Question

# The percentage of N in 66 g pure ${\left( {{\text{N}}{{\text{H}}_{\text{4}}}} \right)_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$sample is :A . 32B . 28C . 21 D . none of the above

Hint: ${\left( {{\text{N}}{{\text{H}}_{\text{4}}}} \right)_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$, Ammonium sulfate is an inorganic compound. To calculate the percentage at first you have to calculate the molecular weight of the molecule. Ammonium sulfate salt can be prepared from ammonia and sulfuric acid.

Ammonium sulfate can be prepared from the reaction between ${\text{N}}{{\text{H}}_3}$ and ${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$. In this reaction one mole of ${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$ reacts with two moles of ${\text{N}}{{\text{H}}_3}$. As ammonia is a base it absorbs hydrogen ion and forms ammonium ion. Then it combines with the sulfate anion to form the ionic inorganic salt ammonium sulfate. The reaction is shown below.
${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}{\text{ + 2N}}{{\text{H}}_{\text{3}}} \to {\text{2N}}{{\text{H}}_{\text{4}}}^{\text{ + }}{\text{ + S}}{{\text{O}}_{\text{4}}}^{{\text{ - 2}}} \to {\left( {{\text{N}}{{\text{H}}_{\text{4}}}} \right)_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$
Now the molecular weight of ammonium sulfate,${\left( {{\text{N}}{{\text{H}}_{\text{4}}}} \right)_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$ is.
$2 \times \left( {14 + 4} \right) + \left( {32 + 64} \right) \\ = 2 \times 18 + 96 \\ = 36 + 96 \\ = 132 \\$
When this salt is $100\%$pure, the percentage of nitrogen present is
,$= \dfrac{{2 \times 14}}{{132}} \\ = 21.2\% \\$
Now, for 66 gram pure ammonium sulfate the percentage of nitrogen is
$= \dfrac{{2 \times 14}}{{132}} \times 66 \\ = \dfrac{{28}}{{132}} \times 66 \\ = 14\% \\$
This answer is not matching with any of those given answers in the question. So, none of those is the correct answer.

Therefore, the correct option is D.

Note:
Ammonium sulfate is hygroscopic in nature. For alkaline soils ammonium sulfate is used as a fertilizer, it releases ammonium ion into the soil and produces a small amount of acids to maintain the pH balance of the soil. Ammonium sulfate also contributes an essential nitrogen element into the soil for the growth of the crops.