Calcium hydroxide is prepared by adding water to quick lime, CaO.
It is a white powder. It is sparingly soluble in water. The aqueous solution is known as lime water and a suspension of slaked lime in water is known as milk of lime.
When carbon dioxide is passed through lime water, it turns milky due to the formation of calcium carbonate.
Ca(OH)2 + CO2 → CaCO3 + H2O
On passing excess of carbon dioxide, the precipitate dissolves to form calcium hydrogen carbonate.
CaCO3 + CO2 + H2O → Ca(HCO3)2
Milk of lime reacts with chlorine to form hypochlorite, a constituent of bleaching powder.
2Ca (OH)2 + 2Cl2 → CaCl2 + Ca(OCl)2 + 2H2O
Calcium hydroxide is used
i. in the preparation of mortar, a building material.
ii. in white wash due to its disinfectant nature.
iii. in glass making, in tanning industry, in the preparation of bleaching powder and for the purification of sugar.