A sulphate salf of Group 2 element of the Periodic Table is a white , soft substance , which can be moulded 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 moulding purposes Identify the sulphate salt and state , why does it show such a behaviour . Give the reaction involved.

A sulphate salf of Group 2 element of the Periodic Table is a white ,

1.	A sulphate salf of Group 2 element of the Periodic Table is a white , soft substance , which can be moulded 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 moulding purposes Identify the sulphate salt and state , why does it show such a behaviour . Give the reaction involved.
Answer» Solution :The substance which is used for making different shapes is Plaster of Paris . Its chemical name is calcium sulphate HEMIHYDRATE `(CaSO_(4).1//2H_(2)O)`. The two formula UNIT of `CaSO_4` share one molecule of water . As a result, it is soft. When it is left open for some time. it absorbs moisture from the ATMOSPHERE and FORMS gypsum, which is a hard SOLID mass. `underset(("Sulphate salt"))underset(("Soft"))underset("Plaster of Pairs")(CaSO_(4).1/2H_(2)O)+1(1)/(2)H_(2)Orarrunderset(("Hard mass"))underset("Gypusm")(CaSO_(4).2H_(2)O`