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Aluminium Chloride Formula – Structure, Properties, Uses, Sample Questions

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  • Last Updated : 15 Mar, 2022

Aluminum Chloride is a combination of Aluminium and Chlorine elements. Aluminum is represented by Al. It is a lightweight silver metal that belongs to the boron family in the periodic table. Aluminum’s atomic number is 13. The density of it is lower than steel and had a greater affinity towards oxygen. So when aluminum is exposed to air, a thin protective layer of oxide is formed. On the other side Chlorine is a toxic, corrosive green-colored gas that causes irritation to the eyes and problems to the respiratory system. It is the second lightest member of the halogen family.

Aluminum Chloride is formed by an exothermic reaction between metallic aluminum and chlorine. Its chemical formula is AlCl3. Aluminum Chloride is also called Aluminium trichloride. The physical form of aluminum chloride is silvery-white colored powder but due to the presence of contaminants (ferric chloride), it acquires yellow color. It is soluble in various solvents such as water, chloroform, ethanol, CCl4, hydrogen chloride, and slightly soluble in benzene. It was corrosive and toxic.

Aluminum Chloride Structure

Aluminum Chloride Preparation 

There are many ways of preparing AlCl3. All those processes are listed below along with equations.

  • Aluminum Chloride is mainly produced by the exothermic reaction between aluminum and chlorine.

2Al + 3Cl2 —> 2AlCl3 

  • Aluminum Chloride can be formed by reacting the aluminum metal with hydrogen chloride.

2Al + 6HCl → 2AlCl3 +  H2

  • It was even prepared by conducting a single displacement reaction between copper chloride and aluminum metal.

2Al + 3CuCl2 → 2AlCl3 + 3Cu

Physical Properties  of Aluminium Chloride

  • Aluminum Chloride is a poor conductor of electricity in a molten state.
  • The actual color of Aluminium Chloride is white in color but due to the presence of contaminants of Iron trichloride, it turns into yellowish color.
  • It has a very low melting point and boiling point.
  • Aluminum Chloride is in a liquid state when the temperature is above 190o C and pressure at above 2.5 atm.

Chemical Properties of Aluminium Chloride

  • Aluminum Chloride is non-flammable, non-explosive.
  • It is a corrosive solid.
  • Aluminum chloride behaves violently when it reacts with water and bases.
  • It is a lewis acid and an industrial catalyst.

Uses of Aluminium Chloride

  • Used in pesticides & pharmaceuticals.
  • Useful in manufacturing rubber, lubricants, paints, wood preservatives, and also petrochemicals like ethylbenzene.
  • Aluminum Chloride is used in polymerization and isomerization reactions of light-weighted hydrocarbons like the production of ethylbenzene.
  • Acts as a flux in melting aluminum.
  • Aluminum Chloride is used as a catalyst for many chemical reactions. It is used in the preparation of anthraquinone from benzene and phosgene.
  • It is used to attach aldehyde groups to aromatic series.
  • Aluminum Chloride is mixed with aluminum, arene to synthesize arene metal complexes.

Sample Questions

Question 1: How does Aluminium Chloride react with water?

Answer:

Alumunium Chloride is hygroscopic which means it absorb moisture from air. Actually it fumes when in air containing moisture, creating a hissing sound when it comes contact with water. By this reaction Cl ions are replaced with H2O and forms Hexahydrate i.e., Al(H2O)6Cl3. When heat is applied, ammonium hydroxide is obtained as final product by dissipating HCl.

Al(H2O)6Cl3  —> Al(OH)3 + 3HCl + 3H2O

Question 2: What are the melting and boiling points of Aluminium Chloride?

Answer:

The melting point of Aluminium Chloride is 192.6° C when it is anhydrous from. If it is a Hexahydrate then melting point is 100° C. The Boiling point of Aluminium Chloride is 180° C.

Question 3: Is Aluminium Chloride a Lewis Acid?

Answer:

Yes, Aluminium Chloride is a powerful Lewis acid. It forms Lewis Acid-base adducts even with bases that are weak in nature. 

Example 1: Aluminium Chloride forms tetrachloroaluminate (AlCl4) when Chlorine ions are present.

Example 2: AlCl3 react with magnesium and calcium hydride to form tetrahydridoaluminate.

Question 4: What is the molecular weight of Aluminium Chloride (AlCl3)?

Solution:

Molecular weight can be calculated by finding the weight of each element.

Weight of Aluminium = 26.982

Weight of chlorine = 35.453

Here there are three chlorine atoms so the above weight can be multiplied with 3 to give weight of 3 chlorine atoms.

Weight of 3 chlorine atoms = 3 × 35.453 = 106.359

So molecular weight of Aluminium chloride (AlCl3) = 26.982 + 106.359 = 133.341

Hence molecular weight of AlCl3 is 133.341 gram/molecule.

Question 5: Aluminium Chloride is hazardous?

Answer:

  • Aluminium Chloride can explode when it comes contact to water. So precautions need to be taken like wearing gloves, face guards etc. It should be stored in tightly sealed container to protect it from moisture.
  • It corrode metals like stainless steel.
  • Exposure to AlCl3 for long period causes irritation to eyes and problem to respiratory organs.
  • Aluminium Chloride is found to be neurotoxin and can destruct the nerve tissues. So from all these points, it can be concluded that AlCl3 is hazardous if proper precautions are not taken.

Question 6: What is the structure of Aluminium Chloride?

Answer:

The structure of Aluminium Chloride varies based on the factors such as state of compound i.e., solid, liquid or gaseous state and also the temperature it is exposed. In solid state, The structure of AlCl3 is Octahedral. In liquid/molten state, the structure is Tetrahedral. At higher temperature the structure is dissociates from tetrahedral to trigonal planar.

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