Determine the molecular formula of the amine mass fraction of carbon 38.7%, nitrogen 45.15%, hydrogen 16, 15% .. D (H2) = 15.5
Mass ratio of elements in unknown amine:
w (C): w (H): w (N) = 38.7: 16.15: 45.15
Taking into account the atomic masses of the elements, let’s move on to the quantitative ratio:
n (C): n (H): n (N) = w (C) / M (C): w (H) / M (H): w (N) / M (N) =
38.7 / 12: 16.15 / 1: 45.15 / 14 = 3.225: 16.15: 3.225 = 1: 5: 1
This means that in the molecule of the unknown amine there are 5 hydrogen atoms and 1 nitrogen atom per carbon atom. Thus, the formula for this compound can be written as: CnH5nNn.
Molecular weight of unknown amine:
M (CnH5nNn) = M (H2) * DH2 (CnH5nNn) = 2 * 15.5 = 31 (amu).
Let’s compose and solve the equation:
12 * n + 1 * 5n + 14 * n = 31
31n = 31,
n = 1, whence the formula of this amine: CH5N, which corresponds to methylamine (CH3NH2).
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