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Which of the following statement about the composition of the vapour over an ideal 1:1 molar mixture of benzene and toluene is correct? Assume that the temperature is constant at 25°C. (Given: Vapour pressure data at 25°C, benzene = 12.8 kPa, toluene = 3.85 kPa)

1. The vapour will contain a higher percentage of benzene
2. The vapour will contain a higher percentage of toluene
3. The vapour will contain equal amounts of benzene and toluene
4. Not enough information is given to make a prediction

Correct answer: The vapour will contain a higher percentage of benzene

Solution

The vapour pressure of benzene is higher than that of toluene, so benzene will contribute more to the vapour phase. This results in a higher percentage of benzene in the vapour.

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