Question

Two liquids X and Y form an ideal solution at 300K, vapour pressure of the solution containing 1 mole of X and 3 moles of Y is 550 mm Hg. At the same temperature, if 1 mole of V is further added to this solution, vapour pressure of the solution increases by 10 mm Hg. Vapour pressure (in mm Hg) of X and V in their pure states will be respectively

• A. 200 and 300
• B. 300 and 400
• C. 400 and 600
• D. 500 and 600

Answer 1

Answer: (C)

${\rho }_{total}=p_A^o.x_A+p_B^o.x_B$
$550=p_A^o\times \frac{1}{4}+p_B^o\times \frac{3}{4}$
$p_A^o+3p_B^o=2200$ ?(i) When 1 mole of y is further added to the solution $560=p_A^o\times \frac{1}{5}+p_B^o\times \frac{4}{5}$
$p_A^o+4p_B^o=2800$ ...(ii)
On subtraction, (ii) - (i)
$p_B^o=2800-200=600$
On putting the value of
$p_B^o$ Eq. (i)
$p_A^o+3\times 600=220$
$p_A^o=2200-1800=400$
On putting the value of
$p_B^o$ in Eq. (i)
$p_A^o+3\times 600=220$
$p_{A_0}=2200-1800=400$