Concentrating 3% Hydrogen Peroxide

[Hauss32]

Hello All!

Hopefully I will get some good insight from all you fantastic chemists out there! Here is my situation:

I am a Biochemistry student (hardly chemistry, I know), and although I have take 2 general chem. courses and 2 O. chem courses I still know very little about chemistry. Ah the wonders of science. Anyways, I am part of a mentoring program for at-risk youth and would love to do the "elephant toothpaste" KI, H2O2 catalyzed decomposition reaction. But I've heard 3% H2O2 is no good, and 17.5% "food grade" is too expensive for my college budget...

 

Is it possible to concentrate the 3% to maybe 15% safely? Keep in mind I only have a stove and some glassware, and lab glasses are the extent of my safety wear. I hear quite a bit about combustible vapors and things of that nature. Can this be avoided by not boiling the H2O2 dilute and merely warming it for H2O evaporation? Any advice here is appreciated!

 

Please keep in mind I am looking for advice, especially concerning safety. Please do not crush my mostly biological and little chemistry scientific spirit by telling me I'm foolish for inquiring. I'm not a chemist and I know that. Cheers!

 

Also, if you have any other cool science presentations that are cheap but would wow middle school/high school students please let me know!

 

THANKS EVERYONE!!!

[weiming1998]

There are several ways you can concentrate 3% H2O2. One way is by freezing it. Since H2O2 has a lower freezing point than water, it will stay liquid while all the water freezes. It is possible to get the H2O2 to at least 15% with freezing. With fractional crystallisation, a 60% concentrated solution could be made, but this would be difficult to set up.

Another way is by evaporation/boiling. For your purposes, you do not need to fear about combustible vapours (H2O2 vapours are only significantly dangerous/explosive if your H2O2 is above 70% in concentration), but cranking the heat all the way up will only result in the decomposition of the H2O2. Ideally, a vacuum would be used to remove all the water, leaving behind extremely concentrated H2O2 (more than 90% concentration) since H2O2 is less volatile than water, but you can let the 3% H2O2 evaporate on the stove at low heat. Make sure the glassware is clean and free from any sort of metal ions (which catalyses the decomposition of the H2O2).