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Question
A sulphate salt 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. Why does it show such a behaviour? Give the reaction involved.
Solution
The available information suggests that the element present in group 2 of the Periodic Table is calcium (Ca) and the sulphate salt (white in colour) is Plaster of Paris. It can be moulded into different shapes by making its dough with water. When left in the open, Plaster of Paris changes into Gypsum which is a solid mass quite hard in nature and can no longer be used for moulding.
`"CaSO"_4 1//2"H"_2"O" + underset("Plaster of Paris")(3//2 "H"_2"O") -> underset("(Moisture)")("CaSO"_4). underset("Gypsum")(2"H"_2"O")`
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