Derive the molecular formula of a gas containing 80% carbon and hydrogen if its density is 0.714 g / l.

Given:

%%

g / l

To find:

Formula -?

Solution:

1) Find the molar mass of 1 mol of the substance:

M (HC) = p * Vm = 0.714 g / l * 22.4 l / mol = 16 g / mol, – we substitute the molar volume in the calculation formula, since 1 mol of any gas takes 22.4 liters.

Then the molecular weight of the hydrocarbon is 16.

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

16 – 100%

x – 80%,

x = 80% * 16: 100% = 12.8

N (C) = 12.8: Mr (C) = 12.8: 12 = ~ 1 atom.

3) Then the molecular weight of hydrogen accounts for 16 – 12 = 4.

N (H) = 4: Mr (H) = 4: 1 = 4 atoms.

We got a substance with the formula CH4 – methane.

Answer: CH4 is methane.