Nessler's reagent
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| Names | |
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IUPAC name
potassium tetraiodidomercurate(II)
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| Other names
potassium mercuric iodide,
Nessler's reagent (principal component) |
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| Identifiers | |
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3D model (Jmol)
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| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.029.082 |
| EC Number | 231-990-4 |
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PubChem CID
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| UN number | 3287 |
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| Properties | |
| K2[HgI4] | |
| 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 | |
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Other anions
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Mercury(II) iodide |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is   ?) |
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| Infobox references | |
Potassium tetraiodomercurate(II) is an 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.
Crystallizing from a concentrated aqueous solution of mercuric iodide with potassium iodide is the monohydrate KHgI3.H2O, which is pale orange. In aqueous solution this triodido complex adds iodide to give the tetrahedral tetraiodo dianion.
Solutions of K2HgI4 react with Cu(I) salts to give Cu2HgI4.
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.
The formula for the brown precipitate is given as 3HgO.Hg(NH3)2I2 and as NH2.Hg2I3
Nessler's reagent is generally prepared by combining potassium iodide and mercury(II) chloride. Nessler's reagent may be used with Nessler tubes.
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