Another fun reaction that is a favourite demo of chemists is termed "Elephant Toothpaste". This experiment is fairly simple.
What you need:
A graduated cylinder
30% solution of hydrogen peroxide (note: household hydrogen peroxide is 3% solution)
Potassium Iodide-KI (either solid or saturated solution)
Dish soap
Food colouring (a minty green is where the "toothpaste" moniker comes from.)
The potassium iodide is used as a catalyst-it starts the reaction, but is not consumed in the reaction. The actual chemical reaction that happens is the break down of the hydrogen peroxide into water and oxygen very rapidly, accompanied by the production of heat.
2 H2O2 ----> 2 H2O + O2
In the graduated cylinder, you mix the soap, the hydrogen peroxide, and the food colouring. Then very carefully add the potassium iodide. The oxygen gas produced causes the soap to foam up rapidly and make a huge mess to the delight of many (except those who have to clean it up).
This particular reaction has obtained pop culture notoriety by being used on the Big Bang Theory as a method of revenge. Check it out: http://www.youtube.com/watch?v=-pUeOAit7zI
The amount of foam produced on their kitchen counter is absolutely not exaggerated, which is what makes the demo so cool.
There is one small thing in this scene, however, that bugs me every time I see it and therefore feel I should mention it now. Sheldon, while wearing latex gloves (which you should wear if you handle these chemicals-serious burns can arise from 30% H2O2. Just think about the sting 3% gives you.) picks up a glass of Mountain Dew and drinks it. This is just terrible and upsetting lab protocol. There is dangerous chemicals on those gloves and all around, and he's bringing them to his mouth! That is a great way to ingest something that may kill you rapidly. It makes me cringe to watch. I guess you shouldn't expect better from a physicist.
Thank you for the post! I was thinking about doing this at home with my kids and was wondering if you could elaborate a bit on the proper safety protocol that should be followed?
ReplyDeleteI should add that I know better then to keep my drinks near the chemicals, but I just wanted an idea on potential dangers involved. The Big Bang Theory clip does make seem less dangerous than it probably is (Sheldon did dump it on someone, but I'm assuming that you wouldn't want to actually want skin exposure).
ReplyDeleteThe first thing with safety in this reaction is the 30% hydrogen peroxide is corrosive. Trust me, it burns. So gloves are a definite must. Potassium iodide is a mild irritant so again gloves. The products and reactants are definitely something that I would not want to be getting on my skin. Never do any chemistry without safety glasses.
DeleteIt is something that I wouldn't recommend doing at home.
Hmm...my kid-like curiosity is still tugging at me to do it, but the older more risk adverse part of my personality is pulling back. In any event thank you for the information. One last question, if I do decide to do this, how do I responsibly dispose of the end product? Thanks again!
DeleteThe products of the reaction can be rinsed down the sink. At the end you really just have water and potassium iodide and dishsoap.
DeleteThe biggest concern in this experiment is handling the 30% H2O2. With safety glasses and gloves you should be okay.
What my science teacher did was use a more aqueous solution btwn the water and H2O2. It doesnt burn at all
DeleteThere is no such thing as a "more aqueous solution" than water. By definition anything in water is aqueous. Water and any aqueous solution and H2O2 are all miscible, meaning that it would be impossible to add it "between" the solution. 30% H2O2 will burn, and burn very badly.
DeleteOMG I tought I was the only one that noticed that!!! I teach chemistry and I really stress safety in my class and my students watch that show. it just gives a really bad example of lab procedure
ReplyDeleteI am so glad to hear that those who teach chemistry stress safety. In the last two jobs I have had I have actually started the safety programs. I am big into safety.
DeleteRegarding the soda drinking - while bad from a safety perspective, that is what made it funny. As a science teacher myself, I have used that clip to show what not to do (and why). I've never done that reaction before, but it looks great! My concern is, the reaction is exothermic... and the clip clearly shows the foam steaming on the kitchen counter. Then they dump it on top of unprepared, unprotected people. Just how hot does that foam get, and what kind of burn danger does it represent after reaction?
ReplyDeleteIt gets hot enough to be a concern about touching it immediately. Because of both the chemicals involved and the heat created it could have hurt the individuals that it was being drop on.
DeleteI am SURE that they didn't use the actual reaction when dumping it on Kripke. The KI will turn your skin yellow. And, it is exothermic, but not much warmer than a warm shower. I bet they just used dish soap bubbles or something similar for that part of the show.
ReplyDelete