Yes it is a neat demo.
Ammonium dichromate decomposes to produce chromium(III) oxide, nitrogen gas
and water vapor. When this demo is presented in the open on a ceramic plate
or on a heat resistant padded steel gauze, the green oxide fluffy flakes will
tend to fly around and cause a mess. Invariably whoever is performing the
demo will come in contact with the oxide. However, there is a safeway to
perform this demo. It's tricky but it can be done and the oxide can be
disposed of safely afterwards.
Place about 15 grams of ammonium dichromate inside a 1000 ml glass beaker
using a funnel to form a cone. Prepare a wick from a 2.5 cm by 2.5 cm paper
towel rolled and soaked in ethyl or methyl alcohol. Insert the wick into
the top of the cone inside the beaker. Dry your hands and use tongs to light
the wick. Cover the beaker with an unpadded steel wire screen to catch the
flyng oxide particles and watch the volcano erupt. The effect is not as
striking as when it is done in the open but just as impressive.
When proper safety practices and disposal procedures are followed the
demonstration is quite effective. It beats watching the reaction on a video.
Wear safety glasses and an apron while performing this demo.
The chromium oxide can be made into a thick slurry with a little water while
in the beaker, transferred into a container and sealed and disposed of
properly. Do not dump the oxide in the trash can. Granted this procedure
is never 100% safe. Part of doing any laboratory activity is learning to
follow safety standards and recognizing the hazards and the consequences of
whatever we are doing and taking the proper precautions. Learning by doing
is far better than learning through videos. Of course there are limits as to
what we can and cannot and should not do in class.
Have fun doing the demo safely.
Greg Darakjian
Anaheim High School
811 West Lincoln Avenue
Anaheim, Ca 92805
Tel (714) 999-3717