A compound's empirical formula is C_2H_5. If the formula mass is 116 amu, what is the molecular formula?

Mar 30, 2016

${C}_{8} {H}_{20}$

Explanation:

The molecular formula is always a multiple of the empirical formula, the formula obtained by experiment.

What does this mean? Well, that ${\left(\text{Empirical formula}\right)}_{n}$ $=$ $\text{Molecular formula}$.

So we solve for $n$.

$n \times \left\{2 \times 12.011 + 5 \times 1.00794\right\} \cdot g \cdot m o {l}^{-} 1$ $=$ $116 \cdot g \cdot m o {l}^{-} 1$

$n$ $=$ $\frac{116}{29}$ $=$ $4$

$\text{Molecular formula}$ $=$ $4 \times {C}_{2} {H}_{5}$ $=$ ${C}_{8} {H}_{20}$ as required.