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  3. Chemistry
  4. If 8 g of a non-electrolyte solute is dissolved in 114 g of n-octane to reduce its vapour pressure to 80 %, the molar mass (in g mol-1) of the solute is [Given that molar mass of n-octane is 114 g mol-1]

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Q. If $8\,g$ of a non-electrolyte solute is dissolved in $114\, g$ of n-octane to reduce its vapour pressure to $80\%$, the molar mass (in $g \,mol^{-1})$ of the solute is [Given that molar mass of n-octane is $114 \,g\, mol^{-1}]$

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Solution:

Assuming dilute solution,
$\frac{P_{0}-P_{s}}{P_{s}} \approx\frac{P_{0}-P_{s}}{P_{0}}=\frac{n_{\text{Solute}}}{n_{\text{Solvent}}}$
Let $P_{0}=100, V.P.$ reduced to $80\%$,
$\therefore P_{s}=80$
$\frac{100-80}{100}=\frac{8 m}{114 114}$
$m=40$