Question

How do you calculate the percentage composition of iodine in $N{I_3}$?

Answer 1

The percent composition is the percentage of the individual atoms which makes a compound. The percentage is obtained by the ratio of the mass of an atom and the total mass of the compound multiplied by $100$.

Complete step by step answer:
A composition is defined as the mixture of several elements in a definite ratio or proportion. The moles of elements and the atomic masses of the elements are used for calculation. The percent composition is expressed by the relation
$\% {C_E} = \dfrac{{{m_E}}}{M} \times 100$ where ${C_E}$ is the percentage composition of an element, ${m_E}$ is the amount of the individual element and $M$ is the total amount of the compound.
The given compound is nitrogen triiodide. It is composed of one nitrogen ion and three iodine ions. The nitrogen ion is the cation and the iodine ion is the anion. The element nitrogen is in $+ 3$ oxidation state. The iodine ion carries unit negative charge. So to satisfy the three positive charges of nitrogen three iodine ions are required. The molecule is a neutral species.
So at first we need to evaluate the atomic mass of the elements involved in the compound. The elements which consist of nitrogen triiodide are nitrogen and iodine. The chemical formula of nitrogen triiodide is $N{I_3}$.
The atomic mass of $N$ is $14.0067u$ and atomic mass of is $126.9045u$. Thus using the chemical formula of nitrogen triiodide for calculation of molar mass as follows:
Mass of $N$ = $1{\text{ }} \times$ atomic mass of $N$ = $1 \times 14.0067u = 14.0067u$.
Mass of $I$ = $3{\text{ }} \times$ atomic mass of $I$ = $3 \times \;126.9045u\; = 380.7135u$.
Thus the mass of $N{I_3}$ = $14.0067u + 380.7135u = 394.7202u$.

Hence the percentage composition of iodine in $N{I_3}$ is determined as
$\% {\text{ }}N = \dfrac{{380.7135u}}{{394.7202u}}\; \times {\text{ }}100\% = 96.45\%$.

Note: Percent composition is the amount of each element by mass present in a compound. It helps in determining the stoichiometry of each element present in a chemical composition.