Question

The time taken for a certain volume of a gas (x) to diffuse through a small hole is 4 minutes. It takes 5.65 minutes for the same volume of oxygen to diffuse under identical conditions. What is the molecular weight of (x)

Answer 1

Explanation:

Graham's law states that "at constant pressure and temperature the rate of diffusion or effusion of a gas is inversly proportional to the square root of its density" Rate of diffusion ∝1α−−√ If r1andr2 represent the rates of diffusion of two gases and d1andd2 are their respective densities then r1r2=d2d1−−√ (at constant P and T) , r1r2=M2M1−−−√×P1P2 (at constant T) . V1×t2V2×t1=d2d1−−√=M2M1−−−√V∝n (where n is no. of moles), V1∝n1andV2∝n2.

rxrO2=MO2MX−−−−√

V/2V/5.65=32MX−−−√

5.652=32MX−−−√

∴MX=4

Hence answer is (B)