[Chemistry Class Notes] on Slaked Lime Pdf for Exam

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 .

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 – 

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Ca(OH)₂ → CaO + H₂O

Ca(OH)₂ + 2HCl_(diluted)  ? CaCl₂ + 2H₂O

Ca(OH)₂ + H₂SO_4(conc.) ? CaSO₄↓ + 2H₂O

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

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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