| Potassium tetraiodomercurate(II) | |
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potassium tetraiodomercurate(II) |
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Other names
mercuric potassium iodide, |
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| Identifiers | |
| CAS number | 7783-33-7 |
| UN number | 3287 |
| Properties | |
| Molecular formula | HgI4K2 |
| Molar mass | 786.4 g mol−1 |
| Density | 1.16 g/cm3 |
| Hazards | |
| MSDS | External MSDS for Nessler's reagent |
| Related compounds | |
| Other anions | Mercury(II) iodide |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Potassium tetraiodomercurate(II) is an inorganic compound containing potassium cations and the tetraiodomercurate(II) complex 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.
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Named after Julius Neßler, when this solution gives a yellow coloration, it indicates 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.
Nessler's reagent is generally prepared from potassium iodide and mercury(II) chloride. A hot concentrated solution of mercury(II) chloride is added to concentrated solution of potassium iodide, until the precipitate of mercury(II) iodide stops dissolving. The liquid is filtered, and potassium hydroxide and a further bit of mercury(II) chloride solution are added. The resulting solution is then cooled and diluted to required concentration.[1] Nessler's reagent may be used with Nessler tubes.
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