(a) Green crystals of a substance changed their colour on heating in a closed 5
test tube but regained it after sometime when they were allowed to cool
down. Name the substance and write its formula.
(b) Name the compound whose one formula unit is associated with 10 water
molecules. How is it prepared from sodium chloride? Give equations of
related reactions. Give two uses of the compound.
Answers
Answer:
(a) Green crystals of a substance changed their colour on heating in a closed 5
test tube but regained it after sometime when they were allowed to cool
down. Name the substance and write its formula.
(b) Name the compound whose one formula unit is associated with 10 water
molecules. How is it prepared from sodium chloride? Give equations of
related reactions. Give two uses of the compound.
Explanation:
hr
Answer:
Crystals of a substance which changed their colour on heating in a closed test tube but regained it after sometime when they were allowed to cool down are copper sulphate or more specifically hydrated copper sulphate.
Its formula - CuSO
4
.5H
2
O
The phenomena involved is due to the presence of molecules of water of crystallization in the molecule. Water of crystallization is the fixed number of water molecules that are present in one formula unit of a salt. When we heat the crystals of hydrated copper sulphate this water is removed and the salt turns white. But when it is allowed to cool down in open air then it regains its lost water of crystallization and hence regains its colour also.