Question

The percentage of nitrogen by mass in ammonium sulphate is closest to (Atomic masses of H=1, N=14, O=16, S=32)
A.\;\;\;\;\;21\% \\\
B.\;\;\;\;\;24\% \\\
C.\;\;\;\;\;36\% \\\
D.\;\;\;\;\;16\% \\\

Answer 1

The formula of ammonium sulphate is ${(N{H_4})_2}S{O_4}$ .The molar mass also known as molecular mass is the sum of the total mass in grams of all the atoms that make up a mole of a particular molecule.

Complete step by step answer:
To get the percentage composition of nitrogen in ammonium sulphate, we will first find the molar mass of the compound.
Therefore, molar mass of ammonium sulphate ${(N{H_4})_2}S{O_4}$ is:
$= 2[14 + 1(4)] + 32 + (16 \times 4)]$ (Atomic masses are given in the question)
$= 132gmo{l^{ - 1}}$
It is important to note that there are 2 nitrogen atoms each belonging to one ammonium ion, $N{H_4}^ +$.
Now,
The percentage composition of nitrogen in ammonium sulphate is given by dividing the molar mass of the two nitrogen atoms by the molar mass of the compound, and then multiply by $100$
Therefore,
% composition of nitrogen$= \dfrac{{2 \times 14}}{{132}}$
$= 21.2$
This means that every $100g$ of ammonium sulphate contains $21.2g$ of nitrogen.

Hence, option A is correct.

Note:
Mass percent is also known as percent by weight. It is one way of representing the concentration of an element in a compound or a component in a mixture.It describes the amount of solute present in $100g$of the solution.