Question

Plaster of Paris (POP) is formed by heating gypsum.

• A. True
• B. False

Answer 1

The correct option is A True

CaSO₄·2H₂O + heat → CaSO₄·0.5H₂O + 1.5H₂O (discharged as steam)

• Gypsum CaSO₄.2H₂O can be heated on 120^oC so that water evaporates and POP CaSO₄.1/2H₂O formed.
• Plaster of Paris is manufactured by heating gypsum at 373 – 393 K or 150° C/300° F.
• On heating gypsum at 373 – 393 K, it loses water molecules and becomes calcium sulphate hemihydrate.
• This product is known as the plaster of Paris.
• However, when water is mixed with dry plaster of Paris, it re-structures into gypsum.
• As for the process of hardening and settling, it starts around 10 minutes subsequent to blending and is completed in about 45 minutes.
• It is not completely set for 70-75 hours.

CaSO₄.2H₂O → CaSO₄.1/2H₂O + 3/2H₂O

Gypsum POP Water Vapours