# Question #2c86e

May 8, 2017

The molecular formula will be ${C}_{6} {H}_{6}$; no prizes for guessing what this molecule is......

#### Explanation:

As with all these problems, it is useful to assume that there is a $100 \cdot g$ mass of compound, and divide each elemental mass thru by the ATOMIC mass of each component.

And so..........

$\text{moles of carbon} \equiv \frac{92.5 \cdot g}{12.011 \cdot g \cdot m o {l}^{-} 1} = 7.70 \cdot m o l$

$\text{moles of hydrogen} \equiv \frac{7.50 \cdot g}{1.00794 \cdot g \cdot m o {l}^{-} 1} = 7.50 \cdot m o l$

And if we divide thru by the LOWEST molar quantity we gets.....and empirical formula of $C H$.

But the molecular formula is always a whole number of the empirical formula:

$\text{molecular formula"="empirical formula} \times n$

And so $78 \cdot g \cdot m o {l}^{-} 1 = n \times \left(12.011 + 1.00794\right) \cdot g \cdot m o {l}^{-} 1$; clearly, $n = 6$, and the $\text{molecular formula}$ is ${C}_{6} {H}_{6}$, which is what VERY common organic molecule?