Compounds of Calcium
It is manufactured by burning limestone in a kiln at 1070-1270 K
Also known as quicklime, CaO is an important building material. It is a white porous solid (melting point 2870 K) and is used in the manufacture of cement, glass, mortar, calcium chloride, etc. It is also used in sugar refining, for white washing and as basic lining in furnaces.
Calcium hydroxide, Ca(OH)2 is obtained by adding water to quicklime.
CaO + H2O Ca(OH)2
The process is called slaking of lime. The product calcium hydroxide is white amorphous powder and is also called slaked lime. Its suspension in water is known as milk of lime and the filtered solution is called lime water. Chemically both of these are Ca(OH)2.
Calcium Carbonate (CaCO3) occurs in nature as limestone, marble and chalk. In the laboratory, it is prepared by passing carbon dioxide through lime water.
Ca(OH)2 + CO2 CaCO3 + H2O
It may also be obtained by the addition of sodium carbonate to calcium chloride.
CaCl2 + Na2CO3 CaCO3 + 2NaCl
Calcium carbonate is an important building material. It is one of the basic raw materials for manufacturing cement and is also used as a flux.
Calcium sulphate occurs in nature as gypsum, CaSO4.2H2O and as anhydride, CaSO4. In the laboratory, it is prepared by adding dilute sulphuric acid to a calcium salt solution.
Ca2+ + H2SO4 CaSO4 + 2H+
When gypsum (CaSO4.2H2O) is heated, it changes its crystal structure followed by gradual loss of water and forming CaSO4.H2O (Plaster of Paris) at about 400 K and anhydrous CaSO4 at 437 K.
Gypsum (CaSO4.2H2O) is used in the manufacture of Plaster of Paris and cement.
Plaster of Paris
Plaster of Paris is calcium sulphate hemihydrate (CaSO4. H2O). It is obtained by heating gypsum in a kiln to about 400 K.
When made into a paste with water, Plaster of Paris sets to a hard crystalline mass of gypsum. It is used for making casts and patterns. Fractured bones are plastered to make them immobile. It is also used for making blackboard chalks.