You need to find moles of the gas, so you would use the ideal gas law: PV=nRT Pressure Volume n=moles R= gas constant Tenperature in Kelvin n= PV/RT (1.00atm)(1.35L)/(.08206)(332K) = 0.050mol Molar mass is grams per mole, so (3.75g/.050mol) = 75g/mol
