Posted by jeff on .
A sample of hydrogen gas was collected over water at 36°C and 855 mmHg. The volume of the container was 6.50 L. Calculate the number of moles of H2 collected. (Vapor pressure of water is 44.6 torr at 36°C)

chemistry 
DrBob222,
Use PV = nRT
For P: The total P of the system is the pressure of the gas + pressure of water vapor.
Pgas alone = total P  vapor pressure H2O
P gas = 855  44.6 = ??
Now convert P in mm to P in atmospheres.
P mm/760 = P atm.
V is in liters.
Don't forget to convert T to Kelvin.
Solve for n.