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).
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