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BCECE Engineering BCECE Engineering Solved Paper-2015

  • question_answer
    The vapour pressure of pure water is 23.5 mm Hg. Then, the vapour pressure of an aqueous solution which contains 5 mass percent of urea is (Molar mass of urea is 60).

    A) 23mmHg             

    B) 18 mmHg

    C) 31 mmHg            

    D) 35 mmHg

    Correct Answer: A

    Solution :

    Mass of urea = 5g Mass of water = 100 - 5 = 95g Number of moles of urea \[=\frac{5}{60}=\] 0.083 Number of moles of water \[=\frac{95}{18}=5.278\] 18 \[\therefore \] Total number of moles = 5.278 + 0.083 = 5.301 Mole fraction of solvent \[=\frac{5.278}{5.361}\] \[{{p}_{s}}=\] Mole fraction of solvent \[\times {{p}^{\circ }}=\frac{5.278}{5.361}\times 23.5\] \[\text{= 23}\text{.14mm Hg}\approx \text{23mm Hg}\]


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