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Why is it necessary to heat gypsum only at controlled temperature?

Answer and explanation

Correct answer: Only part of water of crystallisation must be removed to form hemihydrate

Gypsum is calcium sulphate dihydrate, CaSO₄·2H₂O. On controlled heating, it loses only part of its water of crystallisation and changes into calcium sulphate hemihydrate, CaSO₄·½H₂O, called plaster of Paris. If heating is excessive, the material may become anhydrous calcium sulphate and lose its useful setting property. Therefore, option A is correct; the other options describe unrelated changes.

Related tags

GypsumPlaster Of ParisControlled HeatingAcidsBasesAnd SaltsAcids Bases And SaltsChemical Substances – Nature And BehaviourChemical Substances Nature And BehaviourScience

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