Q96 (CAPF/2025) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Applied everyday chemistry Answer Verified

Which one among the following statements regarding gypsum is not correct?

On heating gypsum at 373 K, it loses water molecules and becomes CaSO4 · H2O.

On mixing with water, plaster of Paris changes to gypsum.

Plaster of Paris is used for supporting fractured bones.

Although gypsum possesses water of crystallization, it is not a liquid at room temperature.

Result

Your answer: — · Correct: A

Explanation

Statement 1 is incorrect because heating gypsum (CaSO4·2H2O) at 373 K (100°C) results in the formation of Plaster of Paris, which is calcium sulfate hemihydrate (CaSO4·½H2O), not a monohydrate (CaSO4·H2O) [5]. The chemical equation shows that gypsum loses 1.5 molecules of water per formula unit during this partial dehydration [5]. Statement 2 is correct as Plaster of Paris rehydrates into a hard solid mass of gypsum when mixed with water [1]. Statement 3 is correct because doctors use this substance as an orthopedic cast to support and immobilize fractured bones [1]. Statement 4 is also correct; although gypsum contains water of crystallization within its crystal lattice, it remains a solid mineral at room temperature [3]. The fractional formula CaSO4·½H2O represents two formula units of calcium sulfate sharing one water molecule [5].

Sources

[1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Plaster of Paris > p. 33
[5] https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/calcium-sulfate
[3] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 7: Resources > Natural Resources of India > p. 28

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Which one among the following statements regarding gypsum is not correct?

Explanation

SIMILAR QUESTIONS

Which one of the following statements is not correct?

Consider the following statements: 1. Baking soda is used in fire extinguishers. 2. Quicklime is used in the manufacture of glass. 3. Gypsum is used in the manufacture of Plaster of Paris. Which of the statements given above is/are correct ?

Statement I : On mixing with water, Plaster of Paris hardens. Statement II : By combining with water, Plaster of Paris is converted into Gypsum.

Statement I: The blue colour of copper sulphate crystal disappears when it is heated strongly. Statement II : Due to heating, water of crystallization of crystal is lost.