Mercury(II) oxide

An experiment for the preparation of mercuric oxide was first described by 11th century Arab-Spanish alchemist, Maslama al-Majriti, in Rutbat al-hakim.{{Cite book|last=Holmyard |first=E. J. |url=https://books.google.com/books?id=uLsOAwAAQBAJ&dq=majriti+mercuric+oxide&pg=PA257 |title=Inorganic chemistry |date=1931 |publisher=Рипол Классик |isbn=978-5-87636-953-6 |language=en}} It was historically called red precipitate (as opposed to white precepitate being the mercuric amidochloride).

In 1774, Joseph Priestley discovered that oxygen was released by heating mercuric oxide, although he did not identify the gas as oxygen (rather, Priestley called it "dephlogisticated air," as that was the paradigm that he was working under at the time).{{cite book |last=Almqvist |first=Ebbe |title=History of Industrial Gases |url=https://books.google.com/books?id=OI0fTJhydh4C&dq=Joseph+Priestley+oxygen+mercury&pg=PA23 |year=2003 |publisher=Springer |isbn=978-0-306-47277-0 |page=23}}

File:Montroydite.jpg

File:Cinnabar structure.jpg structure]]

The red form of HgO can be made by heating Hg in oxygen at roughly 350 °C, or by pyrolysis of Hg(NO₃)₂.{{Greenwood&Earnshaw}} The yellow form can be obtained by precipitation of aqueous Hg²⁺ with alkali. The difference in color is due to particle size; both forms have the same structure consisting of near linear O-Hg-O units linked in zigzag chains with an Hg-O-Hg angle of 108°.

HgO is soluble in many conventional strong acids through protonation of the anion.{{cite web |title=Characteristic Reactions of Mercury Ions (Hg²⁺ and Hg₂²⁺) |url=https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Qualitative_Analysis/Characteristic_Reactions_of_Select_Metal_Ions/Characteristic_Reactions_of_Mercury_Ions_(Hg_and_Hg) |website=LibreTextsChemistry |access-date=23 July 2024}} The exceptions include acids which form insoluble mercury(II) salts, like mercury(II) iodide in the case of hydroiodic acid. Dissolution is also possible through complexation of the cation; e.g. cyanide ligands form stable water soluble mercury(II) complexes.

Under atmospheric pressure mercuric oxide has two crystalline forms: one is called montroydite (orthorhombic, 2/m 2/m 2/m, Pnma), and the second is analogous to the sulfide mineral cinnabar (hexagonal,

hP6, P3221); both are characterized by Hg-O chains.{{Cite journal | last1 = Aurivillius | first1 = Karin | last2 = Carlsson | first2 = Inga-Britt | last3 = Pedersen | first3 = Christian | last4 = Hartiala | first4 = K. | last5 = Veige | first5 = S. | last6 = Diczfalusy | first6 = E. | title = The Structure of Hexagonal Mercury(II)oxide | journal = Acta Chemica Scandinavica | volume = 12 | pages = 1297–1304 | year = 1958 | url = http://actachemscand.dk/volume.php?select1=2&vol=12 | doi = 10.3891/acta.chem.scand.12-1297 | access-date = November 17, 2010| doi-access = free}} At pressures above 10 GPa both structures convert to a tetragonal form.

Mercury oxide is sometimes used in the production of mercury as it decomposes quite easily. When it decomposes, oxygen gas is generated.{{citation needed|date=September 2023}}

It is also used as a material for cathodes in mercury batteries.{{cite book |last=Moore |first=John W. |author2=Conrad L. Stanitski |author3=Peter C. Jurs |title=Chemistry: The Molecular Science |url=https://archive.org/details/chemistrymolecul0000moor |url-access=registration |quote=Mercury(II) oxide anode mercury battery. |year=2005 |publisher=Thomson Brooks/Cole |isbn=978-0-534-42201-1 |page=[https://archive.org/details/chemistrymolecul0000moor/page/941 941]}}

File:HgOlabel.jpg

Mercury oxide is a highly toxic substance which can be absorbed into the body by inhalation of its aerosol, through the skin and by ingestion. The substance is irritating to the eyes, the skin and the respiratory tract and may have effects on the kidneys, resulting in kidney impairment. In the food chain important to humans, bioaccumulation takes place, specifically in aquatic organisms. The substance is banned as a pesticide in the EU.{{cite web | last = Chemicals Regulation Directorate | title = Banned and Non-Authorised Pesticides in the United Kingdom | url = http://www.pesticides.gov.uk/approvals.asp?id=55 | access-date = 1 December 2009}}

Evaporation at 20 °C is negligible. HgO decomposes on exposure to light or on heating above 500 °C. Heating produces highly toxic mercury fumes and oxygen, which increases the fire hazard. Mercury(II) oxide reacts violently with reducing agents, chlorine, hydrogen peroxide, magnesium (when heated), disulfur dichloride and hydrogen trisulfide. Shock-sensitive compounds are formed with metals and elements such as sulfur and phosphorus.{{cite web| url = http://www.inchem.org/documents/icsc/icsc/eics0981.htm| title = Mercury (II) oxide| access-date = 2009-06-06| publisher = International Occupational Safety and Health Information Centre}}

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{{Reflist}}

{{Commons category|Mercury(II) oxide}}

• [https://web.archive.org/web/20060425193836/http://www.npi.gov.au/database/substance-info/profiles/53.html National Pollutant Inventory – Mercury and compounds fact sheet]
• [http://www.webelements.com/webelements/compounds/text/Hg/Hg1O1-21908532.html Information at Webelements].

{{Mercury compounds}}

{{Oxides}}

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Category:Oxides

Category:Mercury(II) compounds

Category:Inorganic compounds