Aluminium Ore(Bauxite) and Test of Al Ion | Chemistry for JAMB PDF Download

Bauxite Ore of Aluminium

1. Purification of Bauxite:
Bauxite is the main source of aluminium and is a mixture of various minerals, including hydrated aluminium oxides and impurities such as silica, iron oxides, and titanium dioxide.
The purification process involves the following steps:

• Crushing and Grinding: Bauxite ore is crushed and ground to increase its surface area for better chemical reactions.
• Digestion: The crushed ore is mixed with a concentrated solution of sodium hydroxide (NaOH) and heated under pressure. This process dissolves aluminium hydroxide but leaves behind impurities.
• Filtration: The resulting mixture is filtered to separate the insoluble impurities.
• Precipitation: The filtrate is cooled, and aluminium hydroxide is precipitated out by the addition of acid or by carbonation.
• Calcination: The precipitated aluminium hydroxide is heated to obtain alumina (Al₂O₃) by the process of calcination.

2. Electrolytic Extraction of Aluminium:
The electrolytic extraction of aluminium from alumina (Al₂O₃) obtained from bauxite involves the following steps:

• Electrolysis Cell: An electrolytic cell is set up using a carbon anode and a graphite-lined steel cathode.
• Electrolyte: The electrolyte used is molten cryolite (Na₃AlF₆) mixed with alumina (Al₂O₃).
• Electrolysis: When an electric current is passed through the cell, aluminium ions (Al³⁺) are reduced at the cathode to form liquid aluminium, which sinks to the bottom of the cell. Oxygen gas (O₂) is liberated at the anode.
• Collection of Aluminium: The liquid aluminium is periodically siphoned off and further processed to obtain pure aluminium.

Properties of Aluminium

• Aluminium is a lightweight, silvery-white metal with a low density.
• It has high tensile strength and is resistant to corrosion due to the formation of a thin, protective oxide layer on its surface.
• Aluminium is an excellent conductor of heat and electricity.
• It is malleable and ductile, allowing it to be easily formed into various shapes.
• The melting point of aluminium is 660.3°C, and its boiling point is 2467°C.
• Aluminium has good reflectivity and is often used in reflective surfaces and mirrors.

Uses of Aluminium and its Compounds

• Aluminium metal is widely used in various industries, including transportation (aircraft, automobiles, trains), construction (windows, doors, roofing), packaging (cans, foils), and electrical wiring.
• Aluminium alloys are used to manufacture lightweight structures and components.
• Aluminium compounds have diverse applications, such as:
• Aluminium oxide (Al₂O₃) is used as an abrasive in sandpaper and as a refractory material.
• Aluminium hydroxide (Al(OH)₃) is used in antacids and as a flame retardant in plastics.
• Aluminium sulfate (Al₂(SO₄)₃) is used in water purification and as a mordant in dyeing processes.
• Aluminium chloride (AlCl₃) is used as a catalyst in organic synthesis reactions.

Test for Al³⁺

To test for the presence of aluminium ions (Al³⁺), we can perform the following test:

• Add a few drops of sodium hydroxide (NaOH) solution to the unknown solution suspected to contain Al³⁺.
• If a white gelatinous precipitate forms, it indicates the presence of aluminium ions. The precipitate is aluminium hydroxide (Al(OH)₃).
• The precipitate can be further confirmed by its behavior. When excess sodium hydroxide is added, the precipitate dissolves, forming a clear solution due to the formation of a soluble complex ion, [Al(OH)₄]^-.

Conclusion

In conclusion, aluminium is obtained from bauxite ore through the processes of purification and electrolytic extraction. The properties of aluminium include its lightweight nature, corrosion resistance, high conductivity, malleability, and reflectivity. Aluminium finds wide-ranging applications in industries such as transportation, construction, packaging, and electrical wiring. Additionally, various aluminium compounds are used in different fields, such as aluminium oxide in abrasives and refractory materials, aluminium hydroxide in antacids and flame retardants, and aluminium sulfate in water purification. Finally, a test for the presence of aluminium ions can be conducted using sodium hydroxide, which results in the formation of a white precipitate of aluminium hydroxide.