Mercury(II) oxide, also called mercuric oxide or simply mercury oxide, is the

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 ...

with the formula Hg O. It has a red or orange color. Mercury(II) oxide is a solid at room temperature and pressure. The mineral form

montroydite Montroydite is the mineral form of mercury(II) oxide with formula HgO. It is a rare mercury mineral. It was first described for an occurrence in the mercury deposit at Terlingua, Texas and named for Montroyd Sharp who was an owner of the deposit. ...

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 Abu al-Qasim Maslama ibn Ahmad al-Majriti ( ar, أبو القاسم مسلمة بن أحمد المجريطي: c. 950–1007), known or Latin as , was an Arab Muslim astronomer, chemist, mathematician, economist and Scholar in Islamic Spain, ac ...

, in ''Rutbat al-hakim.'' In 1774,

Joseph Priestley Joseph Priestley (; 24 March 1733 – 6 February 1804) was an English chemist, natural philosopher, separatist theologian, grammarian, multi-subject educator, and liberal political theorist. He published over 150 works, and conducted exp ...

discovered that oxygen was released by heating mercuric oxide, although he did not identify the gas as

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

(rather, Priestley called it "

dephlogisticated The phlogiston theory is a superseded scientific theory that postulated the existence of a fire-like element called phlogiston () contained within combustible bodies and released during combustion. The name comes from the Ancient Greek (''burni ...

air," as that was the

paradigm In science and philosophy, a paradigm () is a distinct set of concepts or thought patterns, including theories, research methods, postulates, and standards for what constitute legitimate contributions to a field. Etymology ''Paradigm'' comes f ...

that he was working under at the time).

Synthesis

The red form of HgO can be made by heating Hg in oxygen at roughly 350 °C, or by

pyrolysis The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...

of Hg(NO₃)₂. 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°.

Structure

Under atmospheric pressure mercuric oxide has two crystalline forms: one is called montroydite (

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a r ...

, 2/m 2/m 2/m, Pnma), and the second is analogous to the sulfide mineral

cinnabar Cinnabar (), or cinnabarite (), from the grc, κιννάβαρι (), is the bright scarlet to brick-red form of Mercury sulfide, mercury(II) sulfide (HgS). It is the most common source ore for refining mercury (element), elemental mercury and ...

(

hexagonal In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A '' regular hexagon'' has ...

, hP6, P3221); both are characterized by Hg-O chains. At pressures above 10 GPa both structures convert to a

tetragonal In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square ...

form.

Uses

Hg O is sometimes used in the production of mercury as it decomposes quite easily. When it decomposes, oxygen gas is generated. It is also used as a material for

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...

s in mercury batteries.

Health issues

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 Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance at a rate faster than that at which the substance is lost or eliminated ...

takes place, specifically in aquatic organisms. The substance is banned as a pesticide in the EU. 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.

References

External links

National Pollutant Inventory – Mercury and compounds fact sheet

{{oxygen compounds Oxides Mercury(II) compounds Inorganic compounds