Zinc- Properties, Uses, Ores and Extraction

Introduction to Zinc

Zinc (Zn), with atomic number 30, is a transition element/metal recognized for its vital role in both industrial applications and biological systems. Zinc is one of the most abundant and widely used metals, indispensable in galvanization, alloy production, and enzyme function. As a chemistry scholar, a detailed understanding of zinc’s properties, reactions, and applications will provide deep insight into its significant contributions to both modern industry and biological processes.

Position in the Periodic Table

Atomic number: 30
Symbol: Zn
Block: d-block (transition metals)
Period: 4
Group: 12 (with cadmium and mercury)

Zinc, a Group 12 metal, sits alongside cadmium and mercury in the periodic table. With an electron configuration of [Ar] 3d¹⁰ 4s², zinc behaves as a relatively stable metal, primarily exhibiting a +2 oxidation state, which is typical in its compounds. Zinc’s chemical behavior lacks the variable oxidation states commonly seen in transition metals but retains enough reactivity to participate in various chemical reactions.

Physical Properties of Zinc

Zinc is a bluish-white, shiny metal with distinctive physical properties:

Atomic mass: 65.38 u
Melting point: 419.53°C (787.15°F)
Boiling point: 907°C (1665°F)
Density: 7.14 g/cm³
Electrical conductivity: Moderate conductor of electricity
Crystal structure: Hexagonal close-packed (hcp)

At room temperature, zinc is brittle, but it becomes malleable between 100°C and 150°C, making it easier to shape and work with. Zinc’s low melting point makes it ideal for casting in various industrial applications. Additionally, zinc forms a protective oxide layer when exposed to air, giving it excellent corrosion resistance.

Chemical Properties of Zinc

Zinc is moderately reactive and has a variety of important chemical characteristics. It exhibits a stable +2 oxidation state, forming ionic bonds in most of its compounds.

Oxidation State: Zinc typically forms the Zn²⁺ ion, a stable oxidation state found in nearly all of its compounds.
Reaction with Acids: Zinc readily reacts with dilute acids, such as hydrochloric acid, to produce hydrogen gas and a corresponding zinc salt:
Zn+2HCl→ZnCl₂+H₂

This reaction illustrates the metal’s reducing power and is commonly used in laboratories to generate hydrogen gas.
Reaction with Oxygen: When heated, zinc reacts with oxygen to form zinc oxide (ZnO), a compound that finds use in many industries:
2Zn+O₂→2ZnO

Zinc oxide is amphoteric, meaning it can react with both acids and bases, forming zinc salts or complex ions such as zincates.
Amphoteric Nature: Zinc oxide behaves as both an acid and a base:
- With hydrochloric acid, it forms zinc chloride:ZnO+2HCl→ZnCl₂+H₂O
- With sodium hydroxide, it forms sodium zincate:ZnO+2NaOH+H₂O→Na₂[Zn(OH)₄]
Reactivity with Halogens: Zinc reacts with halogens to form zinc halides (e.g., zinc chloride, ZnCl₂), which are used in various chemical processes.
Complex Ion Formation: Zinc forms stable complexes with ligands such as ammonia and cyanide, giving rise to coordination complexes like [Zn(NH₃)₄]²⁺.

The compounds of zinc are:

Hydrides

The term hydride is used to indicate compounds of the type M_xH_y and it is not necessarily that indicated any compounds listed would behave as same as hydrides chemically.

Zinc hydride: ZnH₂

Fluorides

Zinc difluoride: ZnF₂

Chlorides

Zinc dichloride: ZnCl₂

Bromides

Zinc dibromides: ZnBr₂

Iodides

Zinc diiodide: ZnI₂

Oxides

Zinc oxide: ZnO
Zinc peroxide: ZnO₂

Sulfides

Zinc sulphide: ZnS

Selenides

Zinc selenide: ZnSe

Tellurides

Zinc telluride: ZnTe

Nitrides

Trizinc dinitride: Zn₃N₂

Complexes

Hexaaquozinc dinitrate: Zn(NO₃)₂.6H₂O
Zinc sulphate pentahydrate: ZnSO₄.7H₂O

Ores of Zinc

Calamine → ZnCO₃

Zincite → ZnO

Zinc blende → ZnS

Willemite → ZnO.SiO₂

Extraction and Occurrence

Zinc is the 24th most abundant element in the Earth’s crust. It is primarily found in the form of zinc blende (sphalerite, ZnS), and other important minerals like smithsonite (ZnCO₃) and hemimorphite (Zn₄Si₂O₇(OH)₂·H₂O).

Zinc Extraction Process:

Mining: Zinc is obtained from its ore, sphalerite, through underground or open-pit mining.
Roasting: Zinc sulphide is roasted to produce zinc oxide and sulphur dioxide:2ZnS+3O₂→2ZnO+2SO₂
Reduction (Pyrometallurgical Method): Zinc oxide is reduced with carbon at high temperatures to produce zinc metal:ZnO+C→Zn+CO
Electrolytic Refining: In hydrometallurgical processes, zinc is dissolved in sulfuric acid and recovered by electrolysis.

Uses of Zinc

Zinc has a broad range of applications across many industries due to its unique properties:

1. Galvanization

Zinc is most commonly used for galvanizing iron and steel to protect them from rusting. Galvanized steel is used in infrastructure, automotive industries, and household appliances. The zinc coating acts as a protective layer and corrodes preferentially over iron, thereby preventing oxidation of the underlying metal.

2. Alloys

Zinc is a key component in a variety of alloys, such as:

Brass: An alloy of copper and zinc, used for its durability, corrosion resistance, and aesthetic appeal. Brass is used in musical instruments, plumbing fixtures, and decorative objects.
Zamak: A zinc-aluminum alloy used in die casting, commonly found in automotive parts, hardware, and electrical components.

3. Zinc Oxide (ZnO)

Zinc oxide is used in:

Rubber Industry: As an additive to vulcanize rubber and improve its strength.
Cosmetics and Skincare: ZnO is a key ingredient in sunscreens, ointments, and cosmetics due to its UV-absorbing properties.
Pigments: Used in paints, coatings, and ceramics for its white pigmentation and anti-corrosive properties.
Electronics: ZnO is a semiconductor used in varistors and as a transparent conductor in touch screens.

4. Batteries

Zinc is used in various types of batteries:

Zinc-carbon batteries: Common in household batteries.
Zinc-air batteries: Widely used in hearing aids and other portable devices.

5. Biological Significance

Zinc is essential in biology. It is a trace element necessary for the proper function of over 300 enzymes and is crucial for:

Enzyme Activity: It acts as a cofactor for enzymes involved in DNA synthesis, cell division, and protein synthesis.
Immune Function: Zinc plays a vital role in maintaining immune system function.
Growth and Development: Zinc is essential for proper growth, especially during childhood and adolescence.

Zinc deficiency can lead to impaired immune function, growth retardation, and delayed wound healing. Foods rich in zinc include meat, dairy, seeds, and legumes.