Potassium tetraiodomercurate(II) is an inorganic compound with the chemical formula K2[HgI4]. It consists of potassium cations and tetraiodomercurate(II) anions. It is the active agent in Nessler's reagent, used for detection of ammonia.[2]
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| Names | |
|---|---|
| IUPAC name potassium tetraiodidomercurate(II) | |
| Other names potassium mercuric iodide, Nessler's reagent (principal component) | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.029.082 |
| EC Number |
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PubChem CID | |
| UNII | |
| UN number | 3287 |
CompTox Dashboard (EPA) | |
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| Properties | |
| K2[HgI4][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 (SDS) | 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). | |
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(H2O)I3] instead.[3]
Applications
K2[HgI4] is a precursor to analogous copper and silver salts M2[HgI4] (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 (NH3). At higher concentrations, a brown precipitate derivative of Millon's base (HgO·Hg(NH2)Cl) may form. The sensitivity as a spot test is about 0.3 μg NH3 in 2 μL.[5]
- NH+4 + 2 [HgI4]2− + 4 OH− → HgO·Hg(NH2)I↓ + 7 I− + 3 H2O
The brown precipitate is not fully characterized and may vary from HgO·Hg(NH2)I to 3HgO·Hg(NH3)2I2.[6]