# On heating ammonium dichromate, the gas evolved is?

Aug 5, 2017

On heating ammonium dichromate, the gas evolved is nitrogen.

#### Explanation:

Ammonium dichromate ("NH"_4)_2"Cr"_2"O"_7 decomposes when heated to produce chromium(III) oxide ${\text{Cr"_2"O}}_{3}$, nitrogen gas, and water vapour:

("NH"_4)_2"Cr"_2"O"_7"(s)" → "Cr"_2"O"_3"(s)" + "N"_2"(g)" + "4H"_2"O(g)"

This reaction is the basis of a common demonstration called the "ammonium dichromate volcano".

The decomposing ammonium dichromate gives off orange sparks and throws the green chromium(III) oxide crystals into the air, producing an effect that looks like a miniature volcano.

The chromium(III) oxide crystals are "fluffier" than the original ammonium dichromate.

Thus, even though much of the mass of the starting material escapes as nitrogen gas and water vapour, the product looks like a much larger amount of material.

Here's a video of the demonstration.