1. Tardigrade
  2. Question
  3. Chemistry
  4. The vapour pressure of pure benzene at a certain temperature is 0.850 bar. A non-volatile, non-electrolyte solid weighing 0.5 g when added to 39.0 g of benzene (molar mass mass 78 g mol -1 ). Vapour pressure of the solution, then, is 0.845 bar. What is the molar mass of the solid substance?

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Q. The vapour pressure of pure benzene at a certain temperature is $0.850\,$ bar. A non-volatile, non-electrolyte solid weighing $0.5\, g$ when added to $39.0\, g$ of benzene (molar mass mass $78 \,g\, mol ^{-1}$ ). Vapour pressure of the solution, then, is $0.845$ bar. What is the molar mass of the solid substance?

Solutions

Solution:

$\frac{p^{\circ}-P_{1}}{P^{\circ}} = \frac{w_{2} \times M_{1}}{M_{2}\times w_{1}}$
$\frac{0.850 \, bar -0.845 \, bar}{0.850\, bar}$
$= \frac{0.5 \, g \times 78 \, g \, mol^{-1}}{M_{2} \times 39 \, g}$
$\therefore M_{2} = 170 \, g\, mol^{-1}$