CBSE Class 10 Answered

Calcium oxide (CaO), commonly known as burnt lime, lime or quicklime, is a widely used chemical compound. It is a white, caustic and alkaline crystalline . Calcium oxide is usually made by the thermal decomposition of materials such as limestone, that contain calcium carbonate (CaCO₃; mineral name: calcite) in a lime kiln. This is accomplished by heating the material to above 825°C,^[1] a process called calcination or lime-burning, to liberate a molecule of carbon dioxide (CO₂); leaving CaO

As hydrated or slaked lime, Ca(OH)₂ (mineral name: portlandite), it is used in mortar and plaster to increase the rate of hardening as well as to improve adhesion^{[citation needed]}. Hydrated lime is very simple to make as lime is a basic anhydride and reacts vigorously with water. Lime is also used in glass production and its ability to react with silicates is also used in modern metal production (steel, magnesium, aluminium and other metals) industries to remove impurities as slag.

It is also used in water and sewage treatment to reduce acidity, to soften, as a flocculant, and to remove phosphates and other impurities; in paper making to dissolve lignin, as a coagulant, and in bleaching; in agriculture to improve acidic soils; and in pollution control, in gas scrubbers to desulfurize waste gases and to treat many liquid effluents. It has traditionally been used in the burial of bodies in open graves, to hide the smell of decomposition, as well as in forensic science, to reveal fingerprints. It is a refractory and a dehydrating agent and is used to purify citric acid, glucose, dyes and as a CO₂ absorber. It is also used in pottery, paints and the food industry. Furthermore, quicklime is used in epidemics, plagues, and disasters to disintegrate bodies in order to help fight the spread of disease. CaO is a key ingredient in the nixtamalization process used to create corn hominy and masa or tortilla dough.

A relatively inexpensive substance, CaO produces heat energy by the formation of the hydrate, as in the following equation:^[3]

CaO + H₂O ↔ Ca(OH)₂ + 63.7kJ/mol of CaO