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

1 Answer
anor277
Mar 12, 2017

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.

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