[vishuboy]

Hi,

I had this question on an online quiz:

10 ml of acetone is mixed with 100 ml water. The vapour pressure of water above the solution is
a) equal to the vapour pressure of water
b) equal to the vapour pressur pressure of solution
c) more than the vapour pressure of water
d) less than the vapour pressure of water

In water, there is hydrogen bonding. If i add acetone to it. It might come in between those bonds and might weaken them to some extent. So, the volume should increase and will show +ve deviation. And will lead to greater vapour pressure. If this is true, option C is correct

But the explanations given with answers goes like this "As the acetone is added it displaces molecules from the surface and hence vapour pressure is less"

I am confused why aren't we considering the +ve deviation aspect?

Can someone help me where I went wrong.

[Borek]

http://en.wikipedia.org/wiki/Raoult_Law