Question

The degree of dissociation of $XY$ in case of following reaction is found to be $ 0.4 $ from vapour density measurement. If the observed vapour density of $X Y$ be $100$ then its molecular weight is $ XY\to X+Y $

• A. $ 140 $
• B. $ 70 $
• C. $ 280 $
• D. $ 210 $

Answer 1

Answer: (C)

The degree of dissociation $(\alpha)=\frac{D_{T}-D_{0}}{D_{0}}$
$ 0.4=\frac{D_{T}-100}{100}$
$D_{T}=40+100=140$
$ \therefore D_{T}=\frac{\text { mol. wt. }}{2} $
$\because$ Mol. wt. $=D_{T} \times 2=140 \times 2$
$=280$