What is the molar mass of solute when 5 gram solute dissolved in 70 gran solvent lowers its freezing point…

What is the molar mass of solute when 5 gram solute dissolved in 70 gran solvent lowers its freezing point by $2.5 \mathrm{~K}$ ? If $\mathrm{K}_{\mathrm{f}}=3.5 \mathrm{~K}-\mathrm{Kg} / \mathrm{mol}$.
  1. $100 \mathrm{~g} \mathrm{~mol}^{-1}$
  2. $120 \mathrm{~g} \mathrm{~mol}^{-1}$
  3. $160 \mathrm{~g} \mathrm{~mol}^{-1}$
  4. $140 \mathrm{~g} \mathrm{~mol}^{-1}$

Solution

$\Delta \mathrm{T}_{\mathrm{f}}=\mathrm{K}_{\mathrm{f}} \times \mathrm{m}$ $2.5=3.5 \times \frac{5}{M} \times \frac{1000}{70}$ $\mathrm{M}=100 \mathrm{~g} / \mathrm{mol}$

Asked in: MHT CET 2022 (06 Aug Shift 1)

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