Question

a sample of oxygen gas (O2) at STP has a mass of 48.0 grams. What is the volume of the gas?

Answer 1

P * V = n R T 
1 * 2.50 = n * 0.082 * 273 = 2. 50 / ( 0.082 * 273 ) = 0.11 mol 
mass = mole number * molecular mass 
mass = 0.11 * ( 16 * 2 ) = 3.52 g