Pharaoh’s Snake: Mercury(II) Thiocyanate’s Weirdest Chemical Reaction


Story: 

Wierdest Chemical Reaction I have Ever Freaking Seen!!
Mercury(II) thiocyanate decomposition. This just gives me the creeps.

Other Versions

Pharaoh’s Snake
Mercury(II) thiocyanate decomposition is initiated by heating.

Analysis:

An interesting video in circulation online since few years claims to show a weird and creepy chemical reaction as Mercury(II) Thiocyanate decomposes when heat is applied. The white sugar like powder in appearance comes alive when initiated by heat and grows into what some people even described as a Sponge/Coral reef. What is shown in the video is a fact, and the chemical effect is usually called Pharaoh’s Snake or Pharaoh’s Serpent because of its appearance.

Video grab Showing Mercury(II) Thiocyanate Chemical
Video grab Showing Mercury(II) Thiocyanate Chemical

Pharaoh’s Snake Chemical Reaction

At first look, some people thought the weird formation shown in the video is not real, and could be the result of some video editing or CGI. But as can be seen on the label of the chemical bottle shown in the beginning of the video, the white substance is Hg(SCN)2, aka Mercury(II) Thiocyanate that decomposes upon heat application. The Pharaoh’s Serpent effect is similar to the Black Snake firework with which we used to play and amuse ourselves as children. Earlier, Mercury thiocyanate was also used in pyrotechnics (a firework display) for the effect of the Pharaoh’s serpent or Pharaoh’s snake, but because of its toxicity and safety concerns, the use was later discontinued. On the upside, Mercury thiocyanate has few uses in chemical synthesis, like determination of chloride ions in water.

When Mercury(II) thiocyanate comes in contact with strong enough heat source, a rapid exothermic reaction is initiated that produces a large mass that appears like a winding “snake”. The chemical reaction is described below:

Igniting mercury thiocyanate causes it to form an insoluble brown mass that is primarily carbon nitride, C3N4. Mercury sulphide and carbon disulphide are also produced.

2Hg(SCN)2 → 2HgS + CS2 + C3N4

Carbon disulphide combusts to carbon dioxide and sulphur dioxide:

CS2 + 3O2 → CO2 + 2SO2

The heated C3N4 partially breaks down to form nitrogen gas and dicyan:

2C3N4 → 3(CN)2 + N2

Mercury sulphide reacts with oxygen to form mercury vapour and sulphur dioxide. If the reaction is performed inside a container, you will be able to observe a grey film of mercury coating its inner surface.

HgS + O2 → Hg + SO2

Picture Showing Pharaoh's Snake, Mercury(II) Thiocyanate's Weirdest Chemical Reaction
Pharaoh’s Snake, Mercury(II) Thiocyanate’s Weirdest Chemical Reaction
Picture Showing Pharaoh's Snake, Mercury(II) Thiocyanate's Weirdest Chemical Reaction
Pharaoh’s Snake, Mercury(II) Thiocyanate’s Weirdest Chemical Reaction

Safety Warning

Like all forms of mercury are quite toxic, Mercury(II) thiocyanate is also toxic and is no longer used in fireworks. So it is important to follow safety measures while handling the Mercury(II) thiocyanate and conducting chemical reaction to see Pharaoh’s Serpent effect. Touching the chemical with bare hands, breathing the smoke or touching the ash column and the reaction products during cleanup are all risks that should be considered carefully when performing the reaction. So protective measures should include goggles, lab coat, gloves, a fume hood and a scoopula for transferring the Hg(SCN)2 around.

Hoax or Fact:

Fact.

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References:

What in the name of all that is holy is going on in this video?


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Pharaoh’s Snake: Mercury(II) Thiocyanate’s Weirdest Chemical Reaction

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