Calcium - chemical element Group II with atomic number 20 periodic table, denoted by the symbol Ca (Latin Calcium). Calcium is a soft alkaline earth metal with a silvery-gray color.
Element 20 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 calcium metal in 1808.
Calcium compounds - limestone, marble, gypsum (as well as lime - a product of calcination of limestone) have been used in construction for several thousand years ago.
Calcium is one of the most common 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 most abundant after oxygen, silicon, aluminum and iron).
Finding calcium in nature
Due to its high chemical activity, calcium does not occur in free form in nature.
Calcium accounts for 3.38% of the mass of the earth's crust (5th most abundant after oxygen, silicon, aluminum and iron). Element content in sea water- 400 mg/l.
Isotopes
Calcium occurs in nature as a mixture of six isotopes: 40Ca, 42Ca, 43Ca, 44Ca, 46Ca and 48Ca, of which the most common, 40Ca, accounts for 96.97%. Calcium nuclei contain magic number protons: Z = 20. Isotopes
40
20
Ca20 and
48
20
Ca28 are two of the five nuclei that exist in nature with twice the magic number.
Of the six natural isotopes of calcium, five are stable. The sixth isotope 48Ca, 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 ah and minerals
Most of the calcium is contained in silicates and aluminosilicates of various rocks (granites, gneisses, etc.), especially in feldspar - Ca anorthite.
In the form of sedimentary rocks, calcium compounds are represented by chalk and limestones, consisting mainly of the mineral calcite (CaCO3). The crystalline form of calcite - marble - is much less common in nature.
Calcium minerals such as calcite CaCO3, anhydrite CaSO4, alabaster CaSO4 0.5H2O and gypsum CaSO4 2H2O, fluorite CaF2, apatite Ca5(PO4)3(F,Cl,OH), dolomite MgCO3 CaCO3 are quite widespread. The presence of calcium and magnesium salts in natural water its hardness is determined.
Calcium, vigorously migrating into earth's crust and accumulating in various geochemical systems, forms 385 minerals (fourth place in the number of minerals).
Biological role calcium
Calcium is a common macronutrient in the body of plants, animals and humans. In humans and other vertebrates, most of it is found 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.) are made from various forms of calcium carbonate (lime). Calcium ions are involved in blood clotting 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 calcium concentration in the cytoplasm of human cells is about 10−4 mmol/l, in intercellular fluids it is about 2.5 mmol/l.
Calcium requirements depend on age. For adults aged 19-50 years and children 4-8 years old inclusive daily requirement(RDA) is 1000 mg (contained in approximately 790 ml milk with 1% fat content), and for children aged 9 to 18 years inclusive - 1300 mg per day (contained in approximately 1030 ml milk with 1% fat content). During adolescence, consuming enough calcium is very important due to the rapid growth of the skeleton. However, according to research in the United States, only 11% of girls and 31% of boys aged 12-19 years 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 grains (including whole grain bread and buckwheat), legumes, oranges, greens, and nuts. In "dairy" products based on milk fat ( butter, cream, sour cream, cream-based ice cream) contain virtually no calcium. The more in dairy product milk fat, 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 a major role, which is associated with a large gradient of calcium concentration. Due to the transcellular mechanism, calcium is absorbed to a greater extent in the duodenum (due to the highest concentration of calcitriol receptors there). Due to intercellular passive transfer, calcium absorption is most active in all three sections of the small intestine. Paracellular absorption of calcium is promoted by lactose (milk sugar).
Calcium absorption is inhibited by some animal fats (including cow's milk fat and beef fat, but not lard) and palm oil. Contained in such fats are palmitic and stearic fatty acid are split off during digestion in the intestines and, in their free form, firmly bind calcium, forming calcium palmitate and calcium stearate (insoluble soaps). In the form of this soap, both calcium and fat are lost in the stool. This mechanism is responsible for decreased calcium absorption, decreased bone mineralization, and decreased indirect measures of bone strength in infants using palm oil (palm olein) based infant formulas. In such 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 precisely adjustable and proper nutrition and adequate consumption of low-fat dairy products and vitamin D deficiency does not occur. Long-term deficiency of calcium and/or vitamin D in the diet increases the 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 years inclusive is 2500 mg per day (about 340 g of Edam cheese).
Calcium was discovered in 1808 by Humphry Davy, who, by electrolysis of slaked lime and mercuric oxide, obtained calcium amalgam, as a result of the process of distilling mercury from which the metal remained, called calcium. In Latin lime sounds like calx, it was this name that was chosen by the English chemist for the discovered substance.
Calcium is an element of the main subgroup II of group IV of the periodic table of chemical elements D.I. Mendeleev, has an atomic number of 20 and an atomic mass of 40.08. The accepted designation is Ca (from the Latin - Calcium).
Calcium is a reactive soft alkali metal, silver- white. Due to interaction with oxygen and carbon dioxide, the surface of the metal becomes dull, so calcium requires a special storage regime - a tightly closed container, in which the metal is filled with a layer of liquid paraffin or kerosene.
Calcium is the most well-known of the microelements necessary for humans; the daily requirement for it ranges from 700 to 1500 mg for a healthy adult, but it increases during pregnancy and lactation; this must be taken into account and calcium must be obtained in the form of preparations.
Calcium has very high chemical activity, therefore it is not found in nature in its free (pure) form. However, it is the fifth most common in the earth's crust; it is found in the form of compounds in sedimentary (limestone, chalk) and rocks (granite); feldspar anorite contains a lot of calcium.
It is quite widespread in living organisms; its presence has been found in plants, animals and humans, where it is present mainly in teeth and bone tissue.
An obstacle to the normal absorption of calcium from food products is the consumption of carbohydrates in the form of sweets and alkalis, which neutralize the hydrochloric acid of the stomach, necessary for dissolving calcium. The process of calcium absorption is quite complex, so sometimes it is not enough to get it only from food; additional intake of the microelement is necessary.
To improve the absorption of calcium in the intestine, it is necessary, which tends to facilitate the process of calcium absorption. When taking calcium (in the form of supplements) while eating, absorption is blocked, but taking calcium supplements separately from food does not affect this process in any way.
Almost all of the body's calcium (1 to 1.5 kg) is found in bones and teeth. Calcium is involved in the processes of excitability of nervous tissue, muscle contractility, blood clotting processes, is part of the nucleus and membranes of cells, cellular and tissue fluids, has anti-allergic and anti-inflammatory effects, prevents acidosis, and activates a number of enzymes and hormones. Calcium is also involved in the regulation of cell membrane permeability and has the opposite effect.
Signs of calcium deficiency in the body are the following, at first glance, unrelated symptoms:
Causes of calcium deficiency may include unbalanced diets (especially fasting), low calcium content in food, smoking and addiction to coffee and caffeine-containing drinks, dysbacteriosis, kidney disease, thyroid disease, pregnancy, lactation and menopause.
Excess calcium, which can occur with excessive consumption of dairy products or uncontrolled use of drugs, is characterized by extreme thirst, nausea, vomiting, loss of appetite, weakness and increased urination.
Calcium has found application in the metallothermic production of uranium, in the form of natural compounds it is used as a raw material for the production of gypsum and cement, as a means of disinfection (well-known bleach).
CALCIUM (Latin Calcium), Ca, chemical element of group II of the short form (group 2 of the long form) of the periodic system; refers to alkaline earth metals; atomic number 20; atomic mass 40,078. There are 6 stable isotopes in nature: 40 Ca (96.941%), 42 Ca (0.647%), 43 Ca (0.135%), 44 Ca (2.086%), 46 Ca (0.004%), 48 Ca (0.187%); radioisotopes with mass numbers 34-54 were artificially obtained.
Historical reference. Many natural compounds calcium were known in ancient times and were widely used in construction (for example, gypsum, lime, marble). Calcium metal was first isolated by G. Davy in 1808 during the electrolysis of a mixture of CaO and HgO oxides and the subsequent decomposition of the resulting calcium amalgam. The name comes from the Latin calx (genitive calcis) - lime, soft stone.
Prevalence in nature. The calcium content in the earth's crust is 3.38% by weight. Due to high chemical activity, it is not found in a free state. The most common minerals are anorthite Ca, anhydrite CaSO 4, apatite Ca 5 (PO 4) 3 (F,Cl,OH), gypsum CaSO 4 2H 2 O, calcite and aragonite CaCO 3, perovskite CaTiO 3, fluorite CaF 2, scheelite CaWO 4 . Calcium minerals are found in sedimentary (such as limestone), igneous, and metamorphic rocks. Calcium compounds are found in living organisms: they are the main components of vertebrate bone tissue (hydroxyapatite, fluorapatite), coral skeletons, mollusk shells (calcium carbonate and phosphates), etc. The presence of Ca 2+ ions determines water hardness.
Properties. The configuration of the outer electron shell of the calcium atom is 4s 2; in compounds it exhibits an oxidation state of +2, rarely +1; electronegativity according to Pauling 1.00, atomic radius 180 pm, radius of the Ca 2+ ion 114 pm (coordination number 6). calcium is a silvery-white soft metal; up to 443 °C the modification with a cubic face-centered crystal lattice is stable, above 443 °C - with a cubic body-centered lattice; melting point 842°C, boiling point 1484°C, density 1550 kg/m 3 ; thermal conductivity 125.6 W/(m K).
Calcium is a metal of high chemical activity (stored in hermetically sealed containers or under a layer of mineral oil). Under normal conditions, it easily interacts with oxygen (calcium oxide CaO is formed), when heated - with hydrogen (CaH 2 hydride), halogens (calcium halides), boron (CaB 6 boride), carbon (calcium carbide CaC 2), silicon (Ca silicides 2 Si, CaSi, CaSi 2, Ca 3 Si 4), nitrogen (nitride Ca 3 N 2), phosphorus (phosphides Ca 3 P 2, CaP, CaP 5), chalcogens (chalcogenides of the composition CaX, where X is S, Se, Those). Calcium interacts with other metals (Li, Cu, Ag, Au, Mg, Zn, Al, Pb, Sn, etc.) to form intermetallic compounds. Calcium metal reacts with water to form calcium hydroxide Ca(OH) 2 and H 2 . Reacts vigorously with most acids, forming the corresponding salts (for example, calcium nitrate, calcium sulfate, calcium phosphates). Dissolves in liquid ammonia to form a dark blue solution with metallic conductivity. When ammonia evaporates from such a solution, ammonia is released. Gradually, calcium reacts with ammonia to form the amide Ca(NH 2) 2. Forms various complex compounds, the most important are complexes with oxygen-containing polydentate ligands, for example Ca complexonates.
Biological role. Calcium is a biogenic element. The daily human need for calcium is about 1 g. In living organisms, calcium ions are involved in the processes of muscle contraction and transmission of nerve impulses.
Receipt. Calcium metal is produced by electrolytic and metallothermic methods. The electrolytic method is based on the electrolysis of molten calcium chloride with a touch cathode or a liquid copper-calcium cathode. Calcium is distilled off from the resulting copper-calcium alloy at a temperature of 1000-1080 °C and a pressure of 13-20 kPa. The metallothermic method is based on the reduction of calcium from its oxide with aluminum or silicon at 1100-1200 °C. This produces calcium aluminate or silicate, as well as calcium gas, which is then condensed. World production of calcium compounds and materials containing calcium is about 1 billion tons/year (1998).
Application. Calcium is used as a reducing agent in the production of many metals (Rb, Cs, Zr, Hf, V, etc.). Calcium silicides, as well as alloys of calcium with sodium, zinc and other metals, are used as deoxidizers and desulfurizers of some alloys and oil, to purify argon from oxygen and nitrogen, and in electric vacuum devices as a gas absorber. CaCl 2 chloride is used as a desiccant in chemical synthesis, gypsum is used in medicine. Calcium silicates are the main components of cement.
Lit.: Rodyakin V.V. Calcium, its compounds and alloys. M., 1967; Spitsyn V.I., Martynenko L.I. Inorganic chemistry. M., 1994. Part 2; Inorganic chemistry / Edited by Yu. D. Tretyakov. M., 2004. T. 2.
L. N. Komissarova, M. A. Ryumin.
Introduction
Chemistry is the science of substances, their structure, properties and mutual transformations.
Chemistry is closely related to other natural sciences: physics, biology, geology. Many sections modern science arose at the intersection of these sciences: physical chemistry, geochemistry, biochemistry.
A new specialty in the system of chemical disciplines called “Classification and certification of goods based on chemical composition» founded in 1997 by Uzbek scientists I.R. Askarov and T.T. Riskiev. The results of scientific research, conducted by such Uzbek scientists as A.A. Ibragimov, G.Kh. Khamrakulov, M.A. Rakhimdzhanov, M.Yu. Isakov, K.M. Karimkulov, O.A. Tashpulatov, A.A. Namazov, B.Ya. Abduganiev, Sh.M. Mirkamilov, O. Kulimov, N.Kh. Tukhtaboev and others.
Calcium - being an alkaline earth metal, one of the most important elements on the ground.
Calcium is very important for humans, animals and plants.
Naturally, having such chemical properties, calcium cannot exist in nature in a free state. But calcium compounds - both natural and artificial - have acquired paramount importance.
Ka? licy- element of the main subgroup of the second group, the fourth period of the periodic table of chemical elements D.I. Mendeleev, with atomic number 20, therefore, the nucleus of the calcium atom has 20 positive charges formed by 20 protons; the number of neutrons in the nucleus is 40 - 20 = 20. 20 electrons that neutralize the charge of the nucleus are located at four energy levels. Relative atomic mass 40.078 (4). Indicated by the symbol Ca(lat. Calcium).
1. History of discovery
The name of the element comes from Lat. calx (in the genitive case calcis) - “lime”, “soft stone”. It was proposed by the English chemist Humphry Davy, who isolated calcium metal by the electrolytic method in 1808. Davy subjected to electrolysis a mixture of wet slaked lime with mercuric oxide Hg 2O on a platinum plate, which was the anode. The cathode was a platinum wire immersed in liquid mercury. As a result of electrolysis, calcium amalgam was obtained. Having distilled mercury from it, Davy obtained a metal called calcium.
Calcium compounds - limestone, marble, gypsum (as well as lime - a product of calcination of limestone) have been used in construction for several thousand years ago. Until the end of the 18th century, chemists considered lime to be a simple solid. In 1789, A. Lavoisier suggested that lime, magnesia, barite, alumina and silica are complex substances.
calcium chemical compound
2. Being in nature
Due to its high chemical activity, calcium does not occur in free form in nature.
Calcium accounts for 3.38% of the mass of the earth's crust (5th most abundant after oxygen, silicon, aluminum and iron). The content of the element in sea water is 400 mg/l.
Most of the calcium is contained in silicates and aluminosilicates of various rocks (granites, gneisses, etc.), especially in feldspar - Ca anorthite.
In the form of sedimentary rocks, calcium compounds are represented by chalk and limestones, consisting mainly of the mineral calcite (CaCO 3). The crystalline form of calcite - marble - is much less common in nature.
Quite widespread calcium minerals are:
calcite, limestone, marble, chalk CaCO3 ,
anhydrite CaSO4 ,
alabaster CaSO4 ·0.5H 2O
gypsum CaSO4 2H 2O,
fluorite CaF2 ,
phosphites and apatites Ca 3(P.O. 4)2(F, Cl, OH),
dolomite MgCO3 CaCO 3.
The presence of calcium and magnesium salts in natural water determines its hardness.
Calcium, vigorously migrating in the earth's crust and accumulating in various geochemical systems, forms 385 minerals (the fourth largest number of minerals).
Rice. 1. Calcium deposits in salty influxes
Calcium compounds are found in almost all animal and plant tissues. A significant amount of calcium is found in living organisms. Thus, hydroxyapatite Ca 3(P.O. 4)2OH, or in another entry, 3Ca 3(P.O. 4)2Ca(OH) 2- the basis of bone tissue of vertebrates, including humans; from calcium carbonate CaCO 3consist of the shells and shells of many invertebrates, eggshell etc. 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 intercellular substance of bone tissue).
. Receipt
In industry, calcium is obtained in two ways:
By heating the briquetted mixture of CaO and Al powder at 1170-1200°C in a vacuum of 0.01 - 0.02 mm. rt. Art.; distinguished by reaction:
CaO + 2Al = 3CaO Al2 O 3+ 3Ca
Calcium vapor condenses on a cold surface.
Electrolysis of CaCl melt 2(75-80%) and KCl with a liquid copper-calcium cathode, a Cu - Ca (65% Ca) alloy is prepared, from which calcium is distilled off at a temperature of 950 - 1000 ° C in a vacuum of 0.1 - 0.001 mm. rt. Art. or from (6 parts) CaCl 2and (1 part) CaF2.
A method has also been developed for producing calcium by thermal dissociation of calcium carbide CaC2 .
4. Physical properties
Fig2. Moderately hard, silvery-white metal
Name, symbol, number
Ka ?ltsium/Calcium (Ca), 20
Atomic mass ( molar mass)
40.078 a. e.m. (g/mol)
Electronic configuration
Atomic radius
Covalent radius
Ion radius
Electronegativity
1.00 (Pauling scale)
Electrode potential
Oxidation states
Ionization energy (first electron)
589.4 (6.11) kJ/mol (eV)
Density (at normal conditions)
1.55 g/cm³
Melting temperature
842 o WITH
Heat of Melting
9.20 kJ/mol
Heat of vaporization
153.6 kJ/mol
Molar heat capacity
25.9 J/(K mol)
Molar volume
29.9 cm³/ mole
Lattice structure
cubic face-centered
Lattice parameters
Debye temperature
Thermal conductivity
(300 K) (201) W/(m K)
Simple substance calcium- a soft, reactive alkaline earth metal with a silvery-white color.
The metal calcium exists in two allotropic modifications. Up to 443°C, ?-Ca with a cubic face-centered lattice (parameter a = 0.558 nm) is stable; higher stable is ?-Ca with a cubic body-centered lattice of the ?-Fe type (parameter a = 0.448 nm). Standard enthalpy of transition? ? ? is 0.93 kJ/mol.
With a gradual increase in pressure, it begins to exhibit the properties of a semiconductor, but does not become a semiconductor in the full sense of the word (it is no longer a metal either). With a further increase in pressure, it returns to the metallic state and begins to exhibit superconducting properties (the temperature of superconductivity is six times higher than that of mercury, and far exceeds all other elements in conductivity). The unique behavior of calcium is similar in many ways to strontium (that is, the parallels in the periodic table remain).
Calcium occurs in nature as a mixture of six isotopes: 40Ca, 42Ca, 43Ca, 44Ca, 46Ca and 48Ca, among which the most common - 40Ca - is 96.97%.
Of the six natural isotopes of calcium, five are stable. The sixth isotope, 48Ca, the heaviest of the six and very rare (its isotopic abundance is only 0.187%), was recently discovered to undergo double beta decay with a half-life of 5.3 1019 years.
Calcium is a typical alkaline earth metal. The chemical activity of calcium is high, but lower than that of heavier alkaline earth metals. It easily reacts with oxygen, carbon dioxide and moisture in the air, which is why the surface of calcium metal is usually dull gray, so in the laboratory calcium is usually stored, like other alkaline earth metals, in a tightly closed jar under a layer of kerosene or liquid paraffin.
On the outside energy level there are 2 electrons. In all compounds the oxidation state of calcium is +2.
In the series of standard potentials, calcium is located to the left of hydrogen.
Standard electrode potential of a Ca pair 2+/Ca 0?2.84 V, so calcium actively reacts with cold water(With hot water the reaction proceeds more vigorously), but without ignition:
Calcium reacts with active non-metals (oxygen, chlorine, bromine) under normal conditions:
Ca+Cl2 CaCl2
When heated in air or oxygen, calcium ignites and burns with a red flame with an orange tint.
Calcium reacts with less active non-metals (hydrogen, boron, carbon, silicon, nitrogen, phosphorus and others) when heated, for example:
In addition to calcium phosphide Ca3P2, calcium phosphides of the compositions CaP and CaP5 are also known;
In addition to calcium silicide Ca2Si, calcium silicides of the compositions CaSi, Ca3Si4 and CaSi2 are also known.
The occurrence of the above reactions is usually accompanied by the release of large quantity warmth.
Calcium restores less active metals from their oxides and halides
2Ca + TiO2 2CaO+Ti
Ca+TiCl2 2CaCl2 + Ti
Most of the calcium compounds with non-metals are easily decomposed by water, for example:
The Ca2+ ion is colorless. When soluble calcium salts are added to the flame, the flame turns brick-red.
. Applications of calcium metal
The main use of calcium metal is as a reducing agent in the production of metals, especially nickel, copper and stainless steel. Calcium and its hydride are also used to produce difficult-to-reduce metals such as chromium, thorium and uranium. Calcium-lead alloys are used in batteries and bearing alloys. Calcium granules are also used to remove traces of air from vacuum devices.
1. Metallothermy
Pure metallic calcium is widely used in metallothermy for the production of rare metals.
2. Alloying of alloys
Pure calcium is used to alloy lead used for the production of battery plates and maintenance-free starter lead-acid batteries with low self-discharge. Also, metallic calcium is used for the production of high-quality calcium babbits BKA.
3. Nuclear fusion
Isotope 48Ca is one of the effective and commonly used materials for the production of superheavy elements and the discovery of new elements of the periodic table. This is because calcium-48 is a doubly magic nucleus, so its stability allows it to be sufficiently neutron-rich for a light nucleus; the synthesis of superheavy nuclei requires an excess of neutrons.
. Calcium compounds
1. Calcium oxideCaO (quicklime, burnt lime, boiling water) is a white, refractory substance.
Obtained by burning limestone or chalk at high temperature(above 900 o WITH):
CaCO3 = CaO + CO2
Calcium oxide reacts with water to form slaked lime and release large amounts of heat:
CaO+H2 O = Ca(OH)2 +Q
2. Calcium hydroxideCa(OH) 2- a strong base, slightly soluble in water.
Ca(OH) 2used in various types:
slaked lime - a thin, loose powder, “fluff”, obtained by the action of water on quicklime CaO:
CaO+H2 O = Ca(OH)2
A dough-like mixture of slaked lime with cement, water and sand is used in construction. When carbon dioxide is absorbed from the air, this mixture hardens:
Ca(OH)2 + CO2 = CaCO3 +H2 O
lime milk is a suspension of slaked lime particles Ca(OH) 2in lime water.
It is used for whitewashing in construction, disinfection of tree trunks, in the sugar industry, for tanning leather, and for producing bleach.
lime water - saturated aqueous solution of Ca(OH)2
The solution becomes cloudy in air due to the absorption of carbon dioxide from the air.
But with prolonged passage of carbon dioxide, the solution becomes
transparent due to the formation of soluble calcium bicarbonate:
CaCO3 + CO2 +H2 O = Ca(HCO3 ) 2
In nature, this leads to the following processes. When cold rain or river water, saturated with carbon dioxide, penetrates underground and hits limestones, their dissolution is observed, and in the same places where water saturated with calcium bicarbonate comes to the surface of the earth and heats up sun rays.
This is how large masses of substances are transferred in nature. As a result, huge gaps can form underground, and beautiful stone “icicles” - stalactites and stalagmites - form in caves.
3. Bleaching powder- is a strong oxidizing agent, the main integral part which is the salt CaOCl 2, formed by the interaction of dry slaked lime with chlorine:
Ca(OH)2 +Cl2 = CaOCl2 +H2 O
Chloride of lime is a white powder with a pungent odor, which in moist air under the influence of carbon dioxide gradually decomposes, releasing hypochlorous acid:
2CaOCl2 + CO2 +H2 O = CaCO3 +CaCl2 + 2HClO
Hypochlorous acid decomposes in light:
2HClO = 2HCl + O2
When exposed to bleach of hydrochloric acid chlorine is released:
CaOCl2 + 2HCl = CaCl2 +Cl2 + H2 O
This is the basis for the bleaching and disinfecting properties of bleach.
4. GypsumCaSO 42H 2O is a natural calcium mineral.
When heated to 150-180°C, gypsum loses ¾ water of crystallization and turns into alabaster or burnt gypsum.
2CaSO4 *2H2 O2CaSO4 *H2 O+3H2 O
When mixed with water, alabaster quickly hardens and turns again
2CaSO4 *H2 O+3H2 O2CaSO4 *2H2 O
This property of gypsum is used for the manufacture of casting molds and casts of various objects, as well as as a binding material in construction for plaster and others. Gypsum is widely used in medicine to make plaster casts.
When gypsum is heated at temperatures above 180°C, anhydrous gypsum (calcium anhydride, or dead gypsum) is formed, which is no longer capable of adding water.
CaSO4 *2H2 OCaSO4 +H2 O
Calcium salts such as CaCl2 chloride, CaBr2 bromide, CaI2 iodide and Ca(NO3)2 nitrate are highly soluble in water. Insoluble fluoride in water<#"justify">1. Calcium hydride
By heating calcium in a hydrogen atmosphere<#"justify">2. Calcium oxide
Calcium oxide CaO, in the composition of a solid solution of oxides of other alkaline earth metals<#"justify">3. Optical and laser materials
Calcium fluoride<#"justify">4. Calcium carbide
Calcium carbide<#"justify">Calcium oxide, both in free form and as part of ceramic mixtures, is used in the production of refractory materials.
7. Construction Materials<#"justify">Calcium compounds (mainly carbonate or bicarbonate) are used to coat electrodes in electric arc welding. Calcium compounds are widely used to prepare fluxes for melting and welding metals.
9. Medicines<#"justify">Calcium compounds are widely used as an antihistamine.
·Calcium chloride<#"justify">. Biological role
Calcium is a common macronutrient<#"312" src="doc_zip16.jpg" />
Table 1. Calcium content in some foods
Food products Amount of product Calcium content in a given amount of product, mgMilk and ground products Cheese - Swiss, Graersky 50 g. 493 Cheese - hard, Cheddar, Colby, Edak, Gouda 50 g. 353 Milk - whole, 2%, 1% fat content 1 cup/250 ml 315 Cream 1 cup/250 ml 301 Cheese-Mozzarella, Adyghe, feta cheese 50 269 Yogurt - regular 1 cup/175 ml 292 Moloyuz - dry, in powder form 45 ml 159 Ice cream 1/2 cup 93 Cheese - rustic, creamy 2%, 1% fat (cottage cheese) 1/2 cup 87 Meat, fish, Domestic bird and other foods Sardines, with bones 8 small 153 Salmon, with bones, canned 1/2 can (net weight 13 g) 153 Almonds 1/2 cup 200 Sesame 1/2 cup 100 Beans - cooked (beans, blue beans, spotted beans) 1/2 cup 90 Soybeans - cooked 1 cup 175 Chicken - fried 90 g. 13 Beef - fried 90 g. 7 Bread and grains Round bran bun 1/35 g. 50 Bread - white and wheat 1 piece/30 g. 25 Fruits , and vegetables Broccoli - raw 1/2 cup 38 Oranges 1 medium size/180 g 52 Bananas 1 medium size/175 g 10 Salad 2 large sheets 8 Dried figs 10 270 Combination dishes Milk soup, cream of chicken, mushroom, tomato and broccoli soup 1 cup/250 ml 189 Boiled canned beans 1 cup/250 ml 169
Conclusion
Calcium is one of the most abundant elements on Earth.
Calcium was discovered by the English chemist Humphry Davy in 1808. He isolated calcium metal electrolytically from a mixture of slaked lime and mercuric oxide.
In 1789, A. Lavoisier proposed that lime, magnesia, barite, alumina and silica are complex substances.
There is a lot of it in nature. Not found in free form. Mountains and clay rocks are formed from calcium salts; it is found in sea and river water. It is part of such minerals as marble (chalk), alabaster, gypsum, fluorite, phosphites, apatites and dolomites.
Calcium is also part of living organisms - in all animal and plant tissues, and most importantly, calcium is part of human bone tissue.
Calcium is obtained in two ways:
1.By heating a mixture of quicklime and aluminum.
2.The second method, like all metals, is electrolysis, in in this case melt CaCl2 and KCl with a liquid copper-calcium cathode.
Calcium is a soft, reactive alkaline earth metal, silvery-white in color.
Calcium is a typical alkaline earth metal<#"justify">1.I. Askarov K. Gopirov “Fundamentals of Chemistry” State scientific publishing house “Uzbekistan milliy encyclopedia” Tashkent - 2013 p. 347
2.I.R. Asqarov Sh.H. Abdullaev O. Sh. Abdullaev “Kimyo - oily o`quv yurtlariga kiruvchilar uchun” “TAFAKKUR” nashriyoti Toshkent - 2013
3.N.L. Glinka " general chemistry» Moscow - 1988
.“Schoolchildren's Handbook” Bishkek - 2000 pp. 152-156
.G.P. Khomchenko “Chemistry - a universal collection” Moscow New Wave Publisher Umerenkov - 2008 pp. 301-306
.F.G. Felbdman G.E. Rudzitis “Chemistry 9” Moscow “Enlightenment” - 1990 pp. 127-132
."Universal reference book" Moscow - 2006 pp. 648-651
8.www.google.com //ru.wikipedia.org //wiki // Calcium.
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DEFINITION
Calcium- the twentieth element of the periodic table. Designation - Ca from the Latin "calcium". Located in the fourth period, group IIA. Refers to metals. The core charge is 20.
Calcium is one of the most common elements in nature. The earth's crust contains approximately 3% (wt.). It occurs in numerous deposits of limestone and chalk, as well as marble, which are natural varieties of calcium carbonate CaCO 3 . IN large quantities gypsum CaSO 4 × 2H 2 O, phosphorite Ca 3 (PO 4) 2 and, finally, various calcium-containing silicates are also found.
In the form of a simple substance, calcium is malleable, quite hard metal white (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 hot water quickly displaces hydrogen, forming hydroxide.
Rice. 1. Calcium. Appearance.
The relative molecular mass of a substance (M r) is a number showing how many times the mass of a given molecule is greater than 1/12 the mass of a carbon atom, and the relative atomic mass of an element (A r) is how many times the average mass of atoms of a chemical element is greater than 1/12 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 coincide. They are equal to 40.078.
It is known that in nature calcium can be found in the form of four stable isotopes 40 Ca, 42 Ca, 43 Ca, 44 Ca, 46 Ca and 48 Ca, with a clear predominance of the 40 Ca isotope (99.97%). Their mass numbers are 40, 42, 43, 44, 46 and 48, respectively. The nucleus of an 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 isotopes of calcium with mass numbers from 34 to 57, among which the most stable is 41 Ca with a half-life of 102 thousand years.
At the outer energy level of the calcium atom there are two electrons, which are valence:
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 .
As a result chemical interaction calcium donates its valence electrons, i.e. is their donor, and turns into a positively charged ion:
Ca 0 -2e → Ca 2+ .
In the free state, calcium exists in the form of monoatomic Ca molecules. Here are some properties characterizing the calcium atom and molecule:
Calcium serves as an alloying component in some lead alloys.
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 obtain a cloudy solution of a compound known as “milk of lime” - calcium hydroxide: Ca+ 2H 2 O→ Ca(OH) 2 + H 2. Passed through a solution of calcium hydroxide carbon dioxide 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. |
