Time to think on your feet, and design a test into the presence of CO2, the catch is you can’t release the gas

Design a piece of apparatus to allow you to obtain a sample of the gas without removing the gas jar from the water and demonstrate that the gas is carbon dioxide.

This experiment should take one hour. 


Materials per group

  • Gas jar full of carbon dioxide – set up as below
  • Fresh lime water

Test the gas - diagram

Equipment per group

  • Various lengths of tubing
  • Plastic syringes
  • Items from the junk list
  • Plastic bowl
  • Safety glasses

Health, safety and technical notes

  • Read our standard health and safety guidance here.
  • Wear eye protection. 
  • This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete. 


There are many approaches to this problem, some more ingenious than others. The essential idea is to construct something that will go under the water and collect the gas. During trialling, students designed containers filled with water, which when under the gas jar could be emptied and the gas collected. Syringes connected to rubber tubes were banned! A time element can be introduced to focus the activity.


The experiment can be modified by varying the gas in the gas jar.


This resource is part of a collection of problem-solving activities, designed to engage learners in small group work. Find out how to use these resources, and obtain a list of suggested ‘junk items’ here.