Which of the following compounds is obtained when gypsum is heated at 373 K?

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Which of the following compounds is obtained when gypsum is heated at 373 K?

This question was previously asked in

RRB NTPC 2024 Undergraduate CBT 1 Question Paper (29-Aug-2025) (Shift 1)

CaSO₄.2H₂O

CaSO₄.(1/2H₂O)

CaO

CaSO₄.5H₂O

The correct answer is

CaSO₄.(1/2H₂O)

The correct answer is option 2 I.e. CaSO₄.(1/2H₂O).

When gypsum (CaSO₄ · 2H₂O) is heated at 373 K (100°C), it loses water and forms calcium sulfate hemihydrate (CaSO₄ · ½H₂O), commonly known as Plaster of Paris.

Reaction: CaSO₄·2H₂O (gypsum) → CaSO₄·½H₂O (Plaster of Paris) + 1½H₂O (steam)

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