Derive the molecular formula of HC, the mass fraction of carbon in which is 83.3%.
Derive the molecular formula of HC, the mass fraction of carbon in which is 83.3%. The relative density of the vapors of this substance in terms of hydrogen is 29.
Given:
w% (C) = 83.3%
D (H2) = 29
To find:
Formula -?
Decision:
1) Find the molecular weight of the hydrocarbon by its density in terms of hydrogen:
D (H2) = Mr (UV): Mr (H2)
Mr (HC) = D (H2) * Mr (H2) = 29 * 2 = 58.
2) Knowing the mass fraction of carbon, we find its molecular weight in the composition and the number of atoms:
58 – 100%
x – 83.3%
x = 83.3% * 58: 100% = 48.
N (C) = 48: Mr (C) = 48: 12 = 4 atoms.
3) Then the molecular weight of hydrogen in the composition is 58 – 48 = 10.
N (H) = 10: Mr (H) = 10: 1 = 10 atoms.
We got a substance with the formula C4H10 – butane.
Answer: C4H10 – butane.