Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds
 

Solid carbon dioxide turning into a gas

Demonstration

Apparatus and materials

Polythene bag or balloons, small

CO2 cylinder (syphon type)

Dry ice attachment

Health & Safety and Technical notes


Whether you use a gas cylinder or solid CO2, you should do a risk assessment. 

Solid carbon dioxide must not be handled with bare fingers: use tongs or wear thick gloves. Wear eye protection before breaking a large block (with a hammer and cold chisel). 

You may be able to locate a local supplier for solid CO2. If you have a dry ice attachment and a CO2 cylinder, follow the instructions to get about half a teaspoon of carbon dioxide snow. 
 
For further information about dry ice, see the apparatus entry for CO2 cylinder.

 

Procedure


If using a balloon, stretch the neck of the balloon and hold it open with several fingers whilst about half a teaspoon of carbon dioxide snow is scraped in. Quickly flatten the balloon and knot the neck firmly. A polythene bag is easier to fill but more awkward to seal well.


Teaching notes


Solid carbon dioxide is unusual in that, at room temperature and pressure, it does not turn into a liquid before changing into a gas as it warms up – it sublimes. The change in volume from solid to gas can be seen to be as much as 600 times if the container in which it is expanding is well-sealed and has no holes. 

Alternately you could place a small piece of solid carbon dioxide (say, 0.5 cm3) under the mouth of a gas jar or measuring cylinder which is full of water and inverted over a tank of water so that the bubbles of gas can be collected. 
 
This experiment was safety-checked in January 2005