PROFILPELAJAR.COM

Mercury(II) iodide
	; Mercury(II) iodide (α form)
	; Mercury(II) iodide (β form)
	; β (left) and α (right) forms
Names
	IUPAC name Mercury(II) iodide
	Other names Mercury diiodide; Mercuric iodide; Red mercury (α form only); Coccinite (α form only)
Identifiers
CAS Number	7774-29-0 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:49659 ;
ChemSpider	22893 ;
DrugBank	DB04445 ;
ECHA InfoCard	100.028.976
EC Number	231-873-8;
Gmelin Reference	277788
PubChem CID	24485;
UNII	R03O05RB0P ;
CompTox Dashboard (EPA)	DTXSID9042124 ;
	InChI InChI=1S/Hg.2HI/h;21H/q+2;;/p-2 Key: YFDLHELOZYVNJE-UHFFFAOYSA-L ; InChI=1/Hg.2HI/h;21H/q+2;;/p-2 Key: YFDLHELOZYVNJE-NUQVWONBAE;
	SMILES I[Hg]I;
Properties
Chemical formula	HgI2
Molar mass	454.40 g/mol
Appearance	orange-red powder
Odor	odorless
Density	6.36 g/cm3
Melting point	259 °C (498 °F; 532 K)
Boiling point	350 °C (662 °F; 623 K)
Solubility in water	6 mg/100 mL
Solubility product (Ksp)	2.9×10−29
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
Magnetic susceptibility (χ)	−128.6·10−6 cm3/mol
Refractive index (nD)	2.455
Structure
Crystal structure	Tetrahedral
Pharmacology
ATC code	D08AK30 (WHO)
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H300, H310, H330, H373, H410
Precautionary statements	P260, P262, P264, P270, P271, P273, P280, P284, P301+P310, P302+P350, P304+P340, P310, P314, P320, P321, P322, P330, P361, P363, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)	3 0 0
Flash point	Non-flammable
Related compounds
Other anions	Mercury(II) fluoride; Mercury(II) chloride; Mercury(II) bromide
Other cations	Zinc iodide; Cadmium iodide
Related compounds	Mercury(I) iodide
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

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 126 °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

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. ^{[citation needed]}

It can appear as a precipitate in many reactions.

References

^ John Rumble (June 18, 2018). CRC Handbook of Chemistry and Physics (99 ed.). CRC Press. pp. 5–189. ISBN 978-1138561632.
^ Thermochromism: Mercury(II) Iodide. Jchemed.chem.wisc.edu. Retrieved on 2011-06-02.
^ SCHWARZENBACH, D. (1 January 1969). "The crystal structure and one-dimensional disorder of the orange modification of HgI₂". Zeitschrift für Kristallographie - Crystalline Materials. 128 (1–6): 97–114. doi:10.1524/zkri.1969.128.16.97. S2CID 96682743.
^ Hostettler, Marc; Schwarzenbach, Dieter (February 2005). "Phase diagrams and structures of HgX₂ (X = I, Br, Cl, F)". Comptes Rendus Chimie. 8 (2): 147–156. doi:10.1016/j.crci.2004.06.006.
^ Simage, Oy U.S. patent 6,509,203 Semiconductor imaging device and method for producing same, Issue date: Jan 21, 2003