How many moles are in 33 L of CO₂ gas at STP?

We can assume that the volume of one mole of any gas (within reason) is 22.4 L only if we know that the pressure of the gas is 1 atmosphere (101 kPa) and that the temperature of the gas is zero degrees Celsius (273 K). These are known as standard temperature and pressure (STP). So if the gas in question happens to be at STP then the calculation would be:

3.00 L x 1 mol/22.4 L = 0.134 mol

And 3.00 litres CO2 or any other gas at STP would contain 0.134 moles. If the gas was at some other temperature or pressure, assuming they were “moderate,” you could calculate the number of moles by solving the following formula for n.

PV =nRT Where P is pressure, V is volume, T is temperature in Kelvin and R is the ideal gas constant consistent with the units of volume and pressure used.