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uestion

Asked in: BITSAT-2018

The vapour pressure of water at 20 ^{\circ}C is 17.5 mm  Hg. If 18 g of glucose \left ( C_{6}H_{12}O_{6} \right ) is added to 178.2 g of water at 20 ^{\circ}C the vapour pressure of the resulting solution will be

A.

17.325\: mm \: Hg

B.

17.675\: mm \: Hg

C.

15.750\: mm \: Hg

D.

16.500\: mm \: Hg

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Answers (1)

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In a solution containing nonvolatile solute, the pressure  is directly proportional to its mole fraction.

Psolution = vapor pressure of its pure component × mole fraction in solution

P_{\mathrm{sol}}=P^{\circ} X_{\text { solvent }}

Let A be solute and B be solvent

X_{B}=\frac{n_{B}}{n_{A}+n_{B}}=\frac{\frac{178.2}{18}}{\frac{18}{180}+\frac{178.2}{18}}

X_{B}=\frac{9.9}{9.94}=0.99

P_{\text { solution }}=P^{\circ} X_{\text { solvent }}=17.5 \times 0.99

P_{\text { solution }}=17.32.

Posted by

Pankaj Sanodiya

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