1. The problem statement, all variables and given/known data I am supposed to determine the vapour pressure experimentally of a series of prepared solutions, which are a mixture of 2 different substances in different proportions. This involved attempting to create a "vacuum", placing the liquid inside and then measuring the change in pressure. I was then supposed to compare those values to the "ideal" values I would get, which were calculating using Raoult's law. My problem is, I know how to figure out the change in pressure after I added the liquid, but how does this change in pressure relate to the vapour pressure? (The room pressure was about 770 torr, and after the "vacuum" we had a change of roughly 330/340 torr between room and experimental pressure) 3. The attempt at a solution I really haven't tried much because I don't know where to begin. I calculated the difference between pressure before and after the addition of the liquid, but I don't know how to deduce the vapour pressure from that. The vapour pressure isn't simply the change in pressure, right? Because the values we obtained were in average about 5 or 6 times lower than what was expected. Also, it makes sense to me that the change in pressure we registered would be dependent on the pressure that the liquid was experiencing inside. The higher the pressure, the less it would evaporate. Thanks for whatever help you can give. If you need more info, please ask. I didn't provide everything because I feel I'm just stuck in that particular step, and after I understand that I'll be able to finish it.