$20 \%$ of acetic acid is dissociated when its $5 \mathrm{~g}$ is added to $500 \mathrm{~mL}$ of water. The depression in freezing point of such water is _________ $\times 10^{-3}{ }^{\circ} \mathrm{C}$.
Atomic mass of $\mathrm{C}, \mathrm{H}$ and $\mathrm{O}$ are 12,1 and 16 a.m.u. respectively.
[Given : Molal depression constant and density of water are $1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$ and $1 \mathrm{~g} \mathrm{~cm}^{-3}$ respectively.]
Answer (integer)
372
Solution
$\begin{aligned} & \mathrm{i}=1+(\mathrm{n}-1) \alpha \\\\ & \Rightarrow \mathrm{i}=1+0.2(2-1)=1.2 \\\\ & \Delta \mathrm{T}_{\mathrm{f}}=\mathrm{i} \mathrm{K} \mathrm{K}_{\mathrm{f}} \mathrm{m} \\\\ & \Delta \mathrm{T}_{\mathrm{f}}=1.2 \times 1.86 \times \frac{5 \times 1000}{60 \times 500} \\\\ & \Delta \mathrm{t}_{\mathrm{f}}=0.372 \\\\ & \Delta \mathrm{T}_{\mathrm{f}}=372 \times 10^{-3}\end{aligned}$
About this question
Subject: Chemistry · Chapter: States of Matter · Topic: Gas Laws
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