DEFINITION

calcium hydroxide(slaked lime, portlandite) is a substance white color(Fig. 1), which, when heated, decomposes without melting.

It is poorly soluble in water (a dilute alkaline solution is formed).

Calcium hydroxide is a strong base, slightly soluble in water; 1 l of water dissolves at 20 o C only 1.56 g of Ca(OH) 2 . saturated solution calcium hydroxide is called lime water and has alkaline reaction. In air, lime water quickly becomes cloudy due to the absorption of carbon dioxide and the formation of insoluble calcium carbonate.

Rice. 1. Calcium hydroxide. Appearance.

The main characteristics of calcium hydroxide are shown in the table below:

Obtaining calcium hydroxide

If burnt lime (calcium oxide) is doused with water, the water is absorbed by porous pieces of lime and reacts with it with the release of a significant amount of heat. In this case, part of the water turns into steam, and pieces of lime crumble into a loose mass of calcium hydroxide:

CaO + H 2 O \u003d Ca (OH) 2 + 65 kJ.

Chemical properties of calcium hydroxide

Calcium hydroxide exhibits basic properties, i.e. reacts with non-metals (1, 2), acid oxides (3, 4), acids (5, 6) and salts (7):

2Ca(OH) 2 + 2Cl 2 = Ca(ClO) 2 + CaCl 2 + 2H 2 O (1);

3Ca(OH) 2 + 6H 2 O + 2P 4 = 3Ca(PH 2 O 2) 2 + 2PH 3 (2);

Ca(OH) 2 + CO 2 = CaCO 3 ↓ + H 2 O (3);

Ca(OH) 2 + SO 2 = CaSO 3 ↓ + H 2 O (4);

Ca(OH) 2 + 2HCl dilute = CaCl 2 + 2H 2 O (5);

Ca(OH) 2 + H 2 SO 4 (conc) = CaSO 4 ↓ + 2H 2 O (6);

Ca(OH) 2 + 2NaClO = Ca(ClO) 2 ↓ + 2NaOH (7).

When calcium hydroxide is heated to a temperature of 520 - 580 o C, it decomposes:

Ca (OH) 2 \u003d CaO + H 2 O.

Application of calcium hydroxide

Calcium hydroxide is used in the construction industry. Its mixture with sand and water is called lime mortar and serves to hold bricks together when laying walls. Calcium hydroxide is also used as a plaster. Its hardening occurs first due to the evaporation of water, and then as a result of the absorption of carbon dioxide from the air by slaked lime and the formation of calcium carbonate.

Examples of problem solving

EXAMPLE 1

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. Turns cloudy when exposed to air 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) when calcium salts interact 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 applied 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 table salt. In this case, the reverse process occurs: 2Na + 2Cl + CaR = Na2R + Ca + 2Cl.

The lesson is devoted to the study of substances that are of great practical importance in human life, namely in such an area of ​​​​his life as construction. The teacher will talk about the methods of obtaining, properties and application of calcium oxide and hydroxide.

Topic: Substances and their transformations

Lesson: Calcium oxide and hydroxide. Properties and application

Even in ancient times, people noticed that if you burn limestone, chalk or marble, you get a white powder with special properties. The main component of chalk, marble and limestone is a substance called calcium carbonate. His chemical formula- CaCO 3. When burning limestone, a reaction occurs, the equation of which is:

CaCO 3 \u003d CaO + CO 2

Rice. 1. Minerals based on calcium carbonate

Calcium oxide can also be obtained by direct combustion of calcium in an oxygen atmosphere:

2Ca + O 2 \u003d 2CaO

In this case, the reaction of the combination of calcium with oxygen proceeds with the formation of calcium oxide.

The properties of the resulting calcium oxide are still used in construction. Calcium oxide is the nomenclature name for CaO. In addition to the nomenclature, this substance has several historical names. As you already know, calcium oxide can be obtained by burning limestone, which is why one of its historical names is burnt lime.

If water is added to the resulting calcium oxide, the water will hiss as if it is hot. Therefore, burnt lime was called "boiling". When in contact with water, calcium oxide is quenched, as it were, giving off heat. Therefore, the ongoing process was called quenching, and calcium oxide was called quicklime.

The water vapor formed during quenching loosens the quicklime, as it were, it becomes overgrown with fluff. In this regard, the slaked lime obtained by interacting with water has also become known as fluff.

What happens when quicklime is slaked? It has been established that one molecule of calcium oxide interacts with one molecule of water and only one new substance is formed - slaked lime. This reaction belongs to the type of compound.

CaO + H 2 O \u003d Ca (OH) 2

It is customary to write the formula for slaked lime as follows: Ca (OH) 2. The nomenclature name for this substance is calcium hydroxide:

A mixture of slaked lime and water is called lime mortar, which is used in construction. Since calcium hydroxide is slightly soluble in water, the lime mortar contains a precipitate of calcium hydroxide and the solution itself (lime water).

The use of lime mortar in construction for a strong connection of stones is associated with its hardening in air.

Thus, the whole process of obtaining and using calcium oxide can be represented as a diagram (Fig. 2).

Rice. 2. Obtaining and using calcium oxide

When calcium carbonate is calcined, quicklime is formed - calcium oxide. When mixed with water, calcium oxide turns into slaked lime - calcium hydroxide. A mixture of calcium hydroxide and water, which is sparingly soluble in water, is called lime mortar. When standing in air, the lime mortar reacts with carbon dioxide and turns back into calcium carbonate.

The equation of the reaction corresponding to the process of solidification of lime mortar:

Ca (OH) 2 + CO 2 \u003d CaCO 3 + H 2 O

Lime mortar hardens because it forms insoluble matter- calcium carbonate.

1. Collection of tasks and exercises in chemistry: 8th grade: to textbook. P.A. Orzhekovsky and others. “Chemistry. Grade 8 / P.A. Orzhekovsky, N.A. Titov, F.F. Hegel. - M .: AST: Astrel, 2006. (p. 92-96)

2. Ushakova O.V. Chemistry workbook: 8th grade: to the textbook by P.A. Orzhekovsky and others. “Chemistry. Grade 8” / O.V. Ushakova, P.I. Bespalov, P.A. Orzhekovsky; under. ed. prof. P.A. Orzhekovsky - M.: AST: Astrel: Profizdat, 2006. (p. 84-86)

3. Chemistry. 8th grade. Proc. for general institutions / P.A. Orzhekovsky, L.M. Meshcheryakova, M.M. Shalashova. – M.: Astrel, 2013. (§27)

4. Chemistry: 8th grade: textbook. for general institutions / P.A. Orzhekovsky, L.M. Meshcheryakova, L.S. Pontak. M.: AST: Astrel, 2005. (§33)

5. Encyclopedia for children. Volume 17. Chemistry / Chapter. edited by V.A. Volodin, leading. scientific ed. I. Leenson. – M.: Avanta+, 2003.

Additional web resources

1. Oxide and calcium hydroxide ().

Homework

1) with. 84-86 №№ 1,2,8 from the Workbook in Chemistry: 8th grade: to the textbook by P.A. Orzhekovsky and others. “Chemistry. Grade 8” / O.V. Ushakova, P.I. Bespalov, P.A. Orzhekovsky; under. ed. prof. P.A. Orzhekovsky - M.: AST: Astrel: Profizdat, 2006.

2) p.155-156 No. 2, A1, A2 from the textbook P.A. Orzhekovsky, L.M. Meshcheryakova, M.M. Shalashova "Chemistry: 8th grade", 2013

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 divided powder. Lime milk is an aqueous suspension of alkali, an opaque white liquid. Lime water - transparent water solution alkali, obtained after filtering milk of lime.

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. It 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 into different sides- 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. Whitewash wooden parts 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.
- AT 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.

Slaked lime- chemical substance, strong base. It is a white powder, poorly soluble in water. Obtained by the interaction of calcium oxide (quicklime) with water (the process is called "lime slaking"): CaO + H2O → Ca(OH)2. This reaction is exothermic, with the release of 16 kcal (67 kJ) per mole. When whitewashing rooms. When whitewashing wooden fences and coating rafters - to protect against decay and fire. For the preparation of lime mortar. Lime has been used for building masonry since ancient times. The mixture is usually prepared in the following proportion: three to four parts of sand (by weight) are added to one part of a mixture of calcium hydroxide (slaked lime) with water. In this case, the mixture solidifies according to the reaction: Ca(OH)2 + CO2 → CaCO3↓ + H2O. This is an exothermic reaction, the release of energy is 27 kcal (113 kJ). Simultaneously, the formation of calcium silicate occurs: CaCO3 + SiO2 → CaSiO3 + CO2. As can be seen from the reaction, water is released during the reaction. This is a negative factor, since in rooms built with lime mortar, high humidity remains for a long time. In this regard, and also due to a number of other advantages over calcium hydroxide, cement has practically replaced it as a binder for mortars. For the preparation of silicate concrete. The composition of silicate concrete is the same as the composition of lime mortar, but it is prepared by a different method - a mixture of calcium oxide and quartz sand is treated not with water, but with superheated (174.5-197.4 ° C) water vapor in an autoclave at a pressure of 9-15 atmospheres. To eliminate carbonate hardness of water (water softening). The reaction proceeds according to the equation: Ca(HCO3)2 + Ca(OH)2 → 2CaCO3↓ + 2H2O.

calcium oxide(quicklime) - white crystalline substance, CaO compound. Quicklime and the product of its interaction with water - Ca (OH) 2 (slaked lime or "fluff") are widely used in the construction industry. In industry, calcium oxide is obtained by thermal decomposition of limestone (calcium carbonate): CaCO3 = CaO + CO2. Also, calcium oxide can be obtained by the interaction of simple substances: 2Ca + O2 = 2CaO or by thermal decomposition of calcium hydroxide and calcium salts of some oxygen-containing acids:

2Ca(NO3)2 = 2CaO + 4NO2 + O2. The main volumes are used in construction as lime cement - when mixed with water, calcium oxide turns into hydroxide, which further, absorbing carbon dioxide from the air, hardens strongly, turning into calcium carbonate. However, at present, they try not to use lime cement in the construction of residential buildings, since the resulting structures have the ability to absorb and accumulate dampness. It is categorically unacceptable to use lime cement when laying furnaces - due to thermal decomposition and the release of asphyxiating carbon dioxide into the air. It also finds some use as an affordable and inexpensive refractory material - fused calcium oxide has some resistance to water, which allows it to be used as a refractory where the use of more expensive materials is impractical. Small amounts of calcium oxide are also used in laboratory practice to dry substances that do not react with it. In the food industry, it is registered as a food additive E-529. Calcium oxide is one of the basic oxides. It dissolves in water with the release of energy, forming calcium hydroxide: CaO + H2O ↔ Ca(OH)2 + 63.7 kJ/mol. How the basic oxide reacts with acidic oxides and acids, forming salts: 1. CaO + SO2 = CaSO3 2. CaO + 2HCl = CaCl2 + H2O

Natural calcium compounds. 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). The content of the element in sea water is 400 mg/l. Isotopes. 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 naturally occurring calcium isotopes, five are stable. The sixth 48Ca isotope, the heaviest of the six and very rare (its isotopic abundance is only 0.187%), was recently discovered to undergo double beta decay with a half-life of 5.3×1019 years. in rocks and minerals. Most of the calcium is contained in the composition of silicates and aluminosilicates of various rocks (granites, gneisses, etc.), especially in feldspar - anorthite Ca. In the form of sedimentary rocks, calcium compounds are represented by chalk and limestone, consisting mainly of the mineral calcite (CaCO3). The crystalline form of calcite - marble - is found in nature much less frequently. 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 into earth's crust and accumulating in various geochemical systems, forms 385 minerals (fourth place 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 to form a soluble bicarbonate: CaCO3 + H2O + CO2 ↔ Ca (HCO3) 2 ↔ Ca2+ + 2HCO3− to the right depending on the concentration of carbon dioxide). in the biosphere. Calcium compounds are found in almost all animal and plant tissues. A significant amount of calcium is part of living organisms. In living tissues of humans and animals, 1.4-2% Ca (by mass fraction); in a human body weighing 70 kg, the calcium content is about 1.7 kg (mainly in the composition of the intercellular substance of bone tissue).

magnesium oxide- a chemical compound with the formula MgO, colorless crystals, insoluble in water, fire and explosion proof. Easily reacts with dilute acids and water to form salts and Mg(OH)2: MgO + 2HCl(dil.) → MgCl2 + H2O; MgO + H2O → Mg(OH)2. Obtained by roasting the minerals magnesite and dolomite. 2Mg + O2 = 2MgO. In industry, it is used for the production of refractories, cements, refining of petroleum products, as a filler in the production of rubber. Ultralight magnesium oxide is used as a very fine abrasive for cleaning surfaces, particularly in the electronics industry. In medicine, it is used for increased acidity of gastric juice, as it is caused by an excess content of of hydrochloric acid. Burnt magnesia is also taken in case of accidental ingestion of acids into the stomach. Registered in the food industry as food additive E530. It is an absolute reflector - a substance with a reflection coefficient equal to unity in a wide spectral band. It can be used as an available standard for white.

Magnesia cement- a type of inorganic binder based on magnesium oxide, mixed with chloride and / or magnesium sulfate. magnesium oxide. It can be obtained from magnesite MgCO3 or dolomite by calcination at certain temperatures, followed by grinding. Depending on the type of raw material used, it is called caustic magnesite or caustic dolomite. magnesium chloride. Most often used as a sealer. Magnesium sulfate. Less commonly used as a sealant than magnesium chloride. Allows you to achieve greater water resistance, but with some loss of strength of the material. Fast hardening, high achievable strength. High adhesion to wood.

Gypsum binders. Raw materials for the production of gypsum binders are sulfate rocks containing mainly the mineral gypsum dihydrate. During heat treatment, natural gypsum gradually loses part of the chemically bound water, and at a temperature of 110 to 180 ° C it becomes semi-aqueous gypsum. After fine grinding of this calcined product, a gypsum binder is obtained. During heat treatment of natural gypsum in hermetically sealed apparatus and, consequently, at elevated steam pressure, chemically bound water is released in a drop-liquid state with the formation of a-modification of semi-aqueous gypsum at a temperature of approximately 95 ... 100 ° C.<.P>Both modifications of hemihydrate gypsum differ from each other: the hemihydrate modification is characterized by a coarse-grained structure. Gypsum binders are conditionally divided into building, molding and high-strength gypsum. Building gypsum is a product of firing finely divided gypsum dihydrate. In some plants, after firing, gypsum is subjected to secondary grinding. It belongs to a fine-crystalline variety of a gypsum binder, which increases the water demand when mixing building gypsum with water to a standard dough consistency. In the hardened state, it has low strength - 2 ... 16 MPa. But the compressive strength decreases with wetting of the samples.

Hardness of water. Elimination methods. According to the value of total hardness, soft water (up to 2 mg-eq / l), medium hardness (2-10 mg-eq / l) and hard water (more than 10 mg-eq / l) are distinguished. Thermal softening. Based on boiling water, as a result, thermally unstable calcium and magnesium bicarbonates decompose with the formation of scale: Ca(HCO3)2 → CaCO3↓ + CO2 + H2O. Boiling removes only temporary (carbonate) hardness. Finds application in everyday life. Reactive softening. The method is based on adding soda ash Na2CO3 or slaked lime Ca(OH)2 to water. In this case, calcium and magnesium salts pass into insoluble compounds and, as a result, precipitate. For example, the addition of slaked lime leads to the conversion of calcium salts into insoluble carbonate: a(HCO3)2 + Ca(OH)2 → 2CaCO3↓ + 2H2O purpose: Ca(HCO3)2 + 2Na3PO4 → Ca3(PO4)2↓ + 6NaHCO3 3MgSO4 + 2Na3PO4 → Mg3(PO4)2↓ + 3Na2SO4 Calcium and magnesium orthophosphates are very poorly soluble in water, therefore they are easily separated by mechanical filtration. This method is justified at relatively high water consumption, since it is associated with the solution of a number of specific problems: sediment filtration, accurate dosage of the reagent. Cationization. The method is based on the use of ion-exchange granular loading (most often ion-exchange resins). Such loading, upon contact with water, absorbs cations of hardness salts (calcium and magnesium, iron and manganese). Instead, depending on the ionic form, giving sodium or hydrogen ions. These methods are respectively called Na-cationization and H-cationization. With a properly selected ion-exchange load, water hardness decreases with single-stage sodium cationization to 0.05-0.1 mg-eq / l, with two-stage - up to 0.01 mg-eq / l. In industry, with the help of ion-exchange filters, calcium and magnesium ions are replaced with sodium and potassium ions, obtaining soft water. Reverse osmosis. The method is based on the passage of water through semi-permeable membranes (usually polyamide). Together with hardness salts, most other salts are also removed. The cleaning efficiency can reach 99.9%. This method has found the greatest application in domestic preparation systems. drinking water. As a disadvantage of this method, it should be noted the need for preliminary preparation of water supplied to the reverse osmosis membrane. Electrodialysis. It is based on the removal of salts from water under the action of an electric field. Removal of ions of dissolved substances occurs due to special membranes. As well as when using reverse osmosis technology, other salts are removed, in addition to hardness ions. Water can be completely purified from hardness salts by distillation.

R-elements. Group 3A elements include boron, aluminum, gallium, indium, and thallium. At the outer level, their atoms contain 3 electrons (s2p1). In the unexcited state, there is 1 unpaired p-electron, in the excited state, there are 3 unpaired electrons. The elements of this group often form three bonds. typical degree+3 oxidation state, and only thallium exhibits +1 and +3 oxidation states. 1. The boron atom is dominated by non-metallic properties, since it has a small atomic radius and relatively high electronegativity. As the atomic radii increase, the metallic properties increase. Aluminum, gallium, indium, thallium are amphoteric metals. At

the last two elements are dominated by metallic properties. 2. Elements of group 3A form oxides and hydroxides with the general formula E2O3 and E(OH)3. B2O3- acid oxide, boron hydroxide - B (OH) 3 is known as boric acid (H3BO3), Al2O3, Ga2O3, In2O3, Tl2O3 - amphoteric oxides, Al (OH) 3, Ga (0H) 3, In (OH) 3, Tl (OH) 3 - amphoteric hydroxides. Tl2O is the basic oxide, TlOH is the basic hydroxide. 3. All oxides (except B2O3), hydroxides (except H3BO3) are poorly soluble in water. Salts of aluminum, gallium, indium, thallium are subject to hydrolysis. BOR. The main mineral is borax - Na2B4O7. Non-metal boron, typical oxidation states +3 and -3, is obtained by reduction of its oxide with magnesium: B2O3 + 3Mg = 2B + 3MgO, Non-metal boron, characteristic oxidation states +3 and -3. It dissolves in oxidizing acids, but does not form salts like Al, Ga, In, Tl, but turns into boric acid. 2B + 3H2SO4 conc. = 2H3BO3 + 3SO2 B + 3HNO3 conc. = H3BO3 + 3NO2. When heated, boron reacts with oxygen, halogens, sulfur, nitrogen,

forming, respectively, B2O3, BCl3, B2S3, BN, and with hydrogen - borohydrides B2H6 -

diborane, B4H10 - tetraborane. Boron oxide - B2O3 - acid oxide, dissolving in

water gives weak boric acid - H3BO3 . Boric acid is a white solid

substance, when heated, loses water, turning into tetraboric acid,

and then into boron oxide. Under the action of alkalis on boric acid,

salts of tetraboric acid. B2O3 + 3H2O = 2H3BO3; 4H3BO3 H2B4O7 + 5H2O 2B2O3 + H2O 4H3BO3 + 2NaOH = Na2B4O7 + 7H2O borax - fertilizer. Aluminum- silver-white metal, easily conducts electric current, forms alloys with other metals. The characteristic oxidation state is +3. A fairly active metal and enters into many reactions. However, in air it is covered with a strong oxide film (Al2O3), which is not removed during machining and heating, which makes aluminum products resistant to external influences. The presence of an oxide film gives refractoriness to aluminum (20500C), while aluminum, devoid of a protective film, melts at 660oC. Chemical properties of aluminum 1. Interaction with oxygen. The protective film prevents oxidation in air. But with fine grinding and removal of the oxide film (by immersion in hot alkali), aluminum burns with a dazzling brilliance, with the formation of aluminum oxide, and in the presence of water - aluminum hydroxide. 4Al + 3O2 = 2Al2O3 4Al + 3O2 + 6H2O = 4Al(OH)3. 2. The element actively reacts with non-metals, burning in an atmosphere of fluorine and chlorine, combining with bromine, iodine, sulfur, nitrogen, phosphorus, carbon when heated. It does not directly interact with hydrogen and hydrides of the (AlH3)n type are obtained indirectly. 2Al + 3Cl2 = 2AlCl3; Nitrides, phosphides, sulfides, carbides are hydrolytically unstable: 2AlN + 3H2O = Al(OH)3 + NH3. When heated, aluminum forms aluminum oxide with water, and without heating, aluminum hydroxide. 2Al + 3H2O = Al2O3 + 3H2. Due to its high affinity for oxygen, aluminum takes away oxygen from metal oxides. This reaction proceeds with the release huge amount heat. Powdered aluminum is used to obtain and weld metals, and a mixture of aluminum powder and Fe3O4 is called thermite. 3Fe3O4 + 8Al = 9Fe + 4Al2O3 (3500oC). 5. Aluminum displaces less active metals from salt solutions. Al + 3CuCl2 = 3Cu + 2AlCl3. 6. Aluminum dissolves in non-oxidizing acids with the release of hydrogen. 2Al + 3H2SO4 dil. = Al2(SO4)3 + 3H2. Aluminum is passivated with concentrated H2SO4 and HNO3, so these acids can be stored in an aluminum container, but react with dilute nitric acid. Al + 4HNO3 dil. = Al(NO3)3 + NO + 2H2O.8. Aluminum dissolves in alkalis with the release of hydrogen. 2Al + 2KOH + 6H2O = 2K + 3H2. 9. Aluminum dissolves in solutions of oxidizing agents and alloys with oxidizing agents: 10Al + 6KMnO4 + 24H2SO4 = 5Al2(SO4)3 + 3K2SO4 + 6MnSO4 + 24H2O. Getting aluminum. The main method is the electrolysis of alumina melt. Electrolysis cathode: Al + 3 + 3e \u003d Al0 2Al2O3 4Al + 3O2 anode: 2O-2 - 4e \u003d O20. Aluminium oxide-white refractory substance. Natural varieties - corundum, ruby, sapphire. Amorphous alumina is used as an adsorbent. It is obtained by burning aluminum or calcining aluminum hydroxide: 4Al + 3O2 = 2Al2O3 2Al(OH)3 = Al2O3 + H2O. Does not dissolve in water. amphoteric oxide. Reacts with acids and acid salts and alkalis. Al2O3+ 6HCl = 2AlCl3+ 3H2O. aluminum hydroxide-exists in crystalline and amorphous form, both forms are insoluble in water. It is obtained by the action of alkalis on aluminum salts or by their hydrolysis. With an excess of alkali, the resulting aluminum hydroxide forms a complex salt. Al2(SO4)3 + 6NH4OH = 2Al(OH)3 + 3(NH4)2SO4. When heated, aluminum hydroxide gradually loses water, turning into an oxide. It has amphoteric properties: Al(OH)3 = AlO(OH) + H2O 2AlO(OH) = Al2O3 + H2O.

Kaolinite (white clay) is a clay mineral from the group of hydrous aluminum silicates. Chemical composition of Al4(OH)8; contains 39.5% Al2O3, 46.5% SiO2 and 14% H2O. It forms earthy masses, in which, at high magnifications, small hexagonal crystals are found under an electron microscope. It crystallizes in the monoclinic syngony. The crystalline structure of kaolinite is based on endless sheets of Si-O4 tetrahedra, which have three common oxygens and are bound in pairs through free vertices by aluminum and hydroxide. These sheets are interconnected by weak bonds, which causes a very perfect cleavage of kaolinite and the possibility of different superimposition of one layer on another, which, in turn, leads to some change in the symmetry of the entire crystalline structure. The layered structure of kaolinite gives minerals based on it (clays and kaolins) the property of plasticity. Hardness on a mineralogical scale 1; density 2540-2600 kg/m³; greasy to the touch. When heated to 500-600 °C, kaolinite loses water, and at 1000-1200 °C it decomposes with heat release, giving first sillimanite, and then mullite; This reaction is the basis of ceramic production. Montmorillonite- a clay mineral belonging to a subclass of layered silicates. Feldspars- a group of widespread, in particular - rock-forming minerals from the class of silicates. Most feldspars are representatives of solid solutions of the ternary system of the isomorphic series K - Na - Ca, the final members of which, respectively, are orthoclase (Or), albite (Ab), anorthite (An). There are two isomorphic series: albite (Ab) - orthoclase (Or) and albite (Ab) - anorthite (An). Minerals of the first of them can contain no more than 10% An, and the second - no more than 10% Or. Only in sodium feldspars close to Ab does the solubility of Or and An increase. Members of the first series are called alkaline (K-Na feldspars), the second - plagioclases (Ca-Na feldspars). The continuity of the Ab-Or series manifests itself only at high temperatures; at low temperatures, miscibility breaks with the formation of perthites. Along with sanidine, which is high-temperature, low-temperature potassium feldspars are distinguished - microcline and orthoclase.

Aluminates- salts formed by the action of alkali on freshly precipitated aluminum hydroxide: Al (OH) 3 + NaOH \u003d Na (sodium tetrahydroxoaluminate) Al (OH) 3 + 3NaOH \u003d Na3 (sodium hexahydroxoaluminate) Aluminates are also obtained by dissolving metallic aluminum (or Al2O3) in alkalis: 2Al + 2NaOH + 6H2O \u003d 2Na + ZH2 Ion - - exists in aqueous solutions. Alkali metal aluminates are highly soluble in water; their aqueous solutions, due to hydrolysis, are stable only with an excess of alkali. When Al2O3 is fused with metal oxides, anhydrous aluminates are formed, which can be considered as derivatives of metaaluminum acid HAlO2. For example, calcium metaaluminate Ca(AlO2)2 can be obtained by alloying Al2O3 with CaO. In nature, there are magnesium aluminates, calcium MgAl2O4, CaAl2O4, the mineral chrysoberyl (beryllium aluminate BeAl2O4). Artificial aluminates with the addition of REE activators are phosphors with a long afterglow and with a large accumulation of activation energy. These compounds are formula and structural analogues of the natural mineral spinel - MgAl2O4. Efficient luminescence in aluminates is ensured by the introduction into their crystal lattice of activators in the form of rare earth elements, in particular divalent europium at a concentration of Eu+2 from 1.10-2 to 8 at.%. The manufacture and formulation of aluminate phosphors, as well as the manufacture of zinc sulfide phosphors, is of an industrial tonnage nature and is quite wide application in light marking and design activities. Sodium aluminate is an intermediate product in the production of Al2O3, it is used in the textile and paper industries, for water purification. Powdered sodium metaaluminate (NaAlO2) is also used as an additive in building concrete as a hardening accelerator: calcium aluminate is the main constituent of fast hardening alumina cement. Preparation: Al2O3 + Na2O =t= 2NaAlO2

Elements of the IVA group in the oxidation state (IV) they form weak acids (H2CO3, H4SiO4, H2[Ce(OH)6], H2 and H2[Pb(OH)b]), exhibiting amphoteric properties. The elements of the IVA group in the free state are reducing agents. The IVA group includes carbon C, silicon Si, germanium Ce, tin Sn, and lead Pb. The IVA group includes p-elements carbon, silicon, germanium, tin and lead. Differing in the number of electronic levels, their unexcited atoms have four s2p2 electrons at the outer level, of which the p-electrons are unpaired. The IVA-group of elements, in addition to typical ones, includes elements of the germanium subgroup: Ge, Sn and Pb. Their valence electronic configuration (ns np2 in the unexcited state) makes it possible to exhibit the properties of both cation and anion formers. However, predominantly covalent bond in crystals of compounds, in fact, it is far from always realized. Within the IVA group, a nonmonotonic dependence of properties on the position of the element in the group is observed. Thus, the EER of germanium turns out to be greater than that of silicon, although the first ionization potential of germanium is lower. All elements of the IVA group form hydrogen compounds of the RH4 type, the stability of which in the series C, Si, Ge, Sn, Pb rapidly weakens. Within the IVA group, a nonmonotonic dependence of properties on the position of the element in the group is observed. Thus, the EER of germanium turns out to be greater than that of silicon, although the first ionization potential of germanium is smaller. This is explained by the existence of a germanium atom, unlike silicon, of a filled internal 3c (10-level, which serves as a screen for p-electrons. Within the IVA group, a nonmonotonic dependence of properties on the position of the element in the group is observed. than silicon, although the first ionization potential of germanium is less.This is due to the existence of a germanium atom, unlike silicon, of a filled internal ZcP0 level, which serves as a screen for p-electrons.If we compare the 3rd and 4th ionization potentials, which characterize the strength of the bond with a nucleus of s - electrons, we can conclude that the effect of penetration for s - electrons in germanium under the layer of Srf electrons predominates. Taking into account the four ionization potentials, it turns out that the bond strength of valence electrons with the nucleus is higher in the germanium atom. This and explains the higher value of the EEC of germanium compared to silicon.The radii of the elements also change nonmonotonically.When going from C to Si to a sharp increase in the atomic radius is observed, and then the radius changes insignificantly. The atomic radii of the elements of the IVA group naturally grow with increasing serial numbers (Table 24), ionization potentials and total electronegativity decrease. Nevertheless, carbon and silicon differ significantly in properties from the other elements of the group. Germanium already has metallic features, while tin and lead predominate over non-metallic ones. In addition, carbon and silicon differ from other elements of the IVA group in the abundance and variety of chemical compounds. Carbon in the majority oxygen compounds(with rare exceptions) exhibits an oxidation state of 4, silicon compounds with an oxidation state of 4 are also quite stable. But from germanium to lead, the strength of compounds in which they exhibit an oxidation state of 4 decreases. Which of the elements of the IVA group is the most common on Earth.

Carbon- chemical element of the 4th group of the main subgroup of the 2nd period of the periodic system of Mendeleev, serial number 6, atomic mass - 12.01115. The carbon content in the earth's crust is 0.1% by weight. Free carbon is found in nature in the form of diamond and graphite. The main mass of carbon in the form of natural carbonates (limestones and dolomites), fossil fuels - anthracite (94-97% C), brown coal (64-80% C), hard coal (76-95% C), oil shale (56- 78% C), oil (82-87% C), combustible natural gases (up to 99% methane), peat (53-56% C), as well as bitumen, etc. It is found in the atmosphere and hydrosphere in the form of carbon dioxide CO2, in the air 0.046% CO2 by mass, in the waters of rivers, seas and oceans ~ 60 times more. Carbon is present in plants and animals (~18%). Carbon enters the human body with food (normally about 300 g per day). The total carbon content in the human body reaches about 21% (15 kg per 70 kg of body weight). Carbon makes up 2/3 of muscle mass and 1/3 of bone mass. It is excreted from the body mainly with exhaled air (carbon dioxide) and urine (urea). The carbon cycle in nature includes a biological cycle, the release of CO2 into the atmosphere during the combustion of fossil fuels, from volcanic gases, hot mineral springs, from the surface layers of ocean waters, etc. The biological cycle consists in the fact that carbon in the form of CO2 is absorbed from the troposphere by plants. Then, from the biosphere, it returns to the geosphere again: with plants, carbon enters the body of animals and humans, and then, when animal and plant materials rot, it enters the soil and, in the form of CO2, enters the atmosphere. In the vapor state and in the form of compounds with nitrogen and hydrogen, carbon is found in the atmosphere of the Sun, planets, it is found in stone and iron meteorites. Most carbon compounds, and above all hydrocarbons, have a pronounced character of covalent compounds. The strength of single, double and triple bonds of C atoms among themselves, the ability to form stable chains and cycles from C atoms determine the existence of a huge number of carbon-containing compounds studied organic chemistry. In nature, the mineral shungite is found, which contains both solid carbon (≈25%) and significant amounts of silicon oxide (≈35%). Carbon reacts with many elements. Compounds with non-metals have their own names - methane, tetrafluoromethane. The combustion products of carbon in oxygen are CO and CO2 (carbon monoxide and carbon dioxide, respectively). The unstable carbon suboxide C3O2 and some other oxides are also known. Graphite and amorphous carbon begin to react with hydrogen at a temperature of 1200 °C, with fluorine at 900 °C. Carbon dioxide reacts with water, forming a weak carbonic acid - H2CO3, which forms salts - carbonates. Calcium and magnesium carbonates are the most widely distributed on Earth. Graphite forms inclusion compounds with halogens, alkali metals, and other substances. When an electric discharge is passed between carbon electrodes in a nitrogen atmosphere, cyan is formed. Hydrocyanic acid is obtained by reacting carbon with a mixture of H2 and N2 at high temperatures: When carbon reacts with sulfur, carbon disulfide CS2 is obtained, CS and C3S2 are also known. With most metals, aluminum and calcium, carbon forms carbides, for example: (aluminum carbide); (calcium carbide). The reaction of carbon with water vapor is important in industry.