Question

Glauber’s salt is:
(A) Hepta hydrate
(B) Decahydrate
(C) Pentahydrate
(D) Dihydrate

Answer 1

Hint: Glauber’s salt occurs as white or colorless monoclinic crystals which are formed when sodium sulfate is evaporated. It is also known as mirabilite. To determine the number of water molecules present in Glauber’s salt we need to write the chemical formula name and the molecular formula of the compound.

Complete answer: We know the chemical name of the Glauber’s salt is Sodium sulfate Decahydrate.
So, the molecular formula will be \[N{a_2}S{O_4}.10{H_2}O\]
From the molecular formula we can see that this salt is decahydrate i.e. it contains ten molecules of water present as water of crystallization.
Also, Glauber’s salt is unstable when exposed to dry air as when exposed to such an environment this salt readily undergoes dehydration. So, on dehydration the crystals present in Glauber’s salt are transformed into a white powder. This white powder is known as sodium sulfate with the formula of $N{a_2}S{O_4}$.
This white powder or sodium sulphate is commonly known as thenardite. It possesses the ability to absorb water and convert into mirabilite or Glauber’s salt.
Uses of Glauber’s salt:
i. It is used as a laxative in drugs. Also, it is used in the elimination of excess drugs in the body due to drug overdose.
ii. It is used to make chill mats for laptops and computers.
iii. It is also used in dyeing.

Therefore, the correct answer is Option (B). i.e. Decahydrate.

Note: The geometry of the crystals present in Glauber’s salt is Octahedral. In 1953, Glauber’s salt was used in heat storage in passive solar heating systems because it is anhydrous so the water molecules can easily absorb heat. Also, for questions like these we need to always remember the chemical name and the molecular formula of the compound.