Question

is sulphate salt of group 2 elements of periodic table is a white soft substance which can be moulded into different shape by making its dove when this compound is left in open for sometime it becomes a solid mass and cannot be used for molding purpose identify the sulphate salt and why does it show such behaviour give the reaction involved

Answer 1

The substance which is used for making different shapes is Plaster of Paris. Its chemical name is calcium sulphate hemihydrate (CaS04.1/2H20). The two formula unit of CaS04 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.