Friday, June 1, 2012

Green Flame Reaction

I 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 BangsFlashes, and Explosions – Illustrated Guide to Chemistry Demonstrations. ©2005 Chris Schrempp and

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