# What is the molecular formula of a substance that has an empirical formula of C2H5 and a molecular mass of 58 g/mole?

Nov 14, 2015

The empirical formula is always a multiple of the empirical formula, but remember the multiple may be $1$.
So $M F = \left(E F\right) \times n$. Thus $\left[2 \times 12.011 \cdot g \cdot m o {l}^{- 1} + 5 \times 1.00794 \cdot g \cdot m o {l}^{- 1}\right] \times n = 58 \cdot g \cdot m o {l}^{- 1} .$
It does not take much algebra to find that $n$ $=$ $2$.
Thus the molecular formula $=$ $2 \times {C}_{2} {H}_{5}$ $=$ ${C}_{4} {H}_{10}$, butane.