I really need help with this question, calculate the total pressure of a gaseous mixture containing 0.2 moles of Nitrogen, 0.4 moles of Water vapor and 0.8 moles of Argon. If the partial pressure of Water vapor is 1.2 Atmosphere.

Answer 1

the partial pressures are proportional to the mole fractions
... twice the moles, twice the partial pressure ... etc.

Answer 2

You sure the pressure value is asking for total pressure given only the partial pressure of water vapor? If so, this problem has too many unknowns for the data given. I'm guessing the 1.2 atm is total pressure and the problem is asking for the vapor pressure of water. That would make more sense. :-)

Answer 3

For 0.40mole water in 1.4mole mix => 0.40/1.4 = 0.286 mole fraction of mix
Then Partial Pressure water = 0.286(1.2 atm) = 0.343 atm water vapor pressure x 760-mmHg/atm = 261-mmHg water vapor pressure.