8.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 sometime, it becomes a solid mass and cannot be used for moulding purposes. Identify the sulphate salt and why does it show such a behavior? Give the reaction involved.
Answers
We can consider element as Calcium and its salt as
Calcium sulphate hemi hydrated salt .
Common Name : plaster Of paris
Formula : CaSO4.1/2H20
Chemical Name : calcium sulphate hemi hydrated salt
Plaster of paris is used in making different Ganesh Idols and other decorative items.
But its very important that Plaster of pairs should be stored in Moisture proof container.
Because on exposure to moisture POP turns to hard solid mass called as Gypsum which cannot be used for molding Purpose.
CasO4.1/2H20 +3/2 H20 ---> CaSO4.2H2O
[POP] [Gypsum]
Explanation:
Calcium belongs to group 2. Calcium sulphate is a white soft substance. It is known as Plaster of Paris, which can be moulded into different shapes by making its dough.
When Plaster of Paris is left for some time in open, it turns into solid mass because of reaction with moisture present in the atmosphere. The solid mass so formed is known as gypsum and cannot be further used for moulding.
CaSO
4
.
2
1
H
2
O+1
2
1
H
2
O→CaSO
4
.2H
2
O
Plaster of Paris Gypsum
(Soft) (Hard mass)
(Sulphate salt)
The above said group 2 element is calcium and sulphate of that element is Plaster of Paris. Plaster of Paris shows such behavior because of presence half water molecule as water of crystallization. When it is left open for some time, it absorbs moisture from the atmosphere and forms gypsum, which is a hard solid mass.