Question

The percentage of Nitrogen in Urea ($N{{H}_{2}}CON{{H}_{2}}$) is :
(A) 38.4
(B) 46.6
(C) 59.1
(D) 61.3

Answer 1

We can find the % of nitrogen in urea by following formula.
% Composition of Nitrogen in Urea = $\dfrac{100\times \text{Weight of total nitrogen atoms in compound}}{\text{Molecular weight of Urea}}$
Atomic weight of Nitrogen is 14 $gmmo{{l}^{-1}}$ and Molecular formula of Urea is $C{{H}_{4}}{{N}_{2}}O$.

Complete step by step answer:
To find the percentage of nitrogen in urea, we will need to first find the molecular weight of urea and then we will find the total weight of all nitrogen atoms present in the urea molecule in order to find the percent of nitrogen composition in urea.
We know that,
Atomic weight of Oxygen = 16$gmmo{{l}^{-1}}$
Atomic weight of Hydrogen = 1$gmmo{{l}^{-1}}$
Atomic weight of Carbon = 12$gmmo{{l}^{-1}}$
Atomic weight of Nitrogen = 14$gmmo{{l}^{-1}}$
We can write molecular formula of urea as $C{{H}_{4}}{{N}_{2}}O$

So, molecular weight of Urea = 2(Atomic weight of N) + Atomic weight of C + 4(Atomic weight of H) + Atomic weight of O
Molecular weight of urea = 2(14) + 12 + 4(1) + 16
Molecular weight of Urea = 28 + 12 + 4 + 16
Molecular weight of urea = 60$gmmo{{l}^{-1}}$
Now, there are two total nitrogen atoms present in the urea molecule.
So, weight of nitrogen atoms in urea compound will be 14 + 14 = 28$gmmo{{l}^{-1}}$
Now, we can say that
% Composition of Nitrogen in Urea = $\dfrac{100\times \text{Weight of total nitrogen atoms in compound}}{\text{Molecular weight of Urea}}$
% Nitrogen =$\dfrac{100\times 28}{60}$
% Nitrogen = 46.66%
So, the correct answer is “Option B”.

Note: - Do not forget that in finding % of nitrogen in the compound we need to count the weight of all nitrogen atoms in the compound and that value needs to be put into the formula, do not put just the atomic weight of one nitrogen atom there.