Question

A substance ‘X’ is used in white-washing and is obtained by heating limestone in the absence of air. Identify ‘X’.
1. CaOCl₂
2. Ca (OH)₂
3. CaO
4. CaCO₃

Answer 1

Correct Answer - Option 3 : CaO

Concept:

• Whitewash or lime paint Is a type of paint used to coat walls with white colors. It is made from slaked lime Calcium Hydroxide or Calcium carbonate.
• Whitewash is generally applied in exteriors and has mild antibacterial properties.
• Whitewash curation occurs by its reaction with atmospheric carbon dioxide to form calcium carbonate in the form of calcite. This reaction is known as carbonation or carbonatation.
• Limewash is pure slaked lime in water.
• Limewash and whitewash both cures (dries) to produce the same substance calcite.
• The crystals of calcite produce a nice surface glow on the walls.

Explanation:

• The chemical substance used in whitewashing is CaO, calcium oxide.
• Calcium oxide combines with atmospheric carbon dioxide to form calcium carbonate or calcite.
• CaO is obtained by heating limestone. The reaction is as follows:

CaCO₃ (Limestone) + Δ → CaO ( Calcium oxide or whitewash) + CO₂

• The substance 'X' is thus CaO.

Other uses of CaO are:

• It is used in the manufacture of cement, glass, etc.
• It has medicinal uses and also used as insecticides.
• It is used in the manufacture of caustic soda as it is a basic oxide and its solution in water is alkaline.