Question

The percentage of nitrogen in urea is about:
(A)- $38.4$
(B)- $46.6$
(C)- $59.1$
(D)- $61.3$

Answer 1

Except nitrogen gas in the environment, nitrogen also comes from many sources in nature. And urea is one of the most common sources of nitrogen out of those sources which are available in nature.

Complete answer:
Chemical formula of urea is shown as ${\text{N}}{{\text{H}}_{\text{2}}}{\text{ - CO - N}}{{\text{H}}_{\text{2}}}$, and from this it is clear that:
-In urea one carbonyl group is present.
-With this carbonyl group two amino groups (${\text{N}}{{\text{H}}_{\text{2}}}$) are attached.
To calculate the percentage of nitrogen in urea we can use mass parameter in consideration and follows the following steps:
-First we calculate the molecular mass of urea which is the sum of the masses of all atoms present in an urea molecule.
-As we know that,
Mass of hydrogen = $1$
Mass of nitrogen = $14$
Mass of oxygen = $16$
And mass of carbon = $12$
Now we add all these masses to calculate the molecular mass of urea.
-Molecular mass of urea = $2 \times$(mass of nitrogen) + $4 \times$(mass of hydrogen) + mass of carbon + mass of oxygen
Molecular mass of urea = $\left( {2 \times 14} \right) + \left( {4 \times 1} \right) + 12 + 16$
Molecular mass of urea = $28 + 4 + 12 + 16 = 60$
Hence, the molecular mass of urea is$60$.
-To calculate the percentage of nitrogen present in the urea, we have to use following formula:
$$Percentage{\text{ }}of{\text{ }}nitrogen{\text{ }} =$$$\dfrac{{mass{\text{ }}of{\text{ }}nitrogen}}{{mass{\text{ }}of{\text{ }}urea}} \times 100$Mass of nitrogen in urea is$28$because in urea two atoms of nitrogen are present. Percentage of nitrogen =$\dfrac{{28}}{{60}} \times 100 = 46.6$So, the percentage of nitrogen in urea is about$46.6$.

Hence option (B) is correct.

Note:
In this question during the calculation of percentage of nitrogen, some of you may write $14$ in place of mass of nitrogen which will be wrong, because in urea only one nitrogen is not present.