Q29 / 120 · VITEEE 2011 · Chemistry

The freezing point of a solution composed of $10.0$ gof $\mathrm{KCl}$ in $100 \mathrm{~g}$ of water is $4.5^{\circ} \mathrm{C}$. Calculate the van't Hoff factor, i for this solution.

  • A
    $2.50$
  • Correct answer
    B
    $1.8$
  • C
    $1.2$
  • D
    $1.3$

Solution

$$ \begin{array}{l} \Delta \mathrm{T}_{f}=i K_{f} m \\ m=\frac{10 \times 1000}{74.55 \times 100}=1.34 \mathrm{~m} \\ {[\mathrm{Molecular} \mathrm{Mass} \text { of } \mathrm{KCl}=74.55]} \\ \mathrm{i}=\frac{\Delta \mathrm{T}_{f}}{\mathrm{~K}_{f} \mathrm{~m}}=\frac{4.5^{\circ} \mathrm{C}}{\left(1.86^{\circ} \mathrm{C} / \mathrm{m}\right)(1.34 \mathrm{~m})}=1.8 \end{array} $$

Hence, the correct answer is option: 'B'.

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