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'''Mercury(II) thiocyanate''' ( |
'''Mercury(II) thiocyanate''' (Hg(SCN]])<sub>2</sub>) is an inorganic [[chemical compound]], the [[salt (chemistry)|salt]] of Hg<sup>2+</sup> and the [[thiocyanate]] [[anion]]. It is a white powder. It is best known for its former use in [[pyrotechnics]], as it will produce a large, winding “snake” when ignited. This is known as the [[Black snake (firework)|Pharaoh’s Serpent]].<ref name=snakes>{{ cite journal | author = Davis, T. L. | title = Pyrotechnic Snakes | journal = Journal of Chemical Education | volume = 17 | year = 1940 | issue = 6 | pages = 268–270 | doi = 10.1021/ed017p268 }}</ref> (see video [http://www.youtube.com/watch?v=ritaljhhk7s]) |
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==Synthesis== |
==Synthesis== |
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The first synthesis of mercury thiocyanate was probably completed in |
The first synthesis of mercury thiocyanate was probably completed in 1821 by [[Jöns Jacob Berzelius]] with evidence for the first pure sample occurring in 1866 prepared by a chemist named Hermes.<ref name=snakes/> It is prepared by treating solutions containing mercury(II) and thiocyanate ions. The low [[solubility product]] of mercury thiocyanate causes it to precipitate.<ref>{{ cite journal | author = Sekine, T.; Ishii, T. | title = Studies of the Liquid-Liquid Partition systems. VIII. The Solvent Extraction of Mercury (II) Chloride, Bromide, Iodide and Thiocyanate with Some Organic Solvents | journal = Bulletin of the Chemical Society of Japan | year = 1970 | volume = 43 | issue = 8 | pages = 2422–2429 | doi = 10.1246/bcsj.43.2422 | url = http://www.journalarchive.jst.go.jp/jnlpdf.php?cdjournal=bcsj1926&cdvol=43&noissue=8&startpage=2422&lang=en | format = pdf }}</ref> Most syntheses are achieved by precipitation. The two early syntheses achieved separately by Berzelius and [[Friedrich Wöhler]] were completed using the following reactions: |
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:2 |
:Hg(NO<sub>3</sub>)<sub>2</sub> + 2 KSCN → Hg(SCN)<sub>2</sub> + 2KNO<sub>3</sub> |
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:Hg(NO<sub>3</sub>)<sub>2</sub> <sub> (aq)</sub> + 2 KSCN <sub> (aq)</sub> → Hg(SCN)<sub>2</sub> <sub> (s)</sub> + 2KNO<sub>3</sub> <sub> (aq)</sub> |
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==Pharaoh's serpent== |
==Pharaoh's serpent== |
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This property was discovered soon after the first synthesis of mercury thiocyanate by Wöhler in 1821: "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.<ref name=snakes/> |
This property was discovered soon after the first synthesis of mercury thiocyanate by Wöhler in 1821: "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.<ref name=snakes/> |
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A similar, |
A similar, although less extreme, effect to the Pharaoh's serpent can be achieved using a firework known as a [[black snake (firework)|black snake]]. These are generally benign products, usually consisting of [[sodium bicarbonate]] or a mixture of [[linseed oil]] and [[naphthalene]]s. |
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==Uses |
==Uses== |
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Mercury thiocyanate has a few uses in chemical synthesis. It is |
Mercury thiocyanate has a few uses in chemical synthesis. It is the precursor to potassium tris(thiocyanato)mercurate(II) (K[Hg(SCN)<sub>3</sub>]) and caesium tris(thiocyanato)mercurate(II) (Cs[Hg(SCN)<sub>3</sub>]). The Hg(SCN)<sub>3</sub><sup>-</sup> ion can also exist independently and is easily reacted to form the compounds above amongst others.<ref>{{ cite journal | author = Bowmaker, G. A.; Churakov, A. V.; Harris, R. K.; Howard, J. A. K.; Apperley, D. C. | title = Solid-State <sup>199</sup>Hg MAS NMR Studies of Mercury(II) Thiocyanate Complexes and Related Compounds. Crystal Structure of Hg(SeCN)<sub>2</sub> | journal = Inorganic Chemistry | year = 1998 | volume = 37 | issue = 8 | pages = 1734–1743 | doi = 10.1021/ic9700112 }}</ref> |
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Its reactions with organic halides yield two products, one with the sulfur bound to the organic compound and one with the nitrogen bound to the organic compound.<ref>{{ cite journal | author = Kitamura, T.; Kobayashi, S.; Taniguchi, H. | title = Photolysis of Vinyl Halides. Reaction of Photogenerated Vinyl Cations with Cyanate and Thiocyanate Ions | journal = Journal of Organic Chemistry | year = 1990 | volume = 55 | issue = 6 | pages = 1801–1805 | doi = 10.1021/jo00293a025 }}</ref> |
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It was discovered that mercury thiocyanate can improve detection limits in the determination of chloride ions in water by [[UV-visible spectroscopy]]. This technique was first suggested in 1952 and has been a common method for determination of chloride ions in laboratories worldwide ever since. An automated system was invented in 1964 and then a commercial chloroanalyzer was made available in 1974 by Technicon ([[Tarrytown, NY]], USA). The basic mechanism involves the addition of mercury thiocyanate to a solution with unknown concentration of chloride ions and iron as a [[reagent]]. The chloride ions cause the mercury thiocyanate salt to dissociate and the thiocyanate ion to complex with Fe(III), producing Fe(SCN)<sup>2+</sup>, which absorbs visible light at 450 nm. This absorption allows for the measurement of concentration of Fe(SCN)<sup>2+</sup>, produced as a result of the reaction between chloride ion and mercury thiocyanate. From this value the concentration of chloride can then be calculated.<ref name=cirello>{{ cite journal | author = Cirello-Egamino, J.; Brindle, I. D. | title = Determination of chloride ions by reaction with mercury thiocyanate in the absence of iron(III) using a UV-photometric, flow injection method | journal = Analyst | year = 1995 | volume = 120 | issue = 1 | pages = 183–186 | doi = 10.1039/AN9952000183 }}</ref> |
It was discovered that mercury thiocyanate can improve detection limits in the determination of chloride ions in water by [[UV-visible spectroscopy]]. This technique was first suggested in 1952 and has been a common method for determination of chloride ions in laboratories worldwide ever since. An automated system was invented in 1964 and then a commercial chloroanalyzer was made available in 1974 by Technicon ([[Tarrytown, NY]], USA). The basic mechanism involves the addition of mercury thiocyanate to a solution with unknown concentration of chloride ions and iron as a [[reagent]]. The chloride ions cause the mercury thiocyanate salt to dissociate and the thiocyanate ion to complex with Fe(III), producing Fe(SCN)<sup>2+</sup>, which absorbs visible light at 450 nm. This absorption allows for the measurement of concentration of Fe(SCN)<sup>2+</sup>, produced as a result of the reaction between chloride ion and mercury thiocyanate. From this value the concentration of chloride can then be calculated.<ref name=cirello>{{ cite journal | author = Cirello-Egamino, J.; Brindle, I. D. | title = Determination of chloride ions by reaction with mercury thiocyanate in the absence of iron(III) using a UV-photometric, flow injection method | journal = Analyst | year = 1995 | volume = 120 | issue = 1 | pages = 183–186 | doi = 10.1039/AN9952000183 }}</ref> |
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It is used for determining the concentration of chloride ions in aqueous solution using mercury thiocyanate was discovered. Mercury thiocyanate without iron (III) is added to a solution with an unknown concentration of chloride ions, forming a complex of the mercury thiocyanate and chloride ion that absorbs light at a wavelength of 254 nm, allowing more accurate measurements of concentration than the aforementioned technique using iron.<ref name=cirello/> |
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==References== |
==References== |
Revision as of 13:07, 16 May 2013
Names | |
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Other names
Mercuric thiocyanate
Mercuric sulfocyanate | |
Identifiers | |
ECHA InfoCard | 100.008.886 |
PubChem CID
|
|
CompTox Dashboard (EPA)
|
|
Properties | |
Hg(SCN)2 | |
Molar mass | 316.755 g/mol |
Appearance | White to tan monoclinic powder |
Odor | odorless |
Density | 3.71 g/cm³, solid |
Melting point | 165 °C (decomp.) |
0.069 g/100 mL | |
Solubility in other solvents | Soluble in dilute hydrochloric acid, KCN, ammonia slightly soluble in alcohol, ether |
Hazards | |
NFPA 704 (fire diamond) | |
Lethal dose or concentration (LD, LC): | |
LD50 (median dose)
|
46 mg/kg (rat, oral) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|
Mercury(II) thiocyanate (Hg(SCN]])2) is an inorganic chemical compound, the salt of Hg2+ and the thiocyanate anion. It is a white powder. It is best known for its former use in pyrotechnics, as it will produce a large, winding “snake” when ignited. This is known as the Pharaoh’s Serpent.[1] (see video [1])
Synthesis
The first synthesis of mercury thiocyanate was probably completed in 1821 by Jöns Jacob Berzelius with evidence for the first pure sample occurring in 1866 prepared by a chemist named Hermes.[1] It is prepared by treating solutions containing mercury(II) and thiocyanate ions. The low solubility product of mercury thiocyanate causes it to precipitate.[2] Most syntheses are achieved by precipitation. The two early syntheses achieved separately by Berzelius and Friedrich Wöhler were completed using the following reactions:
- Hg(NO3)2 + 2 KSCN → Hg(SCN)2 + 2KNO3
Pharaoh's serpent
Mercury thiocyanate was formerly used in pyrotechnics causing an effect known as the Pharaoh's serpent or Pharaoh's snake. When the compound is in the presence of a strong enough heat source, a rapid exothermic reaction is started which produces a large mass of coiling serpent-like solid. An inconspicuous flame which is often blue but can also occur in yellow/orange accompanies the combustion. The resulting solid can range from dark graphite grey to light tan in color with the inside generally much darker than the outside.[1]
This property was discovered soon after the first synthesis of mercury thiocyanate by Wöhler in 1821: "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.[1]
A similar, although less extreme, effect to the Pharaoh's serpent can be achieved using a firework known as a black snake. These are generally benign products, usually consisting of sodium bicarbonate or a mixture of linseed oil and naphthalenes.
Uses
Mercury thiocyanate has a few uses in chemical synthesis. It is the precursor to potassium tris(thiocyanato)mercurate(II) (K[Hg(SCN)3]) and caesium tris(thiocyanato)mercurate(II) (Cs[Hg(SCN)3]). The Hg(SCN)3- ion can also exist independently and is easily reacted to form the compounds above amongst others.[3]
Its reactions with organic halides yield two products, one with the sulfur bound to the organic compound and one with the nitrogen bound to the organic compound.[4]
It was discovered that mercury thiocyanate can improve detection limits in the determination of chloride ions in water by UV-visible spectroscopy. This technique was first suggested in 1952 and has been a common method for determination of chloride ions in laboratories worldwide ever since. An automated system was invented in 1964 and then a commercial chloroanalyzer was made available in 1974 by Technicon (Tarrytown, NY, USA). The basic mechanism involves the addition of mercury thiocyanate to a solution with unknown concentration of chloride ions and iron as a reagent. The chloride ions cause the mercury thiocyanate salt to dissociate and the thiocyanate ion to complex with Fe(III), producing Fe(SCN)2+, which absorbs visible light at 450 nm. This absorption allows for the measurement of concentration of Fe(SCN)2+, produced as a result of the reaction between chloride ion and mercury thiocyanate. From this value the concentration of chloride can then be calculated.[5]
It is used for determining the concentration of chloride ions in aqueous solution using mercury thiocyanate was discovered. Mercury thiocyanate without iron (III) is added to a solution with an unknown concentration of chloride ions, forming a complex of the mercury thiocyanate and chloride ion that absorbs light at a wavelength of 254 nm, allowing more accurate measurements of concentration than the aforementioned technique using iron.[5]
References
- ^ a b c d Davis, T. L. (1940). "Pyrotechnic Snakes". Journal of Chemical Education. 17 (6): 268–270. doi:10.1021/ed017p268.
- ^ Sekine, T.; Ishii, T. (1970). "Studies of the Liquid-Liquid Partition systems. VIII. The Solvent Extraction of Mercury (II) Chloride, Bromide, Iodide and Thiocyanate with Some Organic Solvents" (pdf). Bulletin of the Chemical Society of Japan. 43 (8): 2422–2429. doi:10.1246/bcsj.43.2422.
{{cite journal}}
: CS1 maint: multiple names: authors list (link) - ^ Bowmaker, G. A.; Churakov, A. V.; Harris, R. K.; Howard, J. A. K.; Apperley, D. C. (1998). "Solid-State 199Hg MAS NMR Studies of Mercury(II) Thiocyanate Complexes and Related Compounds. Crystal Structure of Hg(SeCN)2". Inorganic Chemistry. 37 (8): 1734–1743. doi:10.1021/ic9700112.
{{cite journal}}
: CS1 maint: multiple names: authors list (link) - ^ Kitamura, T.; Kobayashi, S.; Taniguchi, H. (1990). "Photolysis of Vinyl Halides. Reaction of Photogenerated Vinyl Cations with Cyanate and Thiocyanate Ions". Journal of Organic Chemistry. 55 (6): 1801–1805. doi:10.1021/jo00293a025.
{{cite journal}}
: CS1 maint: multiple names: authors list (link) - ^ a b Cirello-Egamino, J.; Brindle, I. D. (1995). "Determination of chloride ions by reaction with mercury thiocyanate in the absence of iron(III) using a UV-photometric, flow injection method". Analyst. 120 (1): 183–186. doi:10.1039/AN9952000183.
{{cite journal}}
: CS1 maint: multiple names: authors list (link)