The mercury hydroxide It is an inorganic compound in which the metal mercury (Hg) has an oxidation number of 2+. Its chemical formula is Hg (OH)two. However, this species has not yet been obtained in solid form under normal conditions..
Mercury hydroxide or mercuric hydroxide is a short-lived transient intermediate in the formation of mercuric oxide HgO in alkaline solution. From studies carried out in solutions of mercuric oxide HgO, it has been deduced that Hg (OH)two it is a weak base. Other accompanying species are HgOH+ and the Hgtwo+.
Despite not being able to be precipitated in aqueous solution, Hg (OH)two It has been obtained by photochemical reaction of mercury with hydrogen and oxygen at very low temperatures. It has also been obtained in the form of a coprecipitate together with Fe (OH)3, where the presence of halide ions influences the pH at which co-precipitation occurs.
Since it has not been easily obtained pure at the laboratory level, it has not been possible to find any use for this compound, nor to determine the risks of its use. However, it can be deduced that it presents the same risks as the other mercury compounds.
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The structure of mercury (II) hydroxide Hg (OH)two it is based on a linear central portion formed by the mercury atom with the two oxygen atoms on the sides.
Hydrogen atoms are attached to this central structure, each next to each oxygen, which rotate freely around each oxygen. It could be represented in a simple way as follows:
The electronic structure of metallic mercury Hg is as follows:
[Xe] 5d10 6stwo
where [Xe] is the electron configuration of the noble gas xenon.
When observing this electronic structure, it follows that the most stable oxidation state of mercury is the one in which the 2 electrons of layer 6 are lost.s.
In mercuric hydroxide Hg (OH)two, the mercury atom (Hg) is in its 2+ oxidation state. Therefore, in the Hg (OH)two mercury has the following electronic configuration:
[Xe] 5d10
- Mercury (II) hydroxide
- Mercuric hydroxide
- Mercury dihydroxide
236.62 g / mol
According to the information consulted, it is possible that Hg (OH)two be a transitory compound in the formation of HgO in alkaline aqueous medium.
The addition of hydroxyl ions (OH-) to an aqueous solution of mercuric ions Hgtwo+ leads to the precipitation of a yellow solid of mercury (II) oxide HgO, of which Hg (OH)two is a temporary or temporary agent.
In aqueous solution Hg (OH)two It is a very short-lived intermediate, as it quickly releases a water molecule and solid HgO precipitates.
Although it has not been possible to precipitate mercuric hydroxide Hg (OH)two, mercury (II) oxide HgO is somewhat soluble in water, forming a solution of species called “hydroxides”.
These species in water called “hydroxides” are weak bases and, although they sometimes behave like amphoteric, in general Hg (OH)two it is more basic than acid.
When HgO dissolves in HClO4 studies indicate the presence of mercuric ion Hgtwo+, a monohydroxymercuric ion HgOH+ and mercuric hydroxide Hg (OH)two.
The equilibria that occur in such aqueous solutions are as follows:
Hgtwo+ + HtwoO ⇔ HgOH+ + H+
HgOH+ + HtwoO ⇔ Hg (OH)two + H+
In alkaline solutions of NaOH the species Hg (OH) is formed3-.
Mercury (II) Hydroxide Hg (OH)two It cannot be obtained in aqueous solution, because when adding alkali to a solution of mercuric ions Hgtwo+, yellow mercuric oxide HgO precipitates.
However, some researchers managed to obtain mercuric hydroxide Hg (OH) for the first time in 2005two using a mercury arc lamp, starting from the element mercury Hg, hydrogen Htwo and oxygen Otwo.
The reaction is photochemical and was carried out in the presence of solid neon, argon or deuterium at very low temperatures (around 5 K = 5 Kelvin). Evidence of compound formation was obtained by IR (infrared) light absorption spectra.
Hg (OH)two prepared in this way it is very stable under the conditions of experience. It is estimated that the photochemical reaction proceeds through the intermediate O-Hg-O to the stable molecule H-O-Hg-O-H.
If mercury (II) sulfate HgSO dissolves4 and iron (III) sulfate Fetwo(SW4)3 in acidic aqueous solution, and the pH begins to increase by adding a solution of sodium hydroxide NaOH, after a standing time a solid is formed that is inferred to be a co-precipitate of Hg (OH)two and Fe (OH)3.
It has been found that the formation of Hg (OH)two is a critical step in this co-precipitation with Fe (OH)3.
The formation of Hg (OH)two in the precipitate Fe (OH)3-Hg (OH)two strongly depends on the presence of ions such as fluoride, chloride or bromide, on their specific concentration and on the pH of the solution.
In the presence of fluoride (F-), at pH greater than 5, the coprecipitation of Hg (OH)two with Fe (OH)3 it is not affected. But at a pH of 4 the formation of complexes between Hgtwo+ and the F- interferes with the co-precipitation of Hg (OH)two.
In the case of the presence of chloride (Cl-), the co-precipitation of Hg (OH)two occurs at a pH of 7 or higher, that is, preferably in an alkaline medium.
When bromide (Br-), the co-precipitation of Hg (OH)two occurs at even higher pH, that is, pH above 8.5, or more alkaline than with chloride.
From the review of the sources of information available it is deduced that mercury (II) hydroxide Hg (OH)two, Being a compound not yet prepared commercially, it has no known uses.
Using computational simulation techniques in 2013, the structural and energetic characteristics related to the hydration of Hg (OH) were studied.two in a gaseous state.
Metal-ligand coordination and solvation energies were calculated and compared by varying the degree of hydration of Hg (OH)two.
Among other things, it was found that apparently the theoretical oxidation state is 1+ instead of the presumed 2+ usually assigned for Hg (OH)two.
Although Hg (OH)two as such it has not been isolated in sufficient quantity and therefore it has not been used commercially, its specific risks have not been determined, but it can be inferred that it presents the same risks as the rest of mercury salts..
It can be toxic to the nervous system, digestive system, skin, eyes, respiratory system and kidneys..
Inhalation, ingestion or contact with the skin of mercury compounds can cause damage ranging from eye and skin irritation, insomnia, headaches, tremors, damage to the intestinal tract, memory loss, to kidney failure, among other symptoms.
Mercury has been recognized internationally as a pollutant. Most mercury compounds that come into contact with the environment are methylated by bacteria present in soils and sediments, forming methylmercury.
This compound bioaccumulates in living organisms, passing from the soil to plants and from there to animals. In the aquatic environment the transfer is even faster, going from very small to large species in a short time.
Methylmercury has a toxic effect for living beings and in particular for humans, who ingest it through the food chain.
When ingested with food, it is especially harmful for young children and fetuses in pregnant women, since being a neurotoxin it can cause damage to the brain and the nervous system in formation and growth..
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