Chemical elements
  Aluminium
    Isotopes
    Energy
    Preparation
    Physical properties
    Chemical properties
      Aluminium subfluoride
      Aluminium trifluoride
      Aluminium trichloride
      Aluminium tribromide
      Aluminium iodide
      Aluminium chlorate
      Aluminium perchlorate
      Aluminium bromate
      Aluminium periodate
      Aluminium suboxide
      Alumina
      Aluminium sesqui-oxide
      Aluminium peroxide
      Aluminium hydroxides
      Aluminates
      Tricalcium aluminate
      Sodilim aluminate
      Aluminium sesqui-sulphide
      Aluminium selenide
      Aluminium telluride
      Aluminium sulphite
      Aluminium sulphate
      Alums
      Sodium alum
      Potassium alum
      Ammonium alum
      Hydroxylamine alum
      Silver alum
      Pseudo-alums
      Aluminium dithionate
      Aluminium selenite
      Aluminium selenate
      Aluminium chromate
      Aluminium molybdate
      Aluminium silicomolybdate
      Aluminium tungstate
      Aluminium silicotungstate
      Aluminium phosphotungstate
      Aluminium nitride
      Aluminium phosphide
      Aluminium arsenide
      Aluminium nitrate
      Aluminium Phosphates
      Basic aluminium arsenite
      Aluminium carbide
      Aluminium carbonate
      Aluminium thiocyanate
      Aluminium oxalate
      Aluminium alkyls
      Aluminium Hydrocarbon
      Aluminium acetylacetonate
      Aluminium silicide
      Aluminium silicates
      Leucite
      Nephelite
      Spodumene
      Topaz
      Beryl
      Tourmaline
      Axinite
      Sodalite
      Hauynite
      Kaolinite
      Aluminosilicic acids aluminosilicates
      Aluminium Borides
      Aluminium Boride
      Aluminium Boride
      Aluminium borocarbides
      Aluminium borate
      Aluminium sodium perborate
    Applications
    PDB 1a6e-1zca
    PDB 2b8w-3i62
    PDB 3kql-5ukd

Chemical properties of Aluminium





Compounds of Aluminium

Aluminium forms one series of salts, in which it is tervalent. The salts are derived from the basic oxide Al2O3. Those derived from colourless acids are themselves colourless. The soluble salts from hydrates containing considerable water of crystallisation, and the anhydrous salts, dissolve in water with the evolution of a large amount of heat. The salts are not poisonous.

On the ionic hypothesis the salts of aluminium are dissociated in aqueous solution, giving rise to a colourless cation Al•••: -

AlX3Al••• + 3X'.

The ionic mobility of the cation, ⅓ Al•••, is 40.4 at 18° C. Despite the high position occupied by aluminium in the electromotive series, aluminium oxide is only a weak basic oxide and aluminium hydroxide but a feeble base. Accordingly, in aqueous solution, aluminium salts are appreciably hydrolysed, and those derived from moderately strong acids give a decidedly acid reaction. A solution of 1 gram-molecule of aluminium chloride or bromide in 1000 litres of water is hydrolysed to the extent of 4 per cent, at 25°; while the percentage hydrolysis (x) of the chloride in aqueous solution at 99.7 varies with the dilution (v litres per gram-molecule), as follows: -

v3264128256512
x8.013.219.728.241.4


Aluminium hydroxide is a stronger base than ferric hydroxide, but is weaker than beryllium hydroxide. It is possible that, owing to the transformation of aluminium hydroxide into the form of a colloidal hydrosol, the degree of hydrolysis of aluminium salts gives a somewhat exaggerated idea of the weakness of the hydroxide as a base.

Owing to the appreciable hydrolysis of aluminium salts, the soluble salts derived from volatile acids cannot be prepared in the anhydrous state by the evaporation of their aqueous solutions on the steam-bath.

Aqueous solutions of aluminium salts dissolve an appreciable amount of aluminium hydroxide.


Thermochemistry of Aluminium Compounds

The heats of formation, etc., of the more important compounds of aluminium are given in the following table, in kilogram-calories: -

Compound.Heat of Formation. Cals.Heat of Solution. Cals.
AlF3249.0 + 31.3
AlF3.3.5H2O...- 1.7
AlCl3161.4 + 77.6
AlBr3122.0 + 85.3
AlI370.3 + 89.0
Al2O3380.2...
Al(OH)3297.0...
Al2S3126.4...
Al2(SO4)3879.7 ...
Al2(SO4)3.6H2O... + 56.0
Al2(SO4)3.18H2O... + 9.2
Al4C3244.8...
KAl(SO4)2.12H2O...-10.0
(NH4)Al(SO4)2.12H2O...- 9.6


The following data refer to heats of reaction: -

[Al2O3] cryst. + [Na2O]+48.0 Cals.
[Al2O3] amorp. + [Na2O]+55.1 Cals.
[Al] + 3HCl.2OH2O+126.0 Cals.
[Al] + 3HCl.200H2O+127.0 Cals.
⅓[Al(OH)3] + HCl aq.+9.2 Cals.
⅓[Al(OH)3] + HF aq.+11.7 Cals.
⅓[Al(OH)3] + ½H2SO4 aq.+10.5 Cals.
2[AlCl3] + 2⅓(NH3)+167.5 Cals.
2[AlCl3] + 6(NH3)+245.2 Cals.
2[AlCl3] + 10(NH3)+268.2 Cals.
2[AlCl3] + 12(NH3)+317.9 Cals.
2[AlCl3] + 18(NH3)+9.5 Cals.
2[AlCl3] + (H2S)+9.5 Cals.
2[AlCl3] + (SO2)+18.3 Cals.
2[AlCl3] + 2(SO2)+28.9 Cals.
2[AlCl3] + 2[KCl]+26.4 Cals.
2[AlCl3] + 2[NaCl]+11.9 Cals.
2[AlCl3] + 2[NH4Cl]+26.5 Cals.
2[AlCl3] + 3[NaCl]+15.3 Cals.
2[AlCl3] + 3[KCl]+30.5 Cals.
2[AlCl3] + 6[NaCl]+19.5 Cals.
2[AlCl3] + 6[KCl]+366 Cals.
2[AlCl3] + 2[AgCl]+5.0 Cals.
2[AlCl3] + 1.5[CaCl2]+9.3 Cals.
2[AlCl3] + 1.5[SrCl2]+8.7 Cals.
2[AlCl3] + [BaCl2]+5.3 Cals.
2[AlF3] + 6[NaF]+40.7 Cals.
2[AlF3] + 6[KF]+88.8 Cals.
2[AlF3] + 7H2O+65.0 Cals.
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