Derive the molecular formula of aniline containing 77.4% carbon, 7.5% hydrogen and 15.1%

| July 7, 2021 | education

Derive the molecular formula of aniline containing 77.4% carbon, 7.5% hydrogen and 15.1% nitrogen. The vapor density of aniline in air is 3.21.

Let the numbers of carbon, hydrogen and nitrogen atoms in the empirical formula be x, y, z – CxHyNz.
The atomic masses of carbon, hydrogen and nitrogen are 12; one; 14 – respectively.
39.1x: 35.5y: 16Z = 31.84: 28.97: 39.17.
Let’s divide by the corresponding coefficients:
x: y: z = 77.4 / 12: 7.5 / 1: 15.1 / 14.
x: y: z = 6.45: 7.5: 1.078.
Let’s divide by a smaller coefficient:
x: y: z = 6.45 / 1.078: 7.5 / 1.078: 1.078 / 1.078.
x: y: z = 6: 7: 1.
The formula of the substance is C6H7N1.
Now let’s determine the formula of the substance, based on the density of the vapor in the air:
D (X / air) = M (X) / M (air).
M (air) = 29 g / mol.
M (X) = D (X / air) * M (air) = 3.21 * 29 = 93 g / mol.
M (C6H7N1) = 12 * 6 + 1 * 7 + 14 = 93 g / mol.
The ratio M (X) / M (C6H7N1) = 93/93 = 1.
So our simple formula turned out to be the desired one.
Answer: The formula for aniline is C6H7N1.



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