Question

Two liquids A and B form ideal solution. At 300 K, the vapour pressure of a solution containing 1 mole of A and 3 mole of B is 550 mmHg. At the same temperature, if one mole of B is added to this solution, the vapour pressure of the solution increases by 10 mm of Hg. Determine the vapour pressure of A and B in their pure states.

(A) 400 mm, 600 mm 

(B) 600 mm, 400mm 

(C) 300 mm, 200 mm 

(D) 200mm, 300mm

Answer 1

Correct Option (A) 400 mm, 600 mm 

Explanation:

Let the vapour pressure of pure A be = p⁰A; and the vapour pressure of pure B be = p⁰B.

Total vapour pressure of solution (1 mole A + 3 moles B) 

or 2800 = p⁰ _A + 4p⁰ _B ..... (ii)

Solving equation (i) and (ii), p⁰_B = 600 mm of Hg = vapour pressure of pure B

p⁰_A = 400 mm of Hg = vapour pressure of pure A