# What is the difference between the "molecular and empirical formulae?"

Nov 27, 2016

The difference between an empirical formula mass and a molecular mass.........? See here and links.

#### Explanation:

The difference is a whole number multiple.

The molecular formula is always a whole number multiple of the empirical formula. Take a simple molecule such as $\text{ethane, } {H}_{3} C - C {H}_{3}$. The empirical formula is the simplest whole number multiple tha represents the atomic proportion of this formula, i.e. $C {H}_{3}$.

And given that $\text{molecular formula}$ $=$ $n \times \text{empirical formula}$, in this case $n = 2$.

Typically, an analyst can give you a percentage composition of your compound; i.e. %C, H, N; this gives an empirical formula by standard means. And then this empirical formula is converted to a molcular formula if some way of assessing the molecular mass (i.e. mass spec., boiling point elevation) can be found.