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` be 80 find the molar mass of `B` .

Explanation

Rate of diffusion of `A (r_(A))=V/20 mL s^(-1)`
Rate of diffusion of `A (r_(B))=V/10 mL s^(-1)`
Molar mass of `A=M_(A)=80 g mol^(-1)`
Molar mass of `B=M_(B)=?`
According to Graham's law of diffusion
`r_(A)/r_(B)=sqrt(M_(B)/M_(A))`
`V/20xx10/V=sqrt(M_(B)/M_(A))`
or `(10xx10)/(20xx20)=M_(B)/M_(A)` or `1/4=M_(B)/80`
or `M_(B)=80/4=20 g mol^(-1)`