Question

Are the crystals of salts really dry?

Answer 1

Hint: The crystals are actually dry because the water present in them doesn't behave as water but gives them a crystalline structure. Crystals of Copper sulphate look dry but contain water of crystallization.

Complete step by step answer:
- Copper sulphate crystals look dry but contain water for crystallization.
- When we apply some heat to these copper sulphate crystals the water comes out and copper sulphate turns to white in color. If we are going to add water to the white color copper sulphate, it regains its blue color.
- Coming to another example, Plaster of Paris also called as Calcium sulphate hemihydrate.
 - On heating gypsum at 373 K, gypsum loses water and form Plaster of Paris (POP).
 - The conversion of gypsum into POP is as follows.
\[\underset{Gypsum}{\mathop{CaS{{O}_{4}}.2{{H}_{2}}O}}\,\xrightarrow{{}}\underset{Plaster\text{ }of\text{ }Paris}{\mathop{CaS{{O}_{4}}.{\scriptstyle{}^{1}/{}_{2}}{{H}_{2}}O}}\,+1{\scriptstyle{}^{1}/{}_{2}}{{H}_{2}}O\]
- Plaster of Paris is a white powder, when POP reacts with water again changes to gypsum. The chemical reaction is as follows.
\[\underset{Plaster\text{ }of\text{ }Paris}{\mathop{CaS{{O}_{4}}.{\scriptstyle{}^{1}/{}_{2}}{{H}_{2}}O}}\,+1{\scriptstyle{}^{1}/{}_{2}}{{H}_{2}}O\xrightarrow{{}}\underset{Gypsum}{\mathop{CaS{{O}_{4}}.2{{H}_{2}}O}}\,\]
- Means Crystals of the salts are really dry though the presence of water molecules.

- So, the given statement is correct.


Additional information:
- Plaster of Paris is used by doctors to support fractured bones.
- Plaster of Paris is used for decoration and for making toys.
- Plaster of Paris is used to make surfaces smooth.


Note: Crystals of salts are really dry but contain a minimum amount of water of crystallization. In few chemical compounds like copper sulphate crystal the presence of water is going to impart color to the crystals.