Question

A sulphate salt of group two element of periodic table is white, soft substance, which can be moulded into different shapes by making it dough. When this compound is left in open for sometime, it becomes a solid object and cannot be used for moulding purposes. Identify this sulphate salt and explain why does it show such a behaviour. Also give the equation for the reaction involved.

Answer 1

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 WHEN IT DRIES THE WATER OF CRYSTALLIZATION IS REMOVED WHEN LEFT OPEN

HOPE IT WILL HELP!!!!!