The Mole continued... Molar Volume of a Gas
Molar volume is the volume occupied by one mole of any substance. The molar volumes of different substances
can be very different. However, the molar volume of a gas is more predictable than the molar volume of a liquid
or solid.
According to Avogadro’s law, at a given temperature and pressure a given volume of any gas contains the same
number of molecules.
 The volume of a gas is usually measured at a standard temperature and pressure (STP).
 Remember, standard temperature is 0C and standard pressure is 101 kPa.
At STP 1 mole of gas occupies 22.4 liters (1 mole = 22.4 L of gas)
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Question: Determine the volume, in liters, of 0.545 mol of CH4 gas at STP.
Question: How many moles are contained in 46.7 L of Ne at STP?
Would 22.4 L of one gas have the same mass as 22.4 L of another gas?
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A mole of gas has a mass equal to the molar mass.
Only gases with equal molar masses would have the same mass at an equal volume.
Molar Mass and Gas Density
The density of a gas at STP can be used to calculate the molar mass of that gas.
Question: If the density of a gas is 2.86 kg/m3 at STP, what is the molar mass?
Question: The density of a gaseous compound is 1.25 kg/m3 at STP. Determine the molar mass, and identify the
gas as either carbon monoxide or carbon dioxide.
The Mole continued... Molar Volume and Gas Density – Worksheet
1. What is the volume at STP of 3.8 x 10-2 mol CO2?
2. At STP, what is the volume of 0.765 moles of helium?
3. Determine the number of moles in 33.8 L of SO2 gas at STP.
4. How many moles are in 2.3 x 104 L of oxygen gas at STP?
5. At STP the density of a gaseous compound is 0.759 kg/m3. Determine the molar mass.
6. The densities of three gases are 1.70 kg/m3, 0.0893 kg/m3, and 2.86 kg/m3.
Calculate the molar mass of each gas and then identify them as hydrogen, sulfur dioxide, carbon dioxide,
fluorine, or oxygen.
Answers:
1. 0.85 L
2. 17.14 L
3. 1.51 mol
4. 1026.79 mol
5. 17.00 g/mol
6. 38.08 g/mol = F2
2.00 g/mol = H2
64.00 g/mol = SO2