Question

From a certain apparatus, the diffusion rate of hydrogen has an average value of 28.7 cm³ s^–1 . The diffusion of another gas under the same conditions is measured to have an average rate of 7.2 cm³ s^–1 . Identify the gas.

[Hint: Use Graham’s law of diffusion: R₁/R₂ = (M₂/M₁) 1/2, where R₁, R₂ are diffusion rates of gases 1 and 2, and M₁ and M₂ their respective molecular masses. The law is a simple consequence of kinetic theory.]

Answer 1

Rate of diffusion of hydrogen, R1 = 28.7 cm³ s^–1 

Rate of diffusion of another gas, R₂ = 7.2 cm³ s^–1 

According to Graham’s Law of diffusion, we have:

R₁/R₂ = √M₂/M₁ 

 Where,

 M₁ is the molecular mass of hydrogen = 2.020 g

M₂ is the molecular mass of the unknown gas

32 g is the molecular mass of oxygen. Hence, the unknown gas is oxygen.