1. Gas Quiz - Rd 2
A reaction produces 455 mL of oxygen gas collected by water displacement at 22 oC and 735 mm Hg room air pressure. If water vapor pressure at 22 oC is equal to 19.8 mm Hg, what is the mass of oxygen collected?
Given:
PV = nRT
R = L atm
mol K
1 atm = 760 mm Hg

3. First find the pressure of the dry oxygen gas:
Ptotal = PH2O + PO2
735 mm Hg = 19.8 mm Hg + PO2
PO2 = 715 mm Hg = atm

4. Next use PV = nRT to find moles of oxygen
gas, then convert to grams.
PV = n RT
(0.941 atm)(0.455 L) =
( L atm/ mol K)(295 K)
mol O2
x 32.0 g/mol
= g O2