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Mercury(I) oxide
3D model (JSmol)
ECHA InfoCard 100.036.289 Edit this at Wikidata
EC Number
  • 239-934-0
UN number 1641
  • InChI=1S/2Hg.O checkY
  • O1[Hg][Hg]1
  • [O-2].[Hg+][Hg+]
Molar mass 417.183 g·mol−1
Appearance Very dark, orange, opaque crystals
Odor Odourless
Density 9.8 g mL−1
−76.3·10−6 cm3/mol
Occupational safety and health (OHS/OSH):
Main hazards
highly toxic
GHS labelling:[3]
GHS07: Exclamation mark
GHS08: Health hazard
H315, H317, H320, H335, H341, H361, H370, H372
P201, P202, P260, P261, P264, P270, P271, P272, P280, P281, P302+P352, P304+P340, P305+P351+P338, P307+P311, P308+P313, P312, P314, P321, P332+P313, P333+P313, P337+P313, P362, P363, P403+P233, P405, P501
NFPA 704 (fire diamond)
Lethal dose or concentration (LD, LC):
18 mg/kg (oral, rat)[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Mercury(I) oxide, also known as mercurous oxide, is an inorganic metal oxide with the chemical formula Hg2O.

It is a brown/black powder, insoluble in water but soluble in nitric acid. With hydrochloric acid, it reacts to form calomel, Hg2Cl2.[4] Mercury(I) oxide is toxic but without taste or smell. It is chemically unstable and converts to mercury(II) oxide and mercury metal.


  1. ^ a b Chambers, Michael. "ChemIDplus - 15829-53-5 - RPZHFKHTXCZXQV-UHFFFAOYSA-N - Mercurous oxide - Similar structures search, synonyms, formulas, resource links, and other chemical information". Retrieved 2 April 2019.
  2. ^ "Mercuric oxide MSDS". Archived from the original on 2012-10-11.
  3. ^ "Mercury(I) oxide". Retrieved 23 December 2021.
  4. ^ Perry, Dale L. (2011). Handbook of Inorganic Compounds (2nd ed.). Boca Raton: Taylor & Francis. p. 270. ISBN 978-1-4398-1461-1. OCLC 587104373.