Aluminium chloride formula: Aluminium chloride is an inorganic compound and the chemical formula of the same is \({\text{AlC}}{{\text{l}}_3}.\) It is a common compound that includes aluminium and chlorine. It is further referred to as aluminium trichloride. It can also be represented as aluminium \(\left({{\text{III}}} \right)\) chloride.

Aluminium chloride has a wide range of applications. In the Friedel-Crafts process, it acts as a Lewis acid catalyst. It’s also used as a deodorant and antiperspirant. Medications and pesticides include aluminium chloride in it. This article will discuss the aluminium chloride formula in detail. Scroll down to find further details related to aluminium chloride.

Aluminium Chloride Formula: Overview

Aluminium chloride contains three chlorine atoms and one aluminium atom in it. An ionic bond (with a high degree of covalent character) exists between the aluminium and chlorine atoms. During the formation of aluminium chloride, aluminium donates its three outermost shell electrons to three chlorine atoms (one electron each for one chlorine atom). This gives a stable outer electronic configuration for both aluminium and chlorine atoms.

Aluminium chloride can be represented as,

The molar mass of aluminium chloride, \({\text{AlC}}{{\text{l}}_3}\) is \(133.341\,{\text{g}}/{\text{mol}}.\)

The determination of the molecular mass of aluminium chloride indicates that it exists as a dimer having molecular formula \({\text{A}}{{\text{l}}_2}{\text{C}}{{\text{l}}_6}.\) In this compound, the chlorine atoms are arranged tetrahedrally around the central aluminium atom. Its structure can be given as,

The arrow indicates the donation of electrons by chlorine atoms to aluminium atoms to complete the octet.

Note: Aluminium chloride adopts different structures depending upon the physical state and temperature.

Preparation of Aluminium Chloride

Aluminium chloride can be prepared on a large scale using the following methods at a temperature range of \(650\) to \(750\,^\circ {\rm{C}}:\)

1. By the reaction of aluminium metal and chlorine

Aluminium chloride is produced when aluminium is reacted with chlorine. The chemical equation for the reaction can be given as,

\(2{\text{Al}} + 3{\text{C}}{{\text{l}}_2} \to 2{\text{AlC}}{{\text{l}}_3}\)

The above reaction is highly exothermic in nature.

2. By the reaction of aluminium metal with hydrochloric acid

Aluminium chloride is produced when aluminium is reacted with hydrochloric acid. The chemical equation for the reaction can be given as,

\(2{\text{Al}} + 6{\text{HCl}} \to 2{\text{AlC}}{{\text{l}}_3} + 3{{\text{H}}_2}\)

Aluminium chloride is produced when copper chloride reacts with aluminium metal. The chemical equation for the reaction can be given as,

\(2{\text{Al}} + 3{\text{CuC}}{{\text{l}}_2} \to 2{\text{AlC}}{{\text{l}}_3} + 3{\text{Cu}}\)

This is an example of a single displacement reaction.

Properties of Aluminium Chloride

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

Physical Properties of Aluminium Chloride

The physical properties of Aluminium Chloride are as follows:

1. Aluminium chloride appears as a white solid. It sometimes appears as yellow due to the presence of contaminants like iron \(\left({{\text{III}}} \right)\) chloride.
2. It has a very low boiling and melting point.
3. Aluminium chloride is soluble in water, hydrogen chloride, ethanol, chloroform and carbon tetrachloride. It is slightly soluble in benzene.
4. Aluminium chloride is a hygroscopic substance. That is, it has a greater tendency to absorb moisture (water) from the air.

Chemical Properties of Aluminium Chloride

The chemical properties of Aluminium Chloride are as follows:

Aluminium chloride, \({\text{AlC}}{{\text{l}}_3}\) is a Lewis acid. This is because, due to its open valence shell, it can accept lone pair of electrons.

1. Reaction of Aluminium Chloride with Water

Aluminium chloride, \({\text{AlC}}{{\text{l}}_3}\) is a hygroscopic substance. That is, it has a strong affinity towards water. Therefore, it will absorb moisture from the air easily. Generally, aluminium fumes in moist air producing a hissing sound. During such reaction, \(\left[ {{\text{Al}}{{\left({{{\text{H}}_2}{\text{O}}} \right)}_6}} \right]{\text{C}}{{\text{l}}_3},\) the hexahydrate form is formed as the \({\text{C}}{{\text{l}}^ – }\) ligands are replaced by the \({{\text{H}}_2}{\text{O}}\) molecules. When heat is applied, the hydrogen chloride gas is evolved and lost leaving behind the aluminium hydroxide. The chemical equation for the reaction can be given as,

\(\left[{{\text{Al}}{{\left({{{\text{H}}_2}{\text{O}}} \right)}_6}} \right]{\text{C}}{{\text{l}}_3} \to {\text{Al}}{\left({{\text{OH}}} \right)_3} + 3{\text{HCl}} + 3{{\text{H}}_2}{\text{O}}\)

When the temperature is increased further, aluminium oxide (alumina) is formed. The chemical equation for the reaction can be given as,

\(2{\text{Al}}{\left({{\text{OH}}} \right)_3} \to {\text{A}}{{\text{l}}_2}{{\text{O}}_3} + 3{{\text{H}}_2}{\text{O}}\)

2. Reaction of Aluminium Chloride with Sodium Hydroxide

When aluminium chloride is reacted with sodium hydroxide, a white gelatinous precipitate of aluminium hydroxide is obtained. The chemical equation for the reaction can be given as,

\({\text{AlC}}{{\text{l}}_3} + 3{\text{NaOH}} \to {\text{Al}}{\left({{\text{OH}}} \right)_3} + 3{\text{NaCl}}\)

This reaction reveals that, the aqueous solutions of aluminium chloride behave similarly to other aluminium salts containing hydrated \({\text{A}}{{\text{l}}^{3 + }}\) ions.

Aluminium chloride has strong reactions with water and bases, as discussed above. Therefore, it is advised to keep aluminium chloride away from such substances.

Uses of Aluminium Chloride

Aluminium chloride has various uses. Some of the uses of aluminium chloride are mentioned as follows:

1. Aluminium chloride is mainly used as a Lewis acid catalyst in Friedel-Crafts reaction (in both acylations and alkylations).
2. Aluminium chloride can also be used to introduce aldehyde groups on aromatic rings during the Gattermann-Koch reaction.
3. Aluminium chloride is often used as a catalyst in organometallic synthesis too.
4. It is used for the polymerisation of light molecular weight hydrocarbons.
5. It is used for the manufacture of paints.
6. Aluminium chloride can be used as an antiperspirant.
7. It is used for the manufacture of lubricants, rubber, wood preservatives, etc.
8. It is used in pharmaceuticals and pesticides.
9. In aluminium melting, it is used as a flux.

Polyaluminium Chloride Formula

Polyaluminium chloride, which is also known as aluminium chlorohydrate is a group of specific aluminium salts which are generally soluble in water. It appears as an off-white powder. They have the general formula \({\text{A}}{{\text{l}}_{\text{n}}}{\text{C}}{{\text{l}}_{\left({3{\text{n}} – {\text{m}}} \right)}}{\left({{\text{OH}}} \right)_{\text{m}}}.\)

It is commercially prepared by the reaction of aluminium metal (any raw material containing aluminium such as alumina trihydrate, aluminium chloride, aluminium sulfate, etc. can be used) and hydrochloric acid. It is best described as an inorganic polymer. It is most commonly used in cosmetics (as an antiperspirant) and in water purification (as a coagulant).

Summary

Aluminium chloride is an inorganic chemical compound. The chemical formula of aluminium chloride is \({\text{AlC}}{{\text{l}}_3}.\) It is hygroscopic in nature. Hence, it has a higher affinity toward water. It exists as a dimer \(\left( {{\text{A}}{{\text{l}}_2}{\text{C}}{{\text{l}}_6}} \right)\) too. It can be prepared using simple methods which are clearly discussed in this article. It has got several uses. It plays the role of a catalyst in some organic reactions, and it found uses in organometallic synthesis. The other industrial uses of aluminium chloride are also discussed. Polyaluminium chloride, which is best described as an inorganic polymer, is also discussed in this article.

FAQs on Aluminium Chloride

Q.1. What is the formula of aluminium chloride?
Ans: Aluminium chloride is an inorganic compound with the chemical formula \({\text{AlC}}{{\text{l}}_3}.\)

Q.2. What happens when aluminium is mixed with copper chloride?
Ans: When aluminium is mixed with copper chloride, aluminium chloride is formed. That is,
\(2{\text{Al}} + 3{\text{CuC}}{{\text{l}}_2} \to 2{\text{AlC}}{{\text{l}}_3} + 3{\text{Cu}}\)
This is an example of a single displacement reaction.

Q.3. Why aluminium chloride exists as a dimer?
Ans: In aluminium chloride \(\left({{\text{AlC}}{{\text{l}}_3}} \right),\) there are six electrons in the valence shell of aluminium. In order to complete its octet, it accepts electrons from the chlorine atom. As a result, it exists as a dimer, \({\text{A}}{{\text{l}}_2}{\text{C}}{{\text{l}}_6}.\)

Q.4. Is aluminium chloride hazardous?
Ans: Yes, aluminium chloride is a corrosive substance. It is harmful to the skin, eyes and mucous membranes. It also damages the respiratory system if inhaled or in contact with it.

Q.5. Is aluminium chloride acidic or basic?
Ans: Aluminium chloride, \({\text{AlC}}{{\text{l}}_3}\) is a Lewis acid. Also, the aqueous solution of aluminium chloride is acidic in nature.

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