# The empirical formula of a compound is CH. If the molar mass of this compound is about 78 g, what is its molecular formula?

Apr 10, 2016

${C}_{6} {H}_{6}$

#### Explanation:

The $\text{empirical formula}$ is the simplest whole number ration that defines constituent atoms in a species. The $\text{molecular formula}$ is always a multiple of the $\text{empirical formula}$.

Given the above: "molecular formula" =nxx("empirical formula")

Thus $\text{molecular formula} = 78.0 \cdot g \cdot m o {l}^{-} 1 = n \left(12.011 + 1.00794\right) \cdot g \cdot m o {l}^{-} 1$

$n = \frac{78}{12.011 + 1.00794}$ $=$ $6$.

And $\text{molecular formula} = {C}_{6} {H}_{6}$

Sometimes (but not here!) $\text{molecular formula}$ $\equiv$ $\text{empirical formula}$, i.e. the mulitple $n$ $=$ $1$.