The Pharaoh/Black Snake reaction is a highly dangerous chemical reaction that involves the decomposition of mercury (II) thiocyanate, which is a toxic substance, and is considered too hazardous to be used in schools. In addition, the decomposition yields many extremely hazardous substances. THIS REACTION SHOULD NEVER BE CARRIED OUT IN A SCHOOL.
Safety Data Sheets (SDSs) are the best general source of information available for any chemical and they should be consulted as a first step in assessing the risk associated with a chemical’s use and disposal. Science ASSIST has developed a Risk Assessment Template for schools to use see Risk Assessment Template.
Science ASSIST has developed a Recommended List of Chemicals for all schools in Australia. Mercury salts, which include mercury thiocyanate, are considered too hazardous for use in schools and will not be on this list. Science ASSIST strongly advises not to purchase any mercury salts and, if you have some in the chemical store, then they should be disposed of by a licensed waste disposal contractor.
Mercury (II) thiocyanate is a highly toxic chemical and dangerous to the environment. Using mercury (II) thiocyanate, equates to danger—it is fatal if inhaled, swallowed or absorbed through the skin, causes digestive and respiratory tract irritation, may impair fertility and can also cause kidney damage. Mercury (II) thiocyanate is classified as an Acute Toxicity Category 3 on the Safe Work Australia GHS Hazardous Chemical Information List.
The decomposition of mercury (II) thiocyanate yields: carbon nitride, mercury vapours, carbon dioxide and sulfur dioxide. Carbon nitride further decomposes into dicyan gas. Mercury vapours, sulfur dioxide and dicyan gases are all highly toxic and classified as hazardous.
All aspects of this reaction are HAZARDOUS:
- Handling the reagent
- Breathing the smoke
- Touching the ash column
- Contact with the remains of the reaction during clean-up
Suggested alternative activities:
- Dehydration of sucrose using concentrated sulfuric acid. This reaction should be carried out as a demonstration in the fume cupboard and relevant PPE should be worn when handling the acid. See www.rsc.org/education/eic/issues/2007March/ExhibitionChemistry.asp.
- Black Snake Fireworks—involving powdered sugar and sodium bicarbonate in the presence of lighter fluid or alcohol. This reaction should be carried out on a small scale on a bed of sand in a metal tray as a demonstration in the fume cupboard. See https://www.thoughtco.com/make-black-snakes-or-glow-worms-605964 and https://www.youtube.com/watch?v=HtAgxVT2x5s [Note: Science ASSIST recommends that ONLY the sugar and sodium bicarbonate version is used for this activity].
- View the activity on YouTube https://youtu.be/yN9pioJWTk0
‘Sulfur dioxide (SO2) Air quality fact sheet’, Australian Government, Department of Environment website www.environment.gov.au/protection/publications/factsheet-sulfur-dioxide-so2 (2005)
‘Mercury (II) thiocyanate’ Merck Millipore website, Material Safety Data Sheet. http://www.merckmillipore.com/INTERSHOP/web/WFS/Merck-AU-Site/en_US/-/US... (Link updated, October 2018).
‘Mercury and health’, Fact sheet No 361’ World Health Organisation website www.who.int/mediacentre/factsheets/fs361/en/ (September 2013)
‘Material Safety Data Sheet: Mercuric Chloride’, Chem-Supply website https://www.chemsupply.com.au/documents/ML0591CH4B.pdf (July 2011)
‘Hazardous Chemical Information System (HSIS)’, Safe Work Australia website. http://hsis.safeworkaustralia.gov.au/GHSInformation/GHS_Hazardous_Chemical_Information_List (September 2014)
‘How to make black snake fireworks with and without fire’, Instructables website http://www.instructables.com/id/How-to-Make-Black-Snake-Fireworks-With-Without-F/ (Accessed May 2015)
‘How To Make Black Snakes or Glow Worms’, About education website https://www.thoughtco.com/make-black-snakes-or-glow-worms-605964 (Accessed May 2015)
‘Pharoah’s snakes’, Chem-Toddler website www.chem-toddler.com/redox-reactions/pharaohs-snakes.html (Accessed May 2015)
‘The dehydration of sucrose’, Royal Society of Chemistry website www.rsc.org/education/eic/issues/2007March/ExhibitionChemistry.asp (March 2007)