Raoult's law

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yellowjellybean

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When volatile solvents A and B are mixed in equal proportions heat is given off to the surroundings. If pure A has a higher boiling point than pure B, which of the following could NOT be true?

A. The BP of the mixture is less than pure A
B. The BP of the mixture is less than pure B
C. The vapor pressure of the mixture is less than pure A
D. The vapor pressure of the mixture is less than pure B

The answer is B

So on the graph of negative deviation, the total vapor pressure can dip below the vapor pressure of pure A or pure B but not both. Is that correct? So if C can be true, I don't see why B can't be true. Please help me out I've spent too much time on this problem. Thanks.

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Actually the vapor pressure can dip below both pure A and B. The vapor pressure can be anywhere between 0 and below the vapor pressure of B which has the lower boiling point.
 
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