Potassium tetraiodomercurate(II) is an
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
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) (K
2 gI4 in 2.5 mol/L potassium hydroxide, used to detect
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
.
Preparation and structure
Crystallizing from a concentrated
aqueous solution
An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be re ...
of
mercuric iodide
Mercury(II) iodide is a chemical compound with the molecular formula Hg I2. It is typically produced synthetically but can also be found in nature as the extremely rare mineral coccinite. Unlike the related mercury(II) chloride it is hardly solub ...
with potassium iodide is the
monohydrate
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was underst ...
K
2HgI
4.H
2O, which is pale orange.
[F. Wagenknecht, R. Juza, "Potassium Triiodomercurate(II)" in ''Handbook of Preparative Inorganic Chemistry'', 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1100.] In aqueous solution this triodido complex adds iodide to give the tetrahedral tetraiodo dianion.
Solutions of K
2HgI
4 react with Cu(I) salts to give Cu
2HgI
4.
Nessler's reagent
Named after
Julius Neßler
Julius Neßler (6 June 1827 – 19 March 1905) was a German chemist.
He devised the chemical solution '' Nessler's reagent'' which provides a colorimetric measure of ammonia concentration.
Biography
Neßler studied at the University of F ...
(Nessler), an alkaline solution of K
2HgI
4 is called Nessler's reagent. This pale solution becomes deeper yellow in the presence of ammonia. At higher concentrations, a brown
precipitate
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
may form. The sensitivity as a
spot test
Spot analysis, spot test analysis, or spot test is a chemical test, a simple and efficient technique where analytic assays are executed in only one, or a few drops, of a chemical solution, preferably in a great piece of filter paper, without using ...
is about 0.3 μg NH
3 in 2 μL.
:NH
4+ + 2
gI4sup>2− + 4 OH
− → + 7 I
− + 3 H
2O
The formula for the brown precipitate, a derivative of
Millon's base
Mercuric amidochloride is an inorganic compound with the formula .
Preparation and properties
It arises from the reaction of mercury(II) chloride and ammonia (Calomel reaction), where the resulting mercuric amidochloride is highly insoluble.
: ...
, is given as 3HgO·Hg(NH
3)
2I
2 and as NH
2·Hg
2I
3.
References
External links
IARC Monograph: "Mercury and Mercury Compounds"
{{potassium compounds
Iodo complexes
Potassium compounds
Mercury(II) compounds
IARC Group 3 carcinogens
Coordination complexes
Chemical tests