Chemistry:Potassium tetraiodomercurate(II)

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Potassium tetraiodomercurate(II)
Nessler's-reagent-2D.png
Nessler's-reagent-3D-vdW.png
Names
IUPAC name
potassium tetraiodidomercurate(II)
Other names
potassium mercuric iodide,
Nessler's reagent (principal component)
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
EC Number
  • 231-990-4
UNII
UN number 3287
Properties
K
2
[HgI
4
]
[1]
Molar mass 786.406 g·mol−1
Appearance yellow crystals
Odor odorless
Density 4.29 g/cm3
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).
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Infobox references

Potassium tetraiodomercurate(II) is an inorganic compound with the chemical formula K
2
[[[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
2
O)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
2
O

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

References

  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/. 
  5. Template:VogelQualitative4th
  6. Template:VogelQualitative5th

External links