What is dead burnt plaster?

Plaster of Paris is obtained by heating gypsum. Following is the chemical equation for the reaction

 CaSO4.2H2O → CaSO4.1/2H2O + 11/2 H2O

However, when heated beyond 393 K, all the water of crystallisation is lost resulting in the formation of anhydrous calcium sulphate. This anhydrous calcium sulphate obtained by the over-heating of gypsum is known as dead burnt plaster. It does not possess any properties of setting with water. 

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at 200o celcius plaster of paris looses all its water molecules and this anhydrous form is called as dead plaster.

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Plaster Of Paris (POP) has formula . It is also known as Hemihydrate of Calcium Sulphate.

Preparation POP from Gypsum by heating it to 393 K.

Above 393 K, water is liberated to form anhydrous calcium sulphate (CaSO4), known as dead burnt plaster.

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Dead Burnt Plaster - When Heated Above 393 K Plaster Of Paris Gives Anhydrous CaSO4 Which Is called A Dead Burnt Plaster. Preparation-

CaSO4 .2H2O (Above 393 K)--------CaSO4+2H2O

Gypsum Calcium Water

Sulphate

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anhydrous form of POP is known as dead burnt plaster

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Plaster of Paris is formed by heating gypsum at 100 degree celsius.At this temperature Gypsum looses 3/4 of its water of crystallization forming plaster of paris.If the temperature is allowed beyond 100 degree celsius,it will become anhydrous calcium sulphate which is called Dead burnt blaster unlike the plaster of paris it does not have the property to set after mixing with water.

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