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)

$280$

Answer 2

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. $=D_{T} \times 2=140 \times 2$ $=280$