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acids, bases and salts — Science STD 10 — Question

Gujarat BoardEnglish MediumSTD 10Scienceacids, bases and salts3 Marks
Question
Write a short note on plaster of paris $(POP).$
✓

Answer

  • Preparation:
  • When gypsum is heated at $373 \ K$ temperature, it loses water molecules and forms plaster of paris.
  • $2\left[ CaSO _4 \cdot 2 H _2 O \right]( s ) \xrightarrow{373 K} 2\left( CaSO _4\right) \cdot H _2 O ( s )+3 H _2 O ( g )$
  • Gypsum
  • OR
  • $CaSO _4 \cdot 2 H _2 O ( s ) \stackrel{373 K}{\rightarrow} CaSO _4 \cdot \frac{1}{2} H _2 O +1 \frac{1}{2} H _2 O$
  • Gypsum Plaster of paris
  • Plaster of paris is a hemihydrate of calcium sulphate, in which one water molecule is attached with two $Ca ^{2+}$ and two $SO _4^{2-}$ ions.
  • Plaster of paris is a white powder and on mixing it with water, it changes to hard solid mass gypsum.
  • $CaSO _4 \cdot \frac{1}{2} H _2 O +1 \frac{1}{2} H _2 O \rightarrow CaSO _4 \cdot 2 H _2 O$
  • Plaster of paris Gypsum
  • Uses:
  • $(1)$ In construction and in plastering the walls.
  • $(2)$ In orthopedics, it is used for setting fractured bones in the right position.
  • $(3)$ In making cast in dentistry.
  • $(4)$ In making idols.
  • $(5)$ In making chalks for writing on the black board.
  • $(6)$ In laboratory, it is applied as plaster for making the apparatus air tight.

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