Ca oh what a hydroxide. Hydrated lime: formula and chemical composition of limestone
1. Calcium hydroxide (slaked lime) is a poorly soluble substance. We shake a little lime in 2 ml of water (about 2 cm in height of the test tube), let stand for several minutes. Most of the lime will not dissolve, it will settle to the bottom.
2. Drain the solution, filter (if there is no filter, wait until it settles). A clear solution of calcium hydroxide is called lime water. Divide into 2 tubes. We drop the indicator phenolphthalein (f-f) into one, it turns crimson, which proves the main properties of lime:
Ca (OH) 2 Ca 2+ + 2OH -
3. We pass carbon dioxide into the second test tube, lime water becomes cloudy as a result of the formation of insoluble calcium carbonate (this is a qualitative reaction for detecting carbon dioxide):
Ca(OH) 2 + CO 2 = CaCO 3 ↓ + H 2 O
If you have to do these reactions in practice, carbon dioxide can be obtained in a test tube with a gas outlet tube by adding hydrochloric or nitric acid to chalk or soda.
You can pass the exhaled air several times through a straw from a cocktail or juice that you brought with you. Do not shock the commission - blow into a tube from laboratory equipment - nothing can be tasted in the chemistry room!
Ticket number 17
1. Oxides: their classification and chemical properties (interaction with water, acids and alkalis).
Oxides are complex substances consisting of two elements, one of which is oxygen.
Oxides are divided into acidic, basic, amphoteric and non-salt-forming (indifferent).
Acid oxides correspond to acids. Most non-metal oxides and metal oxides in the highest oxidation state, such as CrO 3 , have acidic properties.
Many acidic oxides react with water to form acids. For example, sulfur oxide (IV), or sulfur dioxide, reacts with water to form sulfuric acid:
SO 2 + H 2 O \u003d H 2 SO 3
Acid oxides react with alkalis to form salt and water. For example, carbon monoxide (IV), or carbon dioxide, reacts with sodium hydroxide to form sodium carbonate (soda):
CO 2 + 2NaOH \u003d Na 2 CO 3 + H 2 O
Main bases correspond to oxides. The main ones include oxides of alkali metals (the main subgroup of group I),
magnesium and alkaline earth (the main subgroup of group II, starting with calcium), metal oxides of secondary subgroups in the lowest oxidation state (+1+2).
Oxides of alkali and alkaline earth metals react with water to form bases. So, calcium oxide reacts with water, calcium hydroxide is obtained:
CaO + H 2 O \u003d Ca (OH) 2
Basic oxides react with acids to form salt and water. Calcium oxide reacts with hydrochloric acid to form calcium chloride:
CaO + 2HCl \u003d CaCl 2 + H 2 O
Amphoteric oxides react with both acids and alkalis. So, zinc oxide reacts with hydrochloric acid, zinc chloride is obtained:
ZnO + 2HCl = ZnCl 2 + H 2 O
Zinc oxide also interacts with sodium hydroxide to form sodium zincate:
ZnO + 2NaOH \u003d Na 2 ZnO 2 + H 2 O
Amphoteric oxides do not interact with water. Therefore, the oxide film of zinc and aluminum protects these metals from corrosion.
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 is a clear aqueous solution of alkali, obtained after filtering lime milk.
Slaked lime was named after the method of production: quicklime (calcium oxide) is poured with water (quenched).
Properties
Fine white crystalline powder, odorless. Very poorly soluble in water, completely insoluble in alcohol, easily soluble in dilute nitric and hydrochloric acids. It is fireproof and even prevents fire. When heated, it decomposes into water and calcium oxide.
Strong alkali. 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 in different directions - this must be taken into account when working.
Precautionary measures
Contact with the skin of dry powder particles or drops of calcium hydroxide solution causes irritation, itching, chemical burns, ulcers, and severe pain. Eye damage can cause vision loss. Ingestion of the substance causes a burn of the mucous throat, vomiting, bloody diarrhea, a sharp decrease in pressure, damage to internal organs. Inhalation of dust particles can lead to swelling of the throat that makes it difficult to breathe.
Before calling an ambulance:
- in case of poisoning, give the victim to drink milk or water;
- if the chemical gets into the eyes or on the skin, then the damaged areas should be washed with plenty of water for at least a quarter of an hour;
- if the reagent is accidentally inhaled, then the victim must be taken out of the room and provided with fresh air.
Work with calcium hydroxide should be in well-ventilated areas using protective equipment: rubber gloves, goggles and respirators. Chemical experiments should be carried out in a fume hood.
Application
In the construction industry, a chemical reagent is added to binding solutions, plaster, whitewash, gypsum mortars; on its basis, silicate brick and concrete are made; with its help prepare the soil before laying road surfaces. Whitewashing wooden parts of structures and fences gives them fire-resistant properties and protects them from decay.
- For neutralization of acid gases in metallurgy.
- To obtain solid oils and oil additives - in the oil refining industry.
- In the chemical industry - for the production of sodium and potassium alkalis, bleach ("bleach"), calcium stearate, organic acids.
- In analytical chemistry, lime water serves as an indicator of carbon dioxide (absorbing it, it becomes cloudy).
- With the help of calcium hydroxide, sewage and industrial waters are purified; neutralize the acids of the water entering the water supply systems in order to reduce its corrosive effect; remove carbonates from water (soften water).
- Ca(OH) 2 is used to remove hair from skins in the leather business. 
- Food additive E526 in the food industry: acidity and viscosity regulator, hardener, preservative. Used in the manufacture of juices and drinks, confectionery and flour products, marinades, salt, baby food. It is used in sugar production.
- In dentistry, milk of lime is used to disinfect root canals.
- For the treatment of acid burns - in medicine.
- In agriculture: means for regulating soil pH; as a natural insecticide against ticks, fleas, beetles; for the preparation of the popular fungicide "Bordeaux liquid"; for whitewashing tree trunks from pests and sunburn; as an antimicrobial and antifungal drug for storing vegetables in warehouses; as a mineral fertilizer.
- Calcium hydroxide reduces the electrical resistance of the soil, so it is treated with soil when installing grounding.
- Chemical reagent is used in the production of ebonite, brake linings, hair removal creams.
You can buy slaked lime at a good price, retail and wholesale, with delivery or pickup at the PrimeChemicalsGroup chemical store.
Calcium hydroxide, or as it is traditionally called slaked lime or fluff, is an inorganic compound with the chemical formula Ca(OH)2.
Obtaining calcium hydroxide on an industrial scale is possible by mixing calcium oxide with water, this process is called quenching.
In laboratory conditions, obtaining calcium hydroxide is possible by mixing an aqueous solution of calcium chloride and sodium hydroxide. In mineral form, calcium hydroxide is found in some volcanic, deep and metamorphic rocks. Calcium hydroxide is also obtained by burning coal.
In excess, calcium hydroxide is contained in aggressive water, which is able to dissolve rocks.
Application of calcium hydroxide
Calcium hydroxide has been widely used in the production of building materials such as whitewash, plaster and gypsum mortars. It is used as an inexpensive substitute for alkali in the form of slurries (milk of lime) used in tanneries to remove hair from hides, as well as in sugar production and for whitewashing tree trunks.
Lime water is a saturated aqueous solution of white calcium hydroxide. The antacid properties of calcium hydroxide are used medicinally to treat acid burns.
A useful property of calcium hydroxide is its ability to act as a flocculant that purifies wastewater from suspended and colloidal particles. It is also used to raise the pH of water, since water naturally contains acids that can corrode plumbing pipes.
Calcium hydroxide is also widely used in industries such as:
- Road construction - to improve the quality of earthen soil;
- Metal production – calcium hydroxide is injected into the waste gas stream to neutralize acids such as fluorides and chlorides before being released to the atmosphere;
- In the oil refining industry - for the production of additives to oils;
- In the chemical industry - for the production of calcium stearate;
- In the petrochemical industry - for the production of solid oils of various types;
- Production of antifungal and antimicrobial preservatives - for storing vegetables in hangars.
Calcium hydroxide is used as an additive to seawater to reduce atmospheric CO 2 and mitigate the greenhouse effect.
Also, calcium hydroxide is used as a natural alternative to insecticides, effective in the fight against ticks, fleas, beetles and their faces.
In construction, calcium hydroxide is used to whitewash wooden fences and coat rafters to protect materials from decay and fire, as well as to prepare silicate concrete and lime mortar.
Calcium hydroxide is also involved in the manufacture of ebonite, bleach, tank mixes, depilatory creams and brake linings.
The property of calcium hydroxide to reduce soil resistivity is used in the construction of grounding centers for electrical engineering.
In dentistry, calcium hydroxide is used as a disinfectant for root canals.
In the food industry, calcium hydroxide is used in excess as a food additive E526, which is added during the production of:
- Sugar cane;
- Alcoholic and non-alcoholic drinks;
- power engineers;
- fruit juices;
- Baby food;
- pickled cucumbers;
- food salt;
- Confectionery and sweets;
- cocoa products;
- Corn cakes;
- Flour products and pastries.
In Spain, calcium hydroxide is used to make hominy, as it is believed that it contributes to better absorption of the dish.
Native American Indian tribes use calcium hydroxide as an ingredient in Yapu, a psychedelic tobacco made from the seeds of the Anadenantera leguminous tree.
In Afghanistan, calcium hydroxide is used in the production of Niswar tobacco, which is made from fresh tobacco leaves, indigo, cardamom, menthol, oil, calcium hydroxide, and wood ash. The people of Afghanistan also use calcium hydroxide as a paint for their adobe houses. The largest consumers of calcium hydroxide in the world are countries such as Afghanistan, Pakistan, India, Sweden and Norway.
Properties of calcium hydroxide
Calcium hydroxide - colorless crystals or odorless white powder, which, when heated to 580 ° C, decompose into calcium oxide and water.
The molar mass of calcium hydroxide is 74.093 g/mol, density 2.211 g/cm3, solubility in water 0.189 g/100 ml, acidity (pKa) 12.4, refractive index 1.574.
Calcium hydroxide is insoluble in alcohol.
The harm of calcium hydroxide
If calcium hydroxide comes into contact with the skin, severe irritation, itching, chemical burns and skin necrosis occur.
Accidental ingestion of calcium hydroxide by mouth causes severe sore throat, burning mouth, abdominal pain, vomiting, bloody stools, and a drop in blood pressure. The pH of the blood also rises, it becomes too alkaline, which can cause damage to the internal organs.
When calcium hydroxide powder is inhaled through the nose or mouth, the throat will swell, which can restrict or make breathing difficult. If calcium hydroxide particles enter the lungs, emergency medical attention is needed.
When calcium hydroxide gets into the eyes, loss of vision occurs, accompanied by severe pain.
Providing first aid for calcium hydroxide poisoning
If calcium hydroxide has been ingested, drink a glass of water or milk.
In case of contact with calcium hydroxide on the skin or eyes, thoroughly rinse the affected skin and eyes with plenty of water for at least 15 minutes.
If calcium hydroxide is inhaled, immediately move to fresh air and call an ambulance.
Calcium oxide (CaO) - quicklime or burnt lime- a white fire-resistant substance formed by crystals. It crystallizes in a cubic face-centered crystal lattice. Melting point - 2627 ° C, boiling point - 2850 ° C.
It is called burnt lime because of the method of its production - the burning of calcium carbonate. Roasting is carried out in high shaft kilns. Limestone and fuel are laid in layers in the furnace, and then kindled from below. When heated, calcium carbonate decomposes to form calcium oxide:
Since the concentrations of substances in solid phases are unchanged, the equilibrium constant of this equation can be expressed as follows: K=.
In this case, the gas concentration can be expressed using its partial pressure, that is, the equilibrium in the system is established at a certain pressure of carbon dioxide.
Substance dissociation pressure is the equilibrium partial pressure of a gas resulting from the dissociation of a substance.
To provoke the formation of a new portion of calcium, it is necessary to increase the temperature or remove part of the resulting CO2, and the partial pressure will decrease. By maintaining a constant lower partial pressure than the dissociation pressure, a continuous calcium production process can be achieved. To do this, when burning lime in kilns, make good ventilation.
Receipt:
1) in the interaction of simple substances: 2Ca + O2 = 2CaO;
2) during thermal decomposition of hydroxide and salts: 2Ca(NO3)2 = 2CaO + 4NO2? +O2?.
Chemical properties:
1) interacts with water: CaO + H2O = Ca(OH)2;
2) reacts with non-metal oxides: CaO + SO2 = CaSO3;
3) dissolves in acids, forming salts: CaO + 2HCl = CaCl2 + H2O.
Calcium hydroxide (Ca (OH) 2 - slaked lime, fluff)- a white crystalline substance, crystallizes in a hexagonal crystal lattice. It is a strong base, poorly soluble in water.
lime water- a saturated solution of calcium hydroxide, having an alkaline reaction. It becomes cloudy in air as a result of the absorption of carbon dioxide, forming calcium carbonate.
Receipt:
1) is formed when calcium and calcium oxide are dissolved in the input: CaO + H2O \u003d Ca (OH) 2 + 16 kcal;
2) 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 applying the chemical method, soluble calcium and magnesium salts are converted into insoluble carbonates:
A more modern process for removing water hardness - using cation exchangers.
Cation exchangers- complex substances (natural compounds of silicon and aluminum, high-molecular organic compounds), the general formula of which is Na2R, where R- complex acid residue.
When water passes through a layer of cation exchanger, Na ions (cations) are exchanged for Ca and Mg ions: Ca + Na2R = 2Na + CaR.
Ca ions from the solution pass into the cation exchanger, and Na ions pass from the cation exchanger into the solution. To restore the used cation exchanger, it must be washed with a solution of common salt. In this case, the reverse process occurs: 2Na + 2Cl + CaR = Na2R + Ca + 2Cl.
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. Its chemical formula is 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
The hardening of the lime mortar occurs because an insoluble substance is formed - 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
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