Question

what is the total mass in grams of oxygen in a room measuring 4.0 m by 5.0 m by 2.5 m? assume that the gas is at STP and that air contains 20.95% oxygen by volume

Answer 1

You can figure this out by manipulating the ideal gas law, PV=nRT.

You have the gas at STP, so you should know right away what P and T are. As for V, you can figure it out using the dimensions given in the question. However, you need to keep in mind that the V you use in the equation is NOT the entire volume of the room, but rather just the volume occupied by O2. Finally, instead of using n, use m/MM (mass over molar mass). That lets you solve for mass right away. Also remember that the molar mass is for O2, not just O. Once you plug in all the values and solve for m, you'll have your answer!