Carbon sugar snake

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You will need

A wide baking tray filled with 2 kg of sand
1 tablespoon of bicarbonate soda
4 tablespoons of icing mixture (also known as powdered sugar or confectioners’ sugar)
50 mL of ethanol, lighter fluid or methylated spirits
A BBQ lighter
Bowl & spoon
Fire extinguisher, fire blanket or running water & bucket nearby.

Adult help is essential! Do not run in windy conditions!

A metal baking tray, a yellow BBQ lighter, a plastic bottle with methylated spirits, a blue bowl and metal spoon, a packet of bicarbonate soda and a plasti container with icing mixture in it

Instruction

A hand mixing white powder with a metal spoon in a blue bowl

Combine 4 tablespoons of icing mixture & 1 tablespoon bicarbonate soda in a bowl.

Make a small indentation in the sandpile in your baking tray (making sure the sandpile is at least 5cm deep).

Place your baking tray in a place away from any flammable materials and near your fire extinguisher, fire blanket or bucket of water.

Close of a bottle pouring methylated spirits onto sand

This step is for adults!

Get an adult to pour roughly 20mL of methylated spirits, lighter fluid or ethanol into the indentation in the sand.

Once wet, add small amounts of methylated spirits around the edge of the hole as well (no more than 30mL).

Danger: do not use more than 50mL methylated spirits in total. Do not run in windy conditions!

A metal spoon creating a pile of white powder on sand

Using the spoon, carefully add the mixture of icing mixture and bicarbonate soda to the centre of the indentation in the sand.

This step is for adults!

Firstly, ensure that your fire extinguisher, fire blanket or bucket of water is ready to go nearby.

Use the BBQ lighter to light the edge of the base of the icing mixture & bicarbonate soda pile.

Be careful – this should only be done in still conditions without any wind or drafts to blow on the flame.

A pile of white powder on sand with the top of it burning

Watch this under adult supervision

The flame will move over the powder pile and begin to burn the top of it. Watch the powder closely… you will see small nodules of black carbon start to form and rise off the main powder pile.

Watch this under adult supervision

The nodules of burnt carbon will start to join and rise upwards.

A “carbon sugar snake” will begin to form as the experiment continues.

The process is slow but relentless!

A fire in sand with a black snake-shaped ash column rising out of it and falling to one side

Watch this under adult supervision

The carbon snake will form a column and rise upwards until falling to the side under its own mass.

The sugar pile will continue to burn until all of the methylated spirits is used up and the outer layer of white powder is black. This process will take around 20 to 30 minutes, depending on the amount of methylated spirits that you used.

Don’t touch the carbon sugar snake until the flame has gone out and you have waited at least 10 minutes for it to cool down.

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What is going on?

There are three chemical reactions going on in this science demonstration.

When sugar burns with oxygen, it produces carbon dioxide and water. The carbon dioxide gas and the water gas is what pushes the carbon snake upwards. The combustion of sugar can be written in the following balanced chemical reaction:
C₁₂H₂₂O₁₁ + 12O₂→ 12CO₂ + 11H₂O
Some of the sugar doesn’t completely combust into carbon dioxide & water. Instead, the heat causes the sugar to break down into our carbon and water. The carbon is the component of the snake that makes it black.The thermal decomposition of sugar can be written with the following balanced chemical reaction:
C₁₂H₂₂O₁₁ → 12C + 11H₂O
The bicarbonate soda also decomposes in this experiment. In this case, the bicarbonate soda breaks down to form sodium carbonate, water as a gas and carbon dioxide gas. The sodium carbonate combines with the carbon in the reaction above that expands as the hot gases pass through it. The thermal decomposition of bicarbonate soda can be written in the following balanced equation:
2NaHCO₃ → Na₂CO₃ + H₂O + CO₂

Variables to test

More about variables here

Try changing the ratios of the icing mixture and the bicarbonate soda. Does this make a difference?
If there is no indentation in the sand, will the snake form?