A deep-sea diver uses a gas cylinder with a volume of 13.0 L and a content of 50.1 g of O2 and 33.4 g of He. Calculate the partial pressure of each gas and the total pressure if the temperature of the gas is 22°C.

Question

I got PO= 5.82, PHe=15.5 and Ptotal=21.4 but it says that PO and Ptotatl are wrong, can anyone help?

Answer 1

Your bottle contains 1.57 moles of O2 and 8.35 moles of He, for a total of 9.92 moles. At STP, that gas would occupy 222 liters; at 22 C and 1 atm, it would occupy 240 liters. Since the vlume is 13.0 L, the pressure must be Ptotal = 240/13 = 18.8 atm
The partial pressure of O2 is 15.9% of the total pressure, or 2.98 atm

Your mistake may be in using 16 instead of 32 for the (molecular) weight of oxygen.