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Ash and flames in a foil tray.

Watch that snake grow!

Here’s a fun little firework you can make at home. A couple of simple household chemicals grow into a gigantic black snake!

You will need

  • Icing sugar
  • Bicarb soda
  • A firelighter
  • Long matches or a stick lighter
  • Dry sand
  • Disposable aluminium tray
  • Measuring spoons
  • Cup
  • Spoon
  • Hat
  • Sunscreen

hot hazard iconchemical hazard iconoutdoor hazard icon

Safety: Ask an adult to help.

  • This activity uses fire and chemicals that require adult supervision.
  • Do not do this activity when it is very windy, or when the Fire Danger Rating is high, severe, extreme, or catastrophic, or if there is a Total Fire Ban.
  • When you’re outside, remember to be sun safe with a hat and sunscreen.

What to do

  1. Measuring bicarb into a cup.Measure ½ teaspoon of bicarb soda and 2 teaspoons icing sugar into a cup. Mix them together thoroughly.
  2. Half fill the aluminium tray with sand.
  3. Check the packaging of your firelighters and pay attention to any safety warnings.
  4. Firelighter sitting on a metal tray filled with sand.Put a firelighter on the sand.
  5. Put the tray on the ground outside, in a clear area. Make sure there’s nothing flammable within one metre.
  6. Sand ontop of firelighter in metal tray of sand.Sprinkle a thin layer of sand on top of the firelighter.
  7. White mixture on top of firelighter in tray of sand.Spoon a pile of your sugar and bicarb mix on top of the firelighter.
  8. Lighting the firelighter in the tray of sand.Get an adult to set the firelighter alight.
  9. Ash and flame in metal tray.Watch as the snake grows. Ours kept growing for almost 10 minutes!
  10. Sprinkeling sand on top of ash in metal tray.When the snake has stopped growing, put the fire out by covering it with more sand, or with water.
  11. Leave it for 30 minutes to cool down.
  12. When you’re cleaning up, the ash, sand and firelighter can be thrown in the bin. The tray can be recycled.
  13. After you’re finished, remember to wash your hands!

What’s happening?

Watch that snake grow! By heating icing sugar and bicarb you’ve created a black foam, with gas bubbles in it. If you try holding it after it’s cooled down, you’ll find that the snake doesn’t weigh much.

A lot of the gas that creates the foam’s shape comes from the bicarb soda (NaHCO3). When you heat bicarb up above 100° Celsius, it starts to break down. It turns into a solid called sodium carbonate (Na2CO3), and releases steam (H2O) and carbon dioxide gas (CO2).

The chemical reaction looks like this:
2 NaHCO3 → Na2CO3 + H2O + CO2

So what happens to the sugar? As it heats up, some sugar burns and some caramelises.

Sugar is made of carbon, hydrogen and oxygen (C12H22O11). Sugar starts to caramelise when heated above 160° Celsius or so. In this process, sugar molecules lose some of their hydrogen and oxygen atoms and join together to make larger and more complicated molecules. The more caramelised the substance gets, the darker it becomes.

Once the hydrogen and oxygen atoms are removed, only the sugar’s carbon atoms are left. Carbon can take many forms, including soot and charcoal. Carbon is what makes the snake so black.

Sugar chemistry is complicated, and even scientists still don’t fully understand the science of caramelisation. But it sure makes for a fun experiment!

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