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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3sb109

Which of the following statements about gypsum and plaster of Paris are correct?

  1. AHeating gypsum above about 473 K gives anhydrous CaSO4 (dead burnt plaster) that does not set with water
  2. BPlaster of Paris is the dihydrate
  3. CGypsum heated at about 393 K gives plaster of Paris
  4. DPlaster of Paris sets because it loses water to form a hard mass

Answer: A, C

Mild heating (393 K) converts gypsum to the hemihydrate, and stronger heating (above about 473 K) gives dead burnt plaster which no longer sets. Plaster of Paris is the hemihydrate and sets by taking up water to reform gypsum, not by losing it.
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