Question

A sample of urea contains 1.121 g N, 0.161 g H, 0.480 g C, and 0.640 g O. What is the empiricalformula of urea?

Short answer

Empirical formula of urea is $N_2{H}_{4}CO$.

Step-by-step solution

Finding mole number N and H

The mole number of nitrogen can be determined as,

$$\begin{gathered} =\frac{Mass}{Atomicmass} \\ =\frac{1.121}{14.01} \\ =0.08mol \end{gathered}$$

Mole number for H can be,

$$\begin{gathered} =\frac{Mass}{Atomicmass} \\ =\frac{0.161}{1.0079} \\ =0.1597mol \end{gathered}$$

Finding mole number C and O

The mole number of C can be determined as,

$$\begin{gathered} =\frac{Mass}{Atomicmass} \\ =\frac{0.48}{12.01} \\ =0.04mol \end{gathered}$$

Mole number of O can be,

$$\begin{gathered} =\frac{Mass}{Atomicmass} \\ =\frac{0.640}{15.999} \\ =0.04mol \end{gathered}$$

Dividing moles for empirical formula

On dividing all moles to get the empirical formula by 0.04,

$\begin{array}{rcl}\frac{0.08}{0.04}& =& 2atomsofN\\ \frac{0.1597}{0.04}& =& 4atomsofH\\ \frac{0.0399}{0.04}& =& 1atomofC\\ \frac{0.04}{0.04}& =& 1atomsofO\end{array}$

The empirical formula for urea can be found as $N_2{H}_{4}CO$.