Calcium hydroxide is a kind ofinorganic compound, chemical formula is Ca (OH)two, molecular weight 74.10.be commonly calledHydrated lime(slaked lime) orSlaked lime（hydrate lime）。It is a white hexagonal system powder crystal.Density 2.243g/cmthree。Loss of water at 580 ℃ results in CaO.[3]
After adding water, calcium hydroxide is divided into two layers, and the upper water solution is calledClarified lime water, the lower suspension is calledLime milkorLime slurry。Clear lime water of upper layer can be inspectedcarbon dioxide, the lower turbid liquid lime milk is a kind ofbuilding material。Calcium hydroxide is a kind ofStrong baseIt has bactericidal and antiseptic ability and has corrosive effect on skin and fabric[1]。Calcium hydroxide is used to manufacture bleaching powder, hard water softener, disinfection insecticide, unhairing agent for leather making, sugar refining and building materials.[3]
Chinese name
calcium hydroxide[4]
Foreign name
calcium hydroxide[4]
Alias
Hydrated lime[4]、Slaked lime
chemical formula
Ca(OH)₂
molecular weight
seventy-four point zero nine two seven[2]
CAS login number
1305-62-0[4]
EINECS login number
215-137-3[4]
Melting point
580 ℃[4](water loss, decomposition)
Boiling point
2850 ℃[4]
Water solubility
Slightly soluble(The solubility is 1.65 g/L at 20 ℃)
Density
2.24 g/cm³（25 ℃）
Appearance
White powdery solid
Application
Water solution can verify carbon dioxide, building materials
Lime is the earliest cementitious material used by human beings.In the 8th century BC, the ancient Greeks used lime for building, and China began to use lime in the 7th century BC.Many ancient magnificent murals and compacted foundation sites are preserved with lime.The construction of the Qin Great Wall is also an example.
China is one of the earliest countries to produce and utilize lime.According to archaeological data, smooth and solid walls and ground plastered with lime (about 2800-2300 BC) have been seen in many Longshan cultural sites in the Yellow River basin of China.According to C-14 determination, the lime used in the Longshan period site has been artificially calcined.
With the development of modern industry, lime, as the main material of civil engineering, has opened up a variety of uses in many new industrial sectors.For example, metallurgy, glass, alkali and sugar production, paper making, tanning, calcium carbide and organic chemical industry, carbonized brick, carbonized board, soil improvement, water treatment, gas purification and other aspects all use a large amount of lime.
Calculate chemical data
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Drainage parameter calculation reference value (XlogP)
nothing
Number of hydrogen bond donors
two[4]
Number of hydrogen bond receptors
two[4]
Number of rotatable chemical bonds
zero[4]
Number of tautomers
nothing
Topological molecular polar surface area
two[4]
Number of heavy atoms
three[2]
surface charge
zero
Complexity
zero
Number of covalent bond units
three[2]
Numbering system
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CAS No
1305-62-0
MDL No
MFCD00010901
EINECS No
215-137-3
RTECS No
EW2800000[2]
Physical and chemical properties
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physical property
Density (g/mL, 25/4 ℃): 2.24
Calcium hydroxide is a fine white powder at room temperature, slightly soluble in water, and its clear aqueous solution is commonly known asClarified lime water, emulsion suspension composed of waterLime milk。The solubility decreased with the increase of temperature.Insolublealcohol, soluble inammonium salt, glycerol, can react with acid to generate correspondingCalcium salt。At 580 ℃, it decomposes into calcium oxide and water.
Solubility
Calcium hydroxide in water (100g)solubilityThe change with temperature (in ℃) is:
0 degrees
0.185g
10 degrees
0.176g
20 degrees
0.165g
30 degrees
0.153g
40 degrees
0.141g
50 degrees
0.138g
60 degrees
0.116g
70 degrees
0.106g
80 degrees
0.094g
90 degrees
0.085g
The mainstream explanation for the problem that the solubility of calcium hydroxide decreases with the increase of temperature is that there are two kinds of calcium hydroxidehydrate〔Ca(OH)two·2HtwoO and Ca (OH)two·12HtwoO〕。The solubility of these two hydrates is relatively high, while that of anhydrous calcium hydroxide is very low.With the increase of temperature, these crystal hydrates gradually become anhydrous calcium hydroxide, so the solubility of calcium hydroxide decreases with the increase of temperature.
Solubility curve of calcium hydroxide
chemical property
alkalinity
Calcium hydroxide is a strong alkali, which is harmful to skin and fabricsCorrosion。However, due to its low solubility, the hazard is not as good assodium hydroxideIso alkali is large.Calcium hydroxide canAcid-base indicatoreffect:
Reaction of magnesium chloride with calcium hydroxide:
MgCltwo+Ca(OH)two=CaCltwo+Mg(OH)two↓
toxicology data
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Acute toxicity: oral LD in ratsfifty：7340mg/kg；Oral LDs in micefifty：7300mg/kg。
It is a strong alkaline substance with irritating and corrosive effects.Inhalation of dust is strongly irritating to the respiratory tract and may cause pneumonia.Eye contact also has strong irritation, which may cause burns.[2]
Preparation method
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Industrial preparation
1. Lime digestion
After calcining limestone into calcium oxide, it is digested with water in a ratio of 1: (3~3.5) after selection to generate calcium hydroxide solution, which is purified, separated and deslagging, centrifuged, dried at 150~300 ℃, and screened (more than 120 meshes) to produce calcium hydroxide products.
CaCOthree→CaO+COtwo↑
CaO+HtwoO→Ca(OH)two。
2. Dissolve the reagent calcium chloride in water to prepare a 25% aqueous solution, heat it to 80 ℃, and then add 30% filtered sodium hydroxide solution (which can exceed the theoretical amount by 30%) in batches to react to obtain calcium hydroxide. The slurry mixture obtained is filtered by suction and washed. First, use 0.1% sodium hydroxide solution to wash a large amount of chloride ions, and then use distilled water to wash until the chloride ions are qualified.
3. Diffusion method
First, prepare two solutions: one is 30g recrystallized CaCltwo·6HtwoO dissolved in 50mL water;One is 12g NaOH dissolved in 50mL water and a small amount of Ba (OH) added by droppingtwoPrecipitated carbonate.Fill two 50mL beakers with the two solutions respectively.Carefully put two beakers in the same container, the beaker is 2cm away from the upper edge of the container, cover the container lid, and after standing for 4 weeks, about 1cm of needle shaped crystals grow out, collect and filter, quickly wash, then wash with dilute hydrochloric acid, water, ethanol, and ether in turn, and finally dry at 110 ℃ in a short time.
4. The alkali metalhydroxideCalcium hydroxide can be obtained by reacting the solution with the aqueous solution of calcium salt.Dissolve 46g of calcium nitrate tetrahydrate in 500mL distilled water after boiling to remove gas, cool it to 0 ℃, and add 1mol/LPotassium hydroxideSolution (without COtwo）Keep the solution at 0 ℃ during dropping, filter and separate the precipitated Ca (OH)twoPrecipitate, decant and wash with 12L water for several times, filter and precipitate in sulfuric acid (relative density 1.355) dryer for vacuum drying for 20h to obtain Ca (OH)two。
Laboratory preparation
Put quicklime (CaO) into the beaker and add water.Calcium oxide reacts with water to release heat, and the product is calcium hydroxide.Reaction formula: CaO+HtwoO→Ca(OH)two。
2. Calcium hydroxide is alkaline, so it can be used to reduce the acidity of soil and improve the soil structure.Of pesticidesBordeaux liquidIt is prepared by using lime milk (calcium hydroxide dissolved in water) and copper sulfate aqueous solution in a certain proportion.In winter, the trees shall be protected against insects in winter, and 80 cm lime slurry shall be applied above the roots of the trees.
3. High quality products are mainly used to produce epichlorohydrinPropylene oxide。
4. It can be used in rubber and petrochemical additives. For example, it can be added to lubricating oil in the petroleum industry to prevent coking, sludge deposition, neutralization and corrosion prevention.
5. It is used to produce bleaching powder, bleaching powder essence, disinfectant, antacid, astringent, hard water softener, soil acid inhibitor, unhairing agent, buffer, neutralizer, curing agent, etc.
6. Calcium hydroxide will also react with carbon dioxide in the air to form calcium carbonate that is insoluble in water.In the sugar industry, calcium hydroxide is used to neutralize the acid in the syrup, and then carbon dioxide is introduced to react with the remaining calcium hydroxide to generate sediment which is filtered out, so as to reduce the sour taste of sugar.
Safety measures
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Health hazards
Calcium hydroxide dust or suspension droplets can stimulate mucous membrane, cause sneezing and coughing, saponify fat, absorb water from skin, dissolve protein, stimulate and corrode tissues as alkali.Inhalation of lime dust may cause pneumonia.
Excessive ingestion and absorption of calcium hydroxide can lead to dangerous symptoms, such asdyspnea, internal bleeding, muscle paralysis, hypotension, obstruction of myosin and actin system, increase of blood pH value, leading to visceral damage, etc.
First aid measures
Contact part
First aid measures
Skin contact
Flush immediately with plenty of water, and then apply 3% - 5%Boric acid solution。
Eye contact
Immediately lift the eyelids and use flowing water ornormal salineFlush for at least 15 minutes.Or wash with 3% boric acid solution.Get medical attention.
inhalation
Quickly leave the site to fresh air.If necessary, carry out artificial respiration and seek medical advice.
Ingestion
The poison in the mouth, such as milk, yogurt and other milk products, should be cleaned with protein and other things as soon as possible.Rinse the mouth immediately when the patient is awake, take diluted vinegar or lemon juice orally, and seek medical advice.
Hazard prevention
Protection part
Protective measures
respiratory system protection
Wear a gas mask if necessary.
Eye protection
Wear chemical safety goggles.
Body protection
Wear work clothes (made of anti-corrosion materials).
Hand protection
Wear rubber gloves.
other
After work, take a shower and change clothes.Pay attention to personal hygiene.
security information
Safety terminology
S26: In case of contact with eyes, please wash with plenty of water immediately and ask for doctor's advice.
S37: Wear appropriate gloves.
S39: Wear goggles or mask.
Risk terminology
R41: Serious injury to eyes.
Storage and transportation
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Transport method
The package shall be in good condition and the loading shall be safe.During transportation, the container shall not leak, collapse, fall or be damaged.It is strictly prohibited to mix with combustibles or combustibles, acids, edible chemicals, etc.It is not suitable for transportation in rainy days.
Storage method
Store in a cool and ventilated warehouse.The humidity in the warehouse should preferably not be greater than 85%.It is necessary to seal the package well to avoid moisture absorption.It shall be stored separately from combustibles and acids, and mixed storage is strictly prohibited.The storage area should be equipped with appropriate data to contain leakage.
