# The hydrogen vapor density of the hydrocarbon is 39. Find the molecular formula if the mass

September 30, 2021 | education

| **The hydrogen vapor density of the hydrocarbon is 39. Find the molecular formula if the mass fractions of the elements are: carbon = 92.3%, hydrogen = 7.7%**

Let’s write down the data on the condition of the problem:

1. Given: CxNu – hydrocarbon;

D (H2) = 39;

M (H2) = 2 g / mol;

W (C) = 92.3%

W (H) = 7.7%

Determine the molecular formula.

2. Calculate the molar mass:

M (CxHy) = M (H2) * D (H2) = 2 * 39 = 78 g / mol.

3. Find the number of moles of carbon, hydrogen:

Y (C) = m / M = 92.3 / 12 = 7.7;

Y (H) = m / M = 7.7 / 1 = 7.7.

4. Ratio: X: Y = 7, 7: 7, 7 = 1: 1;

Simplest formula: CH

Molecular Formula: C6H6;

M (C6H6) = 78 g / mol.

Answer: C6H6 – benzene belongs to the class of arenes.

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