Decomposition of Ammonium Dichromate


DESCRIPTION:
This demo decomposes ammonium dichromate using a fuse soaked in ethanol. The reaction is a violent one, that resembles a volcano. Ammonium dichromate is an orange solid, while chromium (III) oxide is a dark green solid.
(NH4)2Cr2O7(s)  →  Cr2O3(s)  +  N2(g)  +  4H2O(g)

TOPICS COVERED:
decomposition reactions
redox
exothermic reactions
color change
chemical change

MATERIALS NEEDED:
– large beaker
– aluminum foil
– ammonium dichromate
– paper
– ethanol
– lighter

PROCEDURE:
1. Spread aluminum foil in the bottom of the fume hood, a square ~12 inches should be sufficient
2. Place a small mound of ammonium dichromate in the bottom of the beaker, and place the beaker on the foil, 7-8g is plenty
3. Make a 4 inch fuse out of rolled paper, soak in ethanol
4. Place the fuse in the mound and light

ADDITIONAL COMMENTS:
This demo looks like a volcano. It takes awhile to clean up though, so it can’t be done all of the time. The demo also produces much more chromium (III) oxide than the amount of ammonium dichromate that was started with.

SAFETY:
Ammonium dichromate is a strong oxidizer, caution should be taken, and goggles worn at all times. Chromium salts are toxic to humans and the environment, so all waste should be disposed of in hazardous waste.

REFERENCES:
Shakhashiri, B.Z. Chemical Demonstrations;  University of Wisconsin Press: Madison, 1983; Vol. 1, pp 81.

STORY: This demo can be presented as a volcano going off.

Handout