Solutions and Colligative Properties - Result Question 18-2
18. When $20$ g of naphthoic acid $\left(\mathrm{C}_{11} \mathrm{H}_8 \mathrm{O}_2\right)$ is dissolved in $50$ g of benzene ( $K_f=1.72 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$ ), a freezing point depression of $2 $ K is observed. The van’t Hoff factor $(i)$ is
(2007, 3M)
(a) $0.5$
(b) $ 1$
(c) $ 2$
(d) $3$
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Answer:
Correct Answer: 18. (a)
Solution:
$ \begin{aligned} & \text { Molality }=\left(\frac{20}{172}\right) \times \frac{1000}{50}=2.325 \mathrm{~m} \\ & \Rightarrow \quad-\Delta T_f=2=i K_f \cdot m \\ & \Rightarrow \quad i=\frac{2}{1.72 \times 2.325}=0.5 \\ \end{aligned} $
BETA
