Question

The vapour pressure of two pure liquids, A and B that form an ideal solution are 300 and 800 torr respectively, at temperature T. A mixture of the vapour of A and B for which the mole fraction of A is 0.25 is slowly compressed at temperature T, Calculate
(a) the composition of the first drop of the condesate,
(b) the total pressure when this drop is formed,
(c) the composition of the solution whose normal boiling point is T,
(d) the pressure when only the last bubble of vapour remains, and
(e) the composition of the last bubble.

Answer 1

Correct Answer - (a) `0.4706`, (b) `564.7` Torn (c) `0.08,0.92` (d) `675` Torr (e) `111.889`

`{:(%ofA,100,47,25,11),(8,0,,,),(%ofB,0,53,75,89),(92,100,,,):}`
Constant Temperature
(a) `Y_(A) = (P_(A)^(@)x_(A))/(P_(A)^(@)x_(A)+P_(B)^(@)(1-x_(A)))rArr0.25`
`= (300x_(A))/(300x_(A)800(1-x_(A)))`
`rArr x_(A) (800)/(1700) = 0.47, x_(B) = 0.53`
(b) `P_(tau) = P_(A)^(0) x_(A) +P_(B)^(0) x_(B) = 300 xx 0.47 +800 xx 0.53`
`= 141.2 +424`
`= 562.2` torr
(c) `760 = 300 x_(A) +800 (1-x_(A)) rArr x_(A) = (40)/(500) = 0.08`
(d) `P_(tau) = 300 xx 0.25 +800 xx 0.75 = 75 +600 = 675` tor
(e) `Y_(A) = (300 xx 0.25)/(675) = (75)/(675) = 0.11, Y_(B) = 0.89`