Question

The empirical formula of a compound is $\mathrm{CH}$. Its molecular weight is $78\mathrm{g}$. The molecular formula of a compound will be

• A. ${\mathrm{C}}_2{\mathrm{H}}_2$
• B. ${\mathrm{C}}_3{\mathrm{H}}_3$
• C. ${\mathrm{C}}_6{\mathrm{H}}_6$
• D. ${\mathrm{C}}_4{\mathrm{H}}_4$

Answer 1

The correct option is C

${\mathrm{C}}_6{\mathrm{H}}_6$

Explanation:

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 $\mathrm{CH}$

$\left(12+1\right)\text{g}=13\text{g}$

Step4. Calculate the value of $n$:

$n=\frac{\text{78 g}}{13\text{g}}=6$

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

$\text{Molecular formula=}{\left[\text{CH}\right]}_6{\text{=C}}_6{\text{H}}_{\text{6}}$

Hence, option (C) is the correct answer. The molecular formula of the compound is ${\mathbf{C}}_{\mathbf{6}}{\mathbf{H}}_{\mathbf{6}}$.