Potassium tetraiodomercurate(II)

Potassium tetraiodomercurate(II)
IUPAC name potassium tetraiodomercurate(II)
Other names mercuric potassium iodide, Nessler's reagent (principal component)
Identifiers
CAS number	7783-33-7 Y=
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
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

The tetraiodomercurate(II) anion

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. The tetraiodomercurate(II) anion is isoelectronic with lead(IV) iodide.

Nessler's reagent

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.^{[citation needed]}

NH₄⁺ + 2[HgI₄]²⁻ + 4OH⁻ → HgO·Hg(NH₂)I + 7I⁻ + 3H₂O

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. Nessler's reagent may be used with Nessler tubes.

References

• 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 

Further reading

• Mok, K. F.; McKee, V. (1990). "Structure of a dipotassium tetraiodomercurate(II) salt with dibenzo-18-crown-6". Acta Crystallographica C 46: 2078. doi:10.1107/S0108270190003742. 

External links

• IARC Monograph: "Mercury and Mercury Compounds"
• National Pollutant Inventory - Mercury and compounds fact sheet