How much does gaseous oxygen (O2) weigh?

First recall the weight of atomic and molecular oxygen: O = 15.99 g/mol and O2 = 32 g/mol

Use the ideal gas law: PV = nRT

P = pressure (in atm); V = volume (in Liters); n = amount of substance (in moles); R = ideal gas constant = 0.0821 (units are (Liters*atm)/(Kelvin*n) ); T = absolute temperature (in Kelvin)

To get the gaseous volume of 1 mole of gas:  V=nRT/P

(1 mol)(0.0821 L/atm/K/mol)(273K)/1atm = 22.4 L gas

1 mole gas (STP) = 22.4L = 32g of O2

(32g/mol)(1L/22.4L/mol)= 1.428 g O2 per gaseous liter at STP

Standard temperature and pressure is 1 atm and 273K or O C

If we assume a ‘room temperature’ of 22 degrees C, then:

V=nRT/P

(1 mol)(0.0821 L/atm/K/mol)(295K)/1atm = 24.2 L gas

(32g/mol)(1L/24.2 L/mol) = 1.322 g of O2 per gaseous liter at 22 degrees C

So if you have 1000 L of gaseous oxygen: 1.322 g/L (1000L) = 1.32 kg