All questions of Representative Elements- Aluminium & Tin for JAMB Exam

The electrolyte used during the electrolytic extraction of aluminium is Aluminium chloride solution.

Aluminium is a highly reactive metal and is not found in its pure form in nature. It is usually found in the form of its oxide, known as alumina (Al2O3). The extraction of aluminium from alumina involves a process called electrolysis, which requires the use of an electrolyte.

Electrolysis Process:
During the electrolysis of alumina, a mixture of alumina and cryolite (Na3AlF6) is used as the electrolyte. Cryolite is added to lower the melting point of alumina, making the electrolytic process more efficient. The mixture is heated to around 950-1000°C to facilitate the flow of ions.

Role of Aluminium Chloride:
Aluminium chloride (AlCl3) is added to the mixture as a flux. It helps to increase the conductivity of the electrolyte and lower its resistance, allowing the flow of electric current more easily. This is essential for the successful extraction of aluminium.

Function of the Electrolyte:
The electrolyte serves as a medium for the movement of ions during electrolysis. When an electric current is passed through the electrolyte, the alumina (Al2O3) dissociates into aluminium ions (Al3+) and oxygen ions (O2-). The aluminium ions migrate towards the cathode (negative electrode), where they gain electrons and are reduced to form aluminium metal. The oxygen ions migrate towards the anode (positive electrode), where they lose electrons and are oxidized to form oxygen gas.

Advantages of Aluminium Chloride:
- Aluminium chloride is a stable compound that can withstand the high temperatures required for the electrolytic extraction process.
- It has a high solubility in the electrolyte, ensuring a sufficient supply of positive aluminium ions for the reduction reaction at the cathode.
- The addition of aluminium chloride helps to increase the conductivity of the electrolyte, allowing for a more efficient flow of electric current.

In conclusion, aluminium chloride is used as a flux in the electrolytic extraction of aluminium to enhance the conductivity of the electrolyte and facilitate the successful extraction of aluminium metal from alumina.

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Aluminium is suitable for electrical wiring due to its low density.

Explanation:
- Low density: Aluminium is a lightweight metal with a low density compared to other metals such as copper. This makes it easier to handle and install in electrical wiring systems.
- Conductivity: Although the question states that aluminium's high thermal conductivity property is not relevant to electrical wiring, it is worth mentioning that aluminium also has good electrical conductivity. It is not as conductive as copper, but its conductivity is still sufficient for use in electrical applications.
- Resistance: Aluminium has a lower electrical resistance compared to materials like rubber or plastics. This means that electrical current can flow more easily through aluminium wires, resulting in less energy loss and more efficient transmission of electricity.
- Melting point: While aluminium does have a relatively high melting point, this property is not directly relevant to its suitability for electrical wiring. The melting point mainly affects the manufacturing and processing of aluminium, rather than its performance as a conductor of electricity.
- Corrosion resistance: Another important property of aluminium is its resistance to corrosion. Aluminium forms a thin layer of oxide on its surface which protects it from further oxidation. This makes aluminium wiring more durable and long-lasting, especially in humid or corrosive environments.
- Cost: Aluminium is also more cost-effective compared to copper, which makes it a popular choice for electrical wiring in many applications. The lower cost of aluminium can significantly reduce the overall cost of electrical installations.
- Flexibility: Aluminium wire is more flexible than copper wire, which can be advantageous in certain situations where wiring needs to be bent or routed through tight spaces.
- Compatibility: Aluminium wire is compatible with various connectors and devices commonly used in electrical systems. This makes it easy to integrate aluminium wiring into existing infrastructure without the need for extensive modifications.
- Code regulations: Aluminium wiring meets the code requirements for electrical installations in many jurisdictions. It is important to follow specific guidelines for installing and maintaining aluminium wiring to ensure safety and prevent issues such as overheating or electrical faults.

Test for the presence of Al3+ ions:

Formation of a white precipitate with sodium hydroxide.

Explanation:
When Al3+ ions are present in a solution, they can be detected by adding sodium hydroxide (NaOH) to the solution. The following reaction takes place:

Al3+ + 3OH- → Al(OH)3

This reaction results in the formation of a white precipitate of aluminum hydroxide (Al(OH)3). This precipitate is insoluble in water and can be easily observed.

Key Points:
- The test involves adding sodium hydroxide solution to the solution being tested for the presence of Al3+ ions.
- The reaction between Al3+ ions and OH- ions forms a white precipitate of aluminum hydroxide.
- The white precipitate is insoluble in water and can be easily observed.
- This test is specific to Al3+ ions as other metal ions may not form a white precipitate with sodium hydroxide.
- The formation of a white precipitate confirms the presence of Al3+ ions in the solution being tested.

Note: The other options mentioned in the question are incorrect:

a) Blue litmus paper turning red is a test for acids.
b) Formation of a green flame is a test for copper (Cu2+) ions.
c) Effervescence with hydrochloric acid is a test for carbonates and bicarbonates.
d) The correct test for the presence of Al3+ ions is the formation of a white precipitate with sodium hydroxide.

The major impurity in bauxite ore is Silicon dioxide (SiO2). Bauxite is a sedimentary rock that is the main ore of aluminum. It is formed through the weathering of aluminum-rich rocks over millions of years. Bauxite is primarily composed of aluminum hydroxide minerals, along with various impurities.

Silicon dioxide, also known as silica, is one of the most common impurities found in bauxite ore. It is a compound composed of silicon and oxygen and is abundant in the Earth's crust. Silica can exist in various forms, including quartz, which is the most common form of silica.

Silica is considered an impurity in the production of aluminum because it affects the quality and properties of the final product. Its presence in bauxite ore can lead to several challenges in the extraction and refining processes.

Here are the reasons why silicon dioxide is considered the major impurity in bauxite ore:

1. High melting point: Silicon dioxide has a high melting point of around 1713 degrees Celsius. This makes it difficult to separate from the aluminum hydroxide minerals during the refining process.

2. Corrosive nature: Silicon dioxide can react with the chemicals used in the refining process, leading to equipment corrosion and increased maintenance costs.

3. Formation of insoluble compounds: Silica can form insoluble compounds with some of the chemicals used in the refining process, causing precipitation and reducing the efficiency of the process.

4. Impurities in the final product: If not properly removed, silicon dioxide can remain in the final aluminum product, affecting its quality and mechanical properties. It can reduce the strength and ductility of the aluminum, making it less suitable for certain applications.

To remove silicon dioxide from bauxite ore, several methods can be employed, including physical separation techniques such as screening and washing, as well as chemical processes like leaching and digestion. These methods aim to separate the impurities from the aluminum hydroxide minerals, resulting in a purer form of bauxite that can be further processed into aluminum.

In conclusion, silicon dioxide is considered the major impurity in bauxite ore due to its high melting point, corrosive nature, formation of insoluble compounds, and its potential to affect the quality of the final aluminum product. Removing this impurity is crucial for the production of high-quality aluminum.

Understanding Aluminium Oxide Properties
Aluminium oxide, commonly known as alumina, possesses several significant properties that make it an interesting compound. Here’s a breakdown of its characteristics and why option 'C' stands out.
Amphoteric Nature
- Aluminium oxide is amphoteric, meaning it can react with both acids and bases.
- This property allows it to neutralize both acidic and basic substances, forming salts and water.
Physical Appearance
- It is indeed a white solid, which is characteristic of many metal oxides.
- This appearance is consistent across various forms of aluminium oxide, such as alpha and gamma alumina.
Solubility in Water
- The statement that aluminium oxide is insoluble in water is what makes option 'C' correct.
- While aluminium oxide does not dissolve in water, it can interact with aqueous solutions, particularly acids or bases.
Reactivity with Acids
- Aluminium oxide readily reacts with acids to form salts.
- For example, when it reacts with hydrochloric acid, it forms aluminium chloride and water.
Conclusion
In summary, the correct answer is option 'C' because aluminium oxide is indeed insoluble in water, contrasting with other properties such as its amphoteric nature, physical appearance, and reactivity with acids. Understanding these properties helps in various applications, including its use in ceramics and as a catalyst in chemical reactions.

Extraction of Aluminium from Bauxite
Aluminium is primarily extracted from its ore, bauxite, through a process known as electrolytic extraction. This method is essential due to the chemical properties of aluminium, which make it highly reactive and, therefore, difficult to isolate from its compounds.
1. Purification of Bauxite
- The first step involves purifying bauxite to remove impurities such as iron oxides and silica.
- This is achieved through the Bayer process, where bauxite is crushed and treated with a hot solution of sodium hydroxide.
- The sodium hydroxide dissolves the aluminium oxide present in bauxite, forming soluble sodium aluminate, while the impurities remain undissolved.
2. Electrolytic Extraction
- The purified sodium aluminate is then subjected to electrolysis.
- The process occurs in an electrolytic cell where molten aluminium oxide (derived from the purified bauxite) is mixed with cryolite (Na3AlF6) to lower the melting point.
- Direct current electricity is passed through the molten mixture, causing the aluminium ions to migrate to the cathode (negative electrode) and reduce to form aluminium metal.
3. Reduction of Bauxite
- While the term "reduction" is often associated with the extraction of metals, in the context of bauxite extraction, it is specifically the electrolytic process that facilitates this reduction.
- Therefore, while reduction of bauxite does occur, the primary method of extraction utilized is electrolytic.
4. Oxidation of Bauxite
- This option is incorrect as oxidation does not play a role in the extraction of aluminium from bauxite.
In summary, the key process used to extract aluminium from bauxite is the electrolytic extraction, which is crucial for obtaining pure aluminium due to its highly reactive nature.