Calculate the molar mass of nonvolatile solute when 1.5 g of it is dissolved in 90 g solvent decreases its…

Calculate the molar mass of nonvolatile solute when 1.5 g of it is dissolved in 90 g solvent decreases its freezing point by 0.25 K . $\left[\mathrm{K}_{\mathrm{f}}=1.2 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right]$
  1. $72 \mathrm{~g} \mathrm{~mol}^{-1}$
  2. $80 \mathrm{~g} \mathrm{~mol}^{-1}$
  3. $88 \mathrm{~g} \mathrm{~mol}^{-1}$
  4. $96 \mathrm{~g} \mathrm{~mol}^{-1}$

Solution

$\begin{aligned} & \mathrm{M}_2=\frac{1000 \mathrm{~K}_{\mathrm{f}} \mathrm{W}_2}{\Delta \mathrm{~T}_{\mathrm{b}} \mathrm{W}_{\mathrm{i}}} \\ & =\frac{1000 \times 1.2 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1} \times 1.5 \mathrm{~g}}{0.25 \mathrm{~K} \times 90 \mathrm{~g}}=80 \mathrm{~g} \mathrm{~mol}^{-1}\end{aligned}$

Asked in: MHT CET 2024 (03 May Shift 1)

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