Calcium- element of the 4th period and PA group Periodic table, serial number 20. Electronic formula atom [ 18 Ar]4s 2 , oxidation states +2 and 0. Refers to alkaline earth metals. It has low electronegativity (1.04) and exhibits metallic (basic) properties. Forms (as a cation) numerous salts and binary compounds. Many calcium salts are slightly soluble in water. In nature - sixth In terms of chemical abundance, the element (third among metals) is found in a bound form. Vital important element for all organisms. The lack of calcium in the soil is compensated by applying lime fertilizers (CaC0 3, CaO, calcium cyanamide CaCN 2, etc.). Calcium, calcium cation and its compounds color the flame of a gas burner dark orange ( qualitative detection).
Calcium Ca
Silvery-white metal, soft, ductile. In humid air it fades 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 (industrially important method — calciumthermia):
Receipt calcium in industry:
Calcium is used to remove non-metal impurities from metal alloys, as a component of light and anti-friction alloys, to isolate rare metals from their oxides.
Calcium oxide CaO
Basic oxide. Technical name: quicklime. White, very hygroscopic. It has an ionic structure Ca 2+ O 2- . Refractory, thermally stable, volatile when ignited. Absorbs moisture and carbon dioxide from the air. Reacts vigorously with water (with high exo- effect), forms a strong alkaline solution(hydroxide precipitate 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, and a component of binding materials in construction.
Equations of the most important reactions:
Receipt Sao in industry— limestone firing (900-1200 °C):
CaCO3 = CaO + CO2
Calcium hydroxide Ca(OH) 2
Basic hydroxide. Technical name is slaked lime. White, hygroscopic. It has an ionic structure: Ca 2+ (OH -) 2. Decomposes when heated moderately. Absorbs moisture and carbon dioxide from the air. Slightly soluble in cold water (an alkaline solution is formed), and even less soluble in boiling water. A clear solution (lime water) quickly becomes cloudy due to the precipitation of hydroxide precipitate (the suspension is called milk of lime). Qualitative reaction for the Ca 2+ ion - passing carbon dioxide through lime water with the appearance of a CaC0 3 precipitate 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 preparing lime mortars - dough-like mixtures (sand + slaked lime + water), serving as a binding material for stone and brickwork, finishing ( plastering) walls and other construction purposes. The hardening (“setting”) of such solutions is due to the absorption of carbon dioxide from the air.
Calcium hydroxide(Ca(OH) 2, slaked lime or “fluff”) - chemical substance, 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”):
Properties
Appearance: white powder, slightly soluble in water:
Calcium hydroxide is a fairly strong base, which is why aqueous solution has an alkaline reaction. 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 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:
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 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.
Links
- Krupsky A.K., Mendeleev D.I.// Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - St. Petersburg. , 1890-1907.
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 her 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 the cold, crampedness 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 saw nothing 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, both 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! isn't 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!”
The lesson is devoted to the study of substances that have a huge practical significance in a person’s life, namely in such an area of his life as construction. The teacher will talk about the methods of production, properties and uses 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. Its chemical formula is CaCO 3. When limestone is fired, a reaction occurs, the equation of which is:
CaCO 3 = CaO + CO 2
Rice. 1. Minerals based on calcium carbonate
Calcium oxide can also be obtained by directly burning calcium in an oxygen atmosphere:
2Ca + O 2 = 2CaO
In this case, a reaction occurs between calcium and oxygen to form calcium oxide.
The properties of the resulting calcium oxide are still used in construction. Calcium oxide is the nomenclature name for the compound 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 you add water to the resulting calcium oxide, the water will hiss as if it were hot. Therefore, burnt lime was called “kipelka”. When it comes into contact with water, calcium oxide seems to be extinguished, giving off heat. Therefore, the process taking place was called slaking, and calcium oxide was called quicklime.
The water vapor generated during slaking loosens the quicklime, and it seems to become covered with fluff. In this regard, the slaked lime obtained by interacting with water began to be called fluff.
What happens when slaking quicklime? 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 is related to the type of compound.
CaO + H 2 O = Ca (OH) 2
The formula of slaked lime is usually written 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, lime mortar contains a precipitate of calcium hydroxide and the solution itself (lime water).
The use of lime mortar in construction to firmly connect stones is associated with its hardening in air.
Thus, the entire process of obtaining and using calcium oxide can be represented in the form of a diagram (Fig. 2).
Rice. 2. Preparation and use of 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, which is slightly soluble in water, and water is called lime mortar. When exposed to air, the lime solution reacts with carbon dioxide and turns back into calcium carbonate.
The reaction equation corresponding to the hardening process of lime mortar:
Ca(OH) 2 + CO 2 = CaCO 3 + H 2 O
Hardening of lime mortar occurs because it forms insoluble substance– calcium carbonate.
1. Collection of problems and exercises in chemistry: 8th grade: for textbooks. P.A. Orzhekovsky and others. “Chemistry. 8th grade” / 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. 8th grade” / 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. Textbook for general education institutions / P.A. Orzhekovsky, L.M. Meshcheryakova, M.M. Shalashova. – M.: Astrel, 2013. (§27)
4. Chemistry: 8th grade: textbook. for general education institutions / P.A. Orzhekovsky, L.M. Meshcheryakova, L.S. Pontak. M.: AST: Astrel, 2005. (§33)
5. Encyclopedia for children. Volume 17. Chemistry / Chapter. ed.V.A. Volodin, Ved. scientific ed. I. Leenson. – M.: Avanta+, 2003.
Additional web resources
1. Calcium oxide and hydroxide ().
Homework
1) p. 84-86 No. 1,2,8 from Workbook in chemistry: 8th grade: to the textbook P.A. Orzhekovsky and others. “Chemistry. 8th grade” / O.V. Ushakova, P.I. Bespalov, P.A. Orzhekovsky; under. ed. prof. P.A. Orzhekovsky - M.: AST: Astrel: Profizdat, 2006.
2) pp. 155-156 No. 2, A1, A2 from the textbook P.A. Orzhekovsky, L.M. Meshcheryakova, M.M. Shalashova “Chemistry: 8th grade,” 2013
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 “slaking 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 hydroxide, or slaked lime as it is traditionally called, is a inorganic compound With chemical formula Ca(OH)2.
It is possible to produce calcium hydroxide on an industrial scale by mixing calcium oxide with water, a process called slaking.
In laboratory conditions, calcium hydroxide can be obtained by mixing an aqueous solution of calcium chloride and sodium hydroxide. In mineral form, calcium hydroxide is found in some volcanic, plutonic and metamorphic rocks. Calcium hydroxide is also produced by burning coal.
Calcium hydroxide is found in excess in aggressive water, which can dissolve rocks.
Applications of calcium hydroxide
Calcium hydroxide is widely used in the production of such building materials, like whitewash, plaster and gypsum mortars. It is used as an inexpensive substitute for alkali in the form of slurries (milk of lime) which are used in tanneries to remove hair from hides, as well as in sugar production and for whitewashing tree trunks.
Limewater is a saturated, white, aqueous solution of calcium hydroxide. The antacid properties of calcium hydroxide are used medically to treat acid burns.
A useful property of calcium hydroxide is its ability to act as a flocculant, cleaning waste water from weighted and colloidal particles. It is also used to increase the pH of water, since in its original form water 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;
- Metals production - calcium hydroxide is introduced into the exhaust gas stream to neutralize acids such as fluorides and chlorides before release to the atmosphere;
- In the oil refining industry - for the production of oil additives;
- IN 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 CO2 and mitigate the greenhouse effect.
Calcium hydroxide is also 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 rotting and fire, as well as to prepare silicate concrete and lime mortar.
Calcium hydroxide also takes part in the manufacturing processes of hard rubber, 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 production:
- Sugar cane;
- Alcoholic and non-alcoholic drinks;
- Energy workers;
- Fruit juices;
- Baby food;
- Pickled cucumbers;
- Table salt;
- Confectionery and sweets;
- Cocoa products;
- Corn tortillas;
- Flour products and baked goods.
In Spain, calcium hydroxide is used to prepare mamaliga, as it is believed that it promotes better absorption of the dish.
Native American Indian tribes use calcium hydroxide as an ingredient in Yapu, a psychedelic tobacco derived from the seeds of legume trees of the Anadenanthera species.
In Afghanistan, calcium hydroxide is used in the production of Niswar tobacco, made from fresh tobacco leaves, indigo, cardamom, menthol, oil, calcium hydroxide and wood ash. Residents of Afghanistan also use calcium hydroxide as 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 is colorless crystals or odorless white powder, which, when heated to 580°C, disintegrate 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 does not dissolve in alcohol.
Harm of calcium hydroxide
When calcium hydroxide comes into contact with the skin, severe irritation, itching, chemical burns and skin necrosis occur.
Accidental ingestion of calcium hydroxide results in severe sore throat, burning in the mouth, abdominal pain, vomiting, bloody stools, and a drop in blood pressure. The blood pH also increases and becomes too alkaline, which can cause damage to internal organs.
Inhaling calcium hydroxide powder through the nose or mouth causes swelling in the throat, 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, vision loss occurs, accompanied by severe pain.
Providing first medical care in case of calcium hydroxide poisoning
If calcium hydroxide was ingested, you should drink a glass of water or milk.
If calcium hydroxide comes into contact with your skin or eyes, rinse the affected skin and eyes thoroughly. a large number water for at least 15 minutes.
If calcium hydroxide is inhaled, move immediately to fresh air and call an ambulance.
