The relative density of the hydrocarbon in terms of hydrogen is 15.

The relative density of the hydrocarbon in terms of hydrogen is 15. The mass fraction of carbon in it is 80%. Determine the molecular formula, name and draw up its structural formula.

Let’s implement the solution:
Let’s designate the hydrocarbon formula: CxNy.
Let’s calculate the molar mass by the formula: M (CxHy) = M (H2) * D (H2) = 2 * 15 = 30 g / mol;
Let’s determine the amount of moles of carbon, hydrogen:
Y (C) = 80/12 = 6.6 mol;
m (C) = Y * M = 6.6 * 12 = 80 g;
m (H) = 100 – 80 = 20 g;
Y (H) = m / M = 20/2 = 10 mol;
The ratio: X: Y = C: H = 6.6: 10 = 1: 1.6 = 1: 2;
Thus, the simplest formula is CH2;
Let’s make calculations according to the general formula: СnH2n + 2 = 30 g / mol;
12n = 30 – 4;
12n = 26;
n = 2.16;
We derive the molecular formula: C2H6 (ethane);
M (C2H6) = 2 * 12 + 1 * 6 = 30 g / mol.
Answer: formula C2H6 (ethane).