Two liquids `A` and `B` are miscible over the whole range of composition and may be treated as ideal (obeying Raoult's law.) At `350K` the vapour pressure of pure `A` is `24.0kPa` and of pure `B` is `12.0 kPa`. A mixture of `60%` `A` and `40%` `B` is distilled at this temperature, what is the pressure in a closed distillation apparatus from which air is exclued ? A small amount of the distillate is collected and and redistilled at `350K` What is the composition

Answer

`21kPa,85.7%` of A

Explanation

`P_(T)=(6)/(10)xx24+(0.4)/(10)xx12(16xx12)/(10)=(192)/(10)=19.2kPa`
`P_(A)'=X_(A)P_(A)=(6)/(10)xx24(144)/(10)=14.4=X_(A)'xx19.2`
so `X_(A)'=(144)192)=75% X_(A)'=25%`
so `P_(T)=(3)/(4)xx24+(1)/(4)xx12=18+3=21kPa`
`& P_(A)=(3)/(4)xx24=18=X_(A)'(21)`
so `X_(A)'=(18)/(21)=(6)/(7)=85.7%` of` A`