What is the molar mass of solute when 2.3 gram non-volatile solute dissolved in 46 gram benzene at…

What is the molar mass of solute when 2.3 gram non-volatile solute dissolved in 46 gram benzene at $30^{\circ} \mathrm{C}$ ? (Relative lowering of vapour pressure is 0.06 and molar mass of benzene is 78 gram mol$^{-1}$ )
  1. 65 gram mol${ }^{-1}$
  2. $80 \mathrm{gram} \mathrm{mol}^{-1}$
  3. 72 gram mol${ }^{-1}$
  4. $48 \mathrm{gram} \mathrm{mol}^{-1}$

Solution

$\begin{aligned} & \frac{\Delta \mathrm{P}}{\mathrm{P}_{\mathrm{A}}^0}=\frac{\mathrm{n}_{\mathrm{B}}}{\mathrm{n}_{\mathrm{A}}}=\frac{\mathrm{W}_{\mathrm{B}}}{\mathrm{M}_{\mathrm{B}}} \times \frac{\mathrm{M}_{\mathrm{A}}}{\mathrm{W}_{\mathrm{A}}} \\ & 0.06=\frac{2.3}{\mathrm{M}_{\mathrm{B}}} \times \frac{78}{46}\end{aligned}$ $M_B=65$

Asked in: MHT CET 2022 (05 Aug Shift 1)

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