Activity

Black snakes

Summary
Ignite sugar and baking soda to make black snakes of carbon puffed up with carbon dioxide gas.
Science content
Chemistry: States of Matter, Properties of Materials (K-7)
Chemistry: Atoms, Molecules (3-7)
Chemistry: Chemical Changes (2, 7)
Physics: Energy forms, Conservation of Energy (1, 3, 4, 5)
Materials
  • sand
  • flammable fuel
  • icing sugar
  • baking soda
  • match or lighter
Procedure

Mix 4 teaspoons icing sugar with1 teaspoon baking soda.
Make a pile of sand on a heat-proof surface, and make a dent in the middle of it.
Pour fuel into the dent, then add some sugar/baking soda mixture.
Light it.

Long black "snakes" of carbon are extruded, made up of carbon and carbonate, puffed up with carbon dioxide gas. They crumble when they are touched (and make your hands black).
The reaction smells like marshmallows over a fire.

The chemistry:
C12H22O11 (sucrose sugar) + 12O2 → 12CO2 + 11H2O (g). This is complete combustion of the sugar in oxygen, which produces heat which makes the reaction continue. The water vapour escapes.
There are also some reaction products that are not made with oxygen (which happen in the centre of the pile):
C12H22O11 (sucrose sugar) → 12 C (black of the snake) + 11 H2O (gas).
2 NaHCO3 (baking soda) → Na2CO3 (carbonate that is also part of the snake) + H2O (gas) + CO2 (gas, which puffs up the snake)

Notes

Try without the sand - add the sugar/baking soda mixture to a metal bowl, pour on the fuel, then light.
Much more dramatic here: https://www.youtube.com/watch?v=sinQ06YzbJI

Grades taught
Gr 4
Gr 5
Teaching site
ingridscience afterschool