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KCET · Chemistry · s Block Elements

Dead burnt plaster is

  1. A \( \mathrm{CaSO}_{4} \)
  2. B \( \mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O} \)
  3. C \( \mathrm{CaSO}_{4} \cdot \mathrm{H}_{2} \mathrm{O} \)
  4. D \( \mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O} \)
Verified Solution

Answer & Solution

Correct Answer

(A) \( \mathrm{CaSO}_{4} \)

Step-by-step Solution

Detailed explanation

When gypsum is heated at temperature above \( 393 \mathrm{~K} \) than, there no water of crystallization is left and anhydrous calcium
sulphate \( \left(\mathrm{CaSO}_{4}\right) \) is formed. This is known as dead burnt plaster.
\[
\mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O} \rightarrow \underset{\text { Gypsum }}{\mathrm{CaSO}_{4}}+2 \mathrm{H}_{2} \mathrm{O}
\]