Single correct option
Plaster of Paris is obtained by heating gypsum at 373 K. Its chemical formula is
- A. CaSO₄·½H₂O
- B. CaSO₄·2H₂O
- C. CaCO₃
- D. CaSO₄
Show answer and solution
Answer: (A) CaSO₄·½H₂O
Gypsum is CaSO₄·2H₂O. On heating to 373 K it loses three-fourths of its water of crystallisation and gives CaSO₄·½H₂O, the Plaster of Paris. It sets into gypsum again when mixed with water. CaCO₃ is limestone, and CaSO₄ is the fully anhydrous form.
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