Solutions Question 11
Question 11 - 2024 (30 Jan Shift 2)
The solution from the following with highest depression in freezing point/lowest freezing point is
(1) $180 g$ of acetic acid dissolved in water
(2) $180 g$ of acetic acid dissolved in benzene
(3) $180 g$ of benzoic acid dissolved in benzene
(4) $180 g$ of glucose dissolved in water
Show Answer
Answer (1)
Solution
$\Delta T _f$ is maximum when $i \times m$ is maximum.
- $m _1=\frac{180}{60}=3, i=1+\alpha$
Hence
$\Delta T _f=(1+\alpha) \cdot k _f=3 \times 1.86=5.58^{\circ} C(\alpha<1)$
-
$m _2=\frac{180}{60}=3, i=0.5, \Delta T _f=\frac{3}{2} \times k _f^{\prime}=7.68^{\circ} C$
-
$m _3=\frac{180}{122}=1.48, i=0.5, \Delta T _f=\frac{1.48}{2} \times k _f^{\prime}=3.8^{\circ} C$
-
$m _4=\frac{180}{180}=1, i=1, \Delta T _f=1 \cdot k _f^{\prime}=1.86^{\circ} C$
As per NCERT, $k _f{ }^{\prime}\left(H _2 O\right)=1.86 k \cdot kgmol^{-1}$
$k _f{ }^{\prime}($ Benzene $)=5.12 k \cdot kgmol^{-1}$
