At , the vapour pressure of benzene is 70 torr and that of methyl benzene is 20 torr. The mole fraction of benzene in the vapour phase at above an equimolar mixture of benzene and methyl benzene is ____ . (Nearest integer)
Answer: 78
Solution
In an equimolar liquid mixture each mole fraction is , so Raoult's law gives the partial pressures
and the total pressure above the solution is torr. By Dalton's law the vapour composition is the ratio of partial to total pressure,
To the nearest integer the mole fraction of benzene in the vapour is .
and the total pressure above the solution is torr. By Dalton's law the vapour composition is the ratio of partial to total pressure,
To the nearest integer the mole fraction of benzene in the vapour is .
JEE Main · 2021 · 20 Jul 2021 · Shift 1 · Integer answer