# A hydrocarbon has 80% carbon content. What is its empirical formula?

Aug 14, 2017

If the hydrocarbon has 80% carbon content, then the empirical formula is $C {H}_{3}$.

#### Explanation:

We assume a mass of $100 \cdot g$ of stuff...

$\text{Moles of carbon} = \frac{80.0 \cdot g}{12.011 \cdot g \cdot m o {l}^{-} 1} = 6.67 \cdot m o l .$

$\text{Moles of hydrogen} = \frac{20.0 \cdot g}{1.00794 \cdot g \cdot m o {l}^{-} 1} = 19.84 \cdot m o l .$

We divide thru by the smallest quantity, i.e.

$C : \frac{6.67 \cdot m o l}{6.67 \cdot m o l} = 1$

$H : \frac{19.84 \cdot m o l}{6.67 \cdot m o l} = 3$

So our empirical formula is $C {H}_{3}$. In fact, this is consistent with a molecular formula of ${C}_{2} {H}_{6}$, i.e. $\text{ethane}$. The question might have asked this, had they quoted a proper value for molecular weight.