Quick Lime (solid Calcium Oxide or CaO)

It is prepared on a commercial scale by heating limestone (CaCO3) in a rotary kiln at    1070-1270K.

                                  CaCO3 CaO + CO2:

Slaked lime (solid Calcium Hydroxide Ca(OH)2) Calcium hydroxide is prepared by adding water to quick lime, CaO. It is a white amorphous powder. It is sparingly soluble in water.

Lime water is the aqueous solution of Ca(OH)2

Milk of lime is the suspension of slaked lime in water.  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 bicarbonate.

                    CaCO3 + CO2 +H2O→Ca(HCO3)2


Calcium carbonate occurs in nature in several forms like limestone, chalk, marble etc. It can be prepared by passing carbon dioxide through slaked lime or by the addition of sodium carbonate to calcium chloride.

Ca(OH)2  + CO2  → CaCO3 + H2O               and    CaCl2 + Na2CO3 → CaCO3 + 2NaCl

Calcium carbonate is a white fluffy powder. It is almost insoluble in water. It reacts with dilute acid to liberate carbon dioxide.

Calcium Sulphate (Plaster of Paris), CaSO4·½H2O

It is a hemihydrate of calcium sulphate. It is obtained when gypsum, CaSO4·2H2O, is heated to 393K.

          2(CaSO4.2H2O)  → 2(CaSO4).H2O + 3H2O

Cement: is a product obtained by combining a material rich in lime, CaO with other material such as clay which contains silica, SiO2 along with the oxides of aluminium, iron and magnesium. The average composition of Portland cement is: CaO, 50-60%; SiO2, 20-25%; Al2O3, 5-10%; MgO, 2-3%; Fe2O3, 1-2% and SO3, 1-2%. For good quality cement, the ratio of silica (SiO2) to alumina (Al2O3) should be between 2.5 and 4 and the ratio of lime (CaO) to the total of the oxides of silicon (SiO2) aluminium (Al2O3) and iron (Fe2O3) should be as close as possible to 2