16-08-2012, 01:11 PM
Elephant’s Toothpaste
Elephant’s Toothpaste.pdf (Size: 244.14 KB / Downloads: 49)
Instructions
1 Gather all the materials and set them up on a desk
with the students gathered around.
2 Empty a full sachet of dry yeast into a cup.
3. Add four table spoons of warm water and stir until
well mixed.
What is hydrogen peroxide?
Hydrogen peroxide (in a much stronger 30% concentration) is a chemical well known
to hairdressers as a bleaching agent. It is also used to bleach paper and many other
industrial chemical processes. In hair dressing bleach, the liquid is incorporated into a
thick gel which clings to hair preventing contact with the scalp.
The chemical symbol H2O2 for hydrogen peroxide is very similar to water’s H2O. The
H2 represents two hydrogen atoms while the O2 represents two oxygen atoms (water
molecules contain only one oxygen atom).
Why does yeast accelerate hydrogen peroxide decomposition?
Hydrogen peroxide is a natural by-product of metabolism. All known animals which
metabolise oxygen produce a natural enzyme called catalase which catalyses the
decomposition of hydrogen peroxide into harmless water and oxygen gas. Catalase is
found in every organ in the body and in particularly high concentrations in the liver.
Hydrogen peroxide is harmful to living things because it is a strong oxidiser which can
cause damage to living cells at the molecular level.
Yeast is a fungi which also produces the catalase enzyme. Adding yeast to hydrogen
peroxide then, rapidly increases (catalyses) the decomposition of hydrogen peroxide
into water, oxygen gas and heat (you will notice that the foam produced feels warm).
In potatoes, catalase is present in sufficient quantities to produce visible bubbles of
oxygen when a freshly cut piece is coated with 3% hydrogen peroxide.
Many other chemicals catalyse the decomposition of hydrogen peroxide into water
and oxygen gas. Some catalysts such as potassium iodide are particularly efficient
catalysts for the decomposition but almost any super fine powder will cause the
decomposition to accelerate.