Solutions and Colligative Properties - Result Question 17-1
17. The freezing point $\left(\right.$ in $\left.^{\circ} \mathrm{C}\right)$ of solution containing $0.1$ g of $\mathrm{K}_3\left[\mathrm{Fe}(\mathrm{CN})_6\right]$ (mol. wt. 329) in $100$ g of water $\left(K_f=1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right)$ is
(2011)
(a) $-2.3 \times 10^{-2}$
(b) $-5.7 \times 10^{-2}$
(c) $-5.7 \times 10^{-3}$
(d) $-1.2 \times 10^{-2}$
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Answer:
Correct Answer: 17. (a)
Solution:
van’t Hoff factor $=4 (3 \mathrm{~K}^{+}+[\mathrm{Fe}(\mathrm{CN})_6]^{3-}$
$\text { Molality } =\frac{0.1}{329} \times \frac{1000}{100}=\frac{1}{329} $
$\Rightarrow \quad-\Delta T_f =i K_f \cdot m $
$= \quad4 \times 1.86 \times \frac{1}{329}=2.3 \times 10^{-2} $
$\Rightarrow \quad T_f =-2.3 \times 10^{-2 \circ} \mathrm{C}$
(As $%$ freezing point of water is $0^{\circ} \mathrm{C}$ )
BETA
