[crazypakithug]

A 2.00L sample of O2(g) was collected over water at a total pressure of 785torr and 25C. When the O2(g) was dried (water vapor removed), the gas had a volume of 1.94L at 25C and 785torr. Calculate the vapor pressure ofwater at 25C. (the correct answer is 24torr)
I have tried solving this using P1V1/T1=P2V2/T2 i pluggedeverything in got .0069-.0067 this was wrong
I tried using g=PM/RT getting the grams of each then i use the equation P=dRT/M for each which would be P=.531-.515 = .016 wrong answer but the closest i got to the real answer.
I have tried god knows what and i think i violated a few laws and i still cant get it. I would appreciate it if anyone could get it.

[Borek]

You need to find water partial pressure in the original mixture. What was the molar fraction of water in the 2.00L? (Hint: use Avogadro's principle).