The vapour pressure of a solvent decreased by 10 mm of mercury, when a non-volalite solute was added to the solvent. The mole fraction of the solute in the solution is 0.2. What should be the mole fraction of the solvent, if the decrease in the vapour pressure is to be 20 mm of mercury?

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0.6

0.8

0.2

0.4

answer is C.

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Detailed Solution

$Mole fraction of solute = \frac{lowering in vapour pressure}{vapour pressure of solvent} When comparing the two scenarios, \frac{0.2}{mole fraction of solute} = \frac{10}{20} mole fraction of solute = 0.4 solvent mole fraction = (1 - 0.4 = 0.6)$

Hence, correct option is: (C) 0.6

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