Question

The total pressure observed by mixing two liquids $A$ and $B$ is $350 \, mm$ Hg when their mole fractions are $0.7$ and $0.3$ respectively The total pressure becomes $410 \,mm \,Hg$ if the mole fractions are changed to $0.2$ and $0.8$ respectively for $A$ and $B$ The vapour pressure of pure $A$ is _________$mm \,Hg$ (Nearest integer) Consider the liquids and solutions behave ideally.

Answer 1

The correct answer is 314
Let V.P. of pure A be PA0​
Let V.P of pure B be PB0​
When XA​=0.7&XB​=0.3
Ps​=350
⇒PA0​×0.7+PB0​×0.3=350....(i)
When XA​=0.2&XB​=0.8
Ps​=410
⇒PA0​×0.2+PB0​×0.8=410,......(ii)
Solving (i) and (ii)
PA0​=314mmHg
PB0​=434mmHg
=(314)