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NDA 2020 GAT · General Knowledge · Chemistry in Everyday Life · medium

Plaster of Paris has the formula CaSO4.1/2H2O. 2. Gypsum, when heated to about 373 K, gives Plaster of Paris.

Single correct option

Consider the following statements.
1. Plaster of Paris has the formula CaSO4.1/2H2O.
2. Gypsum, when heated to about 373 K, gives Plaster of Paris.
Which of the statements given above is/are correct?
  1. A. 1 only
  2. B. 2 only
  3. C. Both 1 and 2
  4. D. Neither 1 nor 2
Show answer and solution

Answer: (C) Both 1 and 2

Plaster of Paris is calcium sulphate hemihydrate, CaSO4.1/2H2O, so statement 1 is correct. Gypsum (CaSO4.2H2O) loses three-quarters of its water of crystallisation on heating to about 373 K, producing Plaster of Paris, so statement 2 is correct. It sets to gypsum on adding water, which is used for casts.
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Original question written in the NDA 2020 GAT pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake