December 2014 - January 2015

# Foaming chemis-tree

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Deanna Cullen, Whitehall High School, Whitehall, Michigan

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This great chemis-tree is the result of a modified version of the elephant toothpaste demo. Deanna Cullen from Whitehall High School, Whitehall, MI sent in this fun photo. To remind readers, the elephant toothpaste is created with hydrogen peroxide (30%) mixed with liquid soap — then a catalyst, often potassium iodide, is added. The hydrogen peroxide decomposes very quickly and the generated oxygen is trapped in soapy bubbles, creating a marvelous foaming effect. There is a safer kid’s version, which requires less concentrated hydrogen peroxide and uses yeast as a catalyst.

If you look closely you can see a large Erlenmeyer flask from which the trapped oxygen is foaming out thus creating the tree shape. Deanna used an upside-down beaker underneath to give the tree some height. The food coloring was added before the catalyst. There was a large tub to catch the mess. Deanna mentioned the reaction happened rather slowly with the foam creating its own Christmas tree effect. Apparently, a year later, students at Deanna’s school are still talking about it.

Even though this demo has become a classic, don’t forget good safety practices.

- Always wear safety goggles. Be aware that the foam can shoot out quickly.
- Always wear plastic gloves when working with 30% hydrogen peroxide.
- This is an exothermic reaction, so the flask becomes quite hot. Wait a considerable amount of time before handling.
- Don’t touch the foam — students will be tempted.

Note: Some of our proofreaders made some additional safety comments.

- The foaming mixture may stain floors and desks because I2 is a by-product of the reaction.
- The reaction can be quite vigorous and may shoot as high as the ceiling, or spray on the floors. The speed of the reaction will be impacted by amount of KI added, along with whether it was added as a solution (very fast), as a finely ground solid (moderate) or as coarse crystals (quite slow).

One year a science instructor was using the same reaction for a different purpose and accidentally put some of the reaction mixture in a sealed glass bottle. Because decomposition of H2O2 produces a large amount of O2 gas, pressure quickly built up and the bottle exploded. It should be noted that hydrogen peroxide should not be stored in sealed glass bottles. Commercial hydrogen peroxide solutions come in plastic bottles with vented caps for a reason.

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