Black snake (firework)
"Black snake" is a term that can refer to two similar types of firework, the Pharaoh's snake and the sugar snake. The "Pharaoh's snake" or "Pharaoh's serpent" is the original version of the black snake experiment. It produces a more impressive snake, but its execution depends upon mercury (II) thiocyanate, which is no longer in common use due to its toxicity. For a "sugar snake", sodium bicarbonate and sugar are the commonly used chemicals. Other sources report the contents as "a nitrated mixture of linseed oil and naphthalenes".
Once lit, both fireworks emit smoke and spew out ash resembling a snake via an intumescent reaction. They remain on the ground and emit no sparks, flares, projectiles, or sound.
This reaction was discovered by Wöhler in 1821, soon after the first synthesis of mercury thiocyanate. It was described as "winding out from itself at the same time worm-like processes, to many times its former bulk, of a very light material of the color of graphite." For some time, a firework product called "Pharaoschlangen" was available to the public in Germany, but was eventually banned when the toxic properties of the product were discovered through the deaths of several children that had mistakenly consumed the resulting solid.
The Pharaoh's snake experiment is conducted in the same manner as the sugar snake experiment, however, the former uses mercury(II) thiocyanate (Hg(SCN)2) instead of powdered sugar with baking soda. This must be done in a fume hood because all mercury compounds are hazardous.
After igniting the reagents, mercury(II) thiocyanate breaks down to form mercury(II) sulfide (HgS), carbon disulfide (CS2), and carbon nitride (C3N4). Graphitic carbon nitride, a pale yellow solid, is the main component of the ash.
2Hg(SCN)2(s) → 2HgS(s) + CS2(l) + C3N4(s)
CS2(l) + 3O2(g) → CO2(g) + 2SO2(g)
2C3N4(s) → 3(CN)2(g) + N2(g)
When mercury(II) sulfide (HgS) reacts with oxygen (O2), it will form gray mercury vapor and sulfur dioxide. If the reaction is performed inside a container, a gray film of mercury coating on its inner surface can be observed.
HgS(s) + O2(g) → Hg(l) + SO2(g)
Solid fuel is used in this experiment. The solid fuel can be sand that is sufficiently covered in ethanol or hexamethylenetetramine. A white mixture of sucrose and sodium bicarbonate will eventually turn black and the snake will grow about 15–50 centimetres (5.9–19.7 in) long after it is lit.
- 2NaHCO3(s) → Na2CO3(s) + H2O(g) + CO2(g)
- C12H22O11(s) + 12O2(g) → 12CO2(g) + 11H2O(g)
- C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g)
- C12H22O11(s) → 12C(s) + 11H2O(g)
The carbon in the reaction makes the snake black. The overall process is exothermic enough that the water produced in the reactions is vaporized. This steam, in addition to the carbon dioxide product, makes the snake lightweight and airy and allows it to grow to a large size from a comparably small amount of starting material.
- Helmenstine, Anne Marie. "How to Make a Pharaoh's Snake Firework". Archived from the original on 17 October 2019. Retrieved 16 October 2019.
- Helmenstine, Anne Marie. "How to Make Black Snake or Glow Worms". Archived from the original on 14 October 2019. Retrieved 16 October 2019.
- "LISTSERV 15.0 - CHEMED-L Archives". Mailer.uwf.edu. Archived from the original on 2006-09-13. Retrieved 2009-04-05.
- Davis, T. L. (1940). "Pyrotechnic Snakes". Journal of Chemical Education. 17 (6): 268–270. doi:10.1021/ed017p268.
- "Sugar snake". MEL Science. MEL Science 2015–2019. Archived from the original on 6 October 2019. Retrieved 28 October 2019.
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