$\mathrm{KBr}$ is $80 \%$ ionized in solution. The freezing point of $0.4$ molal solution of $\mathrm{KBr}$…

$\mathrm{KBr}$ is $80 \%$ ionized in solution. The freezing point of $0.4$ molal solution of $\mathrm{KBr}$ is :
$\mathrm{K}_{\mathrm{f}}\left(\mathrm{H}_{2} \mathrm{O}ight)=1.86 \mathrm{~K} \mathrm{~kg} / \mathrm{mole}$
  1. $274.339 \mathrm{~K}$
  2. $-1.339 \mathrm{~K}$
  3. $257.3 \mathrm{~K}$
  4. $-1.339^{\circ} \mathrm{C}$

Solution

\(\Delta T_f=i K_f m\) \(\begin{array}{rcc} & \mathrm{KBr} & ightarrow \mathrm{K}^{+} & +\mathrm{Br}^{-} \\ & 1 & 0 & 0 \\ & (1-\alpha) & \alpha & \alpha \end{array}\) \(i=1+\alpha\) Here \(\alpha=0.8\) (\(80 \%\) ionization) \(\begin{aligned} & i=1.8 \\ & \Delta T_f=(1.8)(1.86)(0.4)=1.339 K \\ & T_f=-1.339^{\circ} \mathrm{C} \end{aligned}\) *

Asked in: JEE-TOPICTESTS-CHEMISTRY

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