Calcium hydroxide Ca(OH)2 is the chemical formula of slaked lime. Here, in this article you will study about the preparation, properties, chemical reactions and uses of Ca(OH)2
Preparation reactions of Calcium hydroxide Ca(OH)2, slaked lime
Slaked lime is sparingly soluble in water. The solubility of slaked lime decreases with rise in temperature. There are various methods for the preparation of Ca(OH)2 which are listed below :
1. Preparation of Ca(OH)2 from quick lime
The reaction of Quick lime, CaO with H2O forms slaked lime.
CaO ( Quick lime ) + H2O ……………………………> Ca(OH)2 ( slaked lime )
2. Manufacturing of Slaked lime from calcium chloride
When CaCl2 reacts with NaOH it forms slaked lime Ca(OH)2.
CaCl2 + 2 NaOH …………………………….> Ca(OH)2 + 2NaCl
Properties of Calcium Hydroxide ( slaked lime )
1. Heating Slaked lime Ca(OH)2
This is the dehydration reaction of slaked lime to form quick lime.
Ca(OH)2 + >700K ……………………> CaO + H2O
2. Reaction of slaked lime Ca(OH)2 with CO2
The suspension of slaked lime in water is called milk of lime. Lime water is the filtered clear solution of Ca(OH)2 . When we pass CO2 gas through lime water it forms insoluble precipitates of CaCO3.
Ca (OH)2 + CO2 ……………………..> CaCO3 ( White ppt.) + H2O
Excess of CO2 will dissolve calcium bicarbonate white precipitates.
CO2 (excess) + Ca(OH)2 …………………….> Ca(HCO3)2 soluble
If Ca(HCO3)2 clear solution is heated milkiness appears again. This is due to the conversion of Ca(HCO3)2 back to CaCO3.
Ca(HCO3)2 aq…………………………………> CaCO3 (s) + CO2 (g) + H2O (l)
3. Reaction of Calcium hydroxide Ca(OH)2 with Chlorine
Slaked lime reacts with Chlorine to form calcium chloride and calcium hypochlorite Ca(OCl)2
Ca(OH)2 +2Cl2 ……………………………………> CaCl2 + Ca(OCl)2 Bleaching powder + 2H2O
4. Reaction of Calcium hydroxide Ca(OH)2 with acids
Ca(OH)2 is strong base which reacts acids and acidic gases to form salts.
Ca(OH)2 + 2HCl …………………….> CaCl2 + H2O
Slaked lime reacts with acidic gases like SO3 to form calcium sulphate.
Ca(OH)2 + SO3 …………………………… > CaSO4 + H2O
Uses of Calcium hydroxide Ca(OH)2, slaked lime
- slaked lime is used in white washing because it has disinfecting properties
- Calcium hydroxide or slaked lime is used in the preparation of bleaching powder.
- Calcium hydroxide is used in the tanning industry, purification of sugar, or as a building material in the form of mortar.
- Slaked lime is also used for absorbing acidic gases.
- Slaked Lime is used in the form of lime water for the detection of carbon dioxide gas.
FAQs related to Slaked lime, Calcium hydroxide Ca(OH)2
- Is Slaked lime, acidic or basic solution ?
Answer: slaked, lime or calcium hydroxide is a basic solution. Because calcium hydroxide is a source of hydroxide ions.
2. Why is it necessary for slaking of lime in some industrial applications?
Answer : Slaked lime controls the pH of the solution.
3. Why is slakedlime used for white washing?
Answer : Ca(OH)2 reacts with CO2 from the air very slowly to form thin layer of CaCO3 on the walls.
Check out the structure of NH3 here
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