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 | |
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| IUPAC name
potassium tetraiodidomercurate(II)
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| Other names
potassium mercuric iodide,
Nessler's reagent (principal component) | |
| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.029.082 |
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| 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
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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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Preparation
editThe 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
editK2[HgI4] is a precursor to analogous copper and silver salts M2[HgI4] (M=Cu, Ag).[4]
Nessler's reagent
editNessler'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]
References
edit- ^ 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.
- ^ Vogel, Arthur I.; Svehla, G. (1979), Vogel's Textbook of Macro and Semimicro Qualitative Inorganic Analysis (5th ed.), London: Longman, ISBN 0-582-44367-9 – via the Internet Archive
- ^ Wagenknecht, F.; Juza, R. (1963). "Potassium Triiodomercurate(II)". In Brauer, G. (ed.). Handbook of Preparative Inorganic Chemistry. Vol. 1 (2nd ed.). Academic Press. p. 1100 – via the Internet Archive.
- ^ Wagenknecht, F.; Juza, R. (1963). "Copper(I) Tetraiodomercurate(II)". In Brauer, G. (ed.). Handbook of Preparative Inorganic Chemistry. Vol. 1 (2nd ed.). Academic Press. p. 1100 – via the Internet Archive.
- ^ Vogel, Arthur I. (1954), A Textbook of Macro and Semimicro Qualitative Inorganic Analysis (4th ed.), London: Longman, p. 319, ISBN 0-582-44367-9
- ^ Vogel, Arthur I.; Svehla, G. (1979), Vogel's Textbook of Macro and Semimicro Qualitative Inorganic Analysis (5th ed.), London: Longman, pp. 293–294, ISBN 0-582-44367-9 – via the Internet Archive