At 20°C, 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 20°C above an equimolar mixture of benzene and methyl benz

Question

At 20°C, 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 20°C above an equimolar mixture of benzene and methyl benzene is . (Nearest integer)

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Strategy:
 For an equimolar mixture, find the partial pressure of each component using Raoult's law, sum them to get the total pressure, and then use the ratio of benzene's partial pressure to the total pressure to find its mole fraction in the vapour.

Step 1: Identify liquid mole fractions for an equimolar mixture

Step 2: Calculate partial pressures
- 
-

Step 3: Calculate total vapour pressure

Step 4: Find the mole fraction of benzene in the vapour ()

Step 5: Express as 
.
Rounding to

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