Question

The empirical formula of a compound is ${\text{CH}}_{\text{2}}\text{Cl}$. If the molecular mass of the compound is $99\text{g}$, what is the molecular formula of the compound?

Answer 1

Step 1. Empirical formula and molecular formula

• An empirical formula represents the simplest whole-number ratio of various atoms present in a compound.
• The molecular formula shows the exact number of different types of atoms present in a molecule of a compound.

Step 2. Formula to determine value of $n$

$n=\frac{\text{Molecular mass}}{\text{Empirical formula mass}}$

Step 3. Calculation of Empirical formula mass

The empirical formula mass of ${\text{CH}}_{\text{2}}\text{Cl}$

$[12+(2\times 1)+35.5]\text{g}=49.5\text{g}$

Step 4. Calculate the value of $n$

$n=\frac{99\text{g}}{49.5\text{g}}=2$

Step 5. The formula for the calculation of molecular formula

$\text{Molecular formula=}{\left[\text{Empirical formula}\right]}_n$

Step 6. Calculation of molecular formula

$$\begin{gathered} \text{Molecular formula=}{\left[{\text{CH}}_2\text{Cl}\right]}_2 \\ {\text{=C}}_{\text{2}}{\text{H}}_{\text{4}}{\text{Cl}}_{\text{2}} \end{gathered}$$

Hence, the molecular formula of the compound is ${\mathrm{C}}_2{\mathrm{H}}_4{\mathrm{Cl}}_2$.