There is not enough difference in electronegativity between aluminium and chloride to form a simple ionic bond. Its structure changes in different room temperatures. It has an ionic lattice structure with a lot of covalent properties. Anhydrous aluminium chloride forms as a result of aluminium chloride’s reaction with water. 

It reacts with water in 2 different ways, depending on the amount of water added. On reacting with a small amount, or excess amount of water, it produces a solution and precipitate of hexaaquaaluminium ions and aluminium hydroxide along with HCl gas. The aqueous solution of aluminium chloride is acidic.

Aluminium Chloride

Aluminium is 6-coordinated at room temperature. The structure of aluminium and chlorine is an ionic lattice. The sublimation point for aluminium chloride is 180°C at normal atmospheric pressure. An increase in pressure by two atmospheres melts aluminium chloride at 192°C. These temperatures are below the expected range of an ionic compound, suggesting weak interactions between molecules due to the unstable coordination of aluminium at varying temperatures. From 6-coordinated, it becomes 4-coordinated. The arrangement of molecules becomes Al2Cl6, from the original lattice combination. 

This conversion causes a loss of ionic characteristics, which results in the vaporisation of the aluminium chloride. With an increase in temperature, the equilibrium solution for simple aluminium chloride molecules follow the given system:

Al2Cl6 ⇌ 2AlCl3

Aluminium Chloride in Aqueous Solution

In the recorded reaction of aluminium chloride with water, two important chemical reactions are necessary to note :-

AlCl3(s) + aq → [Al(H2O)6]3+(aq) + 3Cl –(aq)

Observations

• A large amount of water is used
• The solution has chloride ions and hydrated aluminium ions.
• The resulting solution is acidic. This is not related to the formation of hydrochloric acid.

[Al(H2O)6]3+(aq) + H2O(l) → [Al(H2O)5OH]2+(aq) + H3O+(aq)

Observations

• The behaviour of hexaaquaaluminium complex ions is similar to those formed from transition metals. 
• Highly charged metal ions withdraw electron density (polarisation) from water molecules attached to aluminium ions through dative covalent bonds. 
• The hydrogen atoms acting as a base are receptive to attacks from water acting as a solvent. 
• The solution is acidic by the formation of hydroxonium ions because of the deprotonated complex ion.

The aluminium chloride does not dissolve in water. It reacts to form hexaaquaaluminium complex ions and chloride ions. The ion is acidic because electrons in the water molecules attract towards the aluminium. This makes hydrogen atoms positive and easily removable from the ion.

Anhydrous Aluminium Chloride And Water

Recorded from aluminium chloride’s reaction with water, it behaves like normal covalent metallic chlorides. It is hydrolysed, under conditions of normal room temperature, on its reaction with water. 

Conditions

• Anhydrous aluminium chloride is stored in a dry container
• Room temperature water
• Huge room space to allow acidic fumes to escape
• Precautionary gear

Observations

• The reaction produces a hissing sound.
• The product is in two different forms, solid and gas.
• Hydrogen chloride is the steamy gaseous product.
• Spluttering aluminium chloride is solid.
• With ordinary concentrations (1 mol dm-3), the pH is 2–3. A higher concentration of solution indicates lower pH.

AlCl3(s) + H2O(l) → AlCl2OH(s) + HCl(g)

Hydrogen chloride gas is produced when there is a little amount of water involved because chloride ions and hydrogen ions combine in the mixture. This is due to the concentration of the solution and heat produced during the reaction. If the temperature is not high, due to excess amount of water, ions remain solvated and HCl gas is not produced.

Laboratory Experiment of Aluminium Chloride Reaction with Water

Handling

Work in dry surroundings when using large quantities of aluminium chloride. Arrange for safety glasses, a laboratory coat, fire protection for emergencies, and gloves. 

Aluminium chloride is not compatible with alcohol, sodium oxide, ethylene oxide, hydrated reagents, caustics, and strong oxidizers. It corrodes transition metals. For generating HCl vapours, heat aluminium chloride in an open container area. It is an exothermic reaction that releases HCl gas. Handle with care, and keep a bucket of dry sand nearby for accidental explosive reactions.

Experimentation of aluminium chloride reaction with water should be done under expert supervision. 

Precautionary Measures

• Physical contact: Avoid physical contact; skin contact should be 0%. Remove solids and other precipitates from the test tube or the container holding aluminium chloride. Ensure that you keep it in a cool dry place, and seek medical attention if solution or precipitate comes in physical contact. Thoroughly wash clothes if some of the solutions are spilt, and remove clothing materials immediately.
• Protection from spilling: Don’t try to wipe the solution if it is spilt. Control the spillage by covering it with sand. Scoop up the sand absorbed solution with protective equipment. Use spark-resistant tools to discard the remains.
• Fire and other exposures: The use of carbon dioxide and halogenated extinguishing agents is not recommended. Although aluminium chloride is not combustible, conventional fire extinguishers shouldn’t be used. Only use class D extinguishers, for example, Met-L-X. 
• Ingesting: Induced vomiting is not recommended. Drink a lot of water, at least two glasses. Seek medical attention as soon as possible before serious symptoms start showing up.

Storage and Disposal

Place it in sealed containers with other non-combustible compounds. Water contaminated storage tubes and containers might pressurise. 

Dispose in sealed, spark-proof boxes as hazardous waste, with precautionary labelling on top.

Conclusion

Aluminium chloride is a chemical compound that is made up of inorganic elements. AlCl3 is the chemical formula for aluminium chloride. It has a hygroscopic property. As a result, it has a stronger attraction for water. It can also be found as a dimer. It can be made utilising basic methods that are covered in detail in this article. It can be used in a variety of ways. It is a catalyst in various organic processes and has also been used in organometallic synthesis. Other applications of aluminium chloride in industry are also mentioned.