Students understand the properties of a gas, how a gas is used in our everyday lives and the safety considerations needed when using a gas.
Show the class a variety of containers where the contents are under pressure such as fly spray, hair mousse, hairspray, a can of soft drink. Ask students to identify what they think all of these have in common.
Introduce the terms ‘compressed’ and ‘pressurised’ to the class and indicate that these containers all contain added gas – that is, they have been compressed and pressurised. Ask them for suggestions about what the words might mean in relation to solids, liquids and gases. What are some examples of things that can be compressed and pressurised? What are some examples of things that cannot be compressed or pressurised?
Organise the class into groups. Ask students if it is easier to compress air or water. Allow students time to share their responses within their group. For each group set up some syringes alongside large containers of water (large enough for students to put both hands into).
Allow each group time to investigate the question by:
- trying to clap their hands under water and comparing it to clapping their hands in the air
- filling a syringe with water and placing a finger over the end then trying to compress the syringe. Ask how far the syringe can be compressed
- filling the syringe with air and repeating the process. Ask how far the syringe can be compressed.
Teacher note: More information on these mini-investigations can be found in Background information (PDF, 494 KB).
Meet together as a class to discuss the students’ findings. Ask what evidence the students have to support their claims.
- Draw students’ attention once again to the pressurised containers on display and ask them to consider why we need to put some things under pressure before we use them.
- View the video Compressed gas cylinders to find out why gases are compressed. (Watch from the 12-second point and end at 45 seconds.) Ask students what would happen if SCUBA diving tanks did not contain compressed gas or if cans of fly spray were not pressurised.
- Pass the pressurised containers around, reminding students not to release the contents of the containers. Ask them to look at the different items and to identify what information on the container tells us the contents are under pressure. Generate a class list of this information.
- Ask students to look again at the containers to identify what safety information is presented. Discuss the dangers of compressed gas. How do we ensure our safety when using these items?
- Brainstorm some other ways that we use gas under pressure. Discuss how the use of these gases helps make life easier. What would our lives be like without compressed gases?
Revisit the list of properties of a gas that was developed earlier in the unit and add any new information or make any changes or modifications.
Ask students to create a poster demonstrating their understanding of the properties and behaviours of a gas and how we use it in our everyday lives. Ensure the poster includes a piece of safety information about the use of compressed gases in our everyday lives.