Which of the following is known as ‘Plaster of Paris’?

Correct Answer CaSO₄⋅1/2H₂O

Key Points Explanation:

• Plaster of Paris (POP) is a quick-setting gypsum plaster consisting of a fine white powder (calcium sulfate hemihydrate), which hardens when moistened and allowed to dry.
• It is also known as the Plaster of Paris because for the preparation of POP, the abundant gypsum was first found near the capital city of France i.e. Paris.
• The chemical formula of the Plaster of Paris is CaSO4.\(\frac{1}{2}\) H2O = 
• Application of Plaster of Paris is as follows

1. It is used as a building material as a protective coating on walls and ceilings.
2. It is used as a moulding and vesting agent for decorative elements.
3. It is also used for aesthetic touch to the construction elements.
4. It is also used as plaster in orthopaedics and as a filling material by dentists, etc.

Confusion Points:

• Gypsum is an ore of Calcium (Ca). The chemical formula of Gypsum is CaSO4. 2H2O.
• Gypsum is mainly used as a fertilizer, as the main constituent in plaster, chalk, etc.
• The plaster of Paris on mixing with water produces gypsum.
• Calcium Sulphate Hemihydrate (CaSO4·1/2 H2O) on hydration leads to the crystallization of gypsum calcium sulphate dihydrate (CaSO4·2H2O).