Converting Between Volume and Moles

How Does One Convert Between Moles and Volume?

To convert between moles and mass, molar volume is utilized as the conversion factor. This introduces a new concept that is easily associated with our previous knowledge of the mole through the diagram below: 

What is Molar Volume?

At standard temperature and pressure (STP) one mole of any gas occupies the same volume. STP is found at 0 °C or 101.325 kPa, and at these levels 1 mole = 22.4 L. Therefore, 22.4 L/mole is the molar volume at STP.

With this conversion factor:

• You can convert from volume to moles
• You can convert from moles to volume 

What's the Process?

Like molar mass conversions, only one mathematical step is needed in these conversions: 

Examples 

• At STP an unknown gas is found to occupy 150 mL. How many moles of gas must there be? 

                         150 mL x 1 mole/ 22.4 Liters

                      = 6.70 milli-moles/ 1 000 

                      = 0.00670 moles  

• At STP, a sample of oxygen gas contains 11.5 moles. How many litters of oxygen gas are there?  

                      11.5 moles x 22.4 Liters/ 1 mole

                   = 258 L  

Below is a video that thoroughly goes over the process of converting moles to volume and back again:

  

-George Spencer