Question

$3.24\, g Hg(NO_{3})_{2}$ (Molecular mass 324) dissolved in 1000 g of water constitutes a solution having a freezing point - $0.0558^{\circ}C$, while $21.68 \,g$ of $HgCl_{2}$ (Molecular mass 271) in 2000 g of water constitutes a solution with a Freezing Point of $- 0.0744^{\circ}C$. The $K_{f}$ of water is $1.86 \,Kg \,mol^{-1}$ About the state of ionisation of the two solids in water can be inferred that

• A. $Hg(NO_{3})_{2}$ is fully ionised but $HgCl_{2}$ is fully unionised
• B. $Hg(NO_{3})_{2}$ and $HgCl_{2}$ both are completely ionised
• C. $Hg(NO_{3})_{2}$ is fully unionised but $HgCl_{2}$ is fully ionised
• D. Both $Hg(NO_{3})_{2}$ and $HgCl_{2}$ are completely unionised

Answer 1

Answer: (A)

$0.0558 = i \times \frac{3.24}{324} \times 1.86$
$i=3 $ (100% ionised)
$0.0744 = i \times \frac{21.68}{271} \times 1.86$
$i=1$ (unionised)