# A compound containing only carbon and hydrogen is analyzed, and is found to contain 20.11% hydrogen on a mass basis. How can the empirical formula of the compound be calculated?

Dec 10, 2015

In 100 g hydrocarbon, there are $\frac{20.11 \cdot g}{1.00794 \cdot g \cdot m o {l}^{- 1}} = 19.95$ $m o l$ $H$, and $\frac{79.89 \cdot g}{12.011 \cdot g \cdot m o {l}^{- 1}} = 19.95$ $m o l$ $C = 6.65 \cdot m o l$ $C$.
We then divide thru by the lowest ratio to give the empirical formula, $C {H}_{3}$.
How did I know that %C was $79.89$?