posted by Jon .
A 70.8mL sample of "wet" O2(g) is collected over water at 29.9 degrees Celsius at a barometric pressure of 743 mmHg. The vapour pressure of water at 29.9 degrees Celsius is 31 mmHg. What is the mole fraction of O2 in the gas collected?
So i found the partial pressure of O2 to be 712 mmHg, and then I found the number of moles of O2 to be 0.00267 mol. Butttt I'm not really sure how to establish the mole fraction? Help!