After liming, the positive agrochemical properties of the soil and its structure can be preserved for several years. This contributes to the creation of favorable conditions for enhancing beneficial microbiological processes to mobilize nutrients. The activity of ammonifiers, nitrifiers, nitrogen-fixing bacteria that live freely in the soil is enhanced.
Liming helps to increase the reproduction of nodule bacteria and improve the supply of nitrogen to the host plant. It has been established that bacterial fertilizers lose their effectiveness on acidic soils.
The effect of liming on the supply of plants with ash elements
Liming contributes to the supply of ash elements to the plant, since the activity of bacteria that decompose organic phosphorus compounds in the soil and promote the transition of iron and aluminum phosphates into calcium phosphate salts available to plants is enhanced. Liming of acidic soils enhances microbiological and biochemical processes, which, in turn, increases the amount of nitrates, as well as assimilable forms of phosphorus and potassium.
The effect of liming on the forms and availability of macronutrients and trace elements
Liming increases the amount of calcium, and when using dolomite flour - magnesium. Simultaneously, the toxic forms of manganese and aluminum become insoluble and pass into the precipitated form. The availability of elements such as iron, copper, zinc, manganese is declining. Nitrogen, sulfur, potassium, calcium, magnesium, phosphorus and molybdenum are becoming more available.
Effect of liming on the action of physiologically acidic fertilizers
Liming increases the effectiveness of physiologically acidic mineral fertilizers, especially ammonia and potash.
The positive effect of physiologically acidic fertilizers fades without lime, and over time can turn into a negative one. So on the fertilized sites, the yields are even less than on the unfertilized ones. The combination of liming with the use of fertilizers increases their effectiveness by 25–50%.
Liming activates enzymatic processes in the soil, which indirectly judge its fertility.
Compiled by: Grigorovskaya P.I.
Page added: 05.12.13 00:40
Last update: 05/22/14 16:25
Literary sources:
Glinka N.L. General chemistry. Textbook for universities. Publisher: L: Chemistry, 1985, p. 731
Mineev V.G. Agrochemistry: Textbook. - 2nd edition, revised and supplemented. - M .: MGU Publishing House, KolosS Publishing House, 2004. - 720 p., L. ill.: ill. – (Classic university textbook).
Petrov B.A., Seliverstov N.F. Mineral nutrition of plants. Reference manual for students and gardeners. Yekaterinburg, 1998. 79 p.
Encyclopedia for children. Volume 17. Chemistry. / Head. ed. V.A. Volodin. - M.: Avanta +, 2000. - 640 p., ill.
Yagodin B.A., Zhukov Yu.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodina. - M.: Kolos, 2002. - 584 p.: silt (Textbooks and teaching aids for students of higher educational institutions).
Images (remastered):
20 Ca Calcium, under license CC BY
Calcium deficiency in wheat, by CIMMYT, licensed under CC BY-NC-SA
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Calcium and its role for humanity - Chemistry
Calcium and its role for 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). Simple substance calcium (CAS number: 7440-70-2) is a soft, reactive alkaline earth metal, silvery white color.
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. Mechanical properties elemental calcium does 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, as structural material elemental calcium is almost never used. 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.
AT rocks oh 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 animals and plant tissues(see also below). A significant amount of calcium is part of living organisms. So, hydroxyapatite Ca5 (PO4) 3OH, or, in another notation, 3Ca3 (PO4) 2 Ca (OH) 2 is the basis bone tissue 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 intercellular substance 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, due to which the surface of metallic calcium is usually dull gray, therefore, in the laboratory, calcium is usually stored, like other alkaline earth metals, in 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 heats up sunbeams, the reverse reaction takes place:
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 enormous electrical 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 the composition of preparations for the prevention of osteoporosis, in 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. From various forms calcium carbonate (lime) are the skeletons of most groups of invertebrates (sponges, coral polyps, shellfish, etc.). 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 acidic environment, vitamin D and vitamin C, lactose, 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.
The content of calcium in the blood, due to the large number of processes associated with it, is precisely regulated, and when proper nutrition there is no shortage. Prolonged absence from the diet can cause cramps, joint pain, drowsiness, growth defects, and constipation. A deeper deficiency leads to permanent muscle cramps and osteoporosis. Abuse of coffee and alcohol can be the causes of calcium deficiency, as part of it is excreted in the urine.
Excessive doses of calcium and vitamin D can cause hypercalcemia, followed by intense calcification of bones and tissues (mainly affecting the urinary system). A prolonged excess disrupts the functioning of muscle and nerve tissues, increases blood clotting and reduces the absorption of zinc by bone cells. The maximum daily safe dose for an adult is 1500 to 1800 milligrams.
Products Calcium, mg/100 g
Sesame 783
Nettle 713
Mallow forest 505
Plantain big 412
Galinsoga 372
Sardines in oil 330
Budra ivy 289
Dog rosehip 257
Almond 252
Plantain lanceolate. 248
Hazelnut 226
Amaranth seed 214
Watercress 214
Soy beans dry 201
Children under 3 years - 600 mg.
Children 4 to 10 years old - 800 mg.
Children 10 to 13 years old - 1000 mg.
Adolescents 13 to 16 years old - 1200 mg.
Youth 16 and older - 1000 mg.
Adults 25 to 50 years old - 800 to 1200 mg.
Pregnant and breastfeeding women - 1500 to 2000 mg.
Conclusion
Calcium is one of the most abundant elements on earth. There is a lot of it in nature: mountain ranges and clay rocks are formed from calcium salts, it is found in sea and river water, and is part of plant and animal organisms.
Calcium constantly surrounds the townspeople: almost all the main building materials - concrete, glass, brick, cement, lime - contain this element in significant quantities.
Naturally, having such chemical properties, calcium cannot be found in nature in a free state. But calcium compounds - both natural and artificial - have become of paramount importance.
Bibliography
1. Editorial board: Knunyants I. L. (editor-in-chief) Chemical encyclopedia: in 5 volumes - Moscow: Soviet Encyclopedia, 1990. - T. 2. - S. 293. - 671 p.
2. Doronin. N. A. Kaltsy, Goshimizdat, 1962. 191 pages with illustrations.
3. Dotsenko VA. - Therapeutic and preventive nutrition. - Q. nutrition, 2001 - N1-p.21-25
4. Bilezikian J. P. Calcium and bone metabolism // In: K. L. Becker, ed.
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Calcium is a metal element of the main subgroup II of group 4 of the period of the periodic system of chemical elements. It belongs to the family of alkaline earth metals. The outer energy level of the calcium atom contains 2 paired s-electrons
Which he is able to give energetically during chemical interactions. Thus, Calcium is a reducing agent and in its compounds has an oxidation state of +2. In nature, calcium occurs only in the form of salts. The mass fraction of calcium in the earth's crust is 3.6%. The main natural calcium mineral is calcite CaCO3 and its varieties - limestone, chalk, marble. There are also living organisms (for example, corals), the backbone of which consists mainly of calcium carbonate. Also important calcium minerals are dolomite CaCO3 MgCO3, fluorite CaF2, gypsum CaSO4 2h3O, apatite, feldspar, etc. Calcium plays an important role in the life of living organisms. Mass fraction of calcium in human body is 1.4-2%. It is part of the teeth, bones, other tissues and organs, participates in the process of blood coagulation, stimulates cardiac activity. To provide the body with a sufficient amount of calcium, it is imperative to consume milk and dairy products, green vegetables, fish. The simple substance calcium is a typical silver-white metal. It is quite hard, plastic, has a density of 1.54 g/cm3 and a melting point of 842? C. Chemically, calcium is very active. Under normal conditions, it easily interacts with oxygen and moisture in the air, so it is stored in hermetically sealed vessels. When heated in air, calcium ignites and forms an oxide: 2Ca + O2 = 2CaO. Calcium reacts with chlorine and bromine when heated, and with fluorine even in the cold. The products of these reactions are the corresponding halides, for example: Ca + Cl2 = CaCl2. When calcium is heated with sulfur, calcium sulfide is formed: Ca + S = CaS. Calcium can also react with other non-metals. Interaction with water leads to the formation of poorly soluble calcium hydroxide and the evolution of gaseous hydrogen : Ca + 2h3O = Ca (OH) 2 + h3. Calcium metal is widely used. It is used as a rozkisnik in the manufacture of steels and alloys, as a reducing agent for the production of some refractory metals.
Calcium is obtained by electrolysis of a calcium chloride melt. Thus, calcium was first obtained in 1808 by Humphry Davy.
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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
AT periodic system element is ranked 20th. 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. For calcium to react with oxygen, it is enough normal conditions. 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 well and electricity. 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 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, Chapetsky is mainly engaged in deliveries mechanical plant. 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.
DEFINITION
Calcium- the twentieth element of the Periodic table. Designation - Ca from the Latin "calcium". Located in the fourth period, IIA group. Refers to metals. The core charge is 20.
Calcium is one of the most abundant elements in nature. It contains approximately 3% (mass) in the earth's crust. It occurs as numerous deposits of limestone and chalk, as well as marble, which are natural varieties of calcium carbonate CaCO 3 . AT large quantities there are also gypsum CaSO 4 × 2H 2 O, phosphorite Ca 3 (PO 4) 2 and, finally, various calcium-containing silicates.
As a simple substance calcium is a malleable, fairly hard white metal (Fig. 1). In air, it quickly becomes covered with a layer of oxide, and when heated, it burns with a bright reddish flame. Calcium reacts relatively slowly with cold water, but from hot water quickly displaces hydrogen, forming hydroxide.
Rice. 1. Calcium. Appearance.
Atomic and molecular weight of calcium
The relative molecular weight of a substance (M r) is a number showing how many times the mass of a given molecule is greater than 1/12 of the mass of a carbon atom, and the relative atomic mass element (A r) - how many times the average mass of atoms of a chemical element is greater than 1/12 of the mass of a carbon atom.
Since in the free state calcium exists in the form of monatomic Ca molecules, the values of its atomic and molecular masses are the same. They are equal to 40.078.
Isotopes of calcium
It is known that in nature calcium can be found in the form of four stable isotopes 40Ca, 42Ca, 43Ca, 44Ca, 46Ca and 48Ca, with a clear predominance of the 40Ca isotope (99.97%). Their mass numbers are 40, 42, 43, 44, 46 and 48, respectively. The nucleus of the atom of the calcium isotope 40 Ca contains twenty protons and twenty neutrons, and the remaining isotopes differ from it only in the number of neutrons.
There are artificial calcium isotopes with mass numbers from 34 to 57, among which the most stable is 41 Ca with a half-life of 102 thousand years.
Calcium ions
At the outer energy level of the calcium atom, there are two electrons that are valence:
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 .
As a result of chemical interaction, calcium gives up its valence electrons, i.e. is their donor, and turns into a positively charged ion:
Ca 0 -2e → Ca 2+.
Molecule and atom of calcium
In the free state, calcium exists in the form of monatomic Ca molecules. Here are some properties that characterize the calcium atom and molecule:
calcium alloys
Calcium serves as an alloying component of some lead alloys.
Examples of problem solving
EXAMPLE 1
| Exercise | Write the reaction equations that can be used to carry out the following transformations: Ca → Ca(OH) 2 → CaCO 3 → Ca(HCO 3) 2. |
| Answer | By dissolving calcium in water, you can get a cloudy solution of a compound known as "milk of lime" - calcium hydroxide: Ca + 2H 2 O → Ca (OH) 2 + H 2. By passing carbon dioxide through a solution of calcium hydroxide, we get calcium carbonate: 2Ca(OH) 2 + CO 2 → CaCO 3 + H 2 O. By adding water to calcium carbonate and continuing to pass carbon dioxide through this mixture, we obtain calcium bicarbonate: CaCO 3 + H 2 O + CO 2 → Ca(HCO 3) 2. |
Calcium(Calcium), Ca, a chemical element of group II of the Mendeleev periodic system, atomic number 20, atomic mass 40.08; silver-white light metal. The natural element is a mixture of six stable isotopes: 40 Ca, 42 Ca, 43 Ca, 44 Ca, 46 Ca and 48 Ca, of which 40 Ca is the most common (96.97%).
Ca compounds - limestone, marble, gypsum (as well as lime - a product of burning 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, G. Davy, subjecting a mixture of wet slaked lime with mercury oxide to electrolysis with a mercury cathode, prepared an amalgam of Ca, and after driving mercury out of it, he obtained a metal called "Calcium" (from Latin calx, genus case calcis - lime) .
Distribution of calcium in nature. In terms of abundance in the earth's crust, Ca occupies the 5th place (after O, Si, Al, and Fe); content 2.96% by weight. It migrates vigorously and accumulates in various geochemical systems, forming 385 minerals (4th place in terms of the number of minerals). There is little Ca in the Earth's mantle and, probably, even less in the Earth's core (0.02% in iron meteorites). Ca predominates in the lower part of the earth's crust, accumulating in basic rocks; most of Ca is enclosed in feldspar - anorthite Ca; content in basic rocks 6.72%, in acidic (granites and others) 1.58%. An exceptionally sharp differentiation of Ca occurs in the biosphere, mainly associated with the "carbonate equilibrium": when carbon dioxide interacts with CaCO 3 carbonate, soluble bicarbonate Ca (HCO 3) 2 is formed: CaCO 3 + H 2 O + CO 2 \u003d Ca (HCO 3) 2 \u003d Ca 2+ + 2HCO 3-. This reaction is reversible and is the basis of Ca redistribution. With a high content of CO 2 in the waters, Ca is in solution, and with a low content of CO 2, the mineral calcite CaCO 3 precipitates, forming powerful deposits of limestone, chalk, and marble.
Biogenic migration also plays a huge role in the history of Ca. In living matter from elements-metals, Ca is the main one. Organisms are known that contain more than 10% Ca (more carbon), building their skeleton from Ca compounds, mainly CaCO 3 (calcareous algae, many molluscs, echinoderms, corals, rhizomes, etc.). With the burial of the skeletons of the sea. animals and plants is associated with the accumulation of colossal masses of algae, coral and other limestones, which, plunging into the depths of the earth and mineralizing, turn into different kinds marble.
Huge areas with a humid climate (forest zones, tundra) are characterized by a deficiency of Ca - here it is easily leached from the soil. This is associated with low soil fertility, low productivity of domestic animals, their small size, and often skeletal diseases. Therefore, liming of soils, feeding domestic animals and birds, etc. is of great importance. On the contrary, CaCO 3 is sparingly soluble in a dry climate, therefore steppe and desert landscapes are rich in Ca. Gypsum CaSO 4 2H 2 O often accumulates in salt marshes and salt lakes.
Rivers bring a lot of Ca into the ocean, but it does not stay in ocean water(average content 0.04%), but concentrated in the skeletons of organisms and after their death is deposited on the bottom mainly in the form of CaCO 3 . Lime silts are widespread on the bottom of all oceans at depths of no more than 4000 m (CaCO 3 dissolves at great depths, organisms there often experience a deficiency of Ca).
An important role in Ca migration is played by The groundwater. In limestone massifs, they vigorously leach CaCO 3 in places, which is associated with the development of karst, the formation of caves, stalactites and stalagmites. In addition to calcite, in the seas of past geological eras, the deposition of Ca phosphates (for example, the Karatau phosphorite deposits in Kazakhstan), dolomite CaCO 3 ·MgCO 3, and gypsum during evaporation were widespread in the seas of past geological epochs.
During geological history biogenic carbonate formation increased, while the chemical precipitation of calcite decreased. In the Precambrian seas (over 600 million years ago) there were no animals with a calcareous skeleton; they have become widespread since the Cambrian (corals, sponges, etc.). This is attributed to the high content of CO 2 in the Precambrian atmosphere.
Physical properties of calcium. The crystal lattice of the α-form of Ca (stable at ordinary temperature) is face-centered cubic, a = 5.56Å. Atomic radius 1.97Å, ionic radius Ca 2+ 1.04Å. Density 1.54 g/cm3 (20 °C). Above 464 °C, the hexagonal β-form is stable. t pl 851 °C, t kip 1482 °C; temperature coefficient linear expansion 22 10 -6 (0-300 °C); thermal conductivity at 20 °C 125.6 W/(m K) or 0.3 cal/(cm s °C); specific heat(0-100°C) 623.9 J/(kg K) or 0.149 cal/(g°C); electrical resistivity at 20 °C 4.6 10 -8 ohm m or 4.6 10 -6 ohm cm; temperature coefficient of electrical resistance 4.57 10 -3 (20 °C). Modulus of elasticity 26 Gn / m 2 (2600 kgf / mm 2); tensile strength 60 MN / m 2 (6 kgf / mm 2); elastic limit 4 MN / m 2 (0.4 kgf / mm 2), yield strength 38 MN / m 2 (3.8 kgf / mm 2); elongation 50%; Brinell hardness 200-300 MN / m 2 (20-30 kgf / mm 2). Calcium of sufficiently high purity is plastic, well pressed, rolled and can be machined.
Chemical properties of calcium. The configuration of the outer electron shell of the Ca 4s 2 atom, according to which Ca in compounds is 2-valent. Chemically Ca is very active. At ordinary temperatures, Ca easily interacts with oxygen and moisture in the air, so it is stored in hermetically sealed vessels or under mineral oil. When heated in air or oxygen, it ignites, giving the basic oxide CaO. Peroxides Ca-CaO 2 and CaO 4 are also known. At first, Ca reacts rapidly with cold water, then the reaction slows down due to the formation of a Ca(OH) 2 film. Ca reacts vigorously with hot water and acids, releasing H 2 (except for concentrated HNO 3). It reacts with fluorine in the cold, and with chlorine and bromine - above 400 ° C, giving CaF 2, CaCl 2 and CaBr 2, respectively. These halides in the molten state form with Ca the so-called subcompounds - CaF, CaCl, in which Ca is formally monovalent. When Ca is heated with sulfur, calcium sulfide CaS is obtained, the latter adds sulfur, forming polysulfides (CaS 2, CaS 4 and others). Interacting with dry hydrogen at 300-400 ° C, Ca forms a hydride CaH 2 - an ionic compound in which hydrogen is an anion. At 500 °C Ca and nitrogen give Ca 3 N 2 nitride; the interaction of Ca with ammonia in the cold leads to the complex ammonia Ca 6 . When heated without access to air with graphite, silicon or phosphorus, Ca gives calcium carbide CaC 2 , silicides Ca 2 Si, CaSi, CaSi 2 and phosphide Ca 3 P 2 , respectively. Ca forms intermetallic compounds with Al, Ag, Au, Cu, Li, Mg, Pb, Sn and others.
Getting Calcium. In industry, Ca is obtained in two ways: 1) by heating a briquetted mixture of CaO and Al powder at 1200 ° C in a vacuum of 0.01-0.02 mm Hg. Art.; released by the reaction: 6CaO + 2 Al \u003d 3CaO Al 2 O 3 + 3Ca Ca vapor condenses on a cold surface; 2) by electrolysis of a melt of CaCl 2 and KCl with a liquid copper-calcium cathode, an alloy of Cu - Ca (65% Ca) is prepared, from which Ca is distilled off at a temperature of 950-1000 ° C in a vacuum of 0.1-0.001 mm Hg. Art.
The use of calcium. 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 from 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. Antifriction materials of the Pb-Na-Ca system, as well as Pb-Ca alloys, which are used for the manufacture of electrical shells, have received great application in technology. cables. Alloy Ca-Si-Ca (silicocalcium) is used as a deoxidizer and degasser in the production of high-quality steels.
calcium in the body. Ca 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 Ca content reaches 38%; in humans - 1.4-2%. Cells of plant and animal organisms need strictly defined ratios of Ca 2+ , 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 the series cell structures, maintaining normal permeability of external cell membranes, for fertilization of eggs of fish and other animals, activation of a number of enzymes. Ca 2+ ions transmit excitation to the muscle fiber, causing it to contract, 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 CaCO 3 (mollusk 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 small intestine. Assimilation of Ca worsens with a decrease in acidity in the intestine and depends on the ratio of Ca, P and fat in food. The optimal Ca / P ratio in cow's milk is about 1.3 (in potatoes 0.15, in beans 0.13, in meat 0.016). With an excess of P or oxalic acid in food, Ca absorption deteriorates. Bile acids accelerate its absorption. The optimal Ca/fat ratio in human food is 0.04-0.08 g of Ca per 1 g of 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).
Calcium is a chemical element of group II with atomic number 20 in the periodic system, denoted by the symbol Ca (lat. Calcium). Calcium is a soft, silvery-gray alkaline earth metal.
20 element of the periodic table 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 metallic calcium in 1808.
Calcium compounds - limestone, marble, gypsum (as well as lime - a product of burning limestone) have been used in construction for several millennia ago.
Calcium is one of the most abundant elements on earth. Calcium compounds are found in almost all animal and plant tissues. It accounts for 3.38% of the mass of the earth's crust (5th place in abundance after oxygen, silicon, aluminum and iron).
Finding calcium 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). Element content in sea water- 400 mg / l.
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%. Calcium nuclei contain the magic number of protons: Z = 20. Isotopes
40
20
Ca20 and
48
20
Ca28 are two of the five doubly magic number nuclei found in nature.
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%), undergoes double beta decay with a half-life of 1.6 1017 years.
In rocks and minerals
Most 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 0.5H2O and gypsum CaSO4 2H2O, 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).
The biological role of calcium
Calcium is a common macronutrient in plants, animals and humans. In humans and other vertebrates, most of it is in the skeleton and teeth. Calcium is found in bones in the form of hydroxyapatite. 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 coagulation processes, and also serve as one of the universal second messengers inside cells and regulate a variety of intracellular processes - muscle contraction, exocytosis, including the secretion of hormones and neurotransmitters. The concentration of calcium in the cytoplasm of human cells is about 10−4 mmol/l, in intercellular fluids about 2.5 mmol/l.
The need for calcium depends on age. For adults aged 19-50 years and children aged 4-8 inclusive, the daily requirement (RDA) is 1000 mg (contained in approximately 790 ml of milk with a fat content of 1%), and for children aged 9 to 18 years inclusive - 1300 mg per day (contained in approximately 1030 ml of milk with a fat content of 1%). AT adolescence the intake of sufficient calcium is very important due to the intensive growth of the skeleton. However, according to research in the US, only 11% of girls and 31% of boys aged 12-19 achieve their needs. In a balanced diet, most of the calcium (about 80%) enters the child's body with dairy products. The remaining calcium comes from cereals (including whole grain bread and buckwheat), legumes, oranges, greens, nuts. Dairy products based on milk fat (butter, cream, sour cream, cream-based ice cream) contain practically no calcium. The more milk fat in a dairy product, the less calcium it contains. Calcium absorption in the intestine occurs in two ways: transcellular (transcellular) and intercellular (paracellular). The first mechanism is mediated by the action of the active form of vitamin D (calcitriol) and its intestinal receptors. It plays a big role in low to moderate calcium intake. With a higher calcium content in the diet, intercellular absorption begins to play the main role, which is associated with a large calcium concentration gradient. Due to the transcellular mechanism, calcium is absorbed to a greater extent in the duodenum (due to the highest concentration of receptors in calcitriol there). Due to intercellular passive transfer, calcium absorption is most active in all three sections of the small intestine. Calcium absorption is paracellularly promoted by lactose (milk sugar).
Calcium absorption is hindered by some animal fats (including cow's milk and beef tallow, but not lard) and palm oil. The palmitic and stearic acids contained in such fats fatty acid are cleaved off during digestion in the intestine and in the free form firmly bind calcium, forming calcium palmitate and calcium stearate (insoluble soaps). In the form of this soap with a chair, both calcium and fat are lost. This mechanism is responsible for decreased calcium absorption, decreased bone mineralization, and reduced indirect indicators of bone strength in infants using infant formulas based on palm oil(palm olein). In these children, the formation of calcium soaps in the intestines is associated with hardening of the stool, a decrease in its frequency, as well as more frequent regurgitation and colic.
The concentration of calcium in the blood, due to its importance for a large number of vital important processes is precisely regulated, and with proper nutrition and sufficient intake of low-fat dairy products and vitamin D, deficiency does not occur. Prolonged deficiency of calcium and/or vitamin D in the diet leads to an increased risk of osteoporosis and causes rickets in infancy.
Excessive doses of calcium and vitamin D can cause hypercalcemia. The maximum safe dose for adults aged 19 to 50 inclusive is 2500 mg per day (about 340 g of Edam cheese).