Zinc hydroxide Zn(OH)2 is an inorganic chemical compound. It also occurs naturally as 3 rare minerals: wülfingite (orthorhombic), ashoverite and sweetite (both tetragonal).

Zinc hydroxide
Zinc hydroxide
Names
IUPAC name
Zinc hydroxide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.039.816 Edit this at Wikidata
UNII
  • InChI=1S/2H2O.Zn/h2*1H2;/q;;+2/p-2 checkY
    Key: UGZADUVQMDAIAO-UHFFFAOYSA-L checkY
  • InChI=1/2H2O.Zn/h2*1H2;/q;;+2/p-2
    Key: UGZADUVQMDAIAO-NUQVWONBAV
  • [Zn+2].[OH-].[OH-]
Properties
Zn(OH)2
Molar mass 99.424 g/mol
Appearance white powder
Density 3.053 g/cm3, solid
Melting point 125 °C (257 °F; 398 K) (decomposition)
slightly soluble
3.0×10−17
Solubility in alcohol insoluble
Acidity (pKa) 3.12, 3.39[1]
−67.0·10−6 cm3/mol
Thermochemistry
−642 kJ·mol−1[2]
Hazards
Flash point Non-flammable
Related compounds
Other anions
Zinc oxide
Other cations
Cadmium hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Like the hydroxides of other metals, such as lead, aluminium, beryllium, tin and chromium, Zinc hydroxide (and Zinc oxide), is amphoteric. Thus it will dissolve readily in a dilute solution of a strong acid, such as HCl, and also in a solution of an alkali such as sodium hydroxide.

Preparation

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It can be prepared by first dissolving zinc oxide in concentrated aqueous solution of sodium hydroxide. The resulting solution is strongly diluted.[3]

Zn2+ + 2 OH → Zn(OH)2.

The initial colorless solution contains the zincate ion:

Zn(OH)2 + 2 OH → Zn(OH)42−.

Zinc hydroxide will dissolve because the ion is normally surrounded by water ligands; when excess sodium hydroxide is added to the solution the hydroxide ions will reduce the complex to a −2 charge and make it soluble. When excess ammonia is added, it sets up an equilibrium which provides hydroxide ions; the formation of hydroxide ions causes a similar reaction as sodium hydroxide and creates a +2 charged complex with a co-ordination number of 4 with the ammonia ligands - this makes the complex soluble so that it dissolves.

Unlike the hydroxides of aluminium and lead, zinc hydroxide also dissolves in excess aqueous ammonia to form a colorless, water-soluble ammine complex.

Applications

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One major use is as an absorbent in surgical dressings. It is also used to find zinc salts by mixing sodium hydroxide with the suspect salt.

References

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  1. ^ Perrin, D. D., ed. (1982) [1969]. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 265. ISBN 0-08-029214-3. LCCN 82-16524.
  2. ^ Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 978-0-618-94690-7.
  3. ^ F. Wagenknecht; R. Juza (1963). "Zinc Sulfide". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2pages=1074. NY,NY: Academic Press.
  • Chemistry in Context - By Graham Hill, John Holman (pp. 283,284)