Aluminium - Overview, Properties & Uses, Sources, FAQs

Physical Properties Of Aluminium

• The physical properties of an element deal with properties such as colour, melting point, boiling point, density, conductivity, and solubility, among others.
• This element has a high reactivity. Steel's rigidity and density of aluminum are around one-third of that of this material.
• Aluminium is a corrosion-resistant metal, and the atomic mass of aluminium is 27amu.
• The boiling point of aluminium is 2,470 degrees Celsius
• It has the ability to conduct electricity in a superconducting state.
• There are numerous unidentified isotopes with an atomic mass of aluminium or mass of Al ranging from twenty-one to forty-one.

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Chemical Properties Of Aluminium

The following are the chemical properties of Aluminium:

1. Aluminium with HCl reaction

At room temperature, aluminium reacts with dilute hydrochloric acid. Aluminium chloride and colourless hydrogen gas are produced when the metal aluminium dissolves in hydrochloric acid. The chemical reaction between aluminium and hydrochloric acid is irreversible.

$2 \mathrm{Al}+6 \mathrm{HCl} \rightarrow 2 \mathrm{AlCl}_3+3 \mathrm{H}_2 \uparrow$

2. Aluminum Reaction with Sodium hydroxide

The action of sodium hydroxide on elemental aluminium, which is an amphoteric metal, also produces sodium aluminate. Once established, the reaction is highly exothermic and is accompanied by the rapid development of hydrogen gas.

$2 \mathrm{NaOH}+2 \mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{NaAlO}_2+3 \mathrm{H}$

3. Aluminum Reaction with water

Aluminium metal forms a thin film of aluminium oxide, a few millimetres thick, that prevents it from interacting with water. According to the equation, aluminium reacts with water to produce hydrogen gas.

$2 \mathrm{Al}+3 \mathrm{H}_2 \mathrm{O} \rightarrow 3 \mathrm{H}_2+\mathrm{Al}_2 \mathrm{O}_3$

Uses Of Aluminium And Aluminium Foil

• As castings, it is employed in the transportation of railways, trucks, and vehicles.
• It's a component of packaging.
• Al (II) compounds are formed when Al metal reacts with oxidants.
• The presence of aluminium can be determined in qualitative analysis using aluminon.
• Aluminium foil, commonly known as tin foil, is a slick, paper-thin sheet of aluminium metal. It is made by rolling atomic mass of aluminium slabs of aluminium until they are less than 0.2 mm thick.
• Insulation, packing, and shipping are just a few of the applications for aluminium foil in the industrial world. It's also commonly available at all grocery stores for usage in the home. Aluminium foil is used in the home to store food, wrap goods, and cover baking surfaces, such as meat, to avoid moisture loss when cooking.
• Aluminium foil is also used to wrap and protect more delicate foods, such as vegetables, while they are being grilled.

Aluminium Ore Extraction

A silky, silvery-white metal that resists corrosion. It is the most plentiful metal in the earth's crust, accounting for 8% of it, and the third most abundant element after oxygen and silicon. Until now, bauxite ore $\left(\mathrm{Al}_2 \mathrm{O}_3 \cdot \mathrm{xH}_2 \mathrm{O}\right)$, a combination of hydrated aluminium oxide, has been the primary source of aluminium.

Cryolite (Na₃AlF₆) and alunite can also be used to recover aluminium. Garnet, topaz, and chrysoberyl are some of the gemstones that contain it. Al is the chemical symbol for this metal. Aluminium is a chemical element that belongs to the boron group and has the symbol Al. It is the most commonly used non-ferrous metal.

Ores of Aluminium

Aluminium is a highly reactive metal that belongs to the periodic table's IIIA group. Aluminium is present in its ores in the form of its oxide in nature. The most important aluminium ores are

• Bauxite – $\mathrm{Al}_2 \mathrm{O}_3 \cdot 2 \mathrm{H}_2 \mathrm{O}$
• Corundum –$\mathrm{Al}_2 \mathrm{O}_3$
• Cryolite – $\mathrm{Na}_3 \mathrm{AlF}_6$

Meltallurgy of Aluminium

Concentration of Ore

• Impurities in bauxite ore include ferric oxide and silica. It is concentrated first by gravity separation of ferric oxide impurities, followed by a magnetic separation process. After that, the ore is concentrated using a chemical process.
• Aluminium ore is referred to as bauxite. Bauxite is refined to produce aluminium oxide, a white powder from which aluminium may be extracted.
• Ferric oxide and silica are two impurities found in bauxite ore. It is concentrated first by separating ferric oxide impurities by gravity, then by a magnetic separation method. The ore is then concentrated by a chemical process.
• Bauxite is the name for aluminium ore. Bauxite is processed to generate aluminium oxide, a white powder that may be used to extract aluminium.

The primary source of aluminium is bauxite ore. Ore dressing entails crushing and pulverising the ore.

Bayer’s Process

Aluminium ore is processed with concentrated sodium hydroxide in this procedure. It produces soluble sodium aluminate, which is filtered out. When the filtrate is heated with water, it produces aluminium hydroxide, which, when heated further, produces alumina.

Hall-Heroult Process

In the extraction of aluminium, the Hall-Héroult technique is commonly utilised. Pure Al₂O₃ is combined with CaF₂ or Na₃AlF₆ in the Hall-Heroult process. As a result, the melting point of aluminium in the aluminium combination is lowered, and its ability to conduct electricity is increased. The vessel is made of steel with a carbon and graphite rod liner.

The cathode is the carbon lining, and the anode is graphite. When electricity is transmitted through a carbon electrode electrolytic cell, oxygen is produced at the anode. Carbon monoxide and carbon dioxide are created when the oxygen produced reacts with the carbon in the anode. In this process of aluminium manufacturing, approximately 0.5 kilogramme of carbon anode is burned for every 1 kg of Al produced.

$2 \mathrm{Al}_2 \mathrm{O}_3+3 \mathrm{C} \rightarrow 4 \mathrm{Al}+3 \mathrm{CO}_2$

The electrolytic reactions:

At the cathode:

$\mathrm{Al}^{3+}+3 \mathrm{e}^{-} \rightarrow \mathrm{Al}(\mathrm{I})$

At anode:

$\begin{aligned} & \mathrm{C}(\mathrm{s})+\mathrm{O}^{2-} \rightarrow \mathrm{CO}(\mathrm{g})+2 \mathrm{e}^{-} \\ & \mathrm{C}(\mathrm{s})+2 \mathrm{O}^2-\rightarrow \mathrm{CO}_2(\mathrm{~g})+4 \mathrm{e}^{-}\end{aligned}$

Positively charged aluminium ions gain electrons from the cathode and create molten aluminium during the electrolysis process.

Oxide ions lose their anode electrons and produce oxygen molecules.

Aluminium is too large to be extracted from its ore by carbon reduction in the electrochemical sequence, which is also known as the reactivity series. Temperatures necessary are far too high to be cost-effective.

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Some Solved Examples

Question 1: Directions: In the following questions, a statement if Assertion (A) is followed by a statement of reason (R).

Assertion: In the metallurgy of aluminium , purified Al₂O₃ is mixed with Na₃AlF₆ or CaF₂ during electrolysis.

Reason: Na₃AlF₆ or CaF₂ lowers the melting point of the mixture and brings the conductivity.

Mark the correct choice as:

1) If both assertion and reason are true and reason is correct explanation of assertion

2) If both assertion and reason are true but reason is not correct explanation of assertion

3) If assertion is true but reason is false

4) If both assertion and reason are false

Solution:

As we learn

Electrolytic Refining -

Many of the metals such as Cu,Au,Ag,Al,Hb etc are purified by this method.

- wherein

The impure metal is made anode while a thin sheet of pure metal acts as a cathode.

In Hall - Heroult process, the electrolysis of molten mass is carried out in an electrolytic cell.

Purified Al₂O₃ is mixed with Na₃AlF₆ or CaF₂ which lowers the melting point of the mixture and brings the conductivity.

Hence reason is correct explanation of assertion.

Hence, the answer is the option (1).

Question 2: In hoope's electrolyte method the Al is deposited at
1) (correct) Cathode
2) Anode
3) On both electrolyte
4) In solution

Solution:

As we have learned

Hoopes electrolytic method -

Used for refining of aluminium(99.98% pure)

- wherein

Aluminium is deposited at the cathode

In Hoope's process, Al is deposited at the Cathode

Hence, the answer is the option (1).

Question 3: Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A) : Aluminium is extracted from bauxite by the electrolysis of molten mixture of $\mathrm{Al}_2 \mathrm{O}_3$ with cryolite.

Reason (R) : The oxidation state of Al in cryolite is $+3$

In the light of the above statements, choose the most appropriate answer from the options given below:

1) Both (A) and (R) are correct and (R) is the correct explanation of (A).

2) (A) is true but (R) is false.

3) Both (A) and (R) are correct but (R) is not the correct explanation of (A).

4) (A) is false but (R) is true.

Solution:

As we have learnt,
Al is extracted from a molten mixture of Alumina $\left(\mathrm{Al}_2 \mathrm{O}_3\right)$ with cryolite $\left(\mathrm{Na}_3 \mathrm{AlF}_6\right)$.
Cryolite is added to decrease the melting point of alumina and also to increase the conductivity of the melt.

Hence, the answer is the option (3).

Question 4: Which of the following chemical reactions represents the Hall-Heroult Process?
1) $\mathrm{Cr}_2 \mathrm{O}_3+2 \mathrm{Al} \rightarrow \mathrm{Al}_2 \mathrm{O}_3+2 \mathrm{Cr}$

2) (correct) $2 \mathrm{Al}_2 \mathrm{O}_3+3 \mathrm{C} \rightarrow 4 \mathrm{Al}+3 \mathrm{CO}_2$

3) $\mathrm{FeO}+\mathrm{CO} \rightarrow \mathrm{Fe}+\mathrm{CO}_2$

4) $2\left[\mathrm{Au}(\mathrm{CN})_2\right]_{(\mathrm{aq})}^{-}+\mathrm{Zn}(\mathrm{~s}) \rightarrow 2 \mathrm{Au}(\mathrm{~s})+\left[\mathrm{Zn}\left(\mathrm{CN}_4\right)\right]^{2-}$

Solution:

Hall-Heroult process is used in the electrolytic refining of aluminum.
A steel vessel with a lining of carbon and graphite rods is used in the process. The carbon lining acts as a cathode, while graphite acts as an anode.

The overall reaction occurring in the process can be represented as

$2 \mathrm{Al}_2 \mathrm{O}_3+3 \mathrm{C} \rightarrow 4 \mathrm{Al}+3 \mathrm{CO}_2$
Hence, the answer is the option (2).

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