Determine the molecular formula of the hydrocarbon, in which the mass fraction of carbon = 85.7%

Determine the molecular formula of the hydrocarbon, in which the mass fraction of carbon = 85.7%, and the relative density of the substance in terms of hydrogen = 28.

Let’s take the mass of hydrocarbon per 100 g.

Find the mass of carbon in the hydrocarbon.

100 g – 100%,

m (H) – 85.7%.

m = (100 g × 85.7%): 100% = 85.7 g.

Let’s find the mass of hydrogen.

100 g – 85.7 g = 14.3 g.

Let’s find the amount of matter of atoms in the compound.

n = m: M.

n (H) = 14.3: 1 = 14.3 mol.

n (C) = 85.7: 12 = 7.14 mol.

We find the ratio of the amounts of substances.

n (C): n (H) = 7.14: 14.3 = 1: 2.

Let’s find the molar mass of the hydrocarbon.

M (H2) = 2 g / mol.

D (H2) = 28 × 2 = 56.

The C4H8 hydrocarbon formula is butene.

M (C4H8) = 12 × 4 + 8 = 56 g / mol.