How many grams of O2 are contained in here?

Question

how many grams of O2 are contained in 10.5L of oxygen measured over water at 25℃ and 740. torr? The vapor pressure of water at 25℃ is 24 torr.

Answer 1

Use the Ideal Gas Law (PV=nRT) and solve for moles. (convert torr to atm.  740 torr / 760 = .97 atm & Temp = 25C + 273 = 298 Kelvin)

n = PV / RT = .97 atm x 10.5 L / .0821 x 298 = 10.185 / 24.466 = .42 moles.  One mole of oxygen (O2 = 16 x 2 = 32) weighs 32 grams / mole.  Multiply the weight of one mole of oxygen by .42 = 13.44 grams