Editing Mercury(II) oxide

{{Chembox
|Verifiedfields = changed
|Watchedfields = changed
|verifiedrevid = 486593291
|ImageFile = HgOpowder.jpg
|ImageName = Mercury(II) oxide
|ImageFile1 = Montroydite-3D-ionic.png
|ImageName1 = Mercury(II) oxide
|IUPACName = Mercury(II) oxide
|OtherNames = Mercuric oxide<br />[[Montroydite]]<br />[[Red mercury]]
|Section1={{Chembox Identifiers
|CASNo = 21908-53-2
|CASNo_Ref = {{cascite|correct|CAS}}
|UNII_Ref = {{fdacite|correct|FDA}}
|UNII = IY191986AO
|UNNumber = 1641
|RTECS = OW8750000
|PubChem = 30856
|KEGG_Ref = {{keggcite|correct|kegg}}
|StdInChI_Ref = {{stdinchicite|correct|chemspider}}
|StdInChI = 1S/Hg.O
|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
|StdInChIKey = UKWHYYKOEPRTIC-UHFFFAOYSA-N
|SMILES = [Hg]=O
|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|ChemSpiderID = 28626
|KEGG = C18670
}}
|Section2={{Chembox Properties
|Hg=1 | O=1
|Appearance = Yellow or red solid
|Odor = odorless
|Density = 11.14 g/cm<sup>3</sup>
|Solubility = 0.0053 g/100 mL (25&nbsp;°C) <br /> 0.0395 g/100 mL (100&nbsp;°C)
|SolubleOther = insoluble in [[ethanol|alcohol]], [[diethyl ether|ether]], [[acetone]], [[ammonia]]
|MeltingPtC = 500
|MeltingPt_notes = (decomposes)
|BandGap = 2.2 eV<ref name=landolt>{{cite book| chapter = Mercury oxide (HgO) crystal structure, physical properties| volume = 41B| doi = 10.1007/b71137| publisher = Springer-Verlag| year = 1999| pages = 1–7| isbn = 978-3-540-64964-9 |title=Semiconductors · II-VI and I-VII Compounds; Semimagnetic Compounds| series = Landolt-Börnstein - Group III Condensed Matter| editor1-last = Madelung| editor1-first = O| editor2-first = U| editor2-last = Rössler| editor3-first = M| editor3-last = Schulz}}</ref>
|RefractIndex = 2.5 (550 nm)<ref name=landolt/>
|MagSus = −44.0·10<sup>−6</sup> cm<sup>3</sup>/mol
}}
|Section3={{Chembox Thermochemistry
|DeltaHf = −90&nbsp;kJ·mol<sup>−1</sup><ref name=b1>{{cite book| author = Zumdahl, Steven S.|title =Chemical Principles 6th Ed.| publisher = Houghton Mifflin Company| year = 2009| isbn = 978-0-618-94690-7|page=A22}}</ref>
|Entropy = 70&nbsp;J·mol<sup>−1</sup>·K<sup>−1</sup><ref name=b1/>
}}
|Section4={{Chembox Hazards
|MainHazards = Extremely toxic, environmental pollutant
|ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics0981.htm ICSC 0981]
|GHSPictograms = {{GHS06}} {{GHS08}} {{GHS09}}
|GHSSignalWord = Danger
|HPhrases = {{H-phrases|H300+H310+H330|H372|H410}}
|PPhrases = {{P-phrases|P260|P262|P264|P270|P271|P273|P280|P284|P301+P316|P302+P352|P304+P340|P316|P320|P321|P330|P361+P364|P391|P403+P233|P405|P501}}
|GHS_ref = <ref>{{cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/30856#datasheet=LCSS|title=Laboratory Chemical Safety Summary (LCSS): Mercuric oxide|id=CID 30856|website=[[PubChem]]|publisher=[[National Center for Biotechnology Information]]|access-date=2022-04-14}}</ref>
|NFPA-H = 4
|NFPA-F = 0
|NFPA-R = 1
|NFPA_ref = <ref>{{cite web|url=https://www.fishersci.com/store/msds?partNumber=AC316791000&countryCode=US&language=en|format=PDF|title=Safety Data Sheet: Mercury(II) oxide|id=Cat No. AC316790000|publisher=[[Thermo Fisher Scientific]]|date=2021-12-25|access-date=2022-04-13}}</ref>
|FlashPt = Non-flammable
|LD50 = 18 mg/kg (oral, rat)<ref>{{cite web|url=https://chem.nlm.nih.gov/chemidplus/rn/21908-53-2|title=Mercuric oxide [ISO]|id=CAS RN: 21908-53-2|website=ChemIDPlus Advanced|publisher=[[United States National Library of Medicine]]|access-date=2022-04-14}}</ref>
}}
|Section5={{Chembox Related
|OtherAnions = [[Mercury sulfide]]<br />[[Mercury selenide]]<br />[[Mercury telluride]]
|OtherCations = [[Zinc oxide]]<br />[[Cadmium oxide]]
|OtherCompounds = [[Mercury(I) oxide]]
}}
}}

'''Mercury(II) oxide''', also called '''mercuric oxide''' or simply '''mercury oxide''', is the [[inorganic compound]] with the formula [[Mercury (element)|Hg]][[oxygen|O]]. It has a red or orange color. Mercury(II) oxide is a solid at room temperature and pressure. The mineral form [[montroydite]] is very rarely found.

==History==
An experiment for the preparation of mercuric oxide was first described by 11th century Arab-Spanish alchemist, [[Maslama al-Majriti]], in ''Rutbat al-hakim.''<ref>{{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}}</ref> It was historically called [[wikt:red precipitate|red precipitate]] (as opposed to [[wikt:white precepitate|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 "[[Phlogiston|dephlogisticated]] air," as that was the [[paradigm]] that he was working under at the time).<ref>{{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}}</ref>

==Synthesis and reactions==
[[File:Montroydite.jpg|thumb|left|Montroydite structure (red atoms are oxygen)]]
[[File:Cinnabar structure.jpg|thumb|left|[[Cinnabar]] structure]]

The red form of HgO can be made by heating Hg in oxygen at roughly 350&nbsp;°C, or by [[pyrolysis]] of [[mercury(II) nitrate|Hg(NO<sub>3</sub>)<sub>2</sub>]].<ref name = "Greenwood">{{Greenwood&Earnshaw}}</ref> The yellow form can be obtained by precipitation of aqueous Hg<sup>2+</sup> with alkali.<ref name = "Greenwood"/> 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°.<ref name = "Greenwood"/>

HgO is soluble in many conventional strong acids through protonation of the anion.<ref>{{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}}</ref> 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.

==Structure==
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 crystal system|hexagonal]],
hP6, P3221); both are characterized by Hg-O chains.<ref>{{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}}</ref> At pressures above 10 GPa both structures convert to a [[tetragonal]] form.<ref name=landolt/>

==Uses==
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 [[cathode]]s in [[mercury battery|mercury batteries]].<ref>{{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]}}</ref>

==Health issues==
[[File:HgOlabel.jpg|thumb|left|The label on an HgO powder bottle.]]
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 [[European Union|EU]].<ref name=bnpuk>{{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}}</ref>

Evaporation at 20&nbsp;°C is negligible. HgO decomposes on exposure to light or on heating above 500&nbsp;°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.<ref>{{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}}</ref>

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==References==
{{Reflist}}

==External links==
{{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}}
{{oxygen compounds}}
{{Authority control}}

[[Category:Oxides]]
[[Category:Mercury(II) compounds]]
[[Category:Inorganic compounds]]