J.R. S. answered • 10/06/18

Ph.D. University Professor with 10+ years Tutoring Experience

When a gas is collected over water, one must subtract the vapor pressure of water from the total pressure in order to find the pressure of the gas itself. Thus, 1.05 atm - 0.0278 atm = 1.0222 atm = pressure of the O

_{2}gas.PV = nRT and solve for n to determine moles of O

_{2}collected.n = PV/RT = (1.0222 atm)(0.5 L)/(0.0821 Latm/Kmol)(296 K) note the use of Kelvin for temperature.

n = 0.02103 moles O

_{2}mass of O

_{2}= 0.02103 moles x 32 g/mole = 0.67 grams (to 2 significant figures)
Julie S.

10/06/18