Discussion Forum

1)

X and Y  are two volatile liquids with molar weights of 10 gmol^-1 and 40 g mol^-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=24 cm, as shown in the figure.

 The tube is filled with an inert gas at 1 atm pressure and a temperature of 300K. Vapours of X and Y react to form a product which is first observed at a distance d cm 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

Answer:

Option C

Explanation:

Plan  This problem can be solved by using the  concept  of Graham's law  of diffusion according to  which rate of diffusion of non-reactive gases under similar conditions of temperature and pressure  are inversely proportional to square  root of their density

Rate of diffusion $\propto$  $\frac{1}{\sqrt{molar weight of gas}}$

 Let distance covered  by X is d, then  distance covered by Y is 24-d 

If r_x and r_y are the rate of diffusion of gases X and Y.

$\frac{r_{x}}{r_{y}}=\frac{d}{24-d}=\sqrt{\frac{40}{10}}=2$

            d=48-2d

                        3d=48= d=16 cm

Hence,(c) is the correct choice