Question

A sulphate salt of the group ${\text{2}}$ element of the periodic table is a white, soft substance, which can be molded 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 molding purposes. Identify the sulphate salt.
A) White Paris
B) Plaster of Paris
C) Calcium hydroxide
D) Calcium carbonate

Answer 1

Hint:The sulphate salt has an element of the group ${\text{2}}$ and the properties of that chemical have been elaborated in the question itself. Analyze the given properties and think about the possible known compound. One can even try to write a chemical reaction for the compound formation and make the correct choice.

Complete step by step answer:
1) First of all we will try to understand the properties given of the chemical compound in the question itself. According to the given properties of the sulphate salt, we can say that the compound may be used for making the various idols and as in building materials.
2) The sulphate salt of the group ${\text{2}}$ element is calcium and its salt is called the calcium sulphate Hemi hydrated salt. Now let us see the reaction of calcium sulphate Hemi hydrated salt as below,
$CaS{O_4} \cdot \dfrac{1}{2}{H_2}O + \dfrac{3}{2}{H_2}O \to CaS{O_4} \cdot 2{H_2}O$
In the above reaction when calcium sulphate Hemi hydrated salt reacts with atmospheric water molecules it forms the solid form of calcium sulphate.
3) The calcium sulphate which is a white and soft substance is also called plaster of Paris. When it gets into contact with the atmospheric water molecules it gets hard and cannot be molded further.
Therefore, the sulphate salt of the group ${\text{2}}$ element of the periodic table is plaster of Paris which shows option B as the correct choice.

Note:
The name plaster of Paris is because it is made from the gypsum material which is found in abundance near Paris. The plaster of Paris is used primarily in building materials and making Lord Ganesh idols and other crafting idols.