Aluminium chloride

Aluminium chloride

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Aluminium chloride:

• Method of preparation of anhydrous aluminium chloride (Al₂Cl₆ or AlCl₃)

1)  By passing dry chlorine gas over heated aluminium :

anhydrous AlCl₃  is obtained.

2Al + 3Cl₂ ——-> 2AlCl₃

2)  By passing dry HCl in heated aluminium :

2Al + 6HCl ———-> 2AlCl₃ + 3H₂

3)  By passing dry chlorine gas over heated alumina and coke :

Al₂O₃ +3C +3Cl₂ ———>  2AlCl₃  + 3CO

• Methods of preparation of hydrated aluminium chloride:

1) By dissolving aluminium in hydro chloric acid :

2Al + 6HCl ——–> 2AlCl₃ + 3H₂

2) By dissolving aluminium hydroxide in HCl :

AlCl₃ solution is obtained which on concentration gives crystals of AlCl₃

Al(OH)₃ + 3HCl ———-> AlCl₃ + 3H₂O

Properties:

1) It is colourless, crystalline solid, soluble in water.

2) Hydrolysis :

Aqueous solution of AlCl₃  is acidic in nature because on hydrolysis ,it gives strong acid.

AlCl₃ + 3H₂O———-> Al(OH)₃ + 3HCl

3) Reaction with Sodium hydroxide (NaOH) :

AlCl₃ + 3NaOH ———-> Al(OH)₃ + 3NaCl

Al(OH)₃ + NaOH ———–> NaAlO₂ + H₂O

4) Reaction with Ammonium hydroxide (NH₄OH) :

White precipitate of aluminium hydroxide is obtained. This precipitate do not dissolve in excess of NH₄OH

AlCl₃ + 3NH₄OH ———> Al(OH)₃ + 3NH₄Cl

5) Reaction with dry ammonia (NH₃ gas) : Addition  compound is obtained.

AlCl₃ + 6NH₃ ———-> AlCl₃. 6NH₃

6) Effect of heat :

On heating aluminium chloride decomposes to give Alumina, hydrochloride and water.

2AlCl₃ . 6H₂O ———-> Al₂O₃ + HCl + H₂O

Uses:

i) It is used as catalyst in friedel craft’s reaction.

ii) It is used as mordant in dye.

Structure of Aluminium chloride:

AlCl₃ is electron deficient compound so it exists as dimer (Al₂Cl₆) .

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