Question

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

Answer 1

Consider the atomic masses of carbon versus hydrogen.

Explanation:

The empirical formula is the `"simplest whole number ratio defining"`
`"constituent atoms in a species."`

The mass ratio may be different, given that the constituent elements may have vastly different masses. For methane, `CH_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 `"mass of carbon:mass of hydrogen"` `=` `3:1` as required.