Calcium hydroxide with salt if gas is formed. Calcium. What we learned

Calcium hydroxide is a chemical substance that has strong foundation. What are its features and Chemical properties Let's look at it in this article.

Characteristics of calcium hydroxide

Crystalline calcium hydroxide is a white powder that decomposes when heated, but is practically insoluble in water. The formula of calcium hydroxide is Ca(OH) 2. In ionic form, the equation for the formation of calcium hydroxide looks like this:

Rice. 1. Equation for the formation of calcium hydroxide.

Calcium hydroxide has other names: slaked lime, milk of lime, lime water

The molar mass of calcium hydroxide is 74.09 g/mol. This means that 74.09 g/mol of calcium hydroxide contains 6.02*10^23 atoms or molecules of this substance.

Calcium hydroxide is used for whitewashing in construction, disinfection of tree trunks, in the sugar industry, for tanning leather, and for producing bleach. A dough-like mixture of slaked lime with cement and sand is used in construction.

Rice. 2. Calcium hydroxide.

Chemical properties of calcium hydroxide

Calcium hydroxide, like all bases, reacts with acids:

Ca(OH) 2 (calcium hydroxide) + H 2 SO 4 (sulfuric acid) = CaSo 4 (salt - calcium sulfate) + 2H 2 O (water).

Calcium hydroxide is also capable of forming compounds with carbon dioxide. A solution of this substance in air becomes cloudy, since calcium hydroxide, like other strong bases, reacts with carbon dioxide dissolved in water:

Ca(OH) 2 +CO 2 (calcium hydroxide)=CaCO 3 (calcium carbonate)+H 2 O (water)

When heated to 400 degrees, calcium hydroxide reacts with carbon monoxide:

Ca(OH) 2 (calcium hydroxide) + CO (carbon monoxide) = CaCO 3 (calcium carbonate) + H 2 (hydrogen).

Calcium hydroxide can react with salts, resulting in the formation of a precipitate:

Ca(OH) 2 (calcium hydroxide) + Na 2 SO 3 (sodium sulfite) = CaSO 3 (calcium sulfite) + 2NaOH (sodium hydroxide).

At a temperature of 520-580 degrees, calcium hydroxide is susceptible to decomposition. As a result, calcium oxide and water are formed:

Rice. 3. Slaked lime.

Ca(OH) 2 (calcium hydroxide) = CaO (calcium oxide) + H 2 O (water).

Calcium hydroxide is produced by chemical reaction calcium oxide (quicklime) with water. This process is called "lime slaking". The equation for the lime slaking reaction is as follows:

CaO (calcium oxide) + H 2 O (water) = Ca (OH) 2 (calcium hydroxide).

What have we learned?

Calcium hydroxide is a strong base, slightly soluble in water. Like any chemical element, it has a number of properties - it is capable of reacting with carbon dioxide, salts, and also decomposes at high temperatures. Calcium hydroxide is used in construction and industry.

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Calcium hydroxide(Ca(OH) 2, slaked lime or “fluff”) is a chemical substance, a strong base. It is a white powder, poorly soluble in water.

Trivial names

Slaked lime- since it is obtained by “quenching” (that is, interaction with water) “quicklime” (calcium oxide).
Lime milk- a suspension (suspension) formed by mixing excess slaked lime with water. Looks like milk.
Lime water- a transparent solution of calcium hydroxide obtained by filtering lime milk.

Receipt

It is obtained by reacting calcium oxide (quicklime) with water (the process is called “slaking lime”):

$\mathsf(CaO + H_2O \rightarrow Ca(OH)_2)$

Properties

Appearance: white powder, slightly soluble in water:

Calcium hydroxide is a fairly strong base, which is why the aqueous solution is alkaline. Solubility decreases with increasing temperature.

Like all bases, it reacts with acids; as an alkali - is a component of the neutralization reaction (see neutralization reaction) with the formation of the corresponding calcium salts:

$\mathsf(Ca(OH)_2 + H_2SO_4 \rightarrow CaSO_4\downarrow + 2H_2O)$

for the same reason, a solution of calcium hydroxide becomes cloudy in air, since calcium hydroxide, like other strong bases, reacts with carbon dioxide dissolved in water:

$\mathsf(Ca(OH)_2 + CO_2 \rightarrow CaCO_3\downarrow + H_2O)$

If you continue to treat with carbon dioxide, the precipitate that has formed will dissolve, as an acidic salt is formed - calcium bicarbonate, and when the solution is heated, the bicarbonate is again destroyed and a precipitate of calcium carbonate precipitates:

$\mathsf(CaCO_3 + H_2O + CO_2 \rightleftarrows Ca(HCO_3)_2)$

Calcium hydroxide reacts with carbon monoxide at a temperature of about 400 °C:

$\mathsf(Ca(OH)_2 + CO \xrightarrow(400^oC) CaCO_3 + H_2)$

How a strong base reacts with salts, but only if the reaction results in a precipitate:

$\mathsf(Ca(OH)_2 + Na_2SO_3 \rightarrow CaSO_3\downarrow + 2NaOH)$

Application

When whitewashing premises.

For preparing 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) and water. During the reaction, water is released. 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 building mortars.
For the preparation of silicate concrete. The composition of silicate concrete is similar to the composition of lime mortar, but its hardening occurs several orders of magnitude faster, since the mixture of calcium oxide and quartz sand is treated not with water, but with superheated (174.5-197.4 °C) water steam in an autoclave at a pressure of 9 -15 atmospheres.
To eliminate carbonate hardness of water (water softening).
For the production of bleach.
For the production of lime fertilizers and neutralization of acidic soils.
Causticization of sodium and potassium carbonate.
Production of other calcium compounds, neutralization of acidic solutions (including industrial wastewater), production of organic acids, etc.
It is registered in the food industry as a food additive E526.
Lime water is a clear solution of calcium hydroxide. It is used to detect carbon dioxide. When interacting with him, she becomes cloudy.
Lime milk is a suspension (suspension) of calcium hydroxide in water, white and opaque. It is used for the production of sugar and the preparation of mixtures to combat plant diseases, whitewashing trunks.
In dentistry - for disinfection of root canals of teeth.
In electrical engineering - when constructing grounding centers in soils with high resistance, as an additive that reduces the resistivity of the soil.
Milk of lime is used as a base in the preparation of the classic fungicide, Bordeaux mixture.

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Notes

Sources and literature

Monastyrev A. Production of cement, lime. - M., 2007.
Stark Johan, Wicht Bernd. Cement and lime / trans. with him. - Kyiv, 2008.

Excerpt describing calcium hydroxide

- Your will! - Sonya cried out with despair in her voice, looking at Natasha’s dress, - your will, it’s long again!
Natasha moved away to look around in the dressing table. The dress was long.
“By God, madam, nothing is long,” said Mavrusha, crawling on the floor behind the young lady.
“Well, it’s long, so we’ll sweep it up, we’ll sweep it up in a minute,” said the determined Dunyasha, taking out a needle from the handkerchief on her chest and getting back to work on the floor.
At this time, the countess entered shyly, with quiet steps, in her current and velvet dress.
- Ooh! my beauty! - the count shouted, - better than all of you!... - He wanted to hug her, but she pulled away, blushing, so as not to crumple.
“Mom, more on the side of the current,” Natasha said. “I’ll cut it,” and she rushed forward, and the girls who were hemming, did not have time to rush after her, tore off a piece of smoke.
- My God! What is this? It's not my fault...
“I’ll sweep it all away, it won’t be visible,” Dunyasha said.
- Beauty, it’s mine! - said the nanny who came in from behind the door. - And Sonyushka, what a beauty!...
At a quarter past ten they finally got into the carriages and drove off. But we still had to stop by the Tauride Garden.
Peronskaya was already ready. Despite her old age and ugliness, she did exactly the same thing as the Rostovs, although not with such haste (this was a common thing for her), but her old, ugly body was also perfumed, washed, powdered, and the ears were also carefully washed , and even, and just like the Rostovs, the old maid enthusiastically admired her mistress’s outfit when she came out into the living room in a yellow dress with a code. Peronskaya praised the Rostovs' toilets.
The Rostovs praised her taste and dress, and, taking care of her hair and dresses, at eleven o'clock they settled into their carriages and drove off.

Since the morning of that day, Natasha had not had a minute of freedom, and not once had time to think about what lay ahead of her.
In the damp, cold air, in the cramped and incomplete darkness of the swaying carriage, for the first time she vividly imagined what awaited her there, at the ball, in the illuminated halls - music, flowers, dancing, the sovereign, all the brilliant youth of St. Petersburg. What awaited her was so beautiful that she did not even believe that it would happen: it was so incongruous with the impression of cold, cramped space and darkness of the carriage. She understood everything that awaited her only when, having walked along the red cloth of the entrance, she entered the entryway, took off her fur coat and walked next to Sonya in front of her mother between the flowers along the illuminated stairs. Only then did she remember how she had to behave at the ball and tried to adopt the majestic manner that she considered necessary for a girl at the ball. But fortunately for her, she felt that her eyes were running wild: she could not see anything clearly, her pulse beat a hundred times a minute, and the blood began to pound at her heart. She could not accept the manner that would make her funny, and she walked, frozen with excitement and trying with all her might to hide it. And this was the very manner that suited her most of all. In front and behind them, talking just as quietly and also in ball gowns, guests entered. The mirrors along the stairs reflected ladies in white, blue, pink dresses, with diamonds and pearls on their open arms and necks.
Natasha looked in the mirrors and in the reflection could not distinguish herself from others. Everything was mixed into one brilliant procession. Upon entering the first hall, the uniform roar of voices, footsteps, and greetings deafened Natasha; the light and shine blinded her even more. The owner and hostess, who had already been standing at the front door for half an hour and said the same words to those entering: “charme de vous voir,” [in admiration that I see you], also greeted the Rostovs and Peronskaya.
Two girls in white dresses, with identical roses in their black hair, sat down in the same way, but the hostess involuntarily fixed her gaze longer on thin Natasha. She looked at her and smiled especially at her, in addition to her masterful smile. Looking at her, the hostess remembered, perhaps, her golden, irrevocable girlhood time, and her first ball. The owner also followed Natasha with his eyes and asked the count who was his daughter?
- Charmante! [Charming!] - he said, kissing the tips of his fingers.
Guests stood in the hall, crowding at the front door, waiting for the sovereign. The Countess placed herself in the front row of this crowd. Natasha heard and felt that several voices asked about her and looked at her. She realized that those who paid attention to her liked her, and this observation calmed her somewhat.
“There are people just like us, and there are people worse than us,” she thought.
Peronskaya named the countess the most significant people who were at the ball.
“This is the Dutch envoy, you see, gray-haired,” said Peronskaya, pointing to an old man with silver gray curly, abundant hair, surrounded by ladies, whom he made laugh for some reason.
“And here she is, the queen of St. Petersburg, Countess Bezukhaya,” she said, pointing to Helen as she entered.
- How good! Will not yield to Marya Antonovna; Look how both young and old flock to her. She is both good and smart... They say the prince... is crazy about her. But these two, although not good, are even more surrounded.
She pointed to a lady passing through the hall with a very ugly daughter.
“This is a millionaire bride,” said Peronskaya. - And here are the grooms.
“This is Bezukhova’s brother, Anatol Kuragin,” she said, pointing to the handsome cavalry guard who walked past them, looking somewhere from the height of his raised head across the ladies. - How good! is not it? They say they will marry him to this rich woman. .And your sauce, Drubetskoy, is also very confusing. They say millions. “Why, it’s the French envoy himself,” she answered about Caulaincourt when the countess asked who it was. - Look like some kind of king. But still, the French are nice, very nice. No miles for society. And here she is! No, our Marya Antonovna is the best! And how simply dressed. Lovely! “And this fat one, with glasses, is a world-class pharmacist,” said Peronskaya, pointing to Bezukhov. “Put him next to your wife: he’s a fool!”

Natural calcium compounds (chalk, marble, limestone, gypsum) and the products of their simplest processing (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 (an alloy of calcium and mercury). From this alloy, having distilled off 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.

Finding in nature and obtaining:

Calcium is the fifth most abundant element in 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 living nature. Natural calcium is a mixture of 6 isotopes with mass numbers from 40 to 48, with 40 Ca accounting for 97% of the total. Nuclear reactions have also produced other isotopes of calcium, for example radioactive 45 Ca.
To obtain a simple calcium substance, electrolysis of molten calcium salts or aluminothermy is used:
4CaO + 2Al = Ca(AlO 2) 2 + 3Ca

Physical properties:

A silver-gray metal with a cubic face-centered lattice, much harder than the alkali metals. Melting point 842°C, boiling point 1484°C, density 1.55 g/cm3. At high pressures and temperatures around 20K goes into the superconductor state.

Chemical properties:

Calcium is not as active as alkali metals, but it must be stored under a layer of mineral oil or in tightly sealed metal drums. Already at normal temperatures 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 an 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, which reacts vigorously with water ("quenched") turning into a 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, Iceland 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 = Ca(HCO 3) 2. The reverse process leads to the appearance of calcium carbonate deposits, in particular formations such as stalactites and stalagmites
It is also found in nature as part 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 carefully heated (180 C), turns into CaSO 4 *0.5H 2 O (“burnt gypsum”, “alabaster”) - a white powder, which, when mixed with water, again forms CaSO 4 *2H 2 O in the form of a solid, quite durable material. Slightly soluble in water, it can dissolve in excess sulfuric acid, forming hydrogen sulfate.

Calcium phosphate Ca 3 (PO 4) 2- (“phosphorite”), insoluble, under the influence of strong acids it turns into more soluble calcium hydro- and dihydrogen phosphates. Feedstock for the production of phosphorus, phosphoric acid, phosphate fertilizers. Calcium phosphates are also included in 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 man.

Calcium fluoride CaF 2 - (natural:"fluorite", "fluorspar"), an insoluble substance of white color. Natural minerals have a variety of colors due to impurities. Glows in the dark when heated and under UV irradiation. It increases the fluidity (“fusibility”) of slags when producing metals, which explains its use as a flux.

Calcium chloride CaCl 2- colorless christ. It is well soluble in water. Forms crystalline hydrate CaCl 2 *6H 2 O. Anhydrous ("fused") calcium chloride is a good desiccant.

Calcium nitrate Ca(NO 3) 2- ("calcium nitrate") colorless. christ. It is well soluble in water. Component pyrotechnic compositions that give the flame a red-orange color.

Calcium carbide CaС 2- reacts with water, forming acetylene, for example: CaС 2 + H 2 O = С 2 H 2 + Ca(OH) 2

Application:

Metallic calcium is used as a strong reducing agent in the production of some difficult-to-reduce metals (“calciothermy”): 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 when obtaining high vacuum and purifying inert gases.
Neutron-excess 48 Ca ions are used for the synthesis of new chemical elements, for example element No. 114, . Another calcium isotope, 45Ca, is used as a radioactive tracer in research biological role calcium and its migration in the environment.

The main area of application for numerous calcium compounds is the production of building materials (cement, building mixtures, plasterboard, etc.).

Calcium is one of the macroelements in living organisms, forming compounds necessary for the construction of both the internal skeleton of vertebrates and the external skeleton of many invertebrates, the shell of eggs. Calcium ions also participate in the regulation of intracellular processes and determine blood clotting. Lack of calcium in childhood leads to rickets, in old age - to osteoporosis. The source of calcium is dairy products, buckwheat, nuts, and its absorption is facilitated by vitamin D. If there is a lack of calcium, various drugs 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). Excessive calcium intake can lead to hypercalcemia - deposition of its compounds in internal organs, and the formation of blood clots in blood vessels. Sources:
Calcium (element) // Wikipedia. URL: http://ru.wikipedia.org/wiki/Calcium (access date: 01/3/2014).
Popular library of chemical elements: Calcium. // URL: http://n-t.ru/ri/ps/pb020.htm (01/3/2014).

Structural formula

Molecular weight: 74.094

Calcium hydroxide, Ca(OH)2 slaked lime or “fluff” is a chemical substance, a strong base. It is a white powder, poorly soluble in water.

Trivial names

Slaked lime - as it is obtained by “quenching” (that is, reacting with water) “quicklime” (calcium oxide).
Lime milk is a slurry (suspension) formed by mixing excess slaked lime with water. Looks like milk.
Lime water is a clear solution of calcium hydroxide obtained by filtering lime milk.

Receipt

It is obtained by reacting calcium oxide (quicklime) with water (the process is called “slaked lime”). This reaction is exothermic, releasing 16 kcal (67 kJ) per mole.

Properties

Appearance: white powder, slightly soluble in water. Calcium hydroxide is a fairly strong base, which is why the aqueous solution is alkaline. Solubility decreases with increasing temperature. Like all bases, it reacts with acids; as an alkali - is a component of the neutralization reaction (see neutralization reaction) with the formation of the corresponding calcium salts. For the same reason, a solution of calcium hydroxide becomes cloudy in air, since calcium hydroxide, like other strong bases, reacts with carbon dioxide dissolved in water. If the treatment with carbon dioxide is continued, the precipitate that has formed will dissolve, as an acidic salt is formed - calcium bicarbonate, and when the solution is heated, the bicarbonate is again destroyed and a precipitate of calcium carbonate precipitates. Calcium hydroxide reacts with carbon monoxide at a temperature of about 400 °C. How a strong base reacts with salts, but only if the reaction results in a precipitate.

Application

When whitewashing premises.
For preparing 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) and water. During the reaction, water is released. 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 building mortars.
For the preparation of silicate concrete. The composition of silicate concrete is similar to the composition of lime mortar, but its hardening occurs several orders of magnitude faster, since the mixture of calcium oxide and quartz sand is treated not with water, but with superheated (174.5-197.4 °C) water steam in an autoclave at a pressure of 9 -15 atmospheres.
To eliminate carbonate hardness of water (water softening).
For the production of bleach.
For the production of lime fertilizers and neutralization of acidic soils.
Causticization of sodium and potassium carbonate.
Leather tanning
Production of other calcium compounds, neutralization of acidic solutions (including industrial wastewater), production of organic acids, etc.
It is registered in the food industry as a food additive E526.
Lime water is a clear solution of calcium hydroxide. It is used to detect carbon dioxide. When interacting with him, she becomes cloudy.
Lime milk is a suspension (suspension) of calcium hydroxide in water, white and opaque. It is used to produce sugar and prepare mixtures to combat plant diseases and whitewash trunks.
In dentistry - for disinfection of root canals of teeth.
In electrical engineering - when constructing grounding centers in soils with high resistance, as an additive that reduces the resistivity of the soil.
Lime milk is used as a base in the preparation of the classic fungicide - Bordeaux mixture.

Calcium oxide (CaO) – quicklime or burnt lime– a white, fire-resistant substance formed by crystals. Crystallizes in a face-centered cubic crystal lattice. Melting point – 2627 °C, boiling point – 2850 °C.

It is called burnt lime because of the method of its preparation - burning calcium carbonate. Firing is carried out in high shaft kilns. Layers of limestone and fuel are placed in the furnace and then lit 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, equilibrium in the system is established at a certain pressure of carbon dioxide.

Substance dissociation pressure– 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 partial pressure lower than the dissociation pressure, a continuous calcium production process can be achieved. To do this, when burning lime in kilns, good ventilation is provided.

Receipt:

1) during 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, which has an alkaline reaction. In air it becomes cloudy as a result of the absorption of carbon dioxide, forming calcium carbonate.

Receipt:

1) is formed by the dissolution of calcium and calcium oxide in the input: CaO + H2O = Ca(OH)2 + 16 kcal;

2) during 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 = 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 the water is called soft. In hard water, soap does not foam well, since calcium and magnesium salts form insoluble compounds with it. It does not cook 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 when carrying out a number of technological processes (dying). Scale formation: Ca + 2HCO3 = H2O + CO2 + CaCO3?.

The factors listed above indicate the need to remove calcium and magnesium salts from 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 calcium and magnesium sulfites and chlorides in water, which are not removed by boiling, which is why it is called constant hardness.

The correct formula is: 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 using the chemical method, soluble calcium and magnesium salts are converted into insoluble carbonates:

A more modern process for eliminating 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 acidic residue.

When water is passed through a layer of cation exchange resin, Na ions (cations) are exchanged for Ca and Mg ions: Ca + Na2R = 2Na + CaR.

Ca ions pass from the solution 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 table salt. In this case, the reverse process occurs: 2Na + 2Cl + CaR = Na2R + Ca + 2Cl.