Aluminium Oxide Formula: Properties, Preparation, Uses

Aluminium oxide is a chemical compound composed of aluminium and oxygen atoms. Aluminium Oxide formula is \({{\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}}.\) In the chemical reaction, aluminium loses three electrons and oxygen receives two. It is commonly known as alumina. 

Aluminium oxide is an odourless white amorphous substance. The chemical makes important contributions in numerous life-extending and societal welfare applications due to its various helpful features. It is also found in the mineral bauxite. In this article, we are going to discuss more about aluminium oxide.

Aluminium Oxide (Al₂O₃)

Aluminium oxide \(\left( {{\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}} \right)\) is an ionic compound. That is, during the formation of aluminium oxide, the transfer of electrons between aluminium and oxygen atoms takes place. Aluminium oxide, \({{\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}}\) can be represented as,

The molar mass of aluminium oxide is approximately equal to \(101.96\;{\rm{g}}/{\rm{mol}}.\)

Aluminium Oxide Chemical Formula

The chemical formula of a compound represents the number of atoms of each element present in one compound molecule. In the criss-cross method, if we know the valency of each element of a compound, we can easily write its formula. The symbol of the positive part is written to the left-hand side and the negative part to its right. The valency of each element is placed as a subscript on the side of the symbol of another element. Subscript \(1\) is not often written.

Using the criss-cross method, the chemical formula of aluminium oxide can be derived.  That is in aluminium oxide, there are aluminium and oxygen ions. The valency of aluminium is three and that of oxygen is two. By crisscrossing the valency numbers and using them as subscripts, we have the formula \({{\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}}.\) That is,

Preparation of Aluminium Oxide (Al₂O₃)

The preparation of aluminium oxide in various methods are explained below:

1. Alumina (Aluminium oxide) can be obtained from Bauxite by the process of leaching

Bauxite is the chief ore of aluminium. It usually contains the impurities like silicon dioxide \(\left( {{\rm{Si}}{{\rm{O}}_2}} \right),\) iron oxides and titanium oxide \(\left( {{\rm{Ti}}{{\rm{O}}_2}} \right).\) The bauxite ore is concentrated with a solution of \({\rm{NaOH}}\) at \(473 – 523\;{\rm{K}}\) and \(35 – 36\) bar pressure. As a result, sodium aluminate \(\left( {{\rm{Si}}{{\rm{O}}_2}} \right.\) is formed as sodium silicate in the solution) is formed leaving the impurities behind. That is,

\({\rm{A}}{{\rm{l}}_2}{{\rm{O}}_3}(\;{\rm{s}}) + 2{\rm{NaOH}}({\rm{aq}}) + 3{{\rm{H}}_2}{\rm{O}}({\rm{I}}) \to 2{\rm{Na}}\left[ {{\rm{Al}}{{({\rm{OH}})}_4}} \right]({\rm{aq}})\)

Carbon dioxide is passed through the solution to neutralize the sodium aluminate present in it. As a result, hydrated aluminium oxide is precipitated. That is,

\(2{\rm{Na}}\left[ {{\rm{Al}}{{({\rm{OH}})}_4}} \right]({\rm{aq}}) + {\rm{C}}{{\rm{O}}_2}(\;{\rm{g}}) \to {\rm{A}}{{\rm{l}}_2}{{\rm{O}}_3} \cdot {\rm{x}}{{\rm{H}}_2}{\rm{O}}({\rm{s}}) + 2{\rm{NaHC}}{{\rm{O}}_3}({\rm{aq}})\)

The hydrated alumina is filtered out, and the sodium silicate remains in the solution. The filtered hydrated alumina is then dried and heated to produce pure \({{\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}}.\) That is, 

2. Aluminium also reacts with oxygen to form aluminium oxide.

That is,

\(4{\rm{Al}} + 3{{\rm{O}}_2} \to 2{\rm{A}}{{\rm{l}}_2}{{\rm{O}}_3}\)

Properties of Aluminium Oxide (Al₂O₃)

Let us discuss the physical and chemical properties of aluminium oxide.

Physical Properties of Aluminium Oxide (Al₂O₃)

1. Aluminium oxide appears as a white solid.
2. It is insoluble in water and in almost all solvents.
3. Aluminium oxide is an electrical insulator, but it shows thermal conductivity for ceramic materials.
4. The melting point \(\left( { \sim 2345\;{\rm{K}}} \right)\) and boiling point \(\left( { \sim 3250\;{\rm{K}}} \right)\) of aluminium oxide are comparatively high.
5. The density of aluminium oxide is \(3.987\;{\rm{g}}/{\rm{c}}{{\rm{m}}^3}.\)

Chemical Properties of Aluminium Oxide (Al₂O₃)

Generally, metal oxides are basic. But, aluminium oxide is an amphoteric oxide. That is, it can react with both acids and bases. When it reacts with an acid, it behaves as a base, and when it reacts with a base, it behaves as an acid. 

For example, aluminium oxide reacts with hydrofluoric acid to form aluminium fluoride salt and water. That is,

\({\rm{A}}{{\rm{l}}_2}{{\rm{O}}_3} + 6{\rm{HF}} \to 2{\rm{Al}}{{\rm{F}}_3} + 3{{\rm{H}}_2}{\rm{O}}\)

Aluminium oxide reacts with hydrochloric acid to form aluminium chloride and water as the products. That is,

\({\rm{A}}{{\rm{l}}_2}{{\rm{O}}_3} + 6{\rm{HCl}} \to 2{\rm{AlC}}{{\rm{l}}_3} + 3{{\rm{H}}_2}{\rm{O}}\)

Similarly, aluminium oxide reacts with sodium hydroxide to form sodium aluminate salt.

\({\rm{A}}{{\rm{l}}_2}{{\rm{O}}_3} + 2{\rm{NaOH}} + 3{{\rm{H}}_2}{\rm{O}} \to 2{\rm{NaAl}}{({\rm{OH}})_4}\)

Aluminium reacts with atmospheric oxygen and forms a protective layer of aluminium oxide on its surface. This aluminium oxide layer helps in the prevention of corrosion of aluminium. This is the reason why aluminium is called a corrosion-resistant metal.

Uses of Aluminium Oxide (Al₂O₃)

Aluminium oxide has got many uses. They include: 

1. Due to the hardness and strength of aluminium oxide, it is majorly used as an abrasive. Aluminium oxide is used as a substitute for industrial diamond, used for making sandpaper, cutting tools, etc.
2. It is most widely used as a material for ceramics.
3. It is used as a filler for plastics.
4. It is a usual ingredient in sunscreen, lipstick, blush and nail polish.
5. It is used for making glass. One of the common glass which contains aluminium oxide is aluminosilicate glass. It contains \(5 – 10\% \) of aluminium oxide.
6. It is used as a catalyst in some industrial reactions. For example, aluminium oxide is used as a catalyst in the Claus process, which is used to convert hydrogen sulphide wastes into elemental sulphur.  
7. Water can be removed from gas streams using aluminium oxide.
8. The flakes of aluminium oxide are used in paints for giving a reflective or decorative effect.
9. For integrated circuits, aluminium oxide is used as an electrical insulator.
10. Transparent aluminium oxide is used in sodium vapour lamps and compact fluorescent lamps.
11. In laboratories, it can be used as a chromatographic medium.
12. It is used in birth control pills and hip replacement in medicine.

Formula of Oxide of Eka-Aluminium

Eka-aluminium was the name given for the element Gallium by Mendeleev before discovering the element Gallium. The chemical name of its most common oxide is gallium (III) oxide. Its chemical formula is \({\rm{G}}{{\rm{a}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}{\rm{.}}\)  It is also known as gallium trioxide. It exists in different polymorphs (solid material in more than one form or crystal structure). Let us discuss more gallium (III) oxide.

Preparation of Gallium (III) oxide [Ga₂O₃]

Gallium (III) oxide can be prepared by the neutralization of acidic or basic solution of gallium salt. As a result of the process, gallium (III) oxide will be precipitated.

Properties of Gallium (III) oxide [Ga₂O₃]

Let us discuss some properties of gallium oxide. 

1. Gallium (III) oxide appears as a white crystalline powder. It is insoluble in water but is soluble in most acids. 
2. Like aluminium oxide, gallium (III) oxide is also amphoteric in nature. That is, it reacts with both acids and bases.

For example, gallium (III) oxide reacts with hydrochloric acid to form gallium trichloride. That is,

\({\rm{G}}{{\rm{a}}_2}{{\rm{O}}_3} + 6{\rm{HCl}} \to 2{\rm{GaC}}{{\rm{l}}_3} + 3{{\rm{H}}_2}{\rm{O}}\)

3. Gallium (III) oxide can be reduced to gallium suboxide by the reduction with hydrogen. That is,

\({\rm{G}}{{\rm{a}}_2}{{\rm{O}}_3} + 2{{\rm{H}}_2} \to {\rm{G}}{{\rm{a}}_2}{\rm{O}} + 2{{\rm{H}}_2}{\rm{O}}\)

It can also be done by the reaction of gallium (III) oxide with gallium metal. That is,

\({\rm{G}}{{\rm{a}}_2}{{\rm{O}}_3} + 4{\rm{Ga}} \to 3{\rm{G}}{{\rm{a}}_2}{\rm{O}}\)

Uses of Gallium (III) oxide [Ga₂O₃]

Gallium (III) oxide has no great commercial value. However, it has got some uses. They include:

1. It is used in lasers and luminescent materials.
2. It is used in gas sensors.
3. It is also used in transistor applications.

Summary

Aluminium oxide is an inorganic compound with the chemical formula \({\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}{\rm{.}}\) It is naturally found as corundum and is commonly known as alumina. Aluminium reacts with atmospheric oxygen to form a natural aluminium oxide layer on its surface. It can be prepared chemically from Bauxite also. In this article, we have discussed more aluminium oxide. The most common oxide of Eka-aluminium known as gallium (III) oxide, is also covered in this article.

FAQs

Q.1. What is the formula of aluminium oxide?
Ans: Aluminium oxide is an inorganic compound with the chemical formula \({\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}{\rm{.}}\) It is an ionic compound.

Q.2. What is the chemical formula of the oxide of Eka-aluminium?
Ans: The chemical name of the common oxide of Eka-Aluminium is gallium (III) oxide. Its chemical formula is \({\rm{G}}{{\rm{a}}_2}{{\rm{O}}_3}.\)

Q.3. What is the formula mass unit of aluminium oxide?
Ans: The formula unit mass of a substance is the sum of the atomic masses of all atoms in an ionic compound’s formula unit. Therefore, the formula unit mass of aluminium oxide can be found as,
Atomic mass of aluminium \(= 26.981\,{\rm{u}}\)
Atomic mass of oxygen \(= 15.999\,{\rm{u}}\)
The formula unit mass of aluminium oxide \(\left( {{\rm{A}}{{\rm{l}}_2}{{\rm{O}}_3}} \right) = (2 \times 26.981) + (3 \times 15.999) = 101.959\,{\rm{u}}\)

Q.4. What are the uses of aluminum oxide?
Ans: Aluminium oxide has got many uses. The important uses of aluminium include its uses in ceramics, abrasive applications, refractories, polishing, etc.

Q.5. Is aluminum oxide toxic to humans?
Ans: Aluminium oxide is a less toxic substance. However, at higher concentrations, it exhibits toxic effects. For example, inhalation of aluminium oxide dust can cause lung problems.

Study Preparation & Properties of Compounds of Aluminium

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