# Organic matter, in which the mass fraction of carbon is 53.3%, hydrogen – 15.6%

Organic matter, in which the mass fraction of carbon is 53.3%, hydrogen – 15.6%, nitrogen – 31.1%, has a relative density in air of 1.551. Derive the molecular formula of this substance.

The molecular weight of air is 29 g / mol. Let’s find the molecular weight of organic matter:
29 * 1.551 = 45 g / mol;

The relative atomic mass of carbon is 12. Let us find the molecular mass of carbon in the substance:
45 * 0.533 = 24 g / mol;

The substance contains 2 carbon atoms.

The relative atomic mass of hydrogen is 1. Let’s find the molecular mass of hydrogen in the substance:
45 * 0.156 = 7 g / mol;

The substance contains 7 hydrogen atoms.

The rest of the molecular weight (14 g / mol) is nitrogen. Since the relative atomic mass of nitrogen is 14, the substance contains 1 nitrogen atom.
Answer: the molecular formula of organic matter is C3H7N.

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