Gas Laws Question?

Question

The total pressure of a 200mL sample of oxygen collected over water at 25Celsius is 1.030 atm.
A) How many moles of gas is present?
B) How many moles of oxygen is present?
C) How many moles of water vapor is present?

Answer 1

Water vapor pressure at 25Celsius is 23.76 Torr, which is 23.76/760.0 = 0.0313 atm.
a) Use ideal gas law:
n = PV/RT = 1.030*0.200/(0.08206*298) = 8.42mMol
c) Again use ideal gas law:
n(water) = PV/RT = 0.0313*0.200/(0.08206*298) = 0.256mMol
b) n(O2) = n - n(water) = 8.17mMol