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).
YesY verify (what is YesYN ?)
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

  1. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  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.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  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.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.

External links

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