What do You Mean by 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
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
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)
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
It is used as an adsorbing agent in medicine.
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.
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.
FAQs on Zinc Hydroxide
1. What is Zinc Hydroxide and what is its chemical formula?
Zinc Hydroxide is an inorganic chemical compound. It appears as a white, amorphous solid. The chemical formula for Zinc Hydroxide is Zn(OH)₂. It is a key compound in understanding the properties of amphoteric substances in chemistry.
2. How is Zinc Hydroxide typically prepared in a laboratory setting?
A common method for preparing Zinc Hydroxide is through a precipitation reaction. This is done by adding a solution of a strong base, like sodium hydroxide (NaOH), to a solution of a soluble zinc salt, such as zinc sulphate (ZnSO₄). The reaction forms a white, gelatinous precipitate of Zinc Hydroxide.
The balanced chemical equation is: ZnSO₄ + 2NaOH → Zn(OH)₂(s) + Na₂SO₄(aq).
3. What are the main physical properties of Zinc Hydroxide?
Zinc Hydroxide exhibits the following key physical properties:
- Appearance: It is a white, gelatinous or amorphous solid.
- Solubility: It is practically insoluble in water but will dissolve in strong acids and excess strong alkalis.
- Odour: It is an odourless compound.
- State: It exists as a solid at room temperature.
4. Why is Zinc Hydroxide considered an amphoteric substance?
Zinc Hydroxide is considered amphoteric because it can react as both an acid and a base. This dual nature is a defining characteristic.
- As a base: It reacts with acids to form a salt and water. For example, with hydrochloric acid, it forms zinc chloride: Zn(OH)₂ + 2HCl → ZnCl₂ + 2H₂O.
- As an acid: It reacts with strong alkalis (bases) to form a complex salt called a zincate. For example, with excess sodium hydroxide, it forms sodium zincate: Zn(OH)₂ + 2NaOH → Na₂[Zn(OH)₄].
5. What happens when Zinc Hydroxide is heated?
When Zinc Hydroxide is heated to a temperature above 125°C, it undergoes thermal decomposition. It breaks down to form zinc oxide (ZnO) and water (H₂O) vapour. Zinc oxide is a white powder that turns yellow when hot and white again when cool. The reaction is: Zn(OH)₂ (s) → ZnO (s) + H₂O (g).
6. What are some common uses of Zinc Hydroxide?
Due to its specific chemical properties, Zinc Hydroxide is used in various applications. A primary use is as an adsorbent in medical dressings and bandages, where it helps absorb fluids from wounds. It is also used as an intermediate in the production of other zinc compounds and can be found in some pigments and flame retardants.
7. How does the solubility of Zinc Hydroxide in ammonium hydroxide differ from its solubility in sodium hydroxide?
This is a key concept in qualitative analysis. While Zinc Hydroxide dissolves in an excess of strong alkali like sodium hydroxide to form sodium zincate (Na₂[Zn(OH)₄]), its behaviour with ammonium hydroxide is different. It also dissolves in excess ammonium hydroxide, but it does so by forming a different complex ion, the tetraamminezinc(II) ion, [Zn(NH₃)₄]²⁺. This difference in reactivity is often used to distinguish between metal hydroxides in the lab.
8. What is the nature of the chemical bonding within Zinc Hydroxide?
The bonding in Zinc Hydroxide, Zn(OH)₂, is primarily ionic. It consists of the zinc cation (Zn²⁺) and two hydroxide anions (OH⁻). However, within each hydroxide anion itself, the bond between the oxygen and hydrogen atoms is a polar covalent bond. Therefore, the compound as a whole is classified as an ionic compound containing polyatomic ions with internal covalent bonds.
