Chapter 6, Problem 7STP

Interpretation Introduction

Interpretation:

The formula of the nitrogen oxide containing 1.29 g of nitrogen and 3.71 g of oxygen needs to be determined.

Concept introduction:

To determine the formula of compound, find the mole number of each element of the compound.

$\text{moles}=\frac{\text{Mass}}{\text{Molar}\text{mass}}$

Answer to Problem 7STP

The formula of the compound is ${\text{NO}}_{\text{3}}$.

Explanation of Solution

Mass of nitrogen=1.29 g

Molar mass of nitrogen = $14.0067\text{g}{\text{mol}}^{-1}$

$\begin{array}{c}\text{Moles}\text{of}\text{nitrogen}=\frac{1.29\text{g}}{14.0067\text{g}{\text{mol}}^{-1}}\\ =0.09\text{mol}\end{array}$

Mass of oxygen=3.71 g

Molar mass of oxygen = $16\text{g}{\text{mol}}^{-1}$

$\begin{array}{c}\text{Moles}\text{of}\text{oxygen}=\frac{3.71\text{g}}{16\text{g}{\text{mol}}^{-1}}\\ =0.23\text{mol}\end{array}$

To calculate the simplest ratio, divide number of moles of each element by the smallest number of moles, that is, 0.09.

Now, $\begin{array}{c}\text{Moles of nitrogen}=\frac{0.09\text{mol}}{0.09\text{mol}}\\ =1\end{array}$

$\begin{array}{c}\text{Moles of oxygen}=\frac{0.23\text{mol}}{0.09\text{mol}}\\ =2.55\\ \approx 3\end{array}$

So, the formula of the nitrogen oxide is ${\text{NO}}_{\text{3}}$.

Conclusion

The formula of the compound can be find out from the mole number of each element of the compound. The formula of the nitrogen oxide is ${\text{NO}}_{\text{3}}$.