Calcium oxide (CaO) - quicklime or burnt lime- a white fire-resistant substance formed by crystals. It crystallizes in a cubic face-centered crystal lattice. Melting point - 2627 ° C, boiling point - 2850 ° C.
It is called burnt lime because of the method of its production - the burning of calcium carbonate. Roasting is carried out in high shaft kilns. Limestone and fuel are laid in layers in the furnace, and then kindled from below. When heated, calcium carbonate decomposes to form calcium oxide:
Since the concentrations of substances in solid phases are unchanged, the equilibrium constant of this equation can be expressed as follows: K=.
In this case, the gas concentration can be expressed using its partial pressure, that is, the equilibrium in the system is established at a certain pressure of carbon dioxide.
Substance dissociation pressure is the equilibrium partial pressure of a gas resulting from the dissociation of a substance.
To provoke the formation of a new portion of calcium, it is necessary to increase the temperature or remove part of the resulting CO2, and the partial pressure will decrease. By maintaining a constant lower partial pressure than the dissociation pressure, a continuous calcium production process can be achieved. To do this, when burning lime in kilns, make good ventilation.
Receipt:
1) in the interaction of simple substances: 2Ca + O2 = 2CaO;
2) during thermal decomposition of hydroxide and salts: 2Ca(NO3)2 = 2CaO + 4NO2? +O2?.
Chemical properties:
1) interacts with water: CaO + H2O = Ca(OH)2;
2) reacts with non-metal oxides: CaO + SO2 = CaSO3;
3) dissolves in acids, forming salts: CaO + 2HCl = CaCl2 + H2O.
Calcium hydroxide (Ca (OH) 2 - slaked lime, fluff)- a white crystalline substance, crystallizes in a hexagonal crystal lattice. It is a strong base, poorly soluble in water.
lime water- a saturated solution of calcium hydroxide, having an alkaline reaction. It becomes cloudy in air as a result of the absorption of carbon dioxide, forming calcium carbonate.
Receipt:
1) is formed when calcium and calcium oxide are dissolved in the input: CaO + H2O \u003d Ca (OH) 2 + 16 kcal;
2) in the interaction of calcium salts with alkalis: Ca(NO3)2 + 2NaOH = Ca(OH)2 + 2NaNO3.
Chemical properties:
1) when heated to 580 ° C, it decomposes: Ca (OH) 2 \u003d CaO + H2O;
2) reacts with acids: Ca(OH)2 + 2HCl = CaCl2 + 2H2O.
58. Water hardness and ways to eliminate it
Since calcium is widely distributed in nature, its salts are found in large quantities in natural waters. Water containing magnesium and calcium salts is called hard water. If salts are present in water in small quantities or absent, then water is called soft. In hard water, soap does not foam well, since calcium and magnesium salts form insoluble compounds with it. It doesn't digest food well. When boiling, scale forms on the walls of steam boilers, which poorly conducts heat, causes an increase in fuel consumption and wear of the boiler walls. Hard water cannot be used in a number of technological processes (dyeing). Scale formation: Ca + 2HCO3 \u003d H2O + CO2 + CaCO3?.
The factors listed above indicate the need to remove calcium and magnesium salts from the water. The process of removing these salts is called water softening, is one of the phases of water treatment (water treatment).
Water treatment– water treatment used for various household and technological processes.
Water hardness is divided into:
1) carbonate hardness (temporary), which is caused by the presence of calcium and magnesium bicarbonates and is eliminated by boiling;
2) non-carbonate hardness (constant), which is caused by the presence of sulfites and chlorides of calcium and magnesium in water, which are not removed during boiling, therefore it is called constant hardness.
The formula is correct: Total hardness = Carbonate hardness + Non-carbonate hardness.
General hardness is eliminated by adding chemicals or using cation exchangers. To completely eliminate hardness, water is sometimes distilled.
When applying the chemical method, soluble calcium and magnesium salts are converted into insoluble carbonates:
A more modern process for removing water hardness - using cation exchangers.
Cation exchangers- complex substances (natural compounds of silicon and aluminum, high-molecular organic compounds), the general formula of which is Na2R, where R- complex acid residue.
When water passes through a layer of cation exchanger, Na ions (cations) are exchanged for Ca and Mg ions: Ca + Na2R = 2Na + CaR.
Ca ions from the solution pass into the cation exchanger, and Na ions pass from the cation exchanger into the solution. To restore the used cation exchanger, it must be washed with a solution of common salt. In this case, the reverse process occurs: 2Na + 2Cl + CaR = Na2R + Ca + 2Cl.
Inorganic compound, calcium alkali. Its formula is Ca(OH) 2 . Since this substance has been known to mankind since ancient times, it has traditional names: slaked lime, lime water, milk of lime, fluff.
Fluff is a finely ground powder. Lime milk is an aqueous suspension of alkali, an opaque white liquid. Lime water is a clear aqueous solution of alkali, obtained after filtering lime milk.
Slaked lime was named after the method of production: quicklime (calcium oxide) is poured with water (quenched).
Properties
Fine white crystalline powder, odorless. Very poorly soluble in water, completely insoluble in alcohol, easily soluble in dilute nitric and hydrochloric acids. It is fireproof and even prevents fire. When heated, it decomposes into water and calcium oxide.
Strong alkali. Enters into neutralization reactions with acids to form salts - carbonates. When interacting with metals, explosive and combustible hydrogen is released. Reacts with carbon oxides (IV) and (II), with salts.
The reaction of obtaining calcium hydroxide by the “quenching” method occurs with a large release of heat, the water begins to boil, the caustic solution is sprayed in different directions - this must be taken into account when working.
Precautionary measures
Contact with the skin of dry powder particles or drops of calcium hydroxide solution causes irritation, itching, chemical burns, ulcers, and severe pain. Eye damage can cause vision loss. Ingestion of the substance causes a burn of the mucous throat, vomiting, bloody diarrhea, a sharp decrease in pressure, damage to internal organs. Inhalation of dust particles can lead to swelling of the throat that makes it difficult to breathe.
Before calling an ambulance:
- in case of poisoning, give the victim to drink milk or water;
- if the chemical gets into the eyes or on the skin, then the damaged areas should be washed with plenty of water for at least a quarter of an hour;
- if the reagent is accidentally inhaled, then the victim must be taken out of the room and provided with fresh air.
Work with calcium hydroxide should be in well-ventilated areas using protective equipment: rubber gloves, goggles and respirators. Chemical experiments should be carried out in a fume hood.
Application
In the construction industry, a chemical reagent is added to binding solutions, plaster, whitewash, gypsum mortars; on its basis, silicate brick and concrete are made; with its help prepare the soil before laying road surfaces. Whitewashing wooden parts of structures and fences gives them fire-resistant properties and protects them from decay.
- For neutralization of acid gases in metallurgy.
- To obtain solid oils and oil additives - in the oil refining industry.
- In the chemical industry - for the production of sodium and potassium alkalis, bleach ("bleach"), calcium stearate, organic acids.
- In analytical chemistry, lime water serves as an indicator of carbon dioxide (absorbing it, it becomes cloudy).
- With the help of calcium hydroxide, sewage and industrial waters are purified; neutralize the acids of the water entering the water supply systems in order to reduce its corrosive effect; remove carbonates from water (soften water).
- Ca(OH) 2 is used to remove hair from skins in the leather business. 
- Food additive E526 in the food industry: acidity and viscosity regulator, hardener, preservative. Used in the manufacture of juices and drinks, confectionery and flour products, marinades, salt, baby food. It is used in sugar production.
- In dentistry, milk of lime is used to disinfect root canals.
- For the treatment of acid burns - in medicine.
- In agriculture: means for regulating soil pH; as a natural insecticide against ticks, fleas, beetles; for the preparation of the popular fungicide "Bordeaux liquid"; for whitewashing tree trunks from pests and sunburn; as an antimicrobial and antifungal drug for storing vegetables in warehouses; as a mineral fertilizer.
- Calcium hydroxide reduces the electrical resistance of the soil, so it is treated with soil when installing grounding.
- Chemical reagent is used in the production of ebonite, brake linings, hair removal creams.
You can buy slaked lime at a good price, retail and wholesale, with delivery or pickup at the PrimeChemicalsGroup chemical store.
Natural calcium compounds (chalk, marble, limestone, gypsum) and their simplest processing products (lime) have been known to people since ancient times. In 1808, the English chemist Humphry Davy electrolyzed wet slaked lime (calcium hydroxide) with a mercury cathode and obtained calcium amalgam (calcium-mercury alloy). From this alloy, having driven away mercury, Davy obtained pure calcium.
He also proposed the name of a new chemical element, from the Latin "calx" denoting the name of limestone, chalk and other soft stones.
Being in nature and getting:
Calcium is the fifth most abundant element in the earth's crust (more than 3%), forms many rocks, many of which are based on calcium carbonate. Some of these rocks are of organic origin (shell rock), showing the important role of calcium in wildlife. Natural calcium is a mixture of 6 isotopes with mass numbers from 40 to 48, with 40 Ca accounting for 97% of the total. Other calcium isotopes have also been obtained by nuclear reactions, for example, radioactive 45 Ca.
To obtain a simple substance of calcium, electrolysis of melts of its salts or aluminothermy is used:
4CaO + 2Al \u003d Ca (AlO 2) 2 + 3Ca
Physical properties:
A silver-gray metal with a face-centered cubic lattice, much harder than the alkali metals. Melting point 842°C, boiling point 1484°C, density 1.55 g/cm 3 . At high pressures and temperatures, about 20 K passes into the state of a superconductor.
Chemical properties:
Calcium is not as active as the alkali metals, yet it must be stored under a layer of mineral oil or in tightly sealed metal drums. Already at ordinary temperature, it reacts with oxygen and nitrogen in the air, as well as with water vapor. When heated, it burns in air with a red-orange flame, forming oxide with an admixture of nitrides. Like magnesium, calcium continues to burn in an atmosphere of carbon dioxide. When heated, it reacts with other non-metals, forming compounds that are not always obvious in composition, for example:
Ca + 6B = CaB 6 or Ca + P => Ca 3 P 2 (also CaP or CaP 5)
In all its compounds, calcium has an oxidation state of +2.
The most important connections:
Calcium oxide CaO- ("quicklime") a white substance, an alkaline oxide, reacts vigorously with water ("extinguished") turning into hydroxide. Obtained by thermal decomposition of calcium carbonate.
Calcium hydroxide Ca(OH) 2- ("slaked lime") white powder, slightly soluble in water (0.16g/100g), strong alkali. A solution ("lime water") is used to detect carbon dioxide.
Calcium carbonate CaCO 3- the basis of most natural calcium minerals (chalk, marble, limestone, shell rock, calcite, Icelandic spar). In its pure form, the substance is white or colorless. crystals, When heated (900-1000 C) decomposes, forming calcium oxide. Not p-rim, reacts with acids, is able to dissolve in water saturated with carbon dioxide, turning into bicarbonate: CaCO 3 + CO 2 + H 2 O \u003d Ca (HCO 3) 2. The reverse process leads to the formation of calcium carbonate deposits, in particular formations such as stalactites and stalagmites.
It occurs in nature also in the composition of dolomite CaCO 3 *MgCO 3
Calcium sulfate CaSO 4- a white substance, in nature CaSO 4 * 2H 2 O ("gypsum", "selenite"). The latter, when heated carefully (180 C), passes into CaSO 4 * 0.5H 2 O ("burnt gypsum", "alabaster") - a white powder, when mixed with water, again forming CaSO 4 * 2H 2 O in the form of a solid, strong enough material. Slightly soluble in water, in excess of sulfuric acid it can dissolve, forming hydrosulfate.
Calcium phosphate Ca 3 (PO 4) 2- ("phosphorite"), insoluble, under the influence of strong acids passes into more soluble calcium hydro- and dihydrogen phosphates. Feedstock for the production of phosphorus, phosphoric acid, phosphate fertilizers. Calcium phosphates are also part of apatites, natural compounds with the approximate formula Ca 5 3 Y, where Y = F, Cl, or OH, respectively, fluorine, chlorine, or hydroxyapatite. Along with phosphorite, apatites are part of the bone skeleton of many living organisms, incl. and a person.
Calcium fluoride CaF 2 - (natural:"fluorite", "fluorspar"), insoluble in white. Natural minerals have a variety of colors due to impurities. Glows in the dark when heated and when exposed to UV radiation. Increases the fluidity ("fusibility") of slags in the production of metals, which is the reason for its use as a flux.
Calcium chloride CaCl 2- colorless crist. in-in well r-rimoe in water. Forms hydrated CaCl 2 *6H 2 O. Anhydrous ("fused") calcium chloride is a good drying agent.
Calcium nitrate Ca(NO 3) 2- ("calcium nitrate") colorless. crist. in-in well r-rimoe in water. A component of pyrotechnic compositions that gives the flame a red-orange color.
Calcium carbide CaС 2- reacts with water, forming acetylene, for example: CaС 2 + H 2 O \u003d C 2 H 2 + Ca (OH) 2
Application:
Metallic calcium is used as a strong reducing agent in the production of some hard-to-recover metals ("calcium term"): chromium, rare earth elements, thorium, uranium, etc. In the metallurgy of copper, nickel, special steels and bronzes, calcium and its alloys are used to remove harmful impurities of sulfur, phosphorus, excess carbon.
Calcium is also used to bind small amounts of oxygen and nitrogen in the production of high vacuum and purification of inert gases.
Neutron-excess ions 48 Ca are used for the synthesis of new chemical elements, such as element No. 114, . Another isotope of calcium, 45 Ca, is used as a radioactive tracer in studies of the biological role of calcium and its migration in the environment.
The main field of application of numerous calcium compounds is the production of building materials (cement, building mixtures, drywall, etc.).
Calcium is one of the macronutrients in the composition of living organisms, forming compounds necessary for building both the internal skeleton of vertebrates and the external skeleton of many invertebrates, egg shells. Calcium ions are also involved in the regulation of intracellular processes, cause blood clotting. Lack of calcium in childhood leads to rickets, in the elderly - to osteoporosis. Dairy products, buckwheat, nuts serve as a source of calcium, and vitamin D contributes to its absorption. In case of calcium deficiency, various preparations are used: calcex, calcium chloride solution, calcium gluconate, etc.
The mass fraction of calcium in the human body is 1.4-1.7%, the daily requirement is 1-1.3 g (depending on age). Excess calcium intake can lead to hypercalcemia - the deposition of its compounds in the internal organs, the formation of blood clots in the blood vessels. Sources:
Calcium (element) // Wikipedia. URL: http://ru.wikipedia.org/wiki/Calcium (date of access: 3.01.2014).
Popular library of chemical elements: Calcium. // URL: http://n-t.ru/ri/ps/pb020.htm (3.01.2014).
Calcium- an element of the 4th period and the PA group of the Periodic System, serial number 20. The electronic formula of the atom is [ 18 Ar] 4s 2, oxidation states +2 and 0. Refers to alkaline earth metals. It has a low electronegativity (1.04), exhibits metallic (basic) properties. Forms (as a cation) numerous salts and binary compounds. Many calcium salts are sparingly soluble in water. In nature - sixth in terms of chemical abundance, the element (the third among metals) is in a bound form. A vital element for all organisms. The lack of calcium in the soil is replenished by the application of lime fertilizers (CaCO 3 , CaO, calcium cyanamide CaCN 2, etc.). Calcium, calcium cation and its compounds color the flame of a gas burner in a dark orange color ( qualitative detection).
Calcium Ca
Silver-white metal, soft, ductile. In humid air, it tarnishes and becomes covered with a film of CaO and Ca(OH) 2. Very reactive; ignites when heated in air, reacts with hydrogen, chlorine, sulfur and graphite:
Reduces other metals from their oxides (an industrially important method is calciumthermy):
Receipt calcium in industry:
Calcium is used to remove non-metal impurities from metal alloys, as a component of light and antifriction alloys, to isolate rare metals from their oxides.
Calcium oxide CaO
basic oxide. The technical name is quicklime. White, highly hygroscopic. Has an ionic structure Ca 2+ O 2- . Refractory, thermally stable, volatile on ignition. Absorbs moisture and carbon dioxide from the air. Reacts vigorously with water (high exo- effect), forms a strongly alkaline solution (hydroxide precipitation is possible), the process is called lime slaking. Reacts with acids, metal and non-metal oxides. It is used for the synthesis of other calcium compounds, in the production of Ca(OH) 2 , CaC 2 and mineral fertilizers, as a flux in metallurgy, a catalyst in organic synthesis, a component of binders in construction.
Equations of the most important reactions:
Receipt Cao in industry– limestone roasting (900-1200 °С):
CaCO3 = CaO + CO2
Calcium hydroxide Ca(OH) 2
basic hydroxide. The technical name is slaked lime. White, hygroscopic. It has an ionic structure Ca 2+ (OH -) 2. Decomposes on moderate heat. Absorbs moisture and carbon dioxide from the air. Slightly soluble in cold water (an alkaline solution is formed), even less so in boiling water. A clear solution (lime water) quickly becomes cloudy due to the precipitation of hydroxide (the suspension is called milk of lime). A qualitative reaction to the Ca 2+ ion is the passage of carbon dioxide through lime water with the appearance of a precipitate of CaCO 3 and its transition into solution. Reacts with acids and acid oxides, enters into ion exchange reactions. It is used in the production of glass, bleaching lime, lime mineral fertilizers, for causticizing soda and softening fresh water, as well as for the preparation of lime mortars - pasty mixtures (sand + slaked lime + water), serving as a binder for stone and brickwork, finishing ( plastering) walls and other construction purposes. The hardening ("seizure") of such solutions is due to the absorption of carbon dioxide from the air.
Calcium hydroxide, or as it is traditionally called slaked lime or fluff, is an inorganic compound with the chemical formula Ca(OH)2.
Obtaining calcium hydroxide on an industrial scale is possible by mixing calcium oxide with water, this process is called quenching.
In laboratory conditions, obtaining calcium hydroxide is possible by mixing an aqueous solution of calcium chloride and sodium hydroxide. In mineral form, calcium hydroxide is found in some volcanic, deep and metamorphic rocks. Calcium hydroxide is also obtained by burning coal.
In excess, calcium hydroxide is found in aggressive water, which is able to dissolve rocks.
Application of calcium hydroxide
Calcium hydroxide has been widely used in the production of building materials such as whitewash, plaster and gypsum mortars. It is used as an inexpensive substitute for alkali in the form of slurries (milk of lime) used in tanneries to remove hair from hides, as well as in sugar production and for whitewashing tree trunks.
Lime water is a saturated aqueous solution of white calcium hydroxide. The antacid properties of calcium hydroxide are used medicinally to treat acid burns.
A useful property of calcium hydroxide is its ability to act as a flocculant that purifies wastewater from suspended and colloidal particles. It is also used to raise the pH of water, since water naturally contains acids that can corrode plumbing pipes.
Calcium hydroxide is also widely used in industries such as:
- Road construction - to improve the quality of earthen soil;
- Metal production – calcium hydroxide is injected into the waste gas stream to neutralize acids such as fluorides and chlorides before being released to the atmosphere;
- In the oil refining industry - for the production of additives to oils;
- In the chemical industry - for the production of calcium stearate;
- In the petrochemical industry - for the production of solid oils of various types;
- Production of antifungal and antimicrobial preservatives - for storing vegetables in hangars.
Calcium hydroxide is used as an additive to seawater to reduce atmospheric CO 2 and mitigate the greenhouse effect.
Also, calcium hydroxide is used as a natural alternative to insecticides, effective in the fight against ticks, fleas, beetles and their faces.
In construction, calcium hydroxide is used to whitewash wooden fences and coat rafters to protect materials from decay and fire, as well as to prepare silicate concrete and lime mortar.
Calcium hydroxide is also involved in the manufacture of ebonite, bleach, tank mixes, depilatory creams and brake linings.
The property of calcium hydroxide to reduce soil resistivity is used in the construction of grounding centers for electrical engineering.
In dentistry, calcium hydroxide is used as a disinfectant for root canals.
In the food industry, calcium hydroxide is used in excess as a food additive E526, which is added during the production of:
- Sugar cane;
- Alcoholic and non-alcoholic drinks;
- power engineers;
- fruit juices;
- Baby food;
- pickled cucumbers;
- food salt;
- Confectionery and sweets;
- cocoa products;
- Corn cakes;
- Flour products and pastries.
In Spain, calcium hydroxide is used to make hominy, as it is believed that it contributes to better absorption of the dish.
Native American Indian tribes use calcium hydroxide as an ingredient in Yapu, a psychedelic tobacco made from the seeds of the Anadenantera leguminous tree.
In Afghanistan, calcium hydroxide is used in the production of Niswar tobacco, which is made from fresh tobacco leaves, indigo, cardamom, menthol, oil, calcium hydroxide, and wood ash. The people of Afghanistan also use calcium hydroxide as a paint for their adobe houses. The largest consumers of calcium hydroxide in the world are countries such as Afghanistan, Pakistan, India, Sweden and Norway.
Properties of calcium hydroxide
Calcium hydroxide - colorless crystals or odorless white powder, which, when heated to 580 ° C, decompose into calcium oxide and water.
The molar mass of calcium hydroxide is 74.093 g/mol, density 2.211 g/cm3, solubility in water 0.189 g/100 ml, acidity (pKa) 12.4, refractive index 1.574.
Calcium hydroxide is insoluble in alcohol.
The harm of calcium hydroxide
If calcium hydroxide comes into contact with the skin, severe irritation, itching, chemical burns and skin necrosis occur.
Accidental ingestion of calcium hydroxide by mouth causes severe sore throat, burning mouth, abdominal pain, vomiting, bloody stools, and a drop in blood pressure. The pH of the blood also rises, it becomes too alkaline, which can cause damage to the internal organs.
When calcium hydroxide powder is inhaled through the nose or mouth, the throat will swell, which can restrict or make breathing difficult. If calcium hydroxide particles enter the lungs, emergency medical attention is needed.
When calcium hydroxide gets into the eyes, loss of vision occurs, accompanied by severe pain.
Providing first aid for calcium hydroxide poisoning
If calcium hydroxide has been ingested, drink a glass of water or milk.
In case of contact with calcium hydroxide on the skin or eyes, thoroughly rinse the affected skin and eyes with plenty of water for at least 15 minutes.
If calcium hydroxide is inhaled, immediately move to fresh air and call an ambulance.
