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Q.
The vapour pressure of a dilute aqueous solution of glucose is $ 740\,mm $ of mercury at $ 373\,K $ . The mole fraction of the solute is
Chhattisgarh PMTChhattisgarh PMT 2010
Solution:
At STP $(273\, K )$ the vapour pressure of aqueous solution of glucose $=760\, mm Hg$
At $373 \,K$, the $V P=740\, mm \,Hg$
We know that,
Relative lowering of $V P \propto$ mole fraction of solute
$\frac{p^{o}-p}{p^{o}}=X_{A} \frac{760-740}{760}$
$=X_{A} \frac{20}{760}=X_{A} $
$\therefore X_{A}=\frac{2}{76}=\frac{1}{38}$