Air vs chlorine 

This demonstration could follow on from work on the properties of the Group 1 metals and their reaction with water. It is recommended that you always practise demonstrations before carrying them out in front of a class.

Equipment required

  • 3 clean, dry bricks with at least 1 flat surface each
  • Chlorine generator (see below) – dropping funnel, conical flask and delivery tube
  • 3 gas jars with lids
  • Bunsen burner
  • Scalpel
  • Filter paper
  • Indicator paper.


  • Lithium, sodium and potassium (Highly flammable and corrosive). See CLEAPSS Hazcards HC058a, HC095a, HC076.
  • Potassium manganate(VII) (Oxidising agent, harmful). See CLEAPSS Hazcard HC081
  • Concentrated hydrochloric acid (Corrosive). See CLEAPSS Hazcard HC047a
  • Chlorine. See CLEAPSS Hazcard HC022a

Health and safety

  • Wear eye protection during both the demonstration and the chlorine generation.
  • Read our standard health and safety guidance
  • Some chlorine will escape during the demonstration, but it should be safe to carry out the experiment in a well-ventilated laboratory.
  • The gas jars should be filled with chlorine in a fume cupboard beforehand.
  • You will need to fill three gas jars with chlorine.

This can be done using a chlorine generator and must be carried out in a fume cupboard, although the rest of the demonstration can be carried out on a bench if the room is well ventilated. To make a chlorine generator, place a couple of spatulas of potassium manganate(VII) in a conical flask. Attach a delivery tube and a dropping funnel containing concentrated hydrochloric acid (see Figure 1).

Chlorine generator

Check carefully that the acid is hydrochloric acid.

Explosions have occurred through use of the wrong acid.

Allow the acid to drip slowly onto the potassium manganate(VII) and collect the gas by downward delivery.

The gas jar will appear green when enough gas has been collected. When the gas jar has been filled, seal the lid on using a little Vaseline®.

Have three filled gas jars ready prior to the demonstration.

An alternative method for making chlorine is to react sodium chlorate(I) with hydrochloric acid.




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