Green Flame ReactionI performed a favorite demonstration for my students recently where a white powder (boric acid) is mixed with small amount of methanol in a flask and then ignited, the result is an eerie green flame. This year, however, I experimented with the time I let for the reaction to take place. The results were noticeable.
Video 1 shows the first trial where boric acid and methanol were mixed for approximately 45 seconds before it was ignited. The green flame lasted approximately 1 second the flame is much more green in person).
Video 2 shows the second trial where the mixture was shaken for approximately 74 seconds and then ignited. The green flame in this trial lasted approximately 3 seconds.
I varied the reaction times for two other classes and obtained similar results. So there you have it, vigorously shaking the mixture for longer times leads to a longer burning time for the green boric acid ester.
Boric acid has a wide range of uses other than serving as neat demos for chem teachers such as rat poison, antiseptics, acne prevention, and others. Boric acid trimethylester (trimethyl borate) is used as a solvent for the production of waxes and varnish and such.
For those interested, the reaction is as follows:
H3BO3 + 3CH3OH => B(H3CO)3 + 3H2O
This demonstration was modified from Bangs, Flashes, and Explosions – Illustrated Guide to Chemistry Demonstrations. ©2005 Chris Schrempp and ExploScience.com.