Determine the molecular formula of a hydrocarbon containing 87% carbon, 13% hydrogen

Determine the molecular formula of a hydrocarbon containing 87% carbon, 13% hydrogen, if the relative density of its vapor in nitrogen is 2.5%.

Let’s implement the solution:
1. Let’s write down the hydrocarbon formula: CxNy.
2. Determine the molar mass, if the density for nitrogen is known:
3.M (CxHy) = M (N2) * D (N2) = 2.5 * 28 = 70 g / mol.
4. Determine the amount of moles of carbon, hydrogen:
Y (C) = 87/12 = 7.25 mol;
Y (H) = 13/1 = 13 mol;
5. The ratio C: H = X: Y = 7.25: 13 = 1: 2, hence, the simplest formula is CH2.
6. Establish the formula:
CnH2n = 70 g / mol;
12n + 2 = 70;
12n = 68;
n = 5.6
Molecular formula: C5H10 (pentene);
M (C5H10) = 5 * 12 + 1 * 10 = 70 g / mol.
Answer: C5H10 – pentene.