Question

The molecular weight of a gas which diffuse through a porous plug at 1/6 th of the speed of hydrogen under identical conditions is :

• A. 12
• B. 72
• C. 64
• D. 36

Answer 1

Answer: (B)

72

Hydrogen

Molecular weight of $H_2=M_1=2$

Rate of diffusion of $H_2=r_1=r$

Unknown gas

Molecular weight of unknown gas $=M_2=x=?$

Rate of diffusion of unknown gas $=r_2=r/6$

$\frac{r_1}{r_2}=\sqrt{\frac{M_2}{M_1}}\Rightarrow \frac{r}{r/6}=\sqrt{\frac{M_2}{2}}$

$\Rightarrow 6=\sqrt{\frac{x}{2}}\Rightarrow 36=\frac{x}{2}\Rightarrow x=72$