Elephant Toothpaste is a popular demonstration to introduce the concept of decomposition reactions. The chemical reaction involved is the decomposition of hydrogen peroxide into oxygen gas and water. The reaction is very slow at room temperature. Consequently, it requires a catalyst. Manganese dioxide is commonly used to catalyse the reaction. However, bakers yeast works just as well, is easier to clean-up and is non-toxic. The key ingredient for this demo is hydrogen peroxide which is readily available in 6% and 30% solutions. How can you tell whether or not these chemicals are safe to use? Fortunately, most chemicals used in schools come with a HMIS hazard rating.
The Hazardous Materials Identification System (HMIS) is a hazard rating system that ranks the health, flammability, and physical hazards of different chemicals. The HMIS scale ranges from 0-4.
(0-minimal, 1-slight, 2-moderate, 3-serious, 4-severe)
The Health section ranking from 0 to 4 indicates the danger presented by a chemical, either acute or chronic, to living tissue if inhaled, ingested or absorbed. Fire Hazard/Flammability ranks the fire danger presented by a chemical, usually determined by its flash points and boiling points. Reactivity ranks specific physical hazards including compressed gases, explosives, organic peroxides, oxidizers, pyrophoric substances, and unstable reactive and water reactive chemicals.
Considering the HMIS rating of a chemical is a useful way of screening safer alternatives in a given activity. Chemicals with HMIS 0 or 1, e.g., 6% hydrogen peroxide, are generally safe. If you must use a chemical with HMIS 2, e.g., copper(II) sulfate, thoroughly read the MSDS to ensure you understand the hazards and know how to control them. HMIS 3 chemicals, like 30% hydrogen peroxide, are much more hazardous and should only be used by teachers with specific training. HMIS 4 chemicals, e.g., mercury compounds, should not be in schools.
Here are two versions of the elephant toothpaste demo. Have a look at both. The demo with 30% hydrogen peroxide is definitely more spectacular but is it worth the additional hazard and clean-up hassle?
Always consult the MSDS prior to using any chemical.