The relative density of vapors of unsaturated hydrocarbon series ethylene (СnH2n)

The relative density of vapors of unsaturated hydrocarbon series ethylene (СnH2n) for hydrogen is 49. Find the molecular formula of the hydrocarbon.

Relative vapor density: D = M1 / M2, where M1 is the molar mass of alkene, M2 is the molar mass of hydrogen. From here we find: M1 = D * M2 = 49 * 2 g / mol = 98 g / mol. Since the formula for the unknown alkene is CnH2n, we will make an equation, knowing its molar mass, and calculate n. The molar mass of carbon is 12 g / mol, and that of hydrogen is 1 g / mol. Equation: 12 * n + 2 * n = 98. Hence n = 7. Hence the hydrocarbon formula: C7H14.
Answer: C7H14 (heptene).