# Question #ce7a4

Apr 30, 2016

${\text{C"_9"H"_8"O}}_{4}$

#### Explanation:

As it turns out, the problem already provides you with the molecular formula and the empirical formula of aspirin, or acetylsalicyclic acid, ${\text{C"_9"H"_8"O}}_{4}$.

A compound's molecular formula tells you the exact number of atoms of each constituent element present in one molecule of this compound. In your case, one molecule of aspirin contains

• nine atoms of carbon, shown here in black
• eight atoms of hydrogen, shown here in light gray
• four atoms of oxygen, shown here in red

This is why the compound's molecular formula is ${\text{C"_9"H"_8"O}}_{4}$.

Now, the empirical formula tells you the smallest whole number ratio that exists between a compound's constituent elements.

In this case, a $9 : 8 : 4$ ratio between carbon, hydrogen, and oxygen is already the smallest than can be expressed using whole numbers, which means that ${\text{C"_9"H"_8"O}}_{4}$ is also the empirical formula of aspirin.

$\textcolor{g r e e n}{| \overline{\underline{\textcolor{w h i t e}{\frac{a}{a}} \textcolor{b l a c k}{{\text{C"_9"H"_8"O}}_{4}} \textcolor{w h i t e}{\frac{a}{a}} |}}} \to$ empirical and molecular formula