Change in volume from a liquid to a gas for nitrogen
Practical Activity for 14-16
Apparatus and Materials
- A supply of liquid air (or liquid nitrogen)
- Measuring flask, 100 ml
- Chemical balance Method 2
- Measuring cylinder (must have a volume 750 times greater than that of the test tube)
- Rubber tubing
- Small test tubes, similar, 2
- A supply of liquid air and liquid nitrogen
Health & Safety and Technical Notes
Liquid nitrogen presents the following particular risks:
- asphyxiation in oxygen-deficient atmospheres
- fire in oxygen-enriched atmospheres
- cold burns, frost bite & hypothermia from the intense cold
- over-pressurisation from the large volume expansion of the liquid
- manual-handling accidents if using 25 l volumes.
A full risk assessment for using solid CO2 and nitrogen is available (to subscribers) from: CLEAPSS.
- Pour liquid air or nitrogen quickly into the 100 ml measuring flask of known mass.
- Once the jar has been cooled sufficiently, the violent bubbling will cease. Add more liquid to top the level up to the 100 ml mark so that the volume is known.
- Weigh the whole on the balance and find the mass of liquid.
- Calculate the density of liquid nitrogen.
- Measure the density of air (Air is 80% nitrogen. Oxygen and nitrogen have a similar density).
Method 2: To measure the volume change when liquid nitrogen turns into a gas directly.
- Fill the trough and measuring cylinder with water. Invert the measuring cylinder in the trough.
- Find the volume of the test tube by filling it with water and measuring the volume of water.
- Pour liquid nitrogen into the second, dry test tube and when the liquid has stopped bubbling, top up the test tube and quickly fit the rubber tubing.
- Insert the rubber tube into the open end of the measuring cylinder and collect the nitrogen gas.
- Compare the ratio of the volume of nitrogen gas to the volume of liquid nitrogen of the same mass.
- The density of liquid air/nitrogen is about 90 g/100 ml, which is 900 kg /m 3 .
- The density of air/nitrogen is about 1.2 kg /m 3 .
- Hence the volume change when liquid nitrogen becomes gaseous nitrogen is 900/1.2 = 750.
- If there is no liquid air/nitrogen available, then solid carbon dioxide can be allowed to sublime. A small solid lump of carbon dioxide can be put into a measuring tube filled with water, and the volume of the gas measured. It is better to get the carbon dioxide from a solid block because that produced by a cylinder is not compacted enough.