# The density of the hydrocarbon for oxygen = 2.1875, and the mass fraction of hydrogen (H) = 14.3%

The density of the hydrocarbon for oxygen = 2.1875, and the mass fraction of hydrogen (H) = 14.3% Derive the molecular formula.

Let’s implement the solution:
1. Let’s write down the general formula of the hydrocarbon: CxNy.
2. Let’s make a calculation using the formula: M (CxHy) = M (O2) * D (O2) = 32 * 2.1875 = 70 g / mol.
3. Determine the amount of moles of carbon, hydrogen:
Y (H) = 14.3 / 1 = 14.3 mol;
m (H) = Y * M = 14.3 * 2 = 28.6 g;
m (C) = 70 = 28.6 = 41.4 g;
Y (C) = m / M = 41.4 / 12 = 3.45 mol.
4. The ratio: X: Y = C: H = 3.45: 14.3 = 1: 4, thus the simplest formula is CH4.
5. It is necessary to determine the molecular formula of the hydrocarbon:
CnH2n + 2 = 70 g / mol;
12n = 70 – 4;
12n = 66;
N = 5.5;
6. Molecular formula: C5H10 (pentene).
7.M (C5H10) = 12 * 5 + 1 * 10 = 70 g / mol.
Answer: the hydrocarbon formula is C5H10 (pentene).

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