Question

Calculate the percentage composition of nitrogen in urea.

Answer 1

Step 1: Analyze the formula to find percentage composition

• The percentage composition of an element in a compound is given by

$\%\mathrm{composition}\mathrm{of}\mathrm{element}=\frac{\mathrm{Mass}\mathrm{of}\mathrm{element}\mathrm{in}\mathrm{compound}}{\mathrm{Mass}\mathrm{of}\mathrm{compound}}\times 100$

Step 2: Analyze the mass of nitrogen in compound

• The atomic mass of Nitrogen ($\mathrm{N}$) is $14\mathrm{g}$
• In this compound i.e., Urea $\left({\mathrm{H}}_2{\mathrm{NCONH}}_2\right)$, there are two Nitrogen atoms present.
• So, the mass of element in the compound is $2\times 14=28\mathrm{g}{\mathrm{mol}}^{-1}$

Step 3: Find the molar mass of Urea

• To find the molecular mass, we will add the atomic masses of all of the atoms in the molecule.
• So, the molecular mass of ${\mathrm{H}}_2{\mathrm{NCONH}}_2$ $=(4\times 1)+(2\times 14)+12+16$

$$\begin{gathered} =4+28+12+16 \\ =60\mathrm{g}{\mathrm{mol}}^{-1} \end{gathered}$$

Step 4: Find the percentage composition of Nitrogen

• $\%\mathrm{composition}\mathrm{of}\mathrm{Nitrogen}=\frac{\mathrm{Mass}\mathrm{of}\mathrm{Nitrogen}\mathrm{in}\mathrm{Urea}}{\mathrm{Mass}\mathrm{of}\mathrm{Urea}}\times 100$
• Putting the values:

$\%\mathrm{composition}\mathrm{of}\mathrm{Nitrogen}=\frac{28}{60}\times 100=46.6\%$

So, the percentage composition of nitrogen in urea is $46.6\%$.