It is known that the density of a substance in the air is 0.9. The mass fraction of carbon in this substance is 92.3%

| September 7, 2021 | education

It is known that the density of a substance in the air is 0.9. The mass fraction of carbon in this substance is 92.3%, the mass fraction of hydrogen is 7.7%. Determine the formula of the substance.

1) Find the molecular weight of the hydrocarbon by its density in air:

D (air) = Mr (HC): Mr (air), – since air does not have a certain molecular weight, it is conventionally taken as 29

Mr (HC) = D (air) * 29 = 0.9 * 29 = 26.

2) Knowing the mass fraction of carbon, we find its molecular weight in the composition and the number of atoms:

26 – 100%

x – 92.3%,

then x = 92.3% * 26: 100% = 24.

N (C) = 24: Mr (C) = 24: 12 = 2 atoms.

3) Then the molecular weight of hydrogen is 26 – 24 = 2.

N (H) = 2: Mr (H) = 2: 1 = 2 atoms.

We got a substance with the formula C2H2 – acetylene.

Answer: C2H2 – acetylene.



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