Q28 / 150 · MHT CET 2023 (10 May Shift 1) · Chemistry

Find the depression in freezing point of solution when 3.2 gram non volatile solute with molar mass $128 \mathrm{gram} \mathrm{mol}^{-1}$ is dissolved in 80 gram solvent if cryoscopic constant of solvent is $4.8 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$.

  • A
    $3.0 \mathrm{~K}$
  • Correct answer
    B
    $1.5 \mathrm{~K}$
  • C
    $2.0 \mathrm{~K}$
  • D
    $2.5 \mathrm{~K}$

Solution

$\begin{aligned} \Delta \mathrm{T}_{\mathrm{f}} & =\frac{1000 \mathrm{~K}_{\mathrm{f}} \mathrm{W}_2}{\mathrm{M}_2 \mathrm{~W}_1} \\ & =\frac{1000 \mathrm{~g} \mathrm{~kg}^{-1} \times 4.8 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1} \times 3.2 \mathrm{~g}}{128 \mathrm{~g} \mathrm{~mol}^{-1} \times 80 \mathrm{~g}} \\ & =1.5 \mathrm{~K}\end{aligned}$

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

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