Question

: Calculate the percentage of water of crystallisation in Glauber’s salt($N{a_2}S{O_4}.10{H_2}O$)
(A) $45.18\% $
(B) $75.39\% $
(C) $36.33\% $
(D) $55.72\% $

Answer 1

Hint: Glauber’s salt is the decahydrate form of sodium sulphate. The chemical formula is $N{a_2}S{O_4}.10{H_2}O$. It reacts with ten water molecules and has ten molecules of water of crystallisation in it. Mass percentage of an element is calculated by dividing the molar mass of that particular component to the total mass of compound times hundred.

Complete step-by-step answer:We kn1ow that Mass percentage of an element is calculated by dividing the molar mass of that particular component to the total mass of compound times hundred.

Mass percent = molar mass of that particular element /total mass of compound $ \times $$100$
For percentage water of crystallisation:
Atomic mass of oxygen= $16\;gmo{l^{ - 1}}$
Atomic mass of hydrogen=$1g\;mo{l^{ - 1}}$
Atomic mass of sodium=$23\;gmo{l^{ - 1}}$
Atomic mass of sulphur= $32\;gmo{l^{ - 1}}$
So molar mass of Glauber’s salt=$23 \times 2 + 32 + 16 \times 4 \times 10 \times 18$ $ = 323$
Molar mass of ten molecules of water= $10 \times 18 = 180\;gmo{l^{ - 1}}$
Now percentage of water would be molar mass of ten molecules of water divided by total molar mass of compound multiplied by hundred
Percentage of water of crystallisation=$\dfrac{{180}}{{323}} \times 100 = 55.72\% $
Therefore the percentage of water of crystallisation= $55.72\% $

Additional information: Glauber's salt, the decahydrate, is used as a laxative. It is effective for the removal of certain drugs such as paracetamol (acetaminophen) from the body, for example, after an overdose. It can also be noted that Glauber’s salt is quite unstable in dry air. When placed in such an environment, this compound is known to rapidly undergo dehydration. It is also known as mirabilite.

Hence the correct answer is option D


Note: Glauber’s salt may be colourless, white, greenish white which forms the crystals with water. Mass prevention is a way of expressing concentration. . It is used as a laxative.