Black snake (firework)
Black snake are two similar types of firework. After being lit, both fireworks may begin to smoke and may spew out ash resembling a snake via an intumescent reaction. They may stay on the ground and do not emit sparks, flares, any form of projectiles, or any sound, but may release smoke.
Pharaoh's snake or Pharaoh's serpent is the original version of the black snake experiment. This traditional version of this firework produces a more impressive snake, but its operation depends upon mercury (II) thiocyanate, which is no longer commonly used because of its toxicity.
For sugar snake, sodium bicarbonate which produces carbon dioxide gas, and sugar forming carbon containing ash, are common chemicals used. Other sources report the contents as "a nitrated mixture of linseed oil and naphthalenes".
Pharaoh's snake is a more dramatic experiment but requires additional safety precautions compared to black snake due to the presence of toxic mercury vapor and other mercury compounds.
This reaction was discovered by Wöhler in 1821, soon after the first synthesis of mercury thiocyanate: "winding out from itself at the same time worm-like processes, to many times its former bulk, a very light material 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 death of several children mistakenly eating the resulting solid.
Pharaoh's snake experiment is conducted same as black snake experiment, but this experiment used mercury(II) thiocyanate (Hg(SCN)2) instead of powdered sugar with baking soda. This must be done in the fume hood because all mercury compounds are hazardous.
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 needed for burning in this experiment. The solid fuel can be sand 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 the snake 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 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, make the snake light and airy and 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.