Zinc Hydroxide

Zinc hydroxide Zn(OH)2 is an inorganic chemical compound. Wulfingite, ashoverite, and sweetite are three rare minerals that contain zinc hydroxide. It's an amphoteric hydroxide. Both bases and acids react with zinc hydroxide. It's an insoluble hydroxide that dissolves when exposed to a strong acid.

• Zn(OH)2 is the chemical formula of Zinc hydroxide.

• The density of zinc hydroxide is 3.05 g/cm³.

• Molecular Weight/ Molar Mass is 99.424 g/mol.

• The Melting Point of zinc hydroxide is 125° C (257° F).

• It is a white powder in appearance.

In this article, you will study Zinc Hydroxide Structure, Physical Properties of Zinc Hydroxide, Chemical Properties of Zinc Hydroxide, and Uses of Zinc Hydroxide in detail.

Zinc Hydroxide Structure

Given below is the structure of zinc hydroxide:

Preparation of Zinc Hydroxide

1. It is prepared by adding a small amount of sodium hydroxide solution to a solution of any zinc salt. 

Zn2+ + 2 OH⁻ → Zn(OH)2

2. Since Zn2+ forms Hexa-aqua ions at high water concentrations and tetra-aqua ions at low water concentrations, this reaction could be written as the aquated ion reacting with hydroxide via proton donation, as shown below.

Zn2+(OH2)4(aq) + OH⁻(aq) → Zn2+(OH2)3OH−(aq) + H2O(l)

3. If too much sodium hydroxide is added, the zinc hydroxide precipitate dissolves, leaving a colourless zincate ion solution:

Zn(OH)2 + 2 OH⁻ → Zn(OH)42-.

Since the ion is naturally surrounded by water ligands, zinc hydroxide will dissolve; when excess sodium hydroxide is added to the solution, the hydroxide ions will reduce the complex to a -2 charge, making it soluble. When ammonia added in excess, an equilibrium is formed that gives hydroxide ions; the formation of hydroxide ions induces a reaction similar to sodium hydroxide, resulting in the formation of a +2 charged complex with a coordination number of 4 with the ammonia ligands, allowing the complex to dissolve.

Physical Properties of Zinc Hydroxide

Chemical Properties of Zinc Hydroxide

As aluminium reacts with zinc hydroxide solution, it forms a white precipitate that is soluble in excess of the reagent, indicating the presence of aluminium.

2Al3+(aq) + 3Zn(OH)2(aq) → 2Al(OH)3(s) + 3Zn

In the presence of ammonia, zinc cations react with hydrogen sulphide, and ammonium chloride forms a white zinc sulphide precipitate that is acid-soluble.

Zn2+(aq) + S2- → ZnS(s)

Uses of Zinc Hydroxide

1. It is used as an adsorbing agent in medicine.

2. It is used in careful dressings to act as a retentive. The zinc compound is applied to large bandages used after surgical procedures to engross the blood from the injury.

3. In the industrial processing of pesticides and pigments, it is used as an intermediate.

Did You Know?

• Zinc is a valuable catalytic agent in hydroxylation and other enzymatic reactions since it is an effective Lewis acid. The metal also has a versatile coordination geometry, allowing proteins to change conformations quickly to conduct biological reactions. Carbonic anhydrase and carboxypeptidase are two zinc-containing enzymes that are important for the regulation of carbon dioxide (CO2) and the digestion of proteins, respectively.

• Carbonic anhydrase converts CO2 into bicarbonate in vertebrate blood, and the same enzyme then converts bicarbonate back to CO2 for exhalation through the lungs. This conversion would take a million times longer without this enzyme at a standard blood pH of 7 or would require a pH of 10 or higher. Plants need the non-related -carbonic anhydrase for leaf formation, indole acetic acid (auxin) synthesis, and alcoholic fermentation.

• Zinc is a trace element that is needed by humans, other mammals, plants, and microorganisms. Zinc is stored and transferred in metallothioneins, which are necessary for the function of over 300 enzymes and 1000 transcription factors. After iron, it is the second most common trace metal in humans, and it is the only metal found in all enzyme groups.