# 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).