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This historical page is being kept for research or reference
purposes and will not be updated.

This historical page is being kept for research or reference
purposes and will not be updated.

2.1 Identity and physical/chemical properties

Aluminum chloride is also known as aluminum trichloride, aluminum chloride (1:3) and trichloroaluminum (ATSDR 2006). It has the Chemical Abstracts Service (CAS) registry number 7446-70-0 and a chemical formula of AlCl3. In its hydrated form, AlCl3-6H2O, it is called hexahydrated aluminum chloride (CAS No. 7784-13-6). Trade names include Aluwets, Anhydrol and Drichlor.

Synonyms for aluminum nitrate include aluminum trinitrate and aluminum (III) nitrate (1:3). The CAS registry number is 13473-90-0 and the chemical formula is Al(NO3)3. The nonahydrate aluminum nitrate, Al(NO3)3-9H2O (CAS No. 7784-27-2), is the stable form of this compound.

Aluminum sulphate can also be identified as alum, alumsulphate (2:3), aluminum trisulphate, dialuminum sulphate and dialuminum trisulphate. The CAS registry number for aluminum sulphate is 10043-01-3 and the chemical formula is Al2(SO4)3. Alum is often represented as Al2(SO4)3-14H2O. It may be found in different hydrated forms. The commercial product, called cake alum or patent alum, is an octadecahydrate aluminum sulphate, Al2(SO4)3-18H2O.

In addition to these three compounds, aluminum polymers such as polyaluminum sulphate (PAS) and polyaluminum chloride (PAC) are used in water treatment. The general formula for PAS is Ala(OH)b(SO4)c, where b + 2c = 3a; for PAC, the general formula is Ala(OH)bClc, where b/a is usually about 2.5 (e.g., Al2(OH)5Cl). Mixed aluminum polymers may also be used; their general formula is Ala(OH)bClc(SO4)d, and b/a varies between 0.4 and 0.6.

Physicochemical properties of the three aluminum salts are presented in Table 2.1..

Table 2.1: Physicochemical properties of aluminum chloride, aluminum nitrate and aluminum sulphate 1
Property Aluminum
chloride		 Aluminum
nitrate		 Aluminum
sulphate
CAS No. 7446-70-0 13473-90-0 10043-01-3
Molecular formula AlCl3 Al(NO3)3 Al2(SO4)3
Molecular weight 133.34 213.00 342.14
Colour White when pure, ordinarily gray or yellow to greenish Colourless2 White, lustrous
Physical state White hexagonal deliquescent or moisture sensitive plates Rhombic crystals2 Crystals, pieces, granules or powder
Density (g/mL) 2.48 No data 1.61
Melting point (°C) 194 at 527 kPa 732 Decomposes at 770
Boiling point (°C) 182.7
(1.00×105 Pa or 752 mm Hg; sublimation temperature)		 Decomposes at 135°C2 No data, substance has no boiling point
Solubility in water
(g/100 mL)		 69.86 (15°C)
(Reacts violently with water)		 63.7 (25°C) 36.4 (20°C)
Solubility in other solvents Soluble in benzene, carbon tetrachloride,
chloroform		 Very soluble in alcohol;
slightly soluble in acetone
almost insoluble in ethyl acetate,
pyridine2		 Insoluble in ethanol
pH No data Aqueous solution is acidic No data
Vapour pressure (Pa) 100
(20°C)		 No data 0 (20°C)
substance has no vapour pressure
1 Taken from Perry and Green (1984), Budaveri et al. (1989), Lewis (1992), European Commission (2000a,b) and ATSDR (2006)
2 Refers to aluminum nitrate nonahydrate (CAS No. 7784-27-2)

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