Mercury(II) iodide

Mercury(II) iodide
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EC Number	Template:Unbulleted list
Template:Longitem	277788
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Template:Longitem	HgI2
Molar mass	454.40 g/mol
Appearance	orange-red powder
Odor	odorless
Density	6.36 g/cm3
Melting point	Template:Chembox CalcTemperatures
Boiling point	Template:Chembox CalcTemperatures
Template:Longitem	2.9Template:E
Solubility	slightly soluble in alcohol, ether, acetone, chloroform, ethyl acetate, CS2, olive oil, castor oil Soluble in excess KI(Potassium iodide) forming soluble complex K2[HgI4 ](Potassium tetraiodomercurate(II)) also known as Nessler's reagent
Template:Longitem	−128.6·10−6 cm3/mol
Template:Longitem	2.455
Template:Longitem	Tetrahedral
Template:Longitem	D08AK30 (WHO)
NFPA 704 (fire diamond)	Template:NFPA 704 diamond
Flash point	Template:Chembox CalcTemperatures
Template:Longitem	Mercury(II) fluoride; Mercury(II) chloride; Mercury(II) bromide
Template:Longitem	Zinc iodide; Cadmium iodide
Template:Longitem	Mercury(I) iodide

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Mercury(II) iodide is a chemical compound with the molecular formula Hg I₂. It is typically produced synthetically but can also be found in nature as the extremely rare mineral coccinite. Unlike the related mercury(II) chloride it is hardly soluble in water (<100 ppm).

Production

Mercury(II) iodide is produced by adding an aqueous solution of potassium iodide to an aqueous solution of mercury(II) chloride with stirring; the precipitate is filtered off, washed and dried at 70 °C.

HgCl₂ + 2 KI → HgI₂ + 2 KCl

Properties

Mercury(II) iodide displays thermochromism; when heated above 127 °C (400 K) it undergoes a phase transition, from the red alpha crystalline form to a pale yellow beta form. As the sample cools, it gradually reacquires its original colour. It has often been used for thermochromism demonstrations.^[2] A third form, which is orange, is also known; this can be formed by recrystallisation and is also metastable, eventually converting back to the red alpha form.^[3] The various forms can exist in a diverse range of crystal structures and as a result mercury(II) iodide possesses a surprisingly complex phase diagram.^[4]

Uses

File:Crystal in VCGS furnace.jpg

Mercury(II) iodide crystals grown in Spacelab

Mercury(II) iodide is used for preparation of Nessler's reagent, used for detection of presence of ammonia.

Mercury(II) iodide is a semiconductor material, used in some x-ray and gamma ray detection and imaging devices operating at room temperatures.^[5]

In veterinary medicine, mercury(II) iodide is used in blister ointments in exostoses, bursal enlargement, etc. Script error: No such module "Unsubst".

It can appear as a precipitate in many reactions.

References

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↑ Thermochromism: Mercury(II) Iodide. Jchemed.chem.wisc.edu. Retrieved on 2011-06-02.
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↑ Simage, Oy U.S. patent 6509203 Semiconductor imaging device and method for producing same, Issue date: Jan 21, 2003