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The chemical name for 'Plaster of Paris' is:
calcium sulphate dihydrate
calcium chloride hexahydrate
calcium sulphate hemihydrate
calcium chloride semihydrate
calcium sulphate hemihydrate
Plaster of Paris (POP) is chemically known as calcium sulphate hemihydrate. It is a white powdery substance produced by heating gypsum at 373 K.
Plaster of Paris (POP) is chemically known as calcium sulphate hemihydrate. It is a white powdery substance produced by heating gypsum at 373 K.
Think of it like a 'thirsty' sponge; when you heat gypsum, you remove most of its water, making it so desperate to get it back that it hardens almost instantly when mixed with water.
POP is HALF-full: hemi- means half, so CaSO4тАЛтЛЕ21тАЛH2тАЛO.
CaSO4тАЛтЛЕ2H2тАЛO373KтАЛCaSO4тАЛтЛЕ21тАЛH2тАЛO+23тАЛH2тАЛO тАФ Dehydration of Gypsum to POP
CaSO4тАЛтЛЕ21тАЛH2тАЛO+23тАЛH2тАЛOтЖТCaSO4тАЛтЛЕ2H2тАЛO тАФ Hardening reaction of POP back to Gypsum
When gypsum (CaSO4тАЛтЛЕ2H2тАЛO) is heated at 373 K, it loses three-fourths of its water of crystallization to form CaSO4тАЛтЛЕ21тАЛH2тАЛO. This product is known as Plaster of Paris, which readily sets into a hard mass upon rehydration.
Plaster of Paris is chemically calcium sulphate hemihydrate.
Gypsum is chemically calcium sulphate dihydrate (CaSO4тАЛтЛЕ2H2тАЛO).
Hardening of POP is an exothermic hydration reaction.
Sets into a hard, solid mass quickly
Excellent for casting and molding
Provides a smooth finish
Must be stored in moisture-proof containers to prevent premature hardening
Used by doctors for supporting fractured bones in the right position
Used for making toys, statues, and decorative ceiling designs
The term 'hemihydrate' corresponds to the 0.5 molecule of water per formula unit of calcium sulphate.
Option A (calcium sulphate dihydrate) is the chemical name for Gypsum, not POP.
Option B (calcium chloride hexahydrate) is an incorrect chemical identity.
C is correct тАФ Plaster of Paris is calcium sulphate hemihydrate with the chemical formula CaSO4тАЛтЛЕ21тАЛH2тАЛO.
Always differentiate between 'dihydrate' (Gypsum) and 'hemihydrate' (POP); they are the most frequently confused pair in chemistry competitive exams.
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