HGO

Mercury(II) oxide (HgO) is an inorganic compound in which mercury is in the +2 oxidation state. It occurs in two polymorphs, red alpha-HgO and yellow beta-HgO, which differ in crystal structure and color. The compound is a solid at room temperature and is sparingly soluble in water.

Preparation and occurrence: HgO is produced commercially by oxidation of elemental mercury or by precipitation from mercuric salts with alkali, followed by dehydration. In the laboratory it can be prepared by reacting mercuric salts, such as mercuric chloride, with sodium hydroxide to form HgO as a precipitate.

Properties and reactions: Upon heating, HgO decomposes to elemental mercury and oxygen gas (2 HgO → 2 Hg + O2). It is insoluble in water but dissolves in acids to give mercuric salts. The two polymorphs have different crystal structures and can interconvert under certain conditions.

Applications: Historically used as a pigment and antiseptic; used in mercury-oxide zinc batteries (a class of dry cells) and as a laboratory source of oxygen. Because of toxicity and environmental concerns, many uses have declined and handling is subject to strict regulations.

Safety: Mercury compounds are highly toxic. Exposure can damage the nervous system and kidneys. Handle HgO in a well-ventilated area with appropriate protective equipment and dispose of waste as hazardous material according to local regulations.