Derive the molecular formula of a hydrocarbon, the mass fraction of hydrogen

Derive the molecular formula of a hydrocarbon, the mass fraction of hydrogen in which is 15.79%, and the density of this substance in air is 3.93.

The molecular weight of air is 29 g / mol. Let’s find the molecular weight of the hydrocarbon:
29 * 3.93 = 114 g / mol;

Let’s find the molecular weight of hydrogen in the compound:
114 * 0.1579 = 18 g / mol (since the relative atomic mass of hydrogen is 1, there will be 18 hydrogen atoms in the hydrocarbon)

Let’s find the molecular weight of carbon in the compound:
114 – 18 = 96 g / mol;

The relative atomic mass of carbon is 12. Find the number of carbon atoms:
96/12 = 8 atoms;

Answer: The molecular formula of the hydrocarbon is C8H18.