Question

Equal volumes of two gases A and B diffuse through a porous pot in $20$ and $10$ seconds respectively. If the molar mass of A is $80$, find the molar mass of B.

Answer 1

according to Graham's Law the rate of effusion or diffusion of a gas is inversely proportional to the square root of the molar mass of the gas. The equation given by this law follows the equation:

$\text{Rate of diffusion}=\frac{1}{\sqrt{\text{molar mass of gas}}}$

$\frac{r_A}{r_B}=\frac{\frac{V}{t_A}}{\frac{V}{t_B}}=\sqrt{\frac{M_B}{M_A}}⟹\frac{\frac{V}{20}}{\frac{V}{10}}=\sqrt{\frac{M_B}{80}}⟹\frac{1}{4}=\frac{M_B}{80}$

$M_B=20gmo{l}^{-1}$.