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 forms one ionic bond with each OH- ions. 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 hexagonal crystal structure.
[Structure of Calcium Hydroxide-Image will be uploaded soon]
[Deducing the Formula of Calcium Hydroxide-Image will be uploaded soon]
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
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. Aqueous solution of calcium hydroxide is called limewater. Its solubility decreases with increase in temperature. Its suspension in water is called milk of lime.
It is insoluble in alcohol.
It is basic or alkaline is nature.
Chemical properties –
Carbonatation – Calcium hydroxide reacts with carbon dioxide to form calcium carbonate and water. 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. Reaction is given below –
Ca(OH)2 → CaO + H2O
Reaction With Dilute HCl (Acid) – When calcium hydroxide reacts with dil. Hydrochloric acid, it gives calcium chloride and water. 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 precipitate of calcium sulphate. 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. 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. 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. Reaction is given below –
3Ca(OH)2 + 12S → 2CaS5 + CaS2O3 + 3H2O
We are using calcium hydroxide from ancient warfare, Roman Empire time to modern industry. you will be amazed to know that Roman empire extensively used lime – based mortars in their architecture and lime is present in the construction material of the great wall of china. Few of its modern age uses are listed below –
For white washing – Slaked lime is used in white washing. 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 of 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.
This was all about slaked lime, if you are looking for NCERT Solutions or detailed study notes on various topics of chemistry then log on to Vedantu or download Vedantu Learning App. By doing so you will get access to free pdfs of NCERT Solutions, study notes, revision notes and mock tests etc.