Standard level
Gases obey Avogadro's law, which says that the number of mol of gas is directly proportional to the volume.
Background
If the volume of closed round bottom flask is measured, and the ambient pressure and temperature is known, then the number of moles of air present can be calculated using the gas laws.
Avogadro's law says that this is the same for all gases.
Subtracting the mass of the gas present, which can be calculated from the moles of air and the average relative mass of the air, allows us to know the mass of an empty flask.
If the flask is then filled with another gas and weighed, the mass of gas present can be determined by subtraction, and from this the relative mass of the gas determined.
Note: The Phyphox application on many smart phones is a rapid and easy way to obtain the ambient pressure.
Chemicals
- Solid carbon dioxide, CO2(s)
- Tap water
Apparatus
- Large round bottomed flask and bung
- Electronic balance
- Weigh a clean, dry round-bottomed flask and bung.
- Using a spatula transfer about 0.5 g of solid carbon dioxide into the flask.
- Cover the opening with a filter paper.
- When all of the solid carbon dioxide has disappeared, place the bung into the flask and reweigh.
- Fill the flask up with water.
- Pour the water into a large measuring cylinder and record the volume.