Structure of Calcium Hydroxide
Slaked lime is the common name that is given to the compound calcium hydroxide which is a chemical compound. It is seen that under standard temperature and pressure this compound is present as a white powdery form which also forms colorless crystals. Some of the other names that are given to Slaked Lime are caustic lime, pickling lime, and slack lime. Students can now know more about Slaked Lime via Vedantu.
As stated above the chemical formula of calcium hydroxide is Ca(OH)2. It is an ionic compound. In which calcium loses its two electrons to polyatomic hydroxide ions. Thus, in slaked lime Ca+2 ions form one ionic bond with each OH- ion. Although oxygen and hydrogen atoms of polyatomic hydroxide anion possess covalent bonds between them. Strong hydrogen bonds exist between the layers of calcium hydroxides. That’s why it has a hexagonal crystal structure.
Deducing the Formula of Calcium Hydroxide.
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Preparation of Calcium Hydroxide
From Calcium Oxide - Commercial production of calcium hydroxide is done by treating quicklime with water. Calcium oxide is commonly known as quicklime. The process of production of calcium hydroxide from lime is called slaking of lime as when a limited quantity of water is mixed with quicklime it disintegrates and crumbles. The reaction involved is given below –
CaO + H2O 🡪 Ca(OH)2
From Calcium Chloride– In laboratories, slaked lime is prepared by mixing aqueous solutions of calcium chloride and caustic soda. Caustic soda is a common name for sodium hydroxide.
CaCl2 + 2NaOH 🡪 Ca(OH)2 + 2NaCl
Properties of Calcium Hydroxide
Physical Properties –
Its molar mass is 74.09 g/mol.
It appears as colorless crystals or white powder.
It is odorless.
Its melting point is 580℃.
It is soluble in water, glycerol, and acids. An aqueous solution of calcium hydroxide is called limewater. Its solubility decreases with an increase in temperature. Its suspension in water is called milk of lime.
It is insoluble in alcohol.
It is basic or alkaline in nature.
Chemical Properties –
Carbonatation – Calcium hydroxide reacts with carbon dioxide to form calcium carbonate and water. The reaction is given below –
Ca(OH)2 + CO2 → CaCO3 + H2O
Decomposition – When calcium hydroxide is heated to 512℃, it decomposes into calcium oxide (quicklime) and water. The reaction is given below –
Ca(OH)2 → CaO + H2O
Reaction With Dilute HCl (Acid) – When calcium hydroxide reacts with dil. Hydrochloric acid gives calcium chloride and water. The reaction is given below-
Ca(OH)2 + 2HCl(diluted) 🡪 CaCl2 + 2H2O
Reaction With Concentrated Acid – When calcium hydroxide reacts with concentrated sulfuric acid, it forms water and precipitates calcium sulfate. The reaction is given below –
Ca(OH)2 + H2SO4(conc.) 🡪 CaSO4↓ + 2H2O
Reaction With Hydrogen Sulfide – When calcium hydroxide reacts with hydrogen sulfide, it gives calcium hydrosulfide and water. The reaction is given below –
Ca(OH)2 + 2H2S 🡪 Ca(HS)2 + 2H2O
Preparation of Ammonia – On reacting with ammonium chloride, calcium hydroxide gives ammonia, calcium chloride, and water. The reaction is given below-
Ca(OH)2 + 2NH4Cl → 2NH3 + CaCl2 + 2H2O
Reaction With Flowers of Sulfur – When these are boiled with calcium hydroxide, they form lime sulfur. The reaction is given below –
3Ca(OH)2 + 12S → 2CaS5 + CaS2O3 + 3H2O
Uses of Calcium Hydroxide
We are using calcium hydroxide from ancient warfare, Roman Empire time to modern industry. You will be amazed to know that the Roman empire extensively used lime-based mortars in their architecture and lime is present in the construction material of the Great Wall of China. A few of its modern age uses are listed below –
For whitewashing – Slaked lime is used in whitewashing. It reacts with carbon dioxide slowly and forms a layer of calcium carbonate on the wall which gives shine to the wall.
For manufacturing of sugar – Slaked lime is used in manufacturing sugar from sugar cane. It makes sugarcane juice alkaline and precipitates its impurities.
It is used in sewage treatment. It is used as a flocculant in water.
It is used in the paper industry.
It is used in pickles.
It is used to process water for various beverages.
It is used to remove the cellulose hull of maize kernels.
It is used as a digestive aid.
It is used in making papadum.
It is also used in paan and tobacco.
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FAQs on Slaked Lime
1. Are there any health hazards related to Slaked lime?
Calcium hydroxide is also commonly called Slaked Lime is a white powder produced by mixing the calcium oxide also called lime with water. The poisoning related to Slaked Lime occurs when someone tries to swallow it. Symptoms related to the poisoning of Slaked Lime vary with various parts of the body and can be provided as follows:
Stomach and intestines:
Vomiting
Severe abdominal pain
Burning sensation in the food pipe
Blood in stool
Vomiting blood
Heart and blood:
Collapse
Low blood pressure
2. What are the solubility characteristics of Slaked Lime?
Slaked Lime is known to be an insoluble compound in water. It is also observed that the dissolution of Slaked Lime in water is an exothermic process and hence according to Le Chatelier’s principle the lowering of temperature tends to favor the heat that is liberated through the process of dissolution and increases the equilibrium constant of dissolution. This solubility also keeps on decreasing as the temperature is being decreased. It is also noticed that the Ksp of the compound turned out to be 5.5 X 10-6. This indicates that the solution will have a basic nature.
3. What are the factors that affect the slaking process?
There are a number of factors that tend to affect the slaking process and can be provided as follows:
Types of limestone used in calcination as the normal types are not pure it is needed to check if the lime provided is pure enough
Water temperature also affects the slaking process
Slaking temperature is the temperature at which the slaking process takes place
Viscosity of slurry
Slaking time
Air slaking
Degree of agitation during slaking
Lime to water ratio
Calcination process to manufacture CaO
4. How can the acidic nature of Slaked Lime be explained?
Slaked Lime consists of two hydroxyl groups and hence it provides two hydroxyl ions per molecule. These two hydroxyl ions are obtained upon dissociation and hence it can be regarded as a bi acidic molecule. Hence the acidity of Slaked Lime is 2.
It is these two hydroxyl groups that are released that provide the acidity of the medium. The value of acidity is 12.63 for the first hydroxyl ion and for the second hydroxyl ion it is 11.57.
5. Why is it necessary to learn about Slaked Lime?
Slaked Lime is one of the important compounds that are highly used in industries, In the construction of buildings and other such uses it is quite important and hence learning more about Slaked Lime allows students to get to know more about it and will also allow them to create the Slaked Lime on their own as well. Students who would like to know more about the Slaked Lime can also check out the Vedantu NCERT Solutions for Chemistry.