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KS2 Science at Home: Week 6

Key Stage 2 Experiment of the week!

Invisible Extinguisher
IMPORTANT - It is essential that an adult should supervise this experiment as it involves fire.

How does it work?  

Ks2 science

If you mix baking soda and vinegar they react to make a gas called Carbon Dioxide (CO2). CO2 is more dense than normal air, which means that it will sink! Because CO2 sinks, it stays in the cup instead of floating away like a normal mix of air would. This means you have a cup full of CO2!

The candle burns thanks to a combustion reaction that requires Oxygen (O2), something we find lots of in the air around us. When you pour your cup of CO2 into the cup containing the candle, the CO2 sinks to the bottom of the cup and surrounds the candle. This displaces (or pushes up) all the normally mixed air, along with all that O2 the fire needs to burn. Then, Your candle is extinguished invisibly.

Materials you need

  • Tall Drinking glass or 16 oz plastic cup
  • Short Drinking glass or 9 oz plastic cup
  • Tea Light
  • Matches or Lighter


  1. Place a tea light in the short drinking glass.
  1. Using a long match or safety lighter, light the tea lights while leaving them in the glass.
  1. In the tall glass, pour 1/2 cup vinegar
  1. Slowly sprinkle 1/2 tsp of baking soda into the tall glass containing the vinegar. You can dump it all in at once, but be ready for a big eruption!
  1. Let the reaction slow down until the foam has disappeared.
  1. Slowly tilt the tall glass on its side over the tea light as if you were pouring the air over it.
  2. If the flame doesn’t go out on your first try, pour another scoop of baking soda into the vinegar and repeat steps 5 & 6.

Some research for next week: What does 'crystallisation' mean?
We will answer this question with next week’s science experiment!