KS3 11 Testing for gasses



  • 1 spatula of potassium permanganate
  • Some cotton wool
  • A splint.
  • 1 test tube of hydrochloric acid
  • A piece of magnesium ribbon,
  • A lit splint
  • 1 test tube of hydrochloric acid,
  • 1 test tube of lime water,
  • Marble chips (1 spatula of)
  • A pipette
  • 1 test tube with 1cm depth of hydrochloric acid,
  • 1 test tube with 1 cm depth of bleach,
  • Damp blue litmus paper.

Oxygen test :

  • Heat the potassium permanganate in a dry test tube with a loose cotton wool plug.
  • Once heated light a splint and blow it out so it is glowing (but not on fire).
  • Remove the test tube from the heat, then take out the cotton wool and insert the glowing splint.


    • Add the magnesium to the hydrochloric acid and hold a lit splint near to the bubbles released (not in the acid but slightly above).
    • If Hydrogen is present it will burn with a squeaky pop

Carbon dioxide

  • Add some marble chips to a test tube of hydrochloric acid. The gas will form close to the surface of the acid.
  • Suck out the gas with a pipette and squeeze it into another test tube containing lime water.
  • If carbon dioxide is present the limewater turns cloudy


  • Add the bleach and Hydrochloric acid together in the same test tube and warm the test tube in your hand. Hold some damp blue litmus paper at the neck of the test tube – if Chlorine is present the paper will discolour.


Know the chemical tests for the following substances:


Carbon dioxide


Chlorine gas