Potassium tetraiodomercurate(II)

Potassium tetraiodomercurate(II)
Names
	IUPAC name potassium tetraiodidomercurate(II)
	Other names potassium mercuric iodide, ; Nessler's reagent (principal component)
Identifiers
CAS Number	7783-33-7 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:51568 ;
ChemSpider	22948 ;
EC Number	231-990-4;
PubChem CID	15980736;
UNII	7N83S6IU0F ;
UN number	3287
	InChI InChI=1S/Hg.4HI.2K/h;41H;;/q+2;;;;;2+1/p-4 Key: OPCMAZHMYZRPID-UHFFFAOYSA-J ;
	SMILES [K+].[K+].I[Hg-2](I)(I)I;
Properties
Chemical formula	K; 2[HgI; 4]
Molar mass	786.406 g·mol−1
Appearance	yellow crystals
Odor	odorless
Density	4.29 g/cm3
Solubility in water	very soluble
Solubility	soluble in alcohol, ether, acetone
Hazards
Safety data sheet	External MSDS for Nessler's reagent
Related compounds
Other anions	Mercury(II) 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

Potassium tetraiodomercurate(II) is an inorganic compound with the chemical formula K
2[[[Chemistry:Mercury (element)|Hg]]I
4]. It consists of potassium cations and tetraiodomercurate(II) anions. It is the active agent in Nessler's reagent, used for detection of ammonia.^[2]

Preparation

The compound crystallizes from a heated solution of mercuric iodide, potassium iodide, and precisely 2% water in acetone. Attempted synthesis in concentrated aqueous solution will give the pale orange monohydrate K[Hg(H
2O)I
3] instead.^[3]

Applications

K
2[HgI
4] is a precursor to analogous copper and silver salts M
2[HgI
4] (M=Cu, Ag).^[4]

Nessler's reagent

Nessler's reagent, named after Julius Neßler (Nessler), is a 0.09 mol/L solution of potassium tetraiodomercurate(II) in 2.5 mol/L potassium hydroxide. This pale solution becomes deeper yellow in the presence of ammonia (NH
3). At higher concentrations, a brown precipitate derivative of Millon's base (HgO · Hg(NH
2)Cl) may form. The sensitivity as a spot test is about 0.3 μg NH
3 in 2 μL.^[5]

NH+
4 + 2 [HgI
4]²⁻ + 4 OH−
→ HgO · Hg(NH
2)I↓ + 7 I−
+ 3 H
2O

The brown precipitate is not fully characterized and may vary from HgO · Hg(NH
2)I to 3HgO · Hg(NH
3)
2I
2.^[6]

References

↑ Lide, David R., ed (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. p. 4-82. ISBN 978-1-4200-9084-0.
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↑ Wagenknecht, F.; Juza, R. (1963). "Potassium Triiodomercurate(II)". in Brauer, G.. Handbook of Preparative Inorganic Chemistry. 1 (2nd ed.). Academic Press. p. 1100. https://archive.org/details/Handbook_of_Preparative_Inorganic_Chemistry_1_2_Brauer/page/n1155/.
↑ Wagenknecht, F.; Juza, R. (1963). "Copper(I) Tetraiodomercurate(II)". in Brauer, G.. Handbook of Preparative Inorganic Chemistry. 1 (2nd ed.). Academic Press. p. 1100. https://archive.org/details/Handbook_of_Preparative_Inorganic_Chemistry_1_2_Brauer/page/n1155/.
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External links

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Original source: https://en.wikipedia.org/wiki/Potassium tetraiodomercurate(II). Read more

[crc-1] Lide, David R., ed (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. p. 4-82. ISBN 978-1-4200-9084-0.

[2] Template:VogelQualitative

[3] Wagenknecht, F.; Juza, R. (1963). "Potassium Triiodomercurate(II)". in Brauer, G.. Handbook of Preparative Inorganic Chemistry. 1 (2nd ed.). Academic Press. p. 1100. https://archive.org/details/Handbook_of_Preparative_Inorganic_Chemistry_1_2_Brauer/page/n1155/.

[4] Wagenknecht, F.; Juza, R. (1963). "Copper(I) Tetraiodomercurate(II)". in Brauer, G.. Handbook of Preparative Inorganic Chemistry. 1 (2nd ed.). Academic Press. p. 1100. https://archive.org/details/Handbook_of_Preparative_Inorganic_Chemistry_1_2_Brauer/page/n1155/.

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[6] Template:VogelQualitative5th

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