In the hardening stage of plaster of paris, the compound formed is

In the hardening stage of plaster of paris, the compound formed is
  1. $\mathrm{CaSO}_4$
  2. $Orthorhombic$ $\mathrm{CaSO}_4 \cdot 2 \mathrm{H}_2 \mathrm{O}$
  3. $\mathrm{CaSO}_4 \cdot \mathrm{H}_2 \mathrm{O}$
  4. $Monoclinic$ $\mathrm{CaSO}_4 \cdot 2 \mathrm{H}_2 \mathrm{O}$

Solution

Plaster of paris absorb water to form monoclinic gypsum which is a hard substance. $ \mathrm{CaSO}_4 \cdot \frac{1}{2} \mathrm{H}_2 \mathrm{O} \stackrel{3 / 2 \mathrm{H}_2 \mathrm{O}}{\longrightarrow} \mathrm{CaSO}_4 \cdot 2 \mathrm{H}_2 \mathrm{O} $ (monoclinic gypsum)

Asked in: AP EAMCET 2004

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