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What Happens When Burn NH4Cr2O7 with HgSCN?

(NH4)2Cr2O7

Image credit: Ammonium dichromate by Reytan via Wikimedia Commons. Public domain.

Among all the chemical reactions one might have seen, the following filmed one should be probably regarded as the most amazing and terrific scene. After you light the pile of reactants, it would start to present a picture in which tentacles seemed to crawl out of a portal to Hell.

In fact, what you have seen in the video below is really related to two reactions: one is involved in decomposing ammonium dichromate and the other is the combustion reaction of mercury (II) –thiocyanate.

Ammonium dichromate is kind of orange powder. Upon the introduction of heat, it could generate nitrogen gas, water, and ammonium (III) oxide, the dark powder, which appeared to be the volcano you had observed.

The occurrence of tentacles is indeed the result that heat is introduced to mercury (II) thiocyanate. As it is heated, this white solid would be expanded to be a dark, tentacle-like mass owing to its role in decomposing carbon nitride. Additionally, in this process, sulfur dioxide and mercury (II) sulfide would be created as well.

Such reaction is appropriately nicknamed the Pharoah’s Serpent, which sells well as fireworks in the market. However people now get to realize that it is also toxic besides its celebrating functions.

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