# Why is the ratio of the mass of carbon to the mass of hydrogen 3:1 with respect to methane?

Mar 12, 2017

Consider the atomic masses of carbon versus hydrogen.

#### Explanation:

The empirical formula is the $\text{simplest whole number ratio defining}$
$\text{constituent atoms in a species.}$

The mass ratio may be different, given that the constituent elements may have vastly different masses. For methane, $C {H}_{4}$, the empirical formula is the same as the molecular formula. But for the molecule, we can work out the carbon percentage by mass:

"Mass of 1 mol carbon"/"Mass of 1 mol methane"xx100%=

(12.011*g*mol^-1)/(16.04*g*mol^-1)xx100%=75%

And clearly, for a binary compound, i.e. 2 elements only, the hydrogen percentage by mass is 25%. And thus $\text{mass of carbon:mass of hydrogen}$ $=$ $3 : 1$ as required.