Zinc hydroxide Zn

Zinc

Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

(OH

Hydroxide

Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

)₂ is an inorganic chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

. It also occurs naturally as 3 rare minerals: wülfingite (orthorhombic), ashoverite

Ashoverite

Ashoverite is one of three polymorphs of zinc hydroxide, Zn2. It is a rare mineral first found in a limestone quarry near Ashover, Derbyshire, England, in 1988. It has also been found in the Harz mountain range in Germany, and in Namibia....

 and sweetite

Sweetite

Sweetite has a general formula of Zn2. The name is given after a curator of mineral department of The British Museum, Jessie May Sweet...

 (both tetragonal).

Like the hydroxides of other metals, such as lead, aluminium

Aluminium hydroxide

Aluminium hydroxide, Al3, ATH, sometimes erroneously called Hydrate of alumina, is found in nature as the mineral gibbsite and its three, much more rare forms, polymorphs: bayerite, doyleite and nordstrandite. Closely related are aluminium oxide hydroxide, AlO, and aluminium oxide, Al2O3,...

, beryllium

Beryllium hydroxide

Beryllium hydroxide, Be2 is an amphoteric hydroxide, dissolving in both acids and alkalis. Industrially it is produced as a by-product in the extraction of beryllium metal from the ores, beryl and bertrandite. When alkali is added to beryllium salt solutions the α-form is formed. If this left to...

, tin and chromium, zinc hydroxide (and zinc oxide

Zinc oxide

Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...

), is amphoteric. Thus it will dissolve readily in a dilute solution of a strong acid

Strong acid

A strong acid is an acid that ionizes completely in an aqueous solution by losing one proton, according to the equationFor sulfuric acid which is diprotic, the "strong acid" designation refers only to dissociation of the first protonMore precisely, the acid must be stronger in aqueous solution than...

, such as HCl

HCL

HCL or HCl can stand for:* Hairy cell leukemia, an uncommon and slowly progressing B cell leukemia* Hardware compatibility list...

, and also in a solution of an alkali such as sodium hydroxide.

It can be prepared by adding sodium hydroxide solution, but not in excess, to a solution of any zinc salt. A white precipitate will be seen:
Zn²⁺ + 2OH^- → Zn(OH)₂.

If excess sodium hydroxide is added, the precipitate of zinc hydroxide will dissolve, forming a colorless solution of zincate ion: Zn(OH)₂ + 2OH^- → Zn(OH)₄^2-. This property can be used as a test for zinc ions in solution, but it is not exclusive, since aluminum and lead compounds behave in a very similar manner. Unlike the hydroxides of aluminum and lead, zinc hydroxide also dissolves in aqueous ammonia to form a colourless, water-soluble ammine complex.

One major use is as an absorbent in surgical dressings.