Potassium tetraiodomercurate(II)

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Potassium tetraiodomercurate(II)
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Names
IUPAC name
potassium tetraiodidomercurate(II)
Other names
potassium mercuric iodide,
Nessler's reagent (principal component)
Identifiers
7783-33-7 YesY
Jmol 3D model Interactive image
PubChem 24542
UN number 3287
  • InChI=1S/Hg.4HI.2K/h;4*1H;;/q+2;;;;;2*+1/p-4
  • [K+].[K+].I[Hg-2](I)(I)I
Properties
K2[HgI4][1]
Appearance yellow crystals
Odor odorless
Density 4.29 g/cm3
very soluble
Solubility soluble in alcohol, ether, acetone
Vapor pressure {{{value}}}
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 the inorganic compound consisting of potassium cations and the tetraiodomercurate(II) anion. It is mainly used as Nessler's reagent, a 0.09 mol/L solution of potassium tetraiodomercurate(II) (K2[HgI4]) in 2.5 mol/L potassium hydroxide, used to detect ammonia.[2]

Preparation and structure

Crystallizing from a concentrated aqueous solution of mercuric iodide with potassium iodide is the monohydrate KHgI3.H2O, which is pale orange.[3] In aqueous solution this triodido complex adds iodide to give the tetrahedral tetraiodo dianion.[4]

Solutions of K2HgI4 react with Cu(I) salts to give Cu2HgI4.[5]

Nessler's reagent

Named after Julius Nessler, an alkaline solution of K2HgI4 is called Nessler's reagent. This pale solution becomes deeper yellow in the presence of ammonia. At higher concentrations, a brown precipitate may form. The sensitivity as a spot test is about 0.3 μg NH3 in 2 μL.[citation needed]

NH4+ + 2[HgI4]2 + 4OH → HgO·Hg(NH2)I ↓ + 7I + 3H2O

The formula for the brown precipitate is given as 3HgO.Hg(NH3)2I2 and as NH2.Hg2I3[6]

Nessler's reagent is generally prepared by combining potassium iodide and mercury(II) chloride.[7] Nessler's reagent may be used with Nessler tubes.

References

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  3. F. Wagenknecht, R. Juza, "Potassium Triiodomercurate(II)" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1100.
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  5. F. Wagenknecht, R. Juza, "Copper(I) Tetraiodomercurate(II)" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1100.
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External links