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we are trying to perform the Elephant Toothpaste experiment involving the reaction of yeast and Hydrogen Peroxide for the students at school.

However, the results have been very underwhelming, likely because we have to use the 3% version of Hydrogen Peroxide.

My question is: What are some other ways to help create a stronger propulsion or thicker foam?

Some things I have been experimenting with are reducing the water mixed with the yeast, and swirling the bottle to mix the yeast and Hydrogen Peroxide. Any advice is much appreciated.

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  • You might try horseradish as a catalyst, rather than yeast. Use the fresh root, not the prepared sauce, and test a few different plants - some are more effective than others.
  • Cosmetic supply stores stock 6% (20 volume) $\ce{H2O2}$, but that concentration is more likely to cause skin irritation or bleach fabrics.
  • The most effective catalyst for decomposing $\ce{H2O2}$ that I've used is potassium permanganate, $\ce{KMnO4}$, but it has a few liabilities:
    • It's a strong oxidant and can start a fire when mixed with organic chemicals.
    • It stains skin and fabric anything from pinkish-purple to black. The stain can be removed with sodium bisulfite, $\ce{NaHSO3}$, sold as an iron-stain remover. That can be a fun demonstration but is not suitable for young students to use.
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I spent a considerable amount of effort improving this demonstration and ended up with this (10 sec. video).

The best result I found was from the following:

  1. Concentrate store-bought 3% $\ce{H2O2}$ to ~30% $\ce{H2O2}$ (or buy the food-grade 30-35% online). Meticulous method is here (6m video).
  2. Make a solution of 1:1 $\ce{KI:H2O}$ by mass, e.g. 50g of each.
  3. Add some dish soap and food coloring to a large Erlenmeyer flask, then add 100 mL of the 30% $\ce{H2O2}$ solution.
  4. Add the 50g/50g solution of $\ce{KI}$ in water.

$\ce{KI}$ is easily purchased online. If you want more of a "toothpaste" effect than the "snowy" effect in the above video, mix the soap/food-coloring/$\ce{H2O2}$ thoroughly before adding $\ce{KI}$.

Safety notes: KI is mostly harmless -- but as in all cases, completely avoid contact with eyes/skin. The iodide will dye your skin brown-yellow (like the hospital stuff used for disinfecting the skin). Concentrated $\ce{H2O2}$ can be very nasty and oxidize your skin, turning it white for a few hours. So use gloves and goggles in all cases. The clean-up for the above video wasn't bad at all but we tossed the towels used to do it.

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H2O2 can cause eye damage. When used with reasonable care, it is unlikely to cause anything but temporary skin bleaching - if kept away from the eyes. That and maybe some ruined clothing (or other surfaces). I'd not use 30% around children, although as a controlled demonstration -physically separated from the audience, it can be safely used. First thing you could do, depending on your resources, is to determine if your 3% is actually near 3%. There are tables which list its density, if you can weigh some out into a volumetric flask, say. If you have a chemical refrigerator, it should be stored cold (and of course, away from sunlight). I guess if it were me, I'd buy some fresh 30% and dilute it for the kids to use (prior to the session). I'd use potassium iodide rather than yeast (what is it that you're trying to teach?) and possibly consider FeCl3 (if the lesson is about catalysts) - although staining would be more of an issue with the iron salt. Make sure that the peroxide isn't phosphate stabilized (if possible). If you really want to use yeast, make sure it's fresh, and I'd give it at least a minute or two in 35°C (95°F, which is just warm, not hot) water. Try different brands. Also consider your liquid dishwashing soap - they're not all the same. Some sources suggest adding glycerol to stabilize the bubbles - I've not tried that, but it seems reasonable (my old bubble recipe calls for 0.5 cups DW soap and 2 Tablespoons glycerine...). No reason you shouldn't add the KI to the soap (technically, it's a detergent) - you'd have to futz around to see if any water was needed and if so how much. At 3%, that means (do the math) that 100 ml will generate ~2 liters of O2 (at room temperature) - so a 20X total expansion maximum (ignoring volume increase due to steam formation from exothermicity). Figure the reaction is only partially complete and that figure drops. Seems to me the important thing is mixing - how the two solutions are added to one another. If it were me, I'd add the soap to the peroxide...although if I was leading a bunch of kids maybe I'd use them to try out different techniques. Proper eye protection is, imho, eye goggles - not safety glasses. This experiment is energetic and uncontrolled, use caution (with anything higher than 3%-6% peroxide).

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