KVPY SB SX Exam 2011 Question Paper

Question : 108 of 120

Marks: +1, -0

At 300 K the vapour pressures of two pure liquids. A and B are 100 and 500 mm Hg. respectively. If in a mixture of A and B, the vapour pressure is 300 mm Hg. the mole fractions o f A in the liquid and in the vapour phase, respectively, are

1/2 and 1/10
1/4 and 1/6
1/4 and 1/10
1/2 and 1/6

Validate

Solution:

Y_A={P_A^0X_A}/{ P_A^0X_A +P_B^0X_B}

={100 . 1/2}/{100 . 1/2+500 . 1/2}=1/6

∵P_s=(P_A^0-P_B^0)X_A+P_B^0

300 = (- 400) X_A + 500

⇒X_A=1/2

∴X_B=1/2

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