Question

A sulphate salt of Group 2 element of the Periodic Table is a white, soft substance, which can be molded into different shapes by making its dough. When this compound is left in open for some time, it becomes a solid mass and cannot be used for mounding purposes

Answer 1

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SULPHATE SALT= CaSO4.1/2H20

CaSO4.1/2H2O - calcium sulphate hemihydrate is the white salt ( PLASTER OF PARIS)

when it can be molded into different shape it is called GYPSUM

CaSO4.12H2O  + 1.1/2H2O ----> CaSO4.2H2O

WHEN IT DRIES IT AGAIN BECOMES PLASTER OF PARIS.

THIS IS BECAUSE THE WATER OF CRYSTALLIZATION IS REMOVED