Question

The empirical formula mass of a compound is one-sixth of its molecular mass. What is the molecular formula corresponding to that substance?

• A. ${\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}$
• B. ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6$
• C. ${\mathrm{C}}_2{\mathrm{H}}_4{\mathrm{O}}_3$
• D. ${\mathrm{C}}_3{\mathrm{H}}_6{\mathrm{O}}_2$

Answer 1

The correct option is B

${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6$

Explanation of the correct option:

The molecular formula gives the exact number of each individual atom present in a molecule, whereas the empirical formula gives the simplest ratio of the number of various atoms present.

(B) ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6$: ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6$ is the molecular formula because when we divide each element of ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6$ by 6 we get a whole number. This is shown below:

$\frac{{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6}{6}={\mathrm{CH}}_2\mathrm{O}$

So, ${\mathrm{CH}}_2\mathrm{O}$ is the empirical formula for ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6$.

Explanation for the incorrect options:

(A) ${\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}$: ${\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}$ is a molecular formula but when we divide each element of ${\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}$by 6 we don't get a whole number.

(C) ${\mathrm{C}}_2{\mathrm{H}}_4{\mathrm{O}}_3$: We cannot divide each element of ${\mathrm{C}}_2{\mathrm{H}}_4{\mathrm{O}}_3$ by 6 to get a whole number. Thus, it is not a molecular formula.

(D) ${\mathrm{C}}_3{\mathrm{H}}_6{\mathrm{O}}_2$: We cannot divide each element of ${\mathrm{C}}_3{\mathrm{H}}_6{\mathrm{O}}_2$ by 6 to get a whole number. Thus, it is not a molecular formula.

Therefore, the correct option is (B).