Question

$X$ and $Y$ are two volatile liquids with molar weights of $10gmo{l}^{-1}$ and $40gmo{l}^{-1}$ respectively. Two cotton plugs, one soaked in $X$ and the other soaked in $Y$, are simultaneously placed at the ends of a tube of length $L=24cm$, as shown in the figure. The tube is filled with an inert gas at 1 atmosphere pressure and a temperature of $300K$. Vapours of $X$ and $Y$ react to form a product which is first observed at a distance $dcm$ from the plug soaked in $X$. Take $X$ and $Y$ to have equal molecular diameters and assume ideal behaviour for the inert gas and the two vapours.

The value of $d$ in cm (shown in the figure), as estimated from Graham’s law, is

• A. 8
• B. 12
• C. 16
• D. 20

Answer 1

Answer: (C)

$\frac{r_x}{I_Y}=\frac{d}{24-d}=\sqrt{\frac{40}{10}}=2$
$d=48-2d$
$3d=48$
$d=16cm$