Elephant Toothpaste-A Way to Prank a Co-Worker?

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.   

A Chemist's April Fools' Joke: Nitrogen Triiodide

I was recently asked about interesting chemical reactions and so I started thinking about a few fun demonstrations that we like to do during National Chemistry Week, or at the University's Open House. Which brought me to nitrogen triiodide.

Nitrogen triiodide (NI3) is a contact explosive. There are many types of explosions and explosive materials, but I will focus on chemical explosives. An explosion is characterised by the rapid increase in volume and release of energy. This is also accompanied by the production of heat, light, sound, and pressure (the shock wave-this is the part of an explosion that does the damage). Generally explosions produce gasses, this is because the production of gasses is an extremely thermodynamically favourable (see blog entry A Diamond is Forever...Or Maybe Not) process. Explosions are detonated by the application of energy. In the case of a contact explosive, only very small amounts of energy need to be applied to the material. This energy can be in the form of heat, light, sound, or physical pressure. 

Nitrogen triiodide is very sensitive as it produces nitrogen gas and iodine, which are way more stable compounds and therefore results in a huge release of energy. It also produces a sound reminiscent of a gunshot. It does, however, leave purple stains due to the iodine. This compound is actually so sensitive that brushing it lightly with a feather can cause an explosion. The sound produced by the explosion can actually cause subsequent explosions of the compound to occur. I think the following video shows it best:

http://www.youtube.com/watch?v=2KlAf936E90 

A great practical joke is to place this on the underside of toilet seats or in the key holes of doors. Small amounts of course. Just to scare people. (Please note: the author of this blog is not recommending that you try this at home.) 

Ask a Chemist!

Hello loyal followers! This is just a request for more questions. I am putting the plea out there. I want to make sure that your questions get answered so please make sure that you are leaving your questions in the comments. To keep this blog going I need your science questions!

Thanks!

Careful of the Icy Patch!

In the winter time, as hardy Canadians, we pour salt onto the icy patches on the sidewalks to keep people from slipping and preventing litigation. But ever wondered why salt? What does the salt do? Well I shall explain this by introducing the concept of "colligative properties".

A colligative property is one where by introducing an impurity of some sort (this is often called the solute) the properties of the solution are changed. What makes a colligative property different from other chemical properties is that a colligative property is only dependent on the number of added impurity molecules, not the type of molecule.

The important colligative property that we need here in Canada during the winter time is: Freezing Point Depression. When you add an impurity, such as salt or sand or antifreeze (ethylene glycol) to a solution of water (or that icy patch on your front walk) the result is that the freezing point of the water becomes lower. This means that even though it is -15 C outside, the ice on your walkway stays liquid. And because freezing point depression is a colligative property, it doesn't make a difference what kind of additive you put on the icy patch. All will cause the freezing point to become depressed. The amount that the freezing point lowers is solely dependent on the amount added, not what is added. 

Freezing point depression is used in undergraduate chemistry labs the world over as a means to determine the purity of the products that they were supposed to isolate. If they have a pure compound then the freezing point should be nice and sharp, and agree with literature standards. If they have an impure compound then their freezing point will be much lower than the standards.  

Another example of a colligative property is Boiling Point Elevation. When you are making pasta and you add a little salt to the water, this does not make the water boil sooner (contrary to what my ninth grade science teacher taught me) it actually raises the temperature that the water boils at. 

Reference:
Laidler, K. J.; Meiser, J. H.; Sanctuary, B. C. Physical Chemistry 4th ed. 2003; Houghton Mifflin Company, Boston, MA.