47. 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 and why does it show such a behaviour? Give the reaction involved.
Steps: Plaster of Paris contains less water and is soft when mixed to a paste; exposure to moisture converts it to the dihydrate (gypsum) forming a hard mass (setting reaction used in casts).