Cobalt

Group IX of the periodic table contains the transition metal cobalt, which is vital in many applications due to its special chemical and physical characteristics. Cobalt is very useful in the creation of magnetic and heat-resistant alloys because of its physical properties, which are comparable to those of iron and nickel. Beyond its industrial uses, cobalt plays a crucial role in biological processes, supporting the proper functioning of the nervous system and DNA production in many living organisms, including humans.

1.0Introduction 

Cobalt (Co) is a transition metal on the periodic table, with an atomic number of 27 and an atomic mass of 58.933195. It was first discovered in 1735 by George Brandt in Stockholm, Sweden. Cobalt has many applications today, including in magnets, paint pigments, glass, and even cancer therapy. The name “cobalt” comes from the German word kobold, meaning "goblin" or "evil spirit," a term used by miners due to the metal's challenging extraction and the health hazards associated with it.

2.0Occurrence of Cobalt

The stable form of cobalt can be produced in supernovae through the r-process, making up about 0.0029% of the Earth’s crust. Pure, or native, cobalt metal is not typically found on Earth due to the abundance of chlorine in seawater and oxygen in the atmosphere, which prevents its formation in a natural metallic form.

While pure cobalt metal is rarely found on Earth, except in meteoric iron, cobalt compounds are more widely distributed. Though cobalt is moderately abundant, its compounds are found in trace amounts in many soils, rocks, animals, and plants.

3.0Physical  properties of Cobalt

4.0Chemical  Properties of Cobalt

Cobalt is a moderately reactive element. It reacts with oxygen in the air, though it does not ignite or burn unless in powdered form. Cobalt also reacts with most acids to produce hydrogen gas but is stable in water at room temperature.

In aqueous solutions, cobalt forms the pink hexaaquacobalt(II) ion, [Co(H₂O)₆]²⁺. This ion, which changes from blue (dry form) to pink (hydrated form), is commonly used in cobalt (II) chloride humidity indicators.

1. Ligand Exchange Reactions

• Exchange with Hydroxide Ions

When hydroxide ions are introduced, they deprotonate the water ligands attached to the cobalt ion, forming a neutral, water-insoluble complex that precipitates:

[Co(H₂O)₆]²⁺+ 2OH⁻→ [Co(H₂O)₄(OH)₂] + 2H₂O

• Exchange with Ammonia

Ammonia acts as both a ligand and a base. Adding a small amount of ammonia forms the same neutral complex as with hydroxide:

[Co(H₂O)₆]²⁺+2NH₃ →  [Co(H₂O)₄(OH)₂] + 2NH₄⁺ 

When excess ammonia is added, it fully replaces water as a ligand, forming hexaamminecobalt(II) ions:

[Co(H₂O)₆]²⁺+ 6NH₃→[Co(NH₃)₆]²⁺+ 6H₂O

The hexaamminecobalt(II) complex readily oxidises to cobalt(III) upon exposure to air, forming a deep red-brown solution due to a mix of cobalt(III) complexes.

2. Oxidation of Hexaaquacobalt(II) Ions

• Using Ammonia and Hydrogen Peroxide

Adding hydrogen peroxide after ammonia accelerates oxidation, turning the solution dark red-brown:

2[Co(NH₃)₆]²⁺+H₂O₂ → 2[Co(NH₃)₆]³⁺+ 2OH⁻

• Using Sodium Hydroxide and Hydrogen Peroxide

With sodium hydroxide, cobalt(II) hydroxide precipitates, and hydrogen peroxide addition produces oxygen bubbles and a chocolate-brown precipitate of cobalt(III).

3. Reaction with Carbonate Ions

Hexaaquacobalt(II) ions react with carbonate ions to form a basic cobalt carbonate precipitate:

Co²⁺+CO₃²⁻→CoCO₃

This precipitate is often a basic carbonate with a general formula.

$xCoCO3\cdot yCo(OH)2\cdot zH2O$

4. Ligand Exchange with Chloride Ions

When concentrated hydrochloric acid is added to a hexaaquacobalt(II) solution, it turns blue as chloride ions replace the water ligands:

[Co(H₂O)₆]²⁺+ 4Cl⁻ ⇌ [CoCl₄]²⁻+ 6H₂O

This reaction is reversible and highlights the colour change associated with ligand exchange.

5.0Uses of Cobalt

Cobalt is a metal with a wide range of applications across various industries. Its diverse uses support sectors such as clean energy, transportation, healthcare, and petrochemicals. Some of the key applications of cobalt include:

• Batteries: Cobalt is crucial in rechargeable battery production, particularly for electric vehicles and mobile devices. It provides stability and enhances performance.
• Aerospace and Defense: Cobalt-based alloys are essential in the aerospace and defence industries because they are used in high-stress, high-temperature components like aircraft engines and gas turbine blades.
• Medical Devices: Cobalt-chromium alloys, known for their biocompatibility and wear resistance, are widely used in medical implants, artificial joints, and dental devices.
• Magnets: Cobalt is a critical material in high-strength magnets for electric motors, wind turbines, and various industrial applications requiring powerful magnetic properties.
• Catalysts: Cobalt catalysts help convert hydrocarbons into valuable products, including plastics and synthetic fibres, in the petrochemical industry.
• Pigments: Cobalt compounds are valued for their rich blue colour and are commonly used in ceramics, glass, and paint.