The mass fraction of the chemical element hydrogen in a gas mixture consisting of hydrogen fluoride

The mass fraction of the chemical element hydrogen in a gas mixture consisting of hydrogen fluoride and hydrogen chloride is 3.82%. Determine the relative density of hydrogen.

To determine the relative density of the mixture for hydrogen, we find the ratio of molar masses:

D = Mr1 / Mr2.

DH2 (HF) = Mr (HF) / Mr (H2) = 20/2 = 10.

DH2 (HCl) = Mr (HCl) / Mr (H2) = 36.5 / 2 = 18.25.

From the mixing rule, we get the expression:

Let DH2 of the mixture be x, then

V (HF) / V (HCl) = 10 – x / x – 18.25 = 3.82.

10 – x = 3.82 – 69.7x.

13.82 = 70.7x.

x = 0.185.

DH2 = 0.185.