Question

Calculate the percentage of nitrogen in $N{H_3}$ .
(Atomic mass of $N = 14,{\text{ }}H = 1{\text{ }}amu$ )

Answer 1

Hint : Here you should recall the concept of molar mass of any chemical compound which refers to the ratio of mass of a sample of that particular compound and the amount of substance in that particular sample (in moles). The molar mass is generally represented as $gmo{l^{ - 1}}$ .

Complete Step By Step Answer:
In order to calculate the percentage of nitrogen in $N{H_3}$ , first of all we have to calculate the molar mass of $N{H_3}$ . We know that the molar mass of any compound can be found out by adding the relative atomic masses of each element present in that particular compound. The number of atoms in a compound can be determined from their chemical formula.
Now, let us calculate the molar mass of the given compound i.e. ammonia having a chemical formula of $N{H_3}$ . We are given the atomic masses of hydrogen and nitrogen as stated below:
$H = 1amu$
$N = 14amu$
From the chemical formula, it is clear that ammonia contains three atoms of hydrogen and one atom of nitrogen and thus molecular mass of this compound can be calculated by adding the mass of three hydrogen atoms and one nitrogen atom as shown below:
$Molecular{\text{ }}mass{\text{ }}of{\text{ }}N{H_3} = (1 \times N) + (3 \times H) = (1 \times 14) + (3 \times 1) = 17u$
Now, we have to calculate the percentage of nitrogen in $N{H_3}$ for which we will use the following formula:
$\% nitrogen{\text{ }}in{\text{ }}N{H_3} = \dfrac{{Atomic{\text{ }}mass{\text{ }}of{\text{ }}nitrogen}}{{Molar{\text{ }}mass{\text{ }}of{\text{ }}N{H_3}}} \times 100$
$= \dfrac{{14}}{{17}} \times 100 = 82.3\%$
Hence, the percentage of nitrogen in $N{H_3}$ is $82.3\%$ .

Note :
Molar mass plays a significant role in chemistry especially during setting up an experiment. During testing principles which involve specific amounts or quantities of a substance, molar mass is used to figure out the exact quantity to be weighed of that particular substance. Basically molar mass is used to determine the stoichiometry in the chemical reactions as well as equations.