Derive the chemical formula of a hydrocarbon if the mass fraction of carbon in it is 80% and the density

Derive the chemical formula of a hydrocarbon if the mass fraction of carbon in it is 80% and the density for methane is 1.875.

1) Find the molecular weight of the hydrocarbon, based on its density for methane:

D (CH4) = Mr (HC): Mr (CH4)

Mr (HC) = D (CH4) * Mr (CH4) = 1.875 * 16 = 30

2) Knowing the mass fraction of carbon in the composition of a substance, we find its molecular weight and the number of atoms in the compound:

Mr (C) = 30 * 0.8 = 24

N (C) = 24: Mr (C) = 24: 12 = 2 atoms.

3) Then the molecular weight of hydrogen in the composition is 30 – 24 = 6, thus:

N (H) = 6: Mr (H) = 6: 1 = 6 atoms.

4) We got a substance with the formula C2H6 – ethane.

Answer: C2H6 is ethane.