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An aqueous solution of methanol in water has vapour pressure:

1. equal to that of water
2. equal to that of methanol
3. more than that of water
4. less than that of water

Correct answer: less than that of water

Solution

In an aqueous methanol solution, water is no longer pure, so its vapour pressure is reduced by the presence of dissolved methanol. By Raoult’s law, the vapour pressure of the solvent in solution is lower than that of the pure solvent, so it is less than that of water.

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